Article: 217116 of rec.radio.amateur.antenna From: "Tom Donaly" Subject: Re: 73 Ohms, How do you get it? References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> Message-ID: Date: Tue, 13 Sep 2005 20:36:32 GMT Harry wrote: > Hi Tim and Reg, > > Thank you for your valuable information. Is there any website or > textbook that actually shows the step-by-step calculation of this magic > number which has been quoted so often in the cable industry? > > You know most video cables and connectors have characteristic > impedance, 75 Ohms. > > I am not afraid of math. I just like to understand the details of its > derivation. > > -- Harry > What you're seeking is in the book _Antenna Theory, Analysis and Design_ by Constantine A. Balanis, ISBN 0-471-59268-4. 73, Tom Donaly, KA6RUH Article: 217117 of rec.radio.amateur.antenna From: "KØHB" References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <6qudnRtjVJhVpLveRVn-tQ@comcast.com> <0ICdncTJkPKeVrveRVn-vA@comcast.com> Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Message-ID: Date: Tue, 13 Sep 2005 22:29:46 GMT "Dee Flint" wrote > > Nothing stops them from calling an immediate emergency meeting to address > temporarily suspending such limits in times of great need. > If a ham can only use their station "in times of great need" it's unlikely they'd have the equipment to put into service, so it's all a moot point. 73, de Hans, K0HB Article: 217118 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: 73 Ohms, How do you get it? Date: Tue, 13 Sep 2005 22:56:10 +0000 (UTC) Message-ID: References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> "Ham op" wrote > Transmission line calculations are much easier than antenna calculations. > ===================================== Antenna conductors ARE transmission lines and the same sort of calculations apply. ---- Reg. Article: 217119 of rec.radio.amateur.antenna Subject: Re: 73 Ohms, How do you get it? From: Cecil Moore Date: Tue, 13 Sep 2005 18:12:08 -0500 Message-ID: <1126653287_28145@spool6-east.superfeed.net> References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> Harry wrote: > I am a newbi in antennas. > > Here's my question: > > I know that a half-wave dipole in free space has > a feed-point impedance of approximately 73 ohms. > > Can anyone tell me **exactly** how this number is calculated. From "Antenna Theory" by Balanis: Rr = 2*Prad/|Io^2| = 73 ohms (4-93) Prad is found by integrating the Poynting Vector over a certain radius. Io is the current maximum magnitude. The ASCII limitation prevents much more than this. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- Article: 217120 of rec.radio.amateur.antenna From: "KØHB" References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <6qudnRtjVJhVpLveRVn-tQ@comcast.com> <0ICdncTJkPKeVrveRVn-vA@comcast.com> Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Message-ID: Date: Tue, 13 Sep 2005 23:19:03 GMT "Dee Flint" wrote > > I was talking about temporarily taking in those left homeless and how it shows > a lack of humanitarianism. > O I C. I have no HOA restrictions, but if I did have some like that, then they'd just be friends visiting for a few weeks. 73, de Hans, K0HB Article: 217121 of rec.radio.amateur.antenna Subject: Re: Hot Flashes From: Cecil Moore Date: Tue, 13 Sep 2005 18:20:50 -0500 Message-ID: <1126653809_28153@spool6-east.superfeed.net> References: <43271ECF.10306@arrl.net> Henry wrote: A funny jpeg but this is an ASCII only newsgroup. It will probably be deleted by the usenet god. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- Article: 217122 of rec.radio.amateur.antenna Subject: Re: 73 Ohms, How do you get it? From: Cecil Moore Date: Tue, 13 Sep 2005 18:23:43 -0500 Message-ID: <1126653984_28157@spool6-east.superfeed.net> References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> Harry wrote: > Thank you for your valuable information. Is there any website or > textbook that actually shows the step-by-step calculation of this magic > number which has been quoted so often in the cable industry? "Antenna Theory" by Balanis, second edition, Chapter 4. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- Article: 217123 of rec.radio.amateur.antenna Subject: Re: 73 Ohms, How do you get it? From: Cecil Moore Date: Tue, 13 Sep 2005 18:43:42 -0500 Message-ID: <1126655181_28167@spool6-east.superfeed.net> References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> Reg Edwards wrote: > Antenna conductors ARE transmission lines and the same sort of > calculations apply. You're right, Reg. Without reflections from the ends of a dipole, the feedpoint impedance would be hundreds of ohms. A standing wave antenna is like a lossy transmission line where the loss is to radiation. And the SWR on a 1/2WL dipole standing wave antenna is quite high - in the neighborhood of 20:1. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- Article: 217124 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: 73 Ohms, How do you get it? Date: Wed, 14 Sep 2005 00:41:57 +0000 (UTC) Message-ID: References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> It is equally correct to say that the radiation resistance of a dipole is 2*73 = 146 ohms, since this is the value when the radiation resistance is assumed to be uniformly distributed along its length as is the conductor resistance. For calculating purposes the radiation and conductor resistances can simply be added together. And when referred to the end of a dipole, at HF the radiation resistance is of the order of Q-squared * 73/2 = 3000 ohms. Although this is somewhat indeterminate because of the difficulty of feeding an isolated dipole at one end. The conductor diameter also plays a significant part. ---- Reg. Article: 217125 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: 73 Ohms, How do you get it? Date: Tue, 13 Sep 2005 17:47:09 -0700 Message-ID: <11iesohk2gnkf80@corp.supernews.com> References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> Just about any antenna textbook will show you the calculation of a half wavelength, infinitely thin dipole in free space. For that special case, the answer ends up being simply 30 * Cin(2 * pi), where Cin is a modification of the cosine integral Ci[*]. That's where the "magic number" comes from. Kraus' _Antennas_ is just one of the many textbooks which give the derivation for this. It takes about 3 pages and 23 equations for Kraus to derive. One assumption made in calculation of this value is that the current distribution is sinusoidal, an assumption that's true only for an infinitely thin antenna. For finite thickness wire, the calculation becomes much more difficult. The radiation resistance changes only slowly with wire diameter, however, so sinusoidal distribution is a reasonably good approximation provided that the antenna is thin. Feedpoint reactance, though, varies much more dramatically with both antenna length and diameter. Calculating its value exactly requires solution of a triple integral equation which can't be solved in closed form. That's why computer programs are used to solve it numerically. To include the effect of ground, you need to calculate the mutual impedance between the antenna and its "image". If the antenna is about 0.2 wavelength above ground or higher (for a half wave antenna -- the height must be greater if the antenna is longer), you can assume that the ground is perfect and get a pretty good result. Below that height, the calculation again becomes much more complicated because the quality of the ground becomes a factor. If you're interested in the numerical methods used, locate the NEC-2 manual (available on the web), which describes it. If you're satisfied with approximate results, the work by S.I. Shelkunoff provides formulas for free-space input impedance of antennas with finite diameter wire which can be solved with a programmable calculator or computer. They're detailed in "Theory of Antennas of Arbitrary Size and Shape", in Sept. 1941 Proceedings of the I.R.E. The formulas for R and X contain many terms involving sine and cosine integrals, which can be approximated with numerical series. You'll find additional information in his book _Advanced Antenna Theory_. For approximate calculations of mutual impedance of thin linear antennas, see "Coupled Antennas" by C.T. Tai, in April 1948 Proceedings of the I.R.E. Those also involve multiple terms of sine and cosine integrals. Before numerical calculations became possible, many very good mathematicians and engineers devised a number of approximation methods of varying complexity and accuracy. You'll find their works in various journals primarily in the 1940s - 1960s. The complexity and difficulty of the problem is why virtually all antenna calculations are done today with computers, using numerical methods such as the moment method. In summary, here are your choices: 1. You can calculate the approximate radiation resistance but not reactance of a thin, free-space antenna by assuming a sinusoidal current distribution and using the method Reg described. To include the effect of ground, you have to calculate or look up from a table the mutual impedance between the antenna and its "image", and modify the feedpoint impedance accordingly by applying the mesh equations for two coupled antennas. This method of including the effect of ground becomes inaccurate below around 0.2 wavelength, if the antenna is over typical earth. 2. You can use various approximation methods to calculate reactance, and resistance with better accuracy. But for the effect of ground, you're still limited to being greater than about 0.2 wavelength high. 3. To accurately include the effect of real ground with low antennas, and/or to get resistance and reactance values with arbitrarily good accuracy requires numerical methods. A computer program is the only practical way to do this. A very good basic description of the moment method can be found in the second and later editions of Kraus' _Antennas_. [*] Cin(x) = ln(gamma * x) - Ci(x), where gamma = Euler's constant, 0.577. . . Ci(x) = the integral from -infinity to x of [cos(v)/v dv] = ln(gamma * x) - (x^2)/(2!2) + (x^4)/(4!4) - (x^6)/(6!6). . . Roy Lewallen, W7EL Harry wrote: > Hi Tim and Reg, > > Thank you for your valuable information. Is there any website or > textbook that actually shows the step-by-step calculation of this magic > number which has been quoted so often in the cable industry? > > You know most video cables and connectors have characteristic > impedance, 75 Ohms. > > I am not afraid of math. I just like to understand the details of its > derivation. > > -- Harry > Article: 217126 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: 73 Ohms, How do you get it? Date: Wed, 14 Sep 2005 00:49:52 +0000 (UTC) Message-ID: References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126653287_28145@spool6-east.superfeed.net> "Cecil Moore" wrote > Prad is found by integrating the Poynting Vector over a > certain radius. ==================================== Cec, what's the Poynting Vector? --- Reg. Article: 217127 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: how to model a loaded vertical ?? Date: Tue, 13 Sep 2005 17:51:23 -0700 Message-ID: <11iet0fapmh7pd2@corp.supernews.com> References: <11i7obsivh8u3c1@corp.supernews.com> <4324780B.9010904@comcast.net> <1126467122_10775@spool6-east.superfeed.net> dansawyeror wrote: > All, > > Thank you for your help to get the basic model in place. It seems to be > working except that ground resistance does not appear to be modeled. > This may be an oversimplification my part in how the source is defined > or connected. It is a simple source connected to the first, lower, > segment. The end of that segment is also connected to a radial system of > 8 quite short radials. I would expect to see the feedpoint impedance > reflect the ground system. However, it seems to reflect the vertical > element only. That value is very close to a theoretical loaded element > over a perfect ground. This ground is a medium ground so it should have > some visible effect. > > Is it obvious what am I doing wrong? It sounds like you're using a MININEC-type ground, which isn't appropriate for this application. Be sure to read the manual sections involving ground modeling. Roy Lewallen, W7EL Article: 217128 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: how to model a loaded vertical ?? Date: Tue, 13 Sep 2005 17:53:16 -0700 Message-ID: <11iet3vqf6q5mf8@corp.supernews.com> References: <11i7obsivh8u3c1@corp.supernews.com> <4324780B.9010904@comcast.net> dansawyeror wrote: > > On the SWR scan is there a way to print or plot the step outputs? I am > trying to determine the resonance point. The SWR scan automatically produces a plot. To print, click File, then Print in the SWR display window. Roy Lewallen, W7EL Article: 217129 of rec.radio.amateur.antenna From: "Bill Turner" Subject: Re: 73 Ohms, How do you get it? Date: 14 Sep 2005 00:54:52 GMT Message-ID: References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> Reg Edwards wrote: > There's no such value as 'exact'. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Nonsense. I have exactly two pencils in my pencil holder. :-) 73, Bill W6WRT Article: 217130 of rec.radio.amateur.antenna From: richardharrison@webtv.net (Richard Harrison) Subject: Re: best HF antenna system next to a trailer? Date: Tue, 13 Sep 2005 20:29:31 -0500 Message-ID: <3627-43277CFB-102@storefull-3253.bay.webtv.net> References: Bill Turner wrote: "Without more information, this comparison is flawed." I agree the information was incomplete. I dfid not reproduce the whole article. The fault was mine, not Phil`s. A low dipole has a high radiation angle. For comparison, Phil was working Airstream net stations in New York, New Jersey, Maryland, Pennsylvania, Ohio, and New England. Phil was located in Ontario near Buffalo, New York when he collected his data. His in-laws lived there. Phil`s home QTH at the time was the highest spot in Western Connecticut, with a line-of-sight path to New York City. Phil had surrounded his mountain top with rhombic antennas pointed toward his likely targets. Amateurs answered when he called. In the Airstream net, most of the contacts were made Sundays on 3963 kHz at 8 am local time. Sky wave was mostly near vertical incidence. The low dipole was good for the job. Not too directional and a lot of radiation nearly straight up. Phil noted that several times when he switched to to the mobile whip, he could not be heard through the QRM. The numbers Phil put in Table 3 are only true under the conditions prevailing when he made the checks. Best regards, Richard Harrison, KB5WZI Article: 217131 of rec.radio.amateur.antenna From: Marshall Goldblatt Subject: Re: How to weather-seal an upside down Tailtwister rotor? Date: Tue, 13 Sep 2005 21:40:18 -0400 Message-ID: <3opd8pF71npnU1@individual.net> References: <3op5feF73ibjU1@individual.net> Dan/W4NTI wrote: > "Marshall Goldblatt" wrote in message > news:3op5feF73ibjU1@individual.net... > >>Hello all, >> >>I have a Tailtwister (TX-2) rotor mounted on a Rohn 25 foldover tower. >>While the tower itself appears to have survived intact, hurricane >>Katrina snapped the mast and destroyed the antennas. I need to fold the >>tower over to work in it, and likely leave it folded over for a fairly >>extended period. This will leave the top of the tower and the rotor >>upside down. Unfortunately, it is still the rainy season here, and the >>last time I needed to do this, rain water got into the rotor and settled >>in the bell, causing rust and other corrosion damage inside the rotor, >>because it is only weather protected when it is upright. I would like >>to seal the rotor to prevent this from happening again, but none of the >>ideas I've had so far (wrapping it in plastic garbage bags, using duct >>tape, using sealing foam) are usable, either because they don't seal >>well enough to keep water out or because stuff may get up inside the >>rotor where I can't get it out. >> >>So, does anyone have any suggestions? >> >>73, Marshall - W4EMB >> >> > > > Maybe ... get some axle grease, or RTV sealant would be better, perhaps. > Both should peal off reasonable well. > > One other thing I am concerned with tho. I always heard that the rotar > must be kept in a vertical position or the grease would drain out of the > bearings? Wives tale ??? I don't know. But I always keep mine vertical > when stored. Don't know about that, but there's no way to keep the rotor vertical when lowering a foldover tower... In any case, it's been folded over (for long periods) many times, and I've never noticed a bearing problem. Article: 217132 of rec.radio.amateur.antenna From: Bob Bob Subject: Re: How to weather-seal an upside down Tailtwister rotor? References: <3op5feF73ibjU1@individual.net> Message-ID: <6pakv2-ti9.ln1@p400bob.personal.cox.net> Date: Tue, 13 Sep 2005 20:25:25 -0500 One of the tricks I learnt early on with RTV sealant in medical ultrasound water tanks is if you wet the surfaces with water and a detergent wetting agent the sealant wont actually adhere to the prewetted surface. Kind of handy if you wanted to force the sealant into a clearance slot and remove it later. Or was it oil? Damn I cant remember! I know kerosene is used to pre the surface for better adhesion... How about paper/masking tape over the gaps and spraying with that gluggy sealant you use on sink drains? Probably not very useful thoughts, sorry! Cheers Bob W5/VK2YQA Dan/W4NTI wrote: > > Maybe ... get some axle grease, or RTV sealant would be better, perhaps. > Both should peal off reasonable well. > > One other thing I am concerned with tho. I always heard that the rotar > must be kept in a vertical position or the grease would drain out of the > bearings? Wives tale ??? I don't know. But I always keep mine vertical > when stored. > > Dan/W4NTI > > Article: 217133 of rec.radio.amateur.antenna From: "Roger Leone" References: Subject: Re: Balanced from unbalanced via a 100 ohm Q section Message-ID: <2ALVe.715$Jm.384@newssvr27.news.prodigy.net> Date: Wed, 14 Sep 2005 02:05:50 GMT "Bob Bob" wrote in message news:g46jv2-ib6.ln1@p400bob.personal.cox.net... > Hi Roger > > Might get around to it today! (Being unemployed is sometimes fun..) > Bob: If your 100 ohm Q section doesn't work out as expected, I have lots of RG-71 (93 ohm) coax that might be worth trying. Let me know if you are interested. 73, Roger Article: 217134 of rec.radio.amateur.antenna From: "RST Engineering" Subject: Re: Corrosion on aluminum antenna Date: Tue, 13 Sep 2005 19:06:54 -0700 Message-ID: <11if1e3fd2r81cc@corp.supernews.com> References: <24snh19iu141gghh6iamqv9peh8q7649gd@4ax.com> <0v-dnX_XAvtEJoLeRVn-rA@comcast.com> <313030303837383543232DCF97@zetnet.co.uk> > Is tin worm like ... Bronze Bitch Borers? I've met a few of them in my time... Jim Article: 217135 of rec.radio.amateur.antenna From: nospam@nouce.bellatlantic.net Subject: Re: best HF antenna system next to a trailer? Message-ID: References: <1126505259.234971.15970@f14g2000cwb.googlegroups.com> <9175-4326EEA5-1@storefull-3254.bay.webtv.net> Date: Wed, 14 Sep 2005 02:11:13 GMT On 13 Sep 2005 16:15:08 GMT, "Bill Turner" wrote: >Richard Harrison wrote: > >> Phil found a simple dipole only a few feet above ground would >> outperform a mobile whip on 40 or 75 meters. >~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > >Without more information, this comparison is flawed. A mobile whip has >a lower angle of radiation than a horizontal dipole. On 40 or 75, the >vertical component of radiation can be quite significant for close-in >stations (100 miles or so). At night, working long distances, the whip >may outperform the dipole. During the day, the dipole will probably >outperform the whip. > >It all depends. >73, Bill W6WRT Correct on radiation angle, however the average mobile whip at 3.8mhz is around 10% efficient. Even at 7Mhz it doesn't improve much efficientcy wise. The low dipole (low being less than .25WL) is close or better than 95% efficient but has a rotten radiation angle for DX however close in it will be very good. Myself in that situation.. I'd put a poles at either end of the trailer (thats 50ft length) and if possible get it up 30ft or better and hang a dipole. If the antenna is 66' (40m) the excess length can hang. The support poles can be anything that will stay up. At 20m 30ft is 1/2WL up and will be decent. Even if you can't do two support poles and only one make that one high as possible and mount a dipole as a sloper. It will be somewhat directional but performace will be far better than any ground mounted vertical that has no ground plane. If money wasn't a limiting factor. put down a base and put up a freestanding tower. The rules remain. More metal, higher the better. Allison KB1GMX Article: 217136 of rec.radio.amateur.antenna Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article From: Cecil Moore Date: Tue, 13 Sep 2005 21:31:51 -0500 Message-ID: <1126665270_28245@spool6-east.superfeed.net> References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <6qudnRtjVJhVpLveRVn-tQ@comcast.com> <0ICdncTJkPKeVrveRVn-vA@comcast.com> <30DVe.1556$Nw6.692@bignews6.bellsouth.net> <88WdnbrHqZgpkbreRVn-tg@comcast.com> <4327720A.61F01CAB@earthlink.net> Michael A. Terrell wrote: > Its just too damn bad you can't tar and feather them and then run > them out of town, like the good old days! ;-) Seems to me a large percentage of the blame lies with the buyers who readily agree to such irrational HOA terms and then complain about them later. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- Article: 217137 of rec.radio.amateur.antenna Subject: Re: 73 Ohms, How do you get it? From: Cecil Moore Date: Tue, 13 Sep 2005 21:45:48 -0500 Message-ID: <1126666107_28257@spool6-east.superfeed.net> References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126653287_28145@spool6-east.superfeed.net> Reg Edwards wrote: > "Cecil Moore" wrote > >>Prad is found by integrating the Poynting Vector over a >>certain radius. > > Cec, what's the Poynting Vector? Same thing as a power flow vector. The dimensions are energy per second per unit area. If the power flow vector is integrated over the entire surface of a sphere of radius r, the result is total radiated power. I thought maybe you and Mr. Poynting might have worked together at some time in the 20th century. :-) > Poynting, John Henry (1852-1914) > English physicist, mathematician, and inventor. He devised > an equation by which the rate of flow of electromagnetic energy > (now called the Poynting vector) can be determined. http://www.cartage.org.lb/en/themes/Biographies/MainBiographies/P/Poynting/1.html -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- Article: 217138 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: 73 Ohms, How do you get it? Date: Wed, 14 Sep 2005 03:31:24 +0000 (UTC) Message-ID: References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> "Reg Edwards" wrote > It is equally correct to say that the radiation resistance of a dipole > is 2*73 = 146 ohms, since this is the value when the radiation > resistance is assumed to be uniformly distributed along its length as > is the conductor resistance. > > For calculating purposes the radiation and conductor resistances can > simply be added together. ===================================== Hints and tips - By the same arithmetical reasoning - The centre feedpoint input resistance of a 1/2-wave dipole is 73 ohms plus HALF of the conductor end-to-end HF resistance, which to be precise sometimes matters. This is exact insofar as 73 is exact - not an approximation. The HF resistance of a copper wire at 20 degrees C is - Rhf = Sqrt( F ) / 12 / d ohms per metre, Where F is the frequency in MHz and d is the wire diameter in millimetres. For example, the end-to-end loss resistance of a 1/2-wave dipole at 1.9 MHz using 16-gauge copper wire is 7.07 ohms, which increases the feedpoint resistance to 73 + 3.53 = 76.53 ohms, to give a radiating efficiency of 95.4 percent. Some people would consider that's enough to lose a contest! Why not start a little notebook to record useful, simple, little formulae such as above which don't appear in Terman et al? Or if they do appear then you can never find the right page in the right volume. ---- Reg. Article: 217139 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: best HF antenna system next to a trailer? Date: Tue, 13 Sep 2005 20:43:23 -0700 Message-ID: <11if72vgu1uln04@corp.supernews.com> References: <1126505259.234971.15970@f14g2000cwb.googlegroups.com> <9175-4326EEA5-1@storefull-3254.bay.webtv.net> An antenna doesn't have a single "radiation angle". It radiates at all angles. The relevant question is how much does it radiate at the particular angle of interest, not at which angle does it radiate the most. An antenna which radiates its maximum at a high angle might well radiate more at a low angle than an antenna with a lower angle of maximum radiation. Roy Lewallen, W7EL nospam@nouce.bellatlantic.net wrote: > On 13 Sep 2005 16:15:08 GMT, "Bill Turner" wrote: >> >>Without more information, this comparison is flawed. A mobile whip has >>a lower angle of radiation than a horizontal dipole. . . > > Correct on radiation angle . . . Article: 217140 of rec.radio.amateur.antenna From: "Joel" Subject: Yet another grounding question Date: Tue, 13 Sep 2005 22:49:27 -0500 Message-ID: After almost 50 years banging around Ham Radio I finely have my tower up.. I have each leg of the tower grounded with 2 inch copper strapping , each to their own ground rod.Those ground rods are all connected together and run off to another ground rod I will use that as a common ground. All the coax that come into the house goes to a outside 5x5 box that has poliphaseres installed in it. The box is brass lined and the brass is lapped to another 2 inch copper strap that goes to the common ground. The station ground is separate until it gets to the common ground.. With all this said,I have a questions.. - I 'should' have the power entrance ground run over to the common ground. But it's over 90 feet away and the house has plastic water pipes.. Does it make sense to run a copper wire or strap that far? If so, should it be berried all the way or run exposed. It seems to me the impedance would be so high in the run, that it would be a waste of copper? TNX Joe AG4QC Article: 217141 of rec.radio.amateur.antenna From: Owen Duffy Subject: Re: loop inductance calculation? Message-ID: References: <6odfi1l8k7bnerl8fucbbbdg17c3mtqg11@4ax.com> Date: Wed, 14 Sep 2005 06:01:17 GMT On Wed, 14 Sep 2005 01:42:03 -0400, TRABEM <> wrote: >What's the approximate inductance for a single turn square loop, 10 >feet per side in free space (if that matters)? There should be an easy >way to calculate this, maybe there is, but I'm not aware of it. > http://www.technick.net/public/code/cp_dpage.php?aiocp_dp=util_inductance_square -- Article: 217142 of rec.radio.amateur.antenna From: David Subject: Open Stub fed J antenna Message-ID: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> Date: Wed, 14 Sep 2005 06:21:54 GMT Does anyone know of where I could find an example of a homebrew open stub fed j antenna. I want to construct a unit for 915 MHz using SMA plug and coaxial cable. Thanks in advance Article: 217143 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: 73 Ohms, How do you get it? Date: Tue, 13 Sep 2005 23:36:35 -0700 Message-ID: <11ifh7o30m2sfca@corp.supernews.com> References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> <11iesohk2gnkf80@corp.supernews.com> <1126670159.827784.237990@g47g2000cwa.googlegroups.com> Harry wrote: > Hi Roy, > > Thanks for all the valuable information. Are you a professor? Not by a long shot. I'm way too poor a student to ever be considered for a job as a teacher. > You may want to write a book titled "Story of the 73 Ohms". It's already been written, by many people who know a great deal more than I. Roy Lewallen, W7EL Article: 217144 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: how to model a loaded vertical ?? Date: Tue, 13 Sep 2005 23:41:08 -0700 Message-ID: <11ifhg8s81ven91@corp.supernews.com> References: <11i7obsivh8u3c1@corp.supernews.com> <4324780B.9010904@comcast.net> <1126467122_10775@spool6-east.superfeed.net> <11iet0fapmh7pd2@corp.supernews.com> <4327A068.6060106@comcast.net> dansawyeror wrote: > Roy, > > Thanks, I did and I have tried all the combinations. > > I would suspect that 'free space' would show a mis match for 'short > radials'. It does not. Simulations of free space dipoles seem accurate. > Am I missing something? You'll need to send me the model description (.EZ file) so I can see what you've got. Attach it to an email to me. > I also tried to simulate several values of real earth. None of them > produced high input impedance values. What ground values represent > suburban clay? We have clay here, and by comparing a dipole and vertical at various times of year, I've estimated that the soil is about equivalent to EZNEC's "poor" quality ground in the summer when it's bone dry and "very good" ground in the winter when soaking wet. It's an approximation at best, though. Roy Lewallen, W7EL Article: 217145 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: loop inductance calculation? Date: Tue, 13 Sep 2005 23:44:35 -0700 Message-ID: <11ifhmngeb6au21@corp.supernews.com> References: <6odfi1l8k7bnerl8fucbbbdg17c3mtqg11@4ax.com> The free demo version of EZNEC (http://eznec.com) will tell you. Choose a low frequency where the loop is electrically very small. Put a source anywhere in the loop and look at the Source Data. It'll give you the reactance which you can convert to inductance at the frequency you chose. The inductance should stay fairly constant with frequency as long as the frequency is low enough that the loop circumference is a very small part of a wavelength. Roy Lewallen, W7EL TRABEM wrote: > What's the approximate inductance for a single turn square loop, 10 > feet per side in free space (if that matters)? There should be an easy > way to calculate this, maybe there is, but I'm not aware of it. > > Thanks > > T Article: 217146 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: loop inductance calculation? Date: Tue, 13 Sep 2005 23:55:48 -0700 Message-ID: <11ifibocus6c2e1@corp.supernews.com> References: <6odfi1l8k7bnerl8fucbbbdg17c3mtqg11@4ax.com> TRABEM wrote: > > What's the relative permeability of air?? "Relative permeability" is the permeability relative to that of free space. The relative permeability of any non-magnetic material, including air, is 1. > > They give this statement on the help page, but I don't understand what > it means. > > Note: µ0 = 4¶·10-7 [Hm-1] (Absolute Permeability) The permeability of free space (µ0) is 4 * pi * 10^-7 webers/amp-m (MKSA units). The permeability (µ) of anything is its relative permeability (µr) times µ0. Roy Lewallen, W7EL Article: 217147 of rec.radio.amateur.antenna From: nospam@nouce.bellatlantic.net Subject: Re: best HF antenna system next to a trailer? Message-ID: References: <1126505259.234971.15970@f14g2000cwb.googlegroups.com> <9175-4326EEA5-1@storefull-3254.bay.webtv.net> <11if72vgu1uln04@corp.supernews.com> Date: Wed, 14 Sep 2005 12:00:22 GMT On Tue, 13 Sep 2005 20:43:23 -0700, Roy Lewallen wrote: >An antenna doesn't have a single "radiation angle". It radiates at all >angles. The relevant question is how much does it radiate at the >particular angle of interest, not at which angle does it radiate the >most. An antenna which radiates its maximum at a high angle might well >radiate more at a low angle than an antenna with a lower angle of >maximum radiation. > >Roy Lewallen, W7EL Hello Roy, I do understand that. I also understand when you say radiation angle your talking about the primary or dominent lobe(s). There may be many other lobes at useful or less than useful angles present as well. However, how does that relate to using a shortend antenna with maybe 10% radiation efficientcy to a dipole at a reasonably attainable height? Allison KB1GMX > >nospam@nouce.bellatlantic.net wrote: >> On 13 Sep 2005 16:15:08 GMT, "Bill Turner" wrote: >>> >>>Without more information, this comparison is flawed. A mobile whip has >>>a lower angle of radiation than a horizontal dipole. . . >> >> Correct on radiation angle . . . Article: 217148 of rec.radio.amateur.antenna Subject: Re: Open Stub fed J antenna From: Cecil Moore Date: Wed, 14 Sep 2005 09:07:22 -0500 Message-ID: <1126707001_31799@spool6-east.superfeed.net> References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> David wrote: > Does anyone know of where I could find an example of a homebrew open stub > fed j antenna. I want to construct a unit for 915 MHz using SMA plug and > coaxial cable. An open stub J-pole is the same as a Zepp. 1/2WL element end fed by 1/4WL balanced series section. The coax connects to the end of the series section. Arrow Antenna makes one for 2m. Plans are available that could possibly be scaled to 915 MHz. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- Article: 217149 of rec.radio.amateur.antenna From: "Richard Fry" References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> <11iesohk2gnkf80@corp.supernews.com> <1126670159.827784.237990@g47g2000cwa.googlegroups.com> Subject: Re: 73 Ohms, How do you get it? Date: Wed, 14 Sep 2005 09:22:19 -0500 Message-ID: <43283245_3@newsfeed.slurp.net> "Harry" wrote about Roy Lewallen: > You may want to write a book titled "Story of the 73 Ohms". ___________ It should include the point that the 73 ohm radiation resistance value applies to a physical 1/2-wave, thin-wire, linear dipole in free space, and that a reactance term of + j42.5 ohms also applies to such a configuration (Kraus 3rd Edition, p. 182). The dipole length needs to be shorted by a few percent in order to zero out the reactance term, at which time the resistance term will be about 65 ohms. RF Article: 217150 of rec.radio.amateur.antenna From: "W5GT" Subject: WTB: 40' self supporting tower in Dallas area Message-ID: Date: Wed, 14 Sep 2005 10:02:02 -0500 I'm looking for a 40' tower in the Dallas area. Rohn 25 or Universal OK. I'd prefer that the tower is down. If rotor / and or beam available will consider. 73s Dave - W5GT w5gt@arrl.net Article: 217151 of rec.radio.amateur.antenna From: Bob Miller Subject: Re: best HF antenna system next to a trailer? Message-ID: References: <1126505259.234971.15970@f14g2000cwb.googlegroups.com> <9175-4326EEA5-1@storefull-3254.bay.webtv.net> <1126670383.884527.133320@f14g2000cwb.googlegroups.com> Date: Wed, 14 Sep 2005 15:44:33 GMT On 13 Sep 2005 20:59:43 -0700, eternalsquire@comcast.net wrote: >Money and space are actually limiting factors, but at least CC&R's >arent! My wife and I have been discussing this, and she really >doesn't like the idea of something 30 to 40 feet high on a small lot. > ...excerpted... > >I think because space, money, and aesthetics are limiting factors, I >need to use precision to my advantage rather than size or height, and a >4 square may help there. > >Comments? > >The Eternal Squire Any reason you're not considering a 20 meter dipole, fed with ladderline to a tuner, for 20 thru 10 meters? Put it 25 feet high, and it's nearly or more than a half wave high on all bands. bob k5qwg Article: 217152 of rec.radio.amateur.antenna From: "Bill Turner" Subject: Re: best HF antenna system next to a trailer? Date: 14 Sep 2005 15:35:43 GMT Message-ID: References: <1126505259.234971.15970@f14g2000cwb.googlegroups.com> <9175-4326EEA5-1@storefull-3254.bay.webtv.net> <11if72vgu1uln04@corp.supernews.com> Roy Lewallen wrote: > > An antenna doesn't have a single "radiation angle". It radiates at > all angles. The relevant question is how much does it radiate at the > particular angle of interest, not at which angle does it radiate the > most. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ That's true, except few if any hams have a specific "angle of interest", since different angles are used at different times. For most of us, the angle of maximum radiation gives a general indication of how the antenna will perform. A better indication would be a graphical representation. It's always a problem when one tries to reduce a complex situation like this down to a single number. 73, Bill W6WRT Article: 217153 of rec.radio.amateur.antenna From: John - KD5YI Subject: Re: Help required to identify antenna type References: Message-ID: Date: Wed, 14 Sep 2005 16:01:23 GMT > "David" wrote in message > news:v5zVe.42161$FA3.13896@news-server.bigpond.net.au... > >>Hi, >> >>I have a Whip antenna that is supposed to give 3dB "gain" at 915MHz. >>After pulling the unit apart and studying the construction, I am not sure >>what style of antenna this is. >> >>The antenna consists of an SMA plug that has RF178 cable soldered to >>centre pin and >>it appears earth braid is connected to ground side of plug. >> >>The cable goes up the inside of 1 6mm Nylon tube for 40mm and then >>exits the tube and winds around 4.5T. It then enters the tube >>again and runs another 80mm. At this point the earth braid is stripped >>leaving only the centre conductor and dielectric to continue another 70mm >>to the top of the Radome (Nylon tube). >> >>I understand the construction of 5/8 antenna but I would not expect the >>braid to be earthed. >> >>Thanks in advance for any help. >> >>Regards >> >>David > Paul P wrote: > Could you post pictures on the binaries or email them to me please? I would > like to see this. > > Thanks in advance, > Paul. > > p.pinyot [at] worldnet [dot] att [dot] net > Hi, Paul - If you have the 2004 ARRL Handbook, the antenna is described on page 20.17 as a resonant feed-line dipole. The figure on that page shows its construction. If you do not have the handbook, I can scan the page and send it to you. Regards, John Article: 217154 of rec.radio.amateur.antenna From: "Jerry" References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <6qudnRtjVJhVpLveRVn-tQ@comcast.com> <0ICdncTJkPKeVrveRVn-vA@comcast.com> <30DVe.1556$Nw6.692@bignews6.bellsouth.net> <88WdnbrHqZgpkbreRVn-tg@comcast.com> <4327720A.61F01CAB@earthlink.net> Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Message-ID: Date: Wed, 14 Sep 2005 12:45:26 -0400 "Michael A. Terrell" wrote in message news:4327720A.61F01CAB@earthlink.net... > > > As someone who lives near Ocala and has to visit a lot of these gated > communities run by HOAs, I find most of them to be jerks who are only > interested in holding onto their perceived power at any cost. The fact > that it hurts others doesn't matter to them. Another HOA in the area > told a retired couple move out, or send their 17 year old grand daughter > away after she lost both of her parents in an accident. She had a few > months till she was to graduate from high school and no other relatives > but it didn't matter to the HOA. People like that are scum, no matter > how expensive their home, or what they drive. > > Its just too damn bad you can't tar and feather them and then run > them out of town, like the good old days! ;-) > > -- > ? > > Michael A. Terrell > Central Florida I am actually quite peaceable and believe in living and letting live in most cases. Who I allow in my home is up to me and whom I refuse entry is not the purvey of HOA Nazis. And, again, it is why I chose an older home (1956) with plenty of room, almost ZERO crime, and NO HOA's. Now should I run into one of those SOB's that start telling me what I can or can't do, then it will become another story. I feel so strongly about property rights that I would go to WAR over it, both nationally...or on a personal basis. Like, I wouldn't be averse to whuppin' some smartmouth's you-know-what over it. Again, being very quiet and peaceable as I certainly am, I am also quite intimidating in stature, so it would be an interesting fight! LOL! Now, it *could* even get down to the point of "You SOB, you can tell me what to do when you get around on the backside of my shotgun, or you got enough a$$ on ya to MAKE me, you *&^%$#"! LMAO! In Charlotte, NC, this year, there was a case where the HOA Nazis and their powermongers went too far with "foreclosures" and the NC legislature put some restrictions on their ability to foreclose with respect to their "rules". Now, foreclosing on someone's house because some Nazi b#####d didn't LIKE the peoples' guests? NOT! (Not me because I don't HAVE that problem) I can see how this could cause somebody to get severely injured or KILLED! You don't MESS with one's home! :( I feel for those who have to put up with such nonsense! OTH, one should NEVER move into such a place, either, so he bears some of the blame. :) Best to all, Jerry Article: 217155 of rec.radio.amateur.antenna From: "nitram578" Subject: FS: KLM 10-4 10 meter beam NIB Message-ID: Date: Wed, 14 Sep 2005 12:50:40 -0500 For sale a NIB KLM 10-4 (4 element 10 meter beam) $100.00 plus shipping. Article: 217156 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: how to model a loaded vertical ?? Date: Wed, 14 Sep 2005 11:25:00 -0700 Message-ID: <11igqo08d5rp800@corp.supernews.com> References: <11i7obsivh8u3c1@corp.supernews.com> <4324780B.9010904@comcast.net> <11iet3vqf6q5mf8@corp.supernews.com> Ham op wrote: > Roy, if he reads the impedance value he can determine resonance by the > absence of the reactive term. > > Do you agree that the SWR scan is a poor method of determining resonance? No, I usually use the SWR sweep to determine resonance. Stepping the cursor and looking at the impedance at each step quickly identifies the resonant frequency to within the closest step. Additional narrower scans are done as necessary to get more precision. What method do you use that's better? Roy Lewallen, W7EL Article: 217157 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: best HF antenna system next to a trailer? Date: Wed, 14 Sep 2005 11:28:05 -0700 Message-ID: <11igqtpiih2553a@corp.supernews.com> References: <1126505259.234971.15970@f14g2000cwb.googlegroups.com> <9175-4326EEA5-1@storefull-3254.bay.webtv.net> <11if72vgu1uln04@corp.supernews.com> <1126715019.030393.275490@o13g2000cwo.googlegroups.com> nm5k@wt.net wrote: > A better indication would be a > graphical representation. > > The EZNEC demo does that well. There is a little green ball > that you can grab with your mouse, and place it at any angle > you wanna check. Makes it quite easy to see, or compare > various angles. MK > Better yet, you can superimpose the plots from two antennas for direct comparison. In v. 4.0, you can even get a numerical readout of the difference between the two in dB at the angle of the cursor (the little green ball). Roy Lewallen, W7EL Article: 217158 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: best HF antenna system next to a trailer? Date: Wed, 14 Sep 2005 11:31:49 -0700 Message-ID: <11igr4q450p1d7e@corp.supernews.com> References: <1126505259.234971.15970@f14g2000cwb.googlegroups.com> <9175-4326EEA5-1@storefull-3254.bay.webtv.net> <11if72vgu1uln04@corp.supernews.com> nospam@nouce.bellatlantic.net wrote: > On Tue, 13 Sep 2005 20:43:23 -0700, Roy Lewallen > wrote: > > >>An antenna doesn't have a single "radiation angle". It radiates at all >>angles. The relevant question is how much does it radiate at the >>particular angle of interest, not at which angle does it radiate the >>most. An antenna which radiates its maximum at a high angle might well >>radiate more at a low angle than an antenna with a lower angle of >>maximum radiation. >> >>Roy Lewallen, W7EL > > > Hello Roy, > > I do understand that. I also understand when you say radiation angle > your talking about the primary or dominent lobe(s). There may be > many other lobes at useful or less than useful angles present as well. > > However, how does that relate to using a shortend antenna with maybe > 10% radiation efficientcy to a dipole at a reasonably attainable > height? > > Allison > KB1GMX The context was that one antenna was better for DX than the other because it had a "lower radiation angle". An antenna with a "low radiation angle" which is 10% efficient probably radiates less at low angles than a more efficient antenna with a "high radiation angle". Therefore it's not a better DX antenna. My point is simply that the angle of maximum radiation is not a valid criterion for comparing antennas. Roy Lewallen, W7EL Article: 217159 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: best HF antenna system next to a trailer? Date: Wed, 14 Sep 2005 11:37:42 -0700 Message-ID: <11igt81c682aheb@corp.supernews.com> References: <1126505259.234971.15970@f14g2000cwb.googlegroups.com> <9175-4326EEA5-1@storefull-3254.bay.webtv.net> <11if72vgu1uln04@corp.supernews.com> Bill Turner wrote: > Roy Lewallen wrote: > > >>An antenna doesn't have a single "radiation angle". It radiates at >>all angles. The relevant question is how much does it radiate at the >>particular angle of interest, not at which angle does it radiate the >>most. > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > That's true, except few if any hams have a specific "angle of > interest", since different angles are used at different times. For > most of us, the angle of maximum radiation gives a general indication > of how the antenna will perform. A better indication would be a > graphical representation. It's always a problem when one tries to > reduce a complex situation like this down to a single number. > > 73, Bill W6WRT I agree, which is why EZNEC produces a graphical output. I encourage people to look at it rather than reducing the pattern to a single number. And I have to emphasize once again that what really counts is the field strength, not the pattern shape. An antenna can have a wonderful looking pattern with nearly all its radiation at low angles, and still be a poor antenna for DX. Or with nearly all its radiation at high angles and be a poor antenna for short range communications. One familiar example is a Beverage antenna, which has a lovely pattern shape but makes a poor transmitting antenna. A quarter wave vertical will nearly always do much better for transmitting, even at the angles favored by the Beverage. Roy Lewallen, W7EL Article: 217160 of rec.radio.amateur.antenna From: "Frank" References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> <11iesohk2gnkf80@corp.supernews.com> Subject: Re: 73 Ohms, How do you get it? Message-ID: Date: Wed, 14 Sep 2005 20:30:28 GMT "Roy Lewallen" wrote in message news:11iesohk2gnkf80@corp.supernews.com... > Just about any antenna textbook will show you the calculation of a half > wavelength, infinitely thin dipole in free space. For that special case, > the answer ends up being simply 30 * Cin(2 * pi), where Cin is a > modification of the cosine integral Ci[*]. That's where the "magic number" > comes from. Kraus' _Antennas_ is just one of the many textbooks which give > the derivation for this. It takes about 3 pages and 23 equations for Kraus > to derive. > > One assumption made in calculation of this value is that the current > distribution is sinusoidal, an assumption that's true only for an > infinitely thin antenna. For finite thickness wire, the calculation > becomes much more difficult. The radiation resistance changes only slowly > with wire diameter, however, so sinusoidal distribution is a reasonably > good approximation provided that the antenna is thin. Feedpoint reactance, > though, varies much more dramatically with both antenna length and > diameter. Calculating its value exactly requires solution of a triple > integral equation which can't be solved in closed form. That's why > computer programs are used to solve it numerically. > > To include the effect of ground, you need to calculate the mutual > impedance between the antenna and its "image". If the antenna is about 0.2 > wavelength above ground or higher (for a half wave antenna -- the height > must be greater if the antenna is longer), you can assume that the ground > is perfect and get a pretty good result. Below that height, the > calculation again becomes much more complicated because the quality of the > ground becomes a factor. If you're interested in the numerical methods > used, locate the NEC-2 manual (available on the web), which describes it. > > If you're satisfied with approximate results, the work by S.I. Shelkunoff > provides formulas for free-space input impedance of antennas with finite > diameter wire which can be solved with a programmable calculator or > computer. They're detailed in "Theory of Antennas of Arbitrary Size and > Shape", in Sept. 1941 Proceedings of the I.R.E. The formulas for R and X > contain many terms involving sine and cosine integrals, which can be > approximated with numerical series. You'll find additional information in > his book _Advanced Antenna Theory_. For approximate calculations of mutual > impedance of thin linear antennas, see "Coupled Antennas" by C.T. Tai, in > April 1948 Proceedings of the I.R.E. Those also involve multiple terms of > sine and cosine integrals. > > Before numerical calculations became possible, many very good > mathematicians and engineers devised a number of approximation methods of > varying complexity and accuracy. You'll find their works in various > journals primarily in the 1940s - 1960s. > > The complexity and difficulty of the problem is why virtually all antenna > calculations are done today with computers, using numerical methods such > as the moment method. > > In summary, here are your choices: > > 1. You can calculate the approximate radiation resistance but not > reactance of a thin, free-space antenna by assuming a sinusoidal current > distribution and using the method Reg described. To include the effect of > ground, you have to calculate or look up from a table the mutual impedance > between the antenna and its "image", and modify the feedpoint impedance > accordingly by applying the mesh equations for two coupled antennas. This > method of including the effect of ground becomes inaccurate below around > 0.2 wavelength, if the antenna is over typical earth. > > 2. You can use various approximation methods to calculate reactance, and > resistance with better accuracy. But for the effect of ground, you're > still limited to being greater than about 0.2 wavelength high. > > 3. To accurately include the effect of real ground with low antennas, > and/or to get resistance and reactance values with arbitrarily good > accuracy requires numerical methods. A computer program is the only > practical way to do this. A very good basic description of the moment > method can be found in the second and later editions of Kraus' _Antennas_. > > [*] Cin(x) = ln(gamma * x) - Ci(x), where gamma = Euler's constant, 0.577. > . . Ci(x) = the integral from -infinity to x of [cos(v)/v dv] = ln(gamma * > x) - (x^2)/(2!2) + (x^4)/(4!4) - (x^6)/(6!6). . . > > Roy Lewallen, W7EL Very interesting references. In particular Kraus' 2nd ed. pp 359 - 408. Also Stutzman and Thiele, 1st ed. pp 306 - 374. Pretty much grad level, needs effort, (for me) even though I took Stutzman and Thiele's antenna course in 1998 (NCEE). Regards, Frank Article: 217161 of rec.radio.amateur.antenna From: "Frank" References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126653287_28145@spool6-east.superfeed.net> <1126666107_28257@spool6-east.superfeed.net> Subject: Re: 73 Ohms, How do you get it? Message-ID: Date: Wed, 14 Sep 2005 20:34:41 GMT >> Cec, what's the Poynting Vector? > > Same thing as a power flow vector. The dimensions are > energy per second per unit area. If the power flow vector > is integrated over the entire surface of a sphere of radius > r, the result is total radiated power. I thought maybe you > and Mr. Poynting might have worked together at some time in > the 20th century. :-) > >> Poynting, John Henry (1852-1914) >> English physicist, mathematician, and inventor. He devised an equation by >> which the rate of flow of electromagnetic energy > > (now called the Poynting vector) can be determined. S = E X H Article: 217162 of rec.radio.amateur.antenna From: Ian Jackson Subject: Re: 73 Ohms, How do you get it? Date: Wed, 14 Sep 2005 21:39:25 +0100 Message-ID: <5MOAq4S9pIKDFwB+@g3ohx.demon.co.uk> References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> In message <1126655181_28167@spool6-east.superfeed.net>, Cecil Moore writes >Reg Edwards wrote: >> Antenna conductors ARE transmission lines and the same sort of >> calculations apply. > >You're right, Reg. Without reflections from the ends of a >dipole, the feedpoint impedance would be hundreds of ohms. >A standing wave antenna is like a lossy transmission line >where the loss is to radiation. And the SWR on a 1/2WL dipole >standing wave antenna is quite high - in the neighborhood of >20:1. Just a quick question. What is the impedance at the centre of an infinitely long dipole (in free space)? Ian. -- Article: 217163 of rec.radio.amateur.antenna Subject: Re: 73 Ohms, How do you get it? From: Cecil Moore Date: Wed, 14 Sep 2005 16:42:53 -0500 Message-ID: <1126734334_299@spool6-east.superfeed.net> References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> <1126655181_28167@spool6-east.superfeed.net> <5MOAq4S9pIKDFwB+@g3ohx.demon.co.uk> Ian Jackson wrote: > Just a quick question. > What is the impedance at the centre of an infinitely long dipole (in > free space)? Same as a terminated dipole in an anechoic chamber? 600-800 ohms? -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- Article: 217164 of rec.radio.amateur.antenna From: "Steve Nosko" Subject: Re: 73 Ohms, How do you get it? Date: Wed, 14 Sep 2005 16:06:10 -0500 Message-ID: References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> Anyway, reading the op carefully, he asked for an exact _explanation_, not an exact calculation result.. Steve, K;9.D,C'I "Bill Turner" wrote in message news:xn0e77aaf2tt5l000@cnews.newsguy.com... > Reg Edwards wrote: > > > There's no such value as 'exact'. > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > Nonsense. I have exactly two pencils in my pencil holder. :-) > > 73, Bill W6WRT Article: 217165 of rec.radio.amateur.antenna From: Owen Duffy Subject: Re: How Handle Multiple Open Wire Lines? Message-ID: References: Date: Wed, 14 Sep 2005 21:50:30 GMT Here is a commercial implementation of MF / HF transmission lines. (They are not telephone lines.) http://members-central.optushome.com.au/vk3ase/feed2.jpg http://members-central.optushome.com.au/vk3ase/feed.jpg Owen On Mon, 1 Aug 2005 17:43:34 -0700, "greg knapp 5" wrote: >I need your advice, as I have never worked with open wire lines before. >I need to feed many different antennas with open wire line and need to run >the feeline from each about 200 feet from the back pasture to the shack. I >don't want to walk out 200 feet and throw knife switches to chose the >antenna/feedline I want to feed, so I plan to run separate 600 ohm open >feeds for each antenna all the way to the shack. >The problem is I don't know what the effect is or how to handle the >multiple open wire feed lines, as they will be parallel for probably 150-200 >feet. I haven't found anything in literature describing this. >For instance, will they interact? how far do you space the feedlines from >one another? If I have 4 feedlines, can I stack them vertically or >horizontally one foot apart from each other? How much is enough separation? >What other precautions do I need? Need they be twisted if they are not near >anything other than the other feed lines? >Any help is appreciated. >73, >Greg, N6GK > -- Article: 217166 of rec.radio.amateur.antenna From: Jim Kelley Subject: Re: 73 Ohms, How do you get it? Date: Wed, 14 Sep 2005 14:38:21 -0700 Message-ID: References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> <1126655181_28167@spool6-east.superfeed.net> <5MOAq4S9pIKDFwB+@g3ohx.demon.co.uk> <1126734334_299@spool6-east.superfeed.net> Cecil Moore wrote: > Ian Jackson wrote: > >> Just a quick question. >> What is the impedance at the centre of an infinitely long dipole (in >> free space)? > > > Same as a terminated dipole in an anechoic chamber? 600-800 ohms? Not at zero Hz. ac6xg Article: 217167 of rec.radio.amateur.antenna From: Jim Kelley Subject: Re: 73 Ohms, How do you get it? Date: Wed, 14 Sep 2005 14:42:37 -0700 Message-ID: References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126653287_28145@spool6-east.superfeed.net> <1126731751.254078.115460@g49g2000cwa.googlegroups.com> Harry wrote: > Hi Cecil, > > I find another formula in Balnais book (section 4.3, 1982 edition) > for Rr: > > Rr = 20 * (pi)^2 * ( l / lamda)^2 (4-37) > > If l = lamda/2, then this formula gives Rr .=. 50 Ohms. > > (4-93) the one you quoted is > > Rr = (120*pi) / (4*pi) * Cin( 2*pi ) = 73 Ohms, (for l = lamda/2) > > where 120*pi is the intrinsic impedance for a free-space medium. > > Would you please explain the difference between these > two formulas (4-37 and 4-93)? > > > Thanks! > > -- Harry 4-37 should apparently read: Rr = 30 * (pi)^2 * (1 / lambda)^2. ac6xg Article: 217168 of rec.radio.amateur.antenna From: David Subject: Re: Open Stub fed J antenna References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <1126707001_31799@spool6-east.superfeed.net> Message-ID: Date: Wed, 14 Sep 2005 22:15:10 GMT Cecil, Thanks for the info. The open stub J looks like it should be suitable for my application being ground independent, omni directional and having low radiation angle. Cecil Moore wrote: > David wrote: > >> Does anyone know of where I could find an example of a homebrew open stub >> fed j antenna. I want to construct a unit for 915 MHz using SMA plug >> and coaxial cable. > > > An open stub J-pole is the same as a Zepp. 1/2WL element > end fed by 1/4WL balanced series section. The coax connects > to the end of the series section. Arrow Antenna makes one > for 2m. Plans are available that could possibly be scaled > to 915 MHz. Article: 217169 of rec.radio.amateur.antenna From: "Jerry Martes" References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <1126707001_31799@spool6-east.superfeed.net> Subject: Re: Open Stub fed J antenna Message-ID: Date: Wed, 14 Sep 2005 23:03:57 GMT Dave Have you considered making a coaxial version of the J-pole? http://www.ansoft.com/news/articles/04.05_MWJ.pdf Jerry "David" wrote in message news:Oh1We.47455$FA3.23606@news-server.bigpond.net.au... > Cecil, > > Thanks for the info. The open stub J looks like it should be suitable for > my application being ground independent, omni directional and having low > radiation angle. > > Cecil Moore wrote: > >> David wrote: >> >>> Does anyone know of where I could find an example of a homebrew open >>> stub >>> fed j antenna. I want to construct a unit for 915 MHz using SMA plug and >>> coaxial cable. >> >> >> An open stub J-pole is the same as a Zepp. 1/2WL element >> end fed by 1/4WL balanced series section. The coax connects >> to the end of the series section. Arrow Antenna makes one >> for 2m. Plans are available that could possibly be scaled >> to 915 MHz. Article: 217170 of rec.radio.amateur.antenna Subject: Re: 73 Ohms, How do you get it? From: Cecil Moore Date: Wed, 14 Sep 2005 18:12:26 -0500 Message-ID: <1126739706_405@spool6-east.superfeed.net> References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126653287_28145@spool6-east.superfeed.net> <1126731751.254078.115460@g49g2000cwa.googlegroups.com> Harry wrote: > Would you please explain the difference between these > two formulas (4-37 and 4-93)? Equation 4-37 is from section "4.3 SMALL DIPOLE", i.e. shorter than 1/2WL. The dipole is so short that its current distribution is triangular, not sinusoidal. Quoting section 4.3: "The radiation resistance of the antenna is strongly dependent upon the current distribution." The "1/2" on the diagram does NOT mean 1/2WL. Equation 4-93 is from section "4.6 HALF-WAVELENGTH DIPOLE". The current distribution on the thin-wire 1/2WL dipole is considered to be sinusoidal. See Figure 4.8. Note the triangular current distribution for L = 1/4WL and the sinusoidal current distribution for L = 1/2WL. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- Article: 217171 of rec.radio.amateur.antenna Subject: Re: Open Stub fed J antenna From: Cecil Moore Date: Wed, 14 Sep 2005 18:13:24 -0500 Message-ID: <1126739764_407@spool6-east.superfeed.net> References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <1126707001_31799@spool6-east.superfeed.net> David wrote: > Thanks for the info. The open stub J looks like it should be suitable > for my application being ground independent, omni directional and having > low radiation angle. Be sure to include a choking function at the feedpoint. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- Article: 217172 of rec.radio.amateur.antenna From: David Subject: Re: Open Stub fed J antenna References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <1126707001_31799@spool6-east.superfeed.net> <1126739764_407@spool6-east.superfeed.net> Message-ID: Date: Thu, 15 Sep 2005 00:34:51 GMT Thanks for the feedback everyone. The article Jerry pointed me to starts looking like the commercial antenna I was initially studying. Their unit though only had a 1/4 wave above the coaxial sleeve. From the SMA plug, the coax coiled around the radome must have been the choke to help reduce RF currents radiating from the earth braid. Then the 1/4 wave length coax forms the match followed by the expose radiating section. It looks like an open stub fed J-pole where the stub is enclosing the inner element rather than being constructed as a rod next to it. Does this seem reasonable ? (PS. I'm a beginner with regards to antenna theory and would like to understand what is happening so that I can experiment with some kind degree of success). Cecil Moore wrote: > David wrote: > >> Thanks for the info. The open stub J looks like it should be suitable >> for my application being ground independent, omni directional and >> having low radiation angle. > > > Be sure to include a choking function at the feedpoint. Article: 217173 of rec.radio.amateur.antenna From: "Jerry" References: <1126505259.234971.15970@f14g2000cwb.googlegroups.com> Subject: Re: best HF antenna system next to a trailer? Message-ID: <2K3We.5007$%Q1.3074@bignews3.bellsouth.net> Date: Wed, 14 Sep 2005 21:03:40 -0400 wrote in message news:1126505259.234971.15970@f14g2000cwb.googlegroups.com... > Hi, > > I'd like some advice for determining the best antenna to put up in my > situation. > > I am getting set to move to a trailer park in northeast arizona, about > 50 miles west of Gallup, NM. Locals have no objection to antennas so > long as people don't have to run into them via normal passage ways. > The trailer is 12 feet high by 15 feet wide by 50 feet long, facing > N-S. Nearest certain ground is electrical panel. The water pipe is > metal but could be interrupted throughout system by PVC. There may > also be significant noise from AC systems in park. > > Good news is that my wife is giving me an entire walk-in closet for my > station, and that I can lay aluminum foil against all surfaces to > create a Faraday cage. > > I have approx 25 to 30 feet between my trailer and neighbors, and a 35 > foot altitude streetlamp 6 feet away curb. Soil conductivity is red > clay, extremely poor. Significant rainfall (monsoons) summer to fall. > Winds gusting to 50 or 60 mph during winter. Soil frosts between > October to March. > > I would like to work CW DX on 40, 30, 20, and 17 meters. 80 and 160 > would > be a bonus. Conventional options such as tower or surplus telephone > pole are out of the question due to cost and lack of available area. > Radials must be buried as children are playing nearby. > > Probable options: > > 1) Load up the streetlamp with an antenna matcher, work against 180 > degrees of buried radials out to 1/8 lambda. > > 2) Solder a series of tin/steel cans (cantenna) using pocket torch and > copper tape to 1/4 lambda with added capacitance hat(s), brace the cans > against the ground and the trailer, work against 270 to 360 degrees of > buried radials out to 3/8 lambda. > > 3) Create a mast from 40 feet of metal pipe and 15 feet of wood rod, > brace against trailer burying pipe end 10 feet, mount an inverted vee > trap dipole in N-S direction for E-W DX. > > 4) Pair of masts on either side of the trailer, mount a delta loop > from each mast, feed one loop and use the other as a reflector. > > 5) Pair of cantennas on each side of the trailer, operating as out of > phase pair of 1/4 lambda verticals. > > Which would be best? And where do I place the lightning arrestor(s)? > > Thanks, > > The Eternal Squire How about the screwdriver antenna. This is compact, can even be "disguised" inside a PVC pipe, can be positioned vertically OR horizontally and can be used to tune a random wire strung into a nearby tree. I used this system on a motor home where we positioned the antenna on the rear ladder with a swivel mount. When traveling, the antenna was positioned at a 45 degree angle and rested in a wooden cradle on top of the bus. At rest, the antenna could be raised to the vertical in a minute or two and tightened with thumbscrews. Because the motor home was mostly fiberglass, we quickly discovered that the antenna could be used in the semi-horizontal position while going down the road with good results! In your case, your trailer would be a "mobile", but you could set it up in several ways to take advantage of various situations, and, also tune a random wire with it. I've done this while on field exercizes with CAP. Now I know I am partial since I make screwdrivers, but you can find a variety of makers on the web. Just try to avoid the ones made of PVC and, of course, there are those that are SUPER expensive. Go for the ones with larger diameter coils and wire sizes and avoid the ones that promise 160 thru 10. Those that promise 160 thru 10 are the ones that are wound on small diameter forms and are wound with 20 gauge wire CLOSELY together (in effect, transformer-wound) which destroys your "Q". I doubt seriously such an antenna would do much "punkin" on 160! Every body runs into compromises at times, so you have to be do the best you can do with what you have to work with. If you have 75 feet of room over your lot, then you might visit www.k1jek.com for an all-band dipole 80-10 Meters. I'm told this is a good choice for short lots. Hope this helps 73 Jerry K4KWH www.qsl.net/k4kwh > Article: 217174 of rec.radio.amateur.antenna From: dplatt@radagast.org (Dave Platt) Subject: Re: Open Stub fed J antenna Date: Thu, 15 Sep 2005 01:09:00 -0000 Message-ID: <11ihidcala4s727@corp.supernews.com> References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <1126739764_407@spool6-east.superfeed.net> In article , David wrote: >The article Jerry pointed me to starts looking like the commercial >antenna I was initially studying. Their unit though only had a 1/4 wave >above the coaxial sleeve. > > From the SMA plug, the coax coiled around the radome must have been the >choke to help reduce RF currents radiating from the earth braid. >Then the 1/4 wave length coax forms the match followed by the expose >radiating section. > >It looks like an open stub fed J-pole where the stub is enclosing the >inner element rather than being constructed as a rod next to it. > >Does this seem reasonable ? (PS. I'm a beginner with regards to antenna >theory and would like to understand what is happening so that I can >experiment with some kind degree of success). Yes, it does. Take a look at the following: http://download.antennex.com/hws/ws1002/sperrtof.pdf A Sperrtof, in effect, is a J-pole whose matching section is a coaxial tube rather than a single rod or wire. It sounds rather like what you're describing. As with all such (I think), the radiating section is 1/2 wavelength long, give or take a smidge, and behaves as an end-fed 1/2-wave dipole. The matching section isn't supposed to radiate significantly. The overall radiation pattern would, I expect, be essentially the same as other J-poles and other end-fed 1/2-wave radiators - similar to a center-fed 1/2-wave dipole, but tilted a bit "upwards" away from the feedpoint. You can distinguish a Sperrtof-type antenna from one of the coaxial dipoles Jerry referred you to, by the length of the single-wire radiator - it's 1/2-wave for a Sperrtof and 1/4-wave for a coaxial dipole (which is really a center-fed dipole). There's an interesting dual-band 2m/440 antenna which was written up in QST in October 2000 - ARRL members can get the article at http://www.arrl.org/members-only/tis/info/pdf/0010050.pdf It's interesting because it's _called_ a J-pole, _looks_ like a J-pole... but electrically it isn't. It's actually a center-fed vertical, not a Zepp. The stub at the bottom acts as a choke/decoupler, not as an impedance transformer. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! Article: 217175 of rec.radio.amateur.antenna From: David Subject: Re: Open Stub fed J antenna References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <1126739764_407@spool6-east.superfeed.net> <11ihidcala4s727@corp.supernews.com> Message-ID: Date: Thu, 15 Sep 2005 01:41:06 GMT Dave, If I scale that up to 915MHz, the dimensions are almost perfect for using RG58 coax instead of the copper tubing.The outer tube would be 5.5mm and inner conductor 1.6mm. Being 50 Ohm coax, I assume therefore I do not need to slide the tap point up as their design did. I suppose I should also add the choke coil at the antenna base for additional isolation of ground currents. The article mentions the top part as 1/2 wave and bottom at 1/4 wave. If the bottom part of their design is 505mm then the antenna must be used for 2m band. If this is the case, how come the radiating element is 1480 long ? The Coaxial antenna mentioned in the article mentioned by Jerry looks good. The version they mention with a GAP would be simple to construct. It is a 1/4 wave radiating element at the top (earth braid stripped back), then 1/4 wave of full coax, then a "small" gap, then the transmission line. They do not mention the size of the gap but I assume any small gap has the same effect of isolating the reverse current ? Should the actual lengths of these sections be modified by "K" depending on diameter of conductor or are they exact 1/4 wave length cuts ? Thanks heaps. Dave Platt wrote: > In article , > David wrote: > > >>The article Jerry pointed me to starts looking like the commercial >>antenna I was initially studying. Their unit though only had a 1/4 wave >>above the coaxial sleeve. >> >>From the SMA plug, the coax coiled around the radome must have been the >>choke to help reduce RF currents radiating from the earth braid. >>Then the 1/4 wave length coax forms the match followed by the expose >>radiating section. >> >>It looks like an open stub fed J-pole where the stub is enclosing the >>inner element rather than being constructed as a rod next to it. >> >>Does this seem reasonable ? (PS. I'm a beginner with regards to antenna >>theory and would like to understand what is happening so that I can >>experiment with some kind degree of success). > > > Yes, it does. Take a look at the following: > > http://download.antennex.com/hws/ws1002/sperrtof.pdf > > A Sperrtof, in effect, is a J-pole whose matching section is a coaxial > tube rather than a single rod or wire. It sounds rather like what > you're describing. > > As with all such (I think), the radiating section is 1/2 wavelength > long, give or take a smidge, and behaves as an end-fed 1/2-wave > dipole. The matching section isn't supposed to radiate significantly. > > The overall radiation pattern would, I expect, be essentially the same > as other J-poles and other end-fed 1/2-wave radiators - similar to a > center-fed 1/2-wave dipole, but tilted a bit "upwards" away from the > feedpoint. > > You can distinguish a Sperrtof-type antenna from one of the coaxial > dipoles Jerry referred you to, by the length of the single-wire > radiator - it's 1/2-wave for a Sperrtof and 1/4-wave for a coaxial > dipole (which is really a center-fed dipole). > > There's an interesting dual-band 2m/440 antenna which was written up > in QST in October 2000 - ARRL members can get the article at > http://www.arrl.org/members-only/tis/info/pdf/0010050.pdf > > It's interesting because it's _called_ a J-pole, _looks_ like a > J-pole... but electrically it isn't. It's actually a center-fed > vertical, not a Zepp. The stub at the bottom acts as a > choke/decoupler, not as an impedance transformer. > Article: 217176 of rec.radio.amateur.antenna Subject: Re: Open Stub fed J antenna From: Cecil Moore Date: Wed, 14 Sep 2005 21:10:14 -0500 Message-ID: <1126750373_543@spool6-east.superfeed.net> References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <1126739764_407@spool6-east.superfeed.net> <11ihidcala4s727@corp.supernews.com> David wrote: > If I scale that up to 915MHz, the dimensions are almost perfect for > using RG58 coax ... I wouldn't use RG58 for anything above HF. It has 20 dB matched line loss per 100 ft at that frequency. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- Article: 217177 of rec.radio.amateur.antenna From: David Subject: Re: Open Stub fed J antenna References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <1126739764_407@spool6-east.superfeed.net> <11ihidcala4s727@corp.supernews.com> <1126750373_543@spool6-east.superfeed.net> Message-ID: <4b5We.47625$FA3.35929@news-server.bigpond.net.au> Date: Thu, 15 Sep 2005 02:41:04 GMT So for the 1/4 wave (81mm) section of the antenna the loss would be about 0.05dB ? at 915 MHz. I typically have between 150mm (When antenna mounted on enclosure) and 2m length (when antenna external to enclosure) cable between transmitter and Antenna. (Around 1.2dB max. loss in coax between transmitter and antenna). Would this usually be acceptable or do you aim for much lower loss in the transmission line ? Max. power is 1 Watt. Most of the transceivers I play around with are around 10mW. Thanks Cecil Moore wrote: > David wrote: > >> If I scale that up to 915MHz, the dimensions are almost perfect for >> using RG58 coax ... > > > I wouldn't use RG58 for anything above HF. It has 20 dB > matched line loss per 100 ft at that frequency. Article: 217178 of rec.radio.amateur.antenna From: "Dale Parfitt" References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <1126739764_407@spool6-east.superfeed.net> <11ihidcala4s727@corp.supernews.com> <1126750373_543@spool6-east.superfeed.net> <4b5We.47625$FA3.35929@news-server.bigpond.net.au> Subject: Re: Open Stub fed J antenna Message-ID: Date: Thu, 15 Sep 2005 12:42:48 GMT "David" wrote in message news:4b5We.47625$FA3.35929@news-server.bigpond.net.au... > So for the 1/4 wave (81mm) section of the antenna the loss would be about > 0.05dB ? at 915 MHz. > 20dB/100' MATCHED line loss. W4OP Article: 217179 of rec.radio.amateur.antenna Subject: Re: Open Stub fed J antenna From: Cecil Moore Date: Thu, 15 Sep 2005 08:07:35 -0500 Message-ID: <1126789815_959@spool6-east.superfeed.net> References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <1126739764_407@spool6-east.superfeed.net> <11ihidcala4s727@corp.supernews.com> <1126750373_543@spool6-east.superfeed.net> <4b5We.47625$FA3.35929@news-server.bigpond.net.au> David wrote: > So for the 1/4 wave (81mm) section of the antenna the loss would be > about 0.05dB ? at 915 MHz. Depends upon whether you leave the insulation on the radiating part or not. But what I was concerned about is the transmission line. You lose about half of your power every 15 feet. Until your last posting, you didn't tell us the length of the transmission line but personally I find 1.2 dB matched line loss in six feet to be unacceptable. Any SWR above 1:1 and the losses are even greater. > Cecil Moore wrote: >> I wouldn't use RG58 for anything above HF. It has 20 dB >> matched line loss per 100 ft at that frequency. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- Article: 217180 of rec.radio.amateur.antenna From: "Fred W4JLE" References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Date: Thu, 15 Sep 2005 10:41:17 -0400 Message-ID: While I would agree with officious and petty, moron and bigot do not apply >from my readings. I get really tired of that old saw being hauled out and applied to people; simply because others disagree with their actions. A few moments spent perusing a dictionary will show that simply refusing to take in a storm victim, while abhorrent to me, does not make one a bigot. "Michael A. Terrell" wrote in message news:4324E0BD.A033E1A@earthlink.net... > "LenAnderson@ieee.org" wrote: > > > > The disaster of hurricane Katrina is of unparalleled proportions > > and ALL humane-thinking citizens can do their part, however big, > > however small. > > > And then, there are the morons and bigots: > > > > -- > ? > > Michael A. Terrell > Central Florida Article: 217181 of rec.radio.amateur.antenna From: "Fred W4JLE" References: <1126505259.234971.15970@f14g2000cwb.googlegroups.com> <9175-4326EEA5-1@storefull-3254.bay.webtv.net> <1126670383.884527.133320@f14g2000cwb.googlegroups.com> Subject: Re: best HF antenna system next to a trailer? Date: Thu, 15 Sep 2005 10:56:26 -0400 Message-ID: <71e25$43298bb2$471c610a$29323@ALLTEL.NET> Smack her in the head and put up a tower, It has worked on all 7 of my wives. :>) wrote in message news:1126670383.884527.133320@f14g2000cwb.googlegroups.com... > Money and space are actually limiting factors, but at least CC&R's > arent! My wife and I have been discussing this, and she really > doesn't like the idea of something 30 to 40 feet high on a small lot. > > Her interest actually is gardening and we had been discussing > containing an area of decent topsoil within a square formed by railroad > ties. She has no objection to 20 to 25 foot high metal poles on the > corners of a square 20 to 25 foot on the side... which turns out to be > the core geometry of a 20 meter 4-square broadside phase array. > > I would lay the poles first in concrete reinforced holes, connect the > feed network and radials on the dirt, and lay feed line underground > from the array to just near the trailer. Then I would lay the railroad > ties along the square, and then fill the square with topsoil. > > Additional radials would need to be buried under a couple inches of red > clay fanning out from the square. > > Variations: > 1) could I create trap verticals from the poles for 20, 17, 15, and 10 > meters, or do I need inscribed squares of seperate verticals because > seperate phased feeds might be needed for these other bands? > 2) could I simply operate the square outside of 20 meters with a tuner > for local operation? > > I think because space, money, and aesthetics are limiting factors, I > need to use precision to my advantage rather than size or height, and a > 4 square may help there. > > Comments? > > The Eternal Squire > Article: 217182 of rec.radio.amateur.antenna From: "Caveat Lector" Subject: Katrina Ham Stories Message-ID: Date: Thu, 15 Sep 2005 08:20:00 -0700 http://ac6v.com/new.htm See big antenna in action Ham Radio Rescue Effort On TV http://easylink.playstream.com/katu/050831ham_operator_530pm.wvx -- CL -- I doubt, therefore I might be ! Article: 217183 of rec.radio.amateur.antenna From: "Fred W4JLE" References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com> Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Date: Thu, 15 Sep 2005 12:00:29 -0400 Message-ID: <31f74$43299abf$471c63c6$12083@ALLTEL.NET> Perhaps you could show me where any of the offered definitions apply to an HOA rule that prohibits non family members from residing in a home. "Richard Clark" wrote in message news:4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com... > On Thu, 15 Sep 2005 10:41:17 -0400, "Fred W4JLE" > wrote: > > >A few moments spent perusing a dictionary will show that simply refusing to > >take in a storm victim, while abhorrent to me, does not make one a bigot. > > > from the Oxford English Dictionary: > > Bigot. 1598. 1. A hypocrite. 2. A superstitious person - 1664. 3. A > person obstinately and unreasonably wedded to a creed, opinion or > ritual - 1661. Intolerant toward others - 1645. > > Hardly seems that the meaning has veered from this in the past 340 > years. > > 73's > Richard Clark, KB7QHC Article: 217184 of rec.radio.amateur.antenna From: Walter Maxwell Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Message-ID: References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com> Date: Thu, 15 Sep 2005 12:01:35 -0400 In light of Colin Powell's position that the fate of the poorer people of New Orleans was not due to racism, but only failing to realize that those people had no means for transportation out of the city, it seems to me that racism and bigotry were not involved. To me it's significant that that position is held by a highly-respected person of color. Walt, W2DU On Thu, 15 Sep 2005 08:36:56 -0700, Richard Clark wrote: >On Thu, 15 Sep 2005 10:41:17 -0400, "Fred W4JLE" >wrote: > >>A few moments spent perusing a dictionary will show that simply refusing to >>take in a storm victim, while abhorrent to me, does not make one a bigot. >> >from the Oxford English Dictionary: > >Bigot. 1598. 1. A hypocrite. 2. A superstitious person - 1664. 3. A >person obstinately and unreasonably wedded to a creed, opinion or >ritual - 1661. Intolerant toward others - 1645. > >Hardly seems that the meaning has veered from this in the past 340 >years. > >73's >Richard Clark, KB7QHC Article: 217185 of rec.radio.amateur.antenna From: "John N9JG" Subject: Wooden I section pole Date: Thu, 15 Sep 2005 11:36:27 -0500 Message-ID: I am in the planning stage for a 160 meters compact loop antenna. A loop antenna may not have metal nearby, so I am planning to use a wooden pole to support the top of the loop. In the ARRL Antenna handbook, it states that "W5QJR made a pole of 2 x 4-inch lumber with 1 x 4-inch boards on either side to form an I section. He held the boards together with 1/4-inch bolts, 2 feet apart and tied rope guys to the top. This made an excellent mast up to 50 feet high." Does anyone have any comments on the feasibility of an unguyed pole using this same type of construction? Naturally, a portion of the pole would have to be underground, and perhaps set in concrete. What about a 50 feet pole, with 10 feet underground ,which would give you a 40 foot mast? An alternative would be to have a contractor install a 40 feet utility pole, but I assume the wooden pole described above would be less of an eyesore (to the neighbors) than a utility pole. Any comments and advice will be appreciated. John, N9JG Article: 217186 of rec.radio.amateur.antenna From: "Fred W4JLE" References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com> Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Date: Thu, 15 Sep 2005 12:40:44 -0400 Message-ID: Even more frustrating is the number of school buses controlled by a black Mayor that never were put in to evacuation service. The same buses now set in water and I am sure they will be replaced at taxpayers expense. As I was somewhat involved in the political debacle, I can tell you from personal experience that Red Cross and amateur radio vans were prohibited >from entering the disaster area. My cynical side says that in the background, a chance was both seen and taken to make George Bush look bad. The democrat political machine in New Orleans is only surpassed by that of Chicago. I know for a fact the Red Cross was told that if they were to feed the people in the superdome they would stay. Some how I find it ironical that a black mayor applied the same wisdom to his people that my mother applied to the neighborhood stay dog I attempted to feed. Where were all the murdered bodies, in the superdome, the press reported on so breathlessly? The must have hid them in Al Capone's vault to make Geraldo look bad; as he worked for the evil Fox network... Of course the more the race card is played, the more money is offered by white America to assuage the implied guilt. Black poloticos have learned this lesson well! "Walter Maxwell" wrote in message news:ma6ji1ta47t9n95hh87nssvc4it2pjlko1@4ax.com... > In light of Colin Powell's position that the fate of the poorer people > of New Orleans was not due to racism, but only failing to realize > that those people had no means for transportation out of the city, it > seems to me that racism and bigotry were not involved. To me it's > significant that that position is held by a highly-respected person of > color. > > Walt, W2DU Article: 217187 of rec.radio.amateur.antenna From: "David G. Nagel" Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Date: Thu, 15 Sep 2005 12:08:23 -0500 Message-ID: <11ijakdlh2ucb26@corp.supernews.com> References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com> If the poor people of New Orleans didn't have transportation out of town it was because their elected Mayor refused to have them humiliated by having to leave town in a school bus or city bus. He wanted Greyhound busses with working air-conditioning for them. It's in the disaster plan to use busses for evacuation. Read it. Walter Maxwell wrote: > In light of Colin Powell's position that the fate of the poorer people > of New Orleans was not due to racism, but only failing to realize > that those people had no means for transportation out of the city, it > seems to me that racism and bigotry were not involved. To me it's > significant that that position is held by a highly-respected person of > color. > > Walt, W2DU > > > On Thu, 15 Sep 2005 08:36:56 -0700, Richard Clark > wrote: > > >>On Thu, 15 Sep 2005 10:41:17 -0400, "Fred W4JLE" >>wrote: >> >> >>>A few moments spent perusing a dictionary will show that simply refusing to >>>take in a storm victim, while abhorrent to me, does not make one a bigot. >>> > >>from the Oxford English Dictionary: > >>Bigot. 1598. 1. A hypocrite. 2. A superstitious person - 1664. 3. A >>person obstinately and unreasonably wedded to a creed, opinion or >>ritual - 1661. Intolerant toward others - 1645. >> >>Hardly seems that the meaning has veered from this in the past 340 >>years. >> >>73's >>Richard Clark, KB7QHC > > Article: 217188 of rec.radio.amateur.antenna Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article From: Cecil Moore Date: Thu, 15 Sep 2005 12:29:47 -0500 Message-ID: <1126805610_1361@spool6-east.superfeed.net> References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com> <11ijakdlh2ucb26@corp.supernews.com> David G. Nagel wrote: > It's in the disaster plan to use busses for evacuation. One news service reported that billions earmarked for mass transit and levee improvements had been spent on advertising for the tourism industry. -- 73, Cecil, http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- Article: 217189 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: Wooden I section pole Date: Thu, 15 Sep 2005 18:05:36 +0000 (UTC) Message-ID: References: A vertical conductor, a metal tube, running diametrically across a large magloop with the tuning capacitor at the top, has no effect either on radiating efficiency or the radiation pattern. It may as well not be there apart from providing a prop or support for the antenna itself. It will, of course, need to be well-insulated from the high-voltage parts. In general, provided the longest dimension of foreign metalwork is much less than 1/2-wavelength, and there is not much of it, negligible loss will be induced in it. This is due to the very low loss resistance of most metals. Metalwork in the vicinity of beam antennas may upset only the radiation pattern. Short lengths of foreign metalwork in close vicinity of tramsmission lines, such as open-wire and ladder lines, will cause neglible loss but will slightly reduce the line impedance Zo which might affect the L and C settings of the tuner. But beware of "semi-conductors", like damp wood such as foliage and tree trunks, in the near-fields of antennas and lines. Their higher impedance provide a better power match to the 'generator'. You can have as much foreign polyethylene as you like. ---- Reg. Article: 217190 of rec.radio.amateur.antenna From: "news-z-non-exist-z" Subject: Re: 73 Ohms, How do you get it? Date: Thu, 15 Sep 2005 21:26:04 +0300 Message-ID: References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> <11iesohk2gnkf80@corp.supernews.com> | "Roy Lewallen" | wrote in message news:11iesohk2gnkf80@corp.supernews.com... | | Just about any antenna textbook will show you the calculation | [...] | ln(gamma * x) - (x^2)/(2!2) + (x^4)/(4!4) - (x^6)/(6!6). . . | | Roy Lewallen, W7EL [... ] and after all that, we finally draw a figure such the one at: http://antennas.ee.duth.gr/Antennas_Notes_II_2005/23.htm pezSV7BAXdag Article: 217191 of rec.radio.amateur.antenna From: dplatt@radagast.org (Dave Platt) Subject: Re: Open Stub fed J antenna Date: Thu, 15 Sep 2005 18:37:48 -0000 Message-ID: <11ijfrs1plk1a5c@corp.supernews.com> References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <11ihidcala4s727@corp.supernews.com> In article , David wrote: >Dave, > >If I scale that up to 915MHz, the dimensions are almost perfect for >using RG58 coax instead of the copper tubing.The outer tube would be >5.5mm and inner conductor 1.6mm. Being 50 Ohm coax, I assume therefore I >do not need to slide the tap point up as their design did. Bad assumption, I think. The portion of the matching section between the tap point and the bottom is a shorted stub, which adds some inductive reactance at the feedpoint. If you don't have it, you won't get a good match. Another approach I've seen to creating the necessary shorted stub is to just use RG-58 and a simple BNC "T" connector. If you look at the Sperrtopf antenna design, picture it made this way: - one long piece of RG-58 1380 mm long, with the upper part of the outer shield removed... that's your radiator, and the portion of the matching section above the feedpoint. - A second section of RG-58, about 100 mm long, with one end shorted. That's the stub. - The feedline RG-58. Now, just connect all three together... radiator/matching section, stub, and feedline. You can solder 'em, or add BNC plugs and use a BNC "T". If you do the latter, remember to include the lengths of the plugs and "T" into account. > I suppose I >should also add the choke coil at the antenna base for additional >isolation of ground currents. Certainly would not hurt to do so. You could either coil the coax below the bottom of the matching section, or add a quarter-wave choke sleeve, or just run the coax through a few ferrite beads. >The article mentions the top part as 1/2 wave and bottom at 1/4 wave. If >the bottom part of their design is 505mm then the antenna must be used >for 2m band. If this is the case, how come the radiating element is 1480 >long ? I think there's some confusion in the antenna schematic diagram, compared with the text and parts list. The diagram appears to show the upper (radiating) portion of the center element being 1480 mm, but the parts list indicates that the *total* length of the inner element is 1480 mm. The latter seems more correct to me... it'd give you a radiating element of (1480 - 505) = 975 mm, which is a bit less than 1/2 physical wavelength at 2 meters. This seems reasonable to me given that the radiating element is fairly thick (10mm) rather than a thin wire. >The Coaxial antenna mentioned in the article mentioned by Jerry looks >good. The version they mention with a GAP would be simple to construct. >It is a 1/4 wave radiating element at the top (earth braid stripped >back), then 1/4 wave of full coax, then a "small" gap, then the >transmission line. They do not mention the size of the gap but I assume >any small gap has the same effect of isolating the reverse current ? I'm not clear about the gap configuration either. The article sort of implies that its size has to be set experimentally, so that the leakage current through the gap is the right amount to cancel out the signal propagating back down the outside of the upper section. The article doesn't say whether the gap is supposed to go around the full circumference of the coax (completely isolating the upper and lower portions of the shield) or only partially around... I infer that it's the latter, because I don't see how the antenna could work with the shield sections fully separated. >Should the actual lengths of these sections be modified by "K" depending >on diameter of conductor or are they exact 1/4 wave length cuts ? Well, I think it's a bit of a compromise. The upper section (the coax center conductor and its surrounding dielectric) is going to have a velocity factor of not much less than 1.0. Cutting to 1/4 physical wavelength, and then trimming a bit, seems likely to work. I think the lower section is likely to be a bit trickier, since there are actually two velocity factors involved. The radiating is done by the RF travelling back down the outside of the coax braid from the feedpoint, and this (like the upper section) will have a velocity factor close to 1.0, which suggests that the gap-to-feedpoint distance should be close to 1/4 physical wavelength. HOWEVER: the signal travelling up the *inside* of the braid, like that travelling up the inner conductor towards the feedpoint, will be travelling more slowly - the velocity factor will be somewhere around .66 - .8 depending on cable type. This means that there will be more than 180 degrees of phase delay between the signal passing the gap going upwards (inside the cable) and the signal reaching the gap from above (travelling back down the outside of the cable). Hence, the gap leakage won't result in full cancellation of the signal travelling down the outside of the coax past the gap. To get the two signals into accurate 180-degree phase opposition, you'd need to make the distance from the feedpoint to the gap a bit less than 1/4 physical wavelength, but a bit more than 1/4 of the coax's usual electrical wavelength. Splitting the difference might work fairly well. I'm not sure what this will do to the antenna's feedpoint impedance / return loss, though, and it'll probably tilt the antenna's radiation pattern somewhat. You will probably need to experiment to get the best compromise between antenna pattern and feedpoint impedance / return loss / SWR. The same is true of the gap size and configuration. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! Article: 217192 of rec.radio.amateur.antenna From: "Percival P. Cassidy" Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com> <31f74$43299abf$471c63c6$12083@ALLTEL.NET> Message-ID: <3gjWe.15460$tc7.10245@fe03.lga> Date: Thu, 15 Sep 2005 14:42:06 -0400 On 09/15/05 01:08 pm Richard Clark tossed the following ingredients into the ever-growing pot of cybersoup: >>Perhaps you could show me where any of the offered definitions apply to an >>HOA rule that prohibits non family members from residing in a home. > Christian charity is not fulfilled by a shrug of the HOA committee, > and members who enjoy the veil of these rules won't find it any easier > getting through the eye of the needle. Amen, Brother. "Perce" Article: 217193 of rec.radio.amateur.antenna From: Allodoxaphobia Subject: Re: 73 Ohms, How do you get it? Date: 15 Sep 2005 18:51:10 GMT Message-ID: References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> <11iesohk2gnkf80@corp.supernews.com> On Thu, 15 Sep 2005 21:26:04 +0300, news-z-non-exist-z wrote: >| "Roy Lewallen" >| wrote in message news:11iesohk2gnkf80@corp.supernews.com... >| >| Just about any antenna textbook will show you the calculation >| [...] >| ln(gamma * x) - (x^2)/(2!2) + (x^4)/(4!4) - (x^6)/(6!6). . . >| >| Roy Lewallen, W7EL > > [... ] and after all that, > we finally draw a figure such the one at: > > http://antennas.ee.duth.gr/Antennas_Notes_II_2005/23.htm > > pezSV7BAXdag Yes, but: http://antennas.ee.duth.gr/Antennas_Notes_II_2005/22.htm explains it best of all! HI!HI! 73 Jonesy -- Marvin L Jones | jonz | W3DHJ | linux Pueblo, Colorado | @ | Jonesy | OS/2 __ 38.24N 104.55W | config.com | DM78rf | SK Article: 217194 of rec.radio.amateur.antenna From: "Fred W4JLE" References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com> <31f74$43299abf$471c63c6$12083@ALLTEL.NET> Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Date: Thu, 15 Sep 2005 14:51:11 -0400 Message-ID: <6906e$4329c2c1$471c63c6$4287@ALLTEL.NET> Weak Richard, but we love you no less. "Richard Clark" wrote in message news:t3aji1hsepkfap9c8i3h0j3t592t8nedfd@4ax.com... > On Thu, 15 Sep 2005 12:00:29 -0400, "Fred W4JLE" > wrote: > > >Perhaps you could show me where any of the offered definitions apply to an > >HOA rule that prohibits non family members from residing in a home. > > You said it yourself: > >>refusing to take in a storm victim > exactly conforms to > >>>Intolerant toward others - 1645. > > otherwise, why would you offer your opinion > >>while abhorrent to me > > Christian charity is not fulfilled by a shrug of the HOA committee, > and members who enjoy the veil of these rules won't find it any easier > getting through the eye of the needle. > > 73's > Richard Clark, KB7QHC Article: 217195 of rec.radio.amateur.antenna From: "Fred W4JLE" References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com> <11ijakdlh2ucb26@corp.supernews.com> <1126805610_1361@spool6-east.superfeed.net> Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Date: Thu, 15 Sep 2005 14:53:01 -0400 Message-ID: Not to mention the purchase of a casino and the construction of a Marina. "Cecil Moore" wrote in message news:1126805610_1361@spool6-east.superfeed.net... > David G. Nagel wrote: > > It's in the disaster plan to use busses for evacuation. > > One news service reported that billions earmarked for mass > transit and levee improvements had been spent on advertising > for the tourism industry. > -- > 73, Cecil, http://www.qsl.net/w5dxp > > ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- > http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups > ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- Article: 217196 of rec.radio.amateur.antenna Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article From: Cecil Moore Date: Thu, 15 Sep 2005 13:55:56 -0500 Message-ID: <1126810780_1703@spool6-east.superfeed.net> References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com> <31f74$43299abf$471c63c6$12083@ALLTEL.NET> Richard Clark wrote: > Christian charity is not fulfilled by a shrug of the HOA committee, > and members who enjoy the veil of these rules won't find it any easier > getting through the eye of the needle. The small "eye of the needle" gate at the walls of a city was sized for human beings. It was camels that couldn't get through it. Camels had to enter through the main gate. -- 73, Cecil, http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- Article: 217197 of rec.radio.amateur.antenna From: "KØHB" References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com> <31f74$43299abf$471c63c6$12083@ALLTEL.NET> Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Message-ID: Date: Thu, 15 Sep 2005 19:09:05 GMT "Richard Clark" wrote > > Christian charity is not fulfilled by a shrug of the HOA committee, > and members who enjoy the veil of these rules won't find it any easier > getting through the eye of the needle. > How is "Christian charity" different from other charity, and do I need to be a member of your cult in order to get through the eye of the needle (and why would I want to?)? 73, de Hans, K0HB -- Homepage: http://www.home.earthlink.net/~k0hb Member: ARRL http://www.arrl.org SOC http://www.qsl.net/soc VWOA http://www.vwoa.org A-1 Operator Club http://www.arrl.org/awards/a1-op/ TCDXA http://www.tcdxa.org MWA http://www.w0aa.org TCFMC http://www.tcfmc.org FISTS http://www.fists.org LVDXA http://www.upstel.net/borken/lvdxa.htm NCI http://www.nocode.org Article: 217198 of rec.radio.amateur.antenna From: nospam@nouce.bellatlantic.net Subject: Re: Open Stub fed J antenna Message-ID: <9ogji11j72vmidsbque5h0utjt7mgj40b2@4ax.com> References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <11ihidcala4s727@corp.supernews.com> <11ijfrs1plk1a5c@corp.supernews.com> Date: Thu, 15 Sep 2005 19:13:28 GMT On Thu, 15 Sep 2005 18:37:48 -0000, dplatt@radagast.org (Dave Platt) wrote: >In article , >David wrote: > >>Dave, >> >>If I scale that up to 915MHz, the dimensions are almost perfect for >>using RG58 coax instead of the copper tubing.The outer tube would be >>5.5mm and inner conductor 1.6mm. Being 50 Ohm coax, I assume therefore I >>do not need to slide the tap point up as their design did. Using RG58 at 900mhz is a lossy situation to be avoided. >Bad assumption, I think. The portion of the matching section between >the tap point and the bottom is a shorted stub, which adds some >inductive reactance at the feedpoint. If you don't have it, you won't >get a good match. True. You can alter the lengths and use the stub section to cancel the inductive or capacitive reactance set up by the radiating element if present. If your radiating element is capacitive (tad shorter) then the stub can be open which will reflect as inductive. It's only a matter of juggling the numbers. >Another approach I've seen to creating the necessary shorted stub is >to just use RG-58 and a simple BNC "T" connector. If you look at the >Sperrtopf antenna design, picture it made this way: > >- one long piece of RG-58 1380 mm long, with the upper part of > the outer shield removed... that's your radiator, and the portion > of the matching section above the feedpoint. > >- A second section of RG-58, about 100 mm long, with one end shorted. > That's the stub. > >- The feedline RG-58. > >Now, just connect all three together... radiator/matching section, >stub, and feedline. You can solder 'em, or add BNC plugs and use a >BNC "T". If you do the latter, remember to include the lengths of the >plugs and "T" into account. > >> I suppose I >>should also add the choke coil at the antenna base for additional >>isolation of ground currents. > >Certainly would not hurt to do so. You could either coil the coax >below the bottom of the matching section, or add a quarter-wave choke >sleeve, or just run the coax through a few ferrite beads. If the antenna feed point is a matched condition what is the RF on the coax shield from? It should be very small. >>The article mentions the top part as 1/2 wave and bottom at 1/4 wave. If >>the bottom part of their design is 505mm then the antenna must be used >>for 2m band. If this is the case, how come the radiating element is 1480 >>long ? > >I think there's some confusion in the antenna schematic diagram, >compared with the text and parts list. The diagram appears to show >the upper (radiating) portion of the center element being 1480 mm, but >the parts list indicates that the *total* length of the inner element >is 1480 mm. For 2m the correct length for the total center element is 1480 (58"). At 2m the halfwave length is in free space is 1M or for real elements about 38" (.95M) or a K around .96-97. >The latter seems more correct to me... it'd give you a radiating >element of (1480 - 505) = 975 mm, which is a bit less than 1/2 >physical wavelength at 2 meters. This seems reasonable to me given >that the radiating element is fairly thick (10mm) rather than a thin >wire. Correct. Thick elements do make a noticeable difference especially when the ratio of wavelength to element diameter gets below 500:1. The effect is elements are shorter, bandwidth wider. >>The Coaxial antenna mentioned in the article mentioned by Jerry looks >>good. The version they mention with a GAP would be simple to construct. >>It is a 1/4 wave radiating element at the top (earth braid stripped >>back), then 1/4 wave of full coax, then a "small" gap, then the >>transmission line. They do not mention the size of the gap but I assume >>any small gap has the same effect of isolating the reverse current ? There is no requirement for the bottom to be coaxial. it can be parallel lines (convential Jpole) in either case the antenna is a 1/2 lamda using a open section of transmission line for matching. >I'm not clear about the gap configuration either. The article sort of >implies that its size has to be set experimentally, so that the >leakage current through the gap is the right amount to cancel out the >signal propagating back down the outside of the upper section. The >article doesn't say whether the gap is supposed to go around the full >circumference of the coax (completely isolating the upper and lower >portions of the shield) or only partially around... I infer that it's >the latter, because I don't see how the antenna could work with the >shield sections fully separated. The gap is fully open. Also that gap sets up a transmisstion line between the outer braid and the inner transmission line braid. There is an interaction between the gap and braid section length. >>Should the actual lengths of these sections be modified by "K" depending >>on diameter of conductor or are they exact 1/4 wave length cuts ? Yes. however the difference between K and free space will be maybe a 2-4% difference. At 2m that comes out to around .5" (12mm) give or take. >Well, I think it's a bit of a compromise. > >The upper section (the coax center conductor and its surrounding >dielectric) is going to have a velocity factor of not much less than >1.0. Cutting to 1/4 physical wavelength, and then trimming a bit, >seems likely to work. Even without insulation it's lower than 1.0 (likely .98 or so) but insulation will increase that. >I think the lower section is likely to be a bit trickier, since >there are actually two velocity factors involved. The radiating is >done by the RF travelling back down the outside of the coax braid from >the feedpoint, and this (like the upper section) will have a velocity >factor close to 1.0, which suggests that the gap-to-feedpoint distance >should be close to 1/4 physical wavelength. > >HOWEVER: the signal travelling up the *inside* of the braid, like that >travelling up the inner conductor towards the feedpoint, will be >travelling more slowly - the velocity factor will be somewhere around >.66 - .8 depending on cable type. This means that there will be more >than 180 degrees of phase delay between the signal passing the gap >going upwards (inside the cable) and the signal reaching the gap from >above (travelling back down the outside of the cable). Hence, the gap >leakage won't result in full cancellation of the signal travelling >down the outside of the coax past the gap. > >To get the two signals into accurate 180-degree phase opposition, >you'd need to make the distance from the feedpoint to the gap a bit >less than 1/4 physical wavelength, but a bit more than 1/4 of the >coax's usual electrical wavelength. Splitting the difference might >work fairly well. > >I'm not sure what this will do to the antenna's feedpoint impedance / >return loss, though, and it'll probably tilt the antenna's radiation >pattern somewhat. You will probably need to experiment to get the >best compromise between antenna pattern and feedpoint impedance / >return loss / SWR. The same is true of the gap size and configuration. If properly matched the feedpoint will be 50ohms and the return loss will be reflective of a good match. Allison Kb1GMX Article: 217199 of rec.radio.amateur.antenna From: "John N9JG" Subject: Re: Wooden I section pole Date: Thu, 15 Sep 2005 14:44:19 -0500 Message-ID: References: This is useful information to know. I don't know why the section about small loops in the Antenna Handbook doesn't mention this. BTW, how far does the near-field extend? "Reg Edwards" wrote in message news:dgcd5g$j7b$1@nwrdmz01.dmz.ncs.ea.ibs-infra.bt.com... >A vertical conductor, a metal tube, running diametrically across a > large magloop with the tuning capacitor at the top, has no effect > either on radiating efficiency or the radiation pattern. It may as > well not be there apart from providing a prop or support for the > antenna itself. It will, of course, need to be well-insulated from the > high-voltage parts. > > In general, provided the longest dimension of foreign metalwork is > much less than 1/2-wavelength, and there is not much of it, negligible > loss will be induced in it. This is due to the very low loss > resistance of most metals. > > Metalwork in the vicinity of beam antennas may upset only the > radiation pattern. > > Short lengths of foreign metalwork in close vicinity of tramsmission > lines, such as open-wire and ladder lines, will cause neglible loss > but will slightly reduce the line impedance Zo which might affect the > L and C settings of the tuner. > > But beware of "semi-conductors", like damp wood such as foliage and > tree trunks, in the near-fields of antennas and lines. Their higher > impedance provide a better power match to the 'generator'. > > You can have as much foreign polyethylene as you like. > ---- > Reg. > > Article: 217201 of rec.radio.amateur.antenna From: "news-z-non-exist-z" Subject: Re: 73 Ohms, How do you get it? Date: Thu, 15 Sep 2005 23:04:17 +0300 Message-ID: References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> <11iesohk2gnkf80@corp.supernews.com> "Allodoxaphobia" wrote in message news:slrndijgku.1fdu.bit-bucket@shell.config.com... | On Thu, 15 Sep 2005 21:26:04 +0300, news-z-non-exist-z wrote: | [...] | Yes, but: | http://antennas.ee.duth.gr/Antennas_Notes_II_2005/22.htm | | explains it best of all! HI!HI! | | 73 | Jonesy d;^) Article: 217202 of rec.radio.amateur.antenna From: "KØHB" References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com> <31f74$43299abf$471c63c6$12083@ALLTEL.NET> <1126813628_2069@spool6-east.superfeed.net> Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Message-ID: Date: Thu, 15 Sep 2005 20:33:13 GMT "Cecil Moore" wrote > > Hans, Richard has obviously followed Christian principles by > selling all that he owns, giving the proceeds to the poor, > and becoming a pennyless missionary. But wait, he appears not > to have sold his computer yet. :-) > -- > 73, Cecil, http://www.qsl.net/w5dxp > Cecil, you are one dangerous dude! Welcome back. I missed you. 73, de Hans, K0HB -- Homepage: http://www.home.earthlink.net/~k0hb Member: ARRL http://www.arrl.org SOC http://www.qsl.net/soc VWOA http://www.vwoa.org A-1 Operator Club http://www.arrl.org/awards/a1-op/ TCDXA http://www.tcdxa.org MWA http://www.w0aa.org TCFMC http://www.tcfmc.org FISTS http://www.fists.org LVDXA http://www.upstel.net/borken/lvdxa.htm NCI http://www.nocode.org Article: 217203 of rec.radio.amateur.antenna From: "Fred W4JLE" References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <11ihidcala4s727@corp.supernews.com> <11ijfrs1plk1a5c@corp.supernews.com> <9ogji11j72vmidsbque5h0utjt7mgj40b2@4ax.com> Subject: Re: Open Stub fed J antenna Date: Thu, 15 Sep 2005 17:57:11 -0400 Message-ID: Suggest you do a google search for baluns coupled with each of the following Maxwell, Cebik, and Lewellen. You will become enlightened grasshopper... wrote in message news:9ogji11j72vmidsbque5h0utjt7mgj40b2@4ax.com... > On Thu, 15 Sep 2005 18:37:48 -0000, dplatt@radagast.org (Dave Platt) > wrote: = > If the antenna feed point is a matched condition what is the RF on the > coax shield from? It should be very small. > Article: 217204 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: best HF antenna system next to a trailer? Date: Thu, 15 Sep 2005 15:47:29 -0700 Message-ID: <11ijug15egav390@corp.supernews.com> References: <1126505259.234971.15970@f14g2000cwb.googlegroups.com> <9175-4326EEA5-1@storefull-3254.bay.webtv.net> <1126670383.884527.133320@f14g2000cwb.googlegroups.com> <1126808854.611763.265930@o13g2000cwo.googlegroups.com> There's that "takeoff angle" again. Having a good "takeoff angle" is no guarantee of good DX performance, and isn't a valid way to compare the performance of two antennas. You should model both the beam and the 4-square. Make sure you include a realistic amount of ground loss resistance for whatever ground system you think you can put down for the 4-square. Superimpose their elevation patterns on the same plot, and see which really does best at low angles. If you don't want to go to the trouble of modeling a beam, you can model a simple dipole which has almost the same elevation pattern as a beam of a few elements (in the forward direction) at the same height. Mentally add the beam's gain relative to a dipole to the dipole's pattern. See if the 4-square really is as good. It might change your mind. Roy Lewallen, W7EL eternalsquire@comcast.net wrote: > I'm deciding to go with a 20 meter 4-square because it can hopefully > provide me with similar directivity and DX takeoff angle as a 20 meter > beam but without the hassle or height of a tower. A dipole only has > directivity in 2 directions, a 4 square can give me directivity in 4 > directions with basic phasing and 8 directions high tech using ARRL > suggestions. The EZNEC plot was pretty awesome. > > The Eternal Squire > Article: 217205 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: best HF antenna system next to a trailer? Date: Thu, 15 Sep 2005 16:06:10 -0700 Message-ID: <11ijvj3ef7flq21@corp.supernews.com> References: <1126505259.234971.15970@f14g2000cwb.googlegroups.com> <9175-4326EEA5-1@storefull-3254.bay.webtv.net> <11if72vgu1uln04@corp.supernews.com> <11igt81c682aheb@corp.supernews.com> <1126810307.672860.211650@g49g2000cwa.googlegroups.com> eternalsquire@comcast.net wrote: > Roy, > > I decided to go with a 20-meter 4 square. I wonder if any people have > experience with 4-squares that they can share with me. I have > considered some construction details give available materials, and I > have some questions. I've built and used a few, for 40 meters. > 1) Can I shorten each element by using an inverted L rather than > straight vertical, with a pipe as vertical part and a wire as > horizontal part? I have heard that matching is far less of a problem > this way also. You can make a 4 square from any kind of element. EZNEC can tell you what effect the element shape will have. I strongly recommend against designing the antenna to get the best or easiest match. Design the antenna for the best performance, then design whatever matching arrangement you need in order to match it. An exception to this general rule is that antennas with an exceptionally low resistance or high reactance might not be practical because of the problem of matching system loss, so such an antenna might need redesign in order to be practical. > > 2) Where can I find or build a reasonably inexpensive phase box? Chapter 8 of the ARRL Antenna Book describes how to design one. See also "The Simplest Phased Array Feed System - That Works" and accompanying program Simpfeed, available from http://eznec.com/Amateur/Articles/. > 3) For the vertical part, I am wanting to a dig a hole 2 foot across by > 3 foot down, and fill with concrete. Into this I would insert a 5 > foot length of 1 1/2 inch steel support pipe about midway, so that 2 > 1/2 feet are above ground. Into this I would mount a 10 foot length > of 3/4 inch steel pipe with a 2 1/2 foot insulated overlap of PVC > pipe. The 3/4 inch steel pipe would be the bottom of the actual > driven element. Into this I would mount a 10 foot length of 1/2 inch > aluminum pipe with a 2 foot metallic contact overlap, and then I would > finish with rod for vertical or wire for inverted L. Wow, for a 20 meter 4-square? For each element on 40, I drove a 1-1/4" 8 foot galvanized chain link fence line pole 4 feet into the ground. (Our soil is clay.) I cut a piece of heavy wall PVC pipe lengthwise into quarters for insulators, and clamped the element to the line pole with muffler clamps with a couple of pieces of the split PVC pipe in between. The elements are three pieces of telescoping 6061-T6 tubing, beginning with, as I recall, 1-1/8" at the bottom. They've been up for around 20 years now and survived a couple of pretty strong wind storms. > > Question: how would the 2 1/2 foot overlap of a non-grounded metal > support pipe interfere with radiation of the vertical element? Any shunt impedance will reduce the null depth if the array is adjusted for the correct base current ratio. This is because a different fraction of the current will be diverted from each element because of their differing base impedances. However, I've found that the 4 foot overlap I have doesn't reduce it noticeably. But my overlapping pipes are parallel and, if I understand your description, yours will be coaxial. That'll result in a lot more shunt capacitance, and a correspondingly greater effect on the null. The main lobe won't be affected much. Roy Lewallen, W7EL Article: 217206 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Open Stub fed J antenna Date: Thu, 15 Sep 2005 16:07:46 -0700 Message-ID: <11ijvm28fliv45e@corp.supernews.com> References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <11ihidcala4s727@corp.supernews.com> <11ijfrs1plk1a5c@corp.supernews.com> <9ogji11j72vmidsbque5h0utjt7mgj40b2@4ax.com> Fred W4JLE wrote: > Suggest you do a google search for baluns coupled with each of the following > Maxwell, Cebik, and Lewellen. > . . . Searching for Lewallen will probably be more fruitful than Lewellen. Roy Lewallen, W7EL Article: 217207 of rec.radio.amateur.antenna From: "Fred W4JLE" References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <11ihidcala4s727@corp.supernews.com> <11ijfrs1plk1a5c@corp.supernews.com> <9ogji11j72vmidsbque5h0utjt7mgj40b2@4ax.com> <11ijvm28fliv45e@corp.supernews.com> Subject: Re: Open Stub fed J antenna Date: Thu, 15 Sep 2005 20:52:04 -0400 Message-ID: Mea Culpa, my fingers slipped when typing, and I in a senior moment failed to proof. In any event your piece on baluns is part of my reference library. "Roy Lewallen" wrote in message news:11ijvm28fliv45e@corp.supernews.com... > Fred W4JLE wrote: > > Suggest you do a google search for baluns coupled with each of the following > > Maxwell, Cebik, and Lewellen. > > . . . > > Searching for Lewallen will probably be more fruitful than Lewellen. > > Roy Lewallen, W7EL Article: 217208 of rec.radio.amateur.antenna From: David Subject: Re: Open Stub fed J antenna References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <11ihidcala4s727@corp.supernews.com> <11ijfrs1plk1a5c@corp.supernews.com> <9ogji11j72vmidsbque5h0utjt7mgj40b2@4ax.com> <11ijvm28fliv45e@corp.supernews.com> Message-ID: Date: Fri, 16 Sep 2005 01:31:19 GMT Thanks everyone for your feedback to my posting. I have now been given a lot of information but am starting to go around in circles. It seems many people are used to operating at lower frequencies with huge lengths of wire and hundred of watts of power. In my application, I am looking for an omni-directional antenna with reasonable "gain" and fairly low radiation angle. The application operates with Data at 920 MHz where power levels are below 1 watt. The antenna must either fix directly to the enclosure (which can be plastic or metal and is usually only around 100mm x 60mm x 40mm) or within 2-3m of the enclosure. Therefore, a unit that does not require ground plane style antenna would be good. The end-fed antenna style is good because I can build it into the end of a SMA connector and use 1/4" nylon tubing as the Radome. Now I just need what goes in the Radome to complete the unit. It is difficult to install Tee BNC connectors and mid tap points on coils or transmission lines etc. Stripping coax cable and coiling the coax on the outside of the Radome is fine as I can cover the unit later with heatshrink. In my search it seemed the J-pole was a good contender due to its performance and low radiation angle and ground independence. The shorted stub version was troublesome but the open stub looked promising. It appeared as though I could simply use coaxial cable to create the antenna and fold back part of the coax over 1/4 wave section. Some have suggested coiling cable to act as a choke at the feed point and others have mentioned not to do this. Would anyone by chance have details of a whip antenna that is proven to work and is similar to what I am trying to construct that I could use as a starting point ? Thanks in advance. Roy Lewallen wrote: > Fred W4JLE wrote: > >> Suggest you do a google search for baluns coupled with each of the >> following >> Maxwell, Cebik, and Lewellen. > > > . . . > > Searching for Lewallen will probably be more fruitful than Lewellen. > > Roy Lewallen, W7EL Article: 217209 of rec.radio.amateur.antenna Subject: Re: Open Stub fed J antenna From: Cecil Moore Date: Thu, 15 Sep 2005 20:43:57 -0500 Message-ID: <1126835197_2699@spool6-east.superfeed.net> References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <11ihidcala4s727@corp.supernews.com> <11ijfrs1plk1a5c@corp.supernews.com> <9ogji11j72vmidsbque5h0utjt7mgj40b2@4ax.com> <11ijvm28fliv45e@corp.supernews.com> David wrote: > Would anyone by chance have details of a whip antenna that is proven to > work and is similar to what I am trying to construct that I could use as > a starting point ? In "Antennas For All Applications", by Kraus and Marhefka, third edition, page 824, a 1/2WL over 1/4WL collinear array vertical is described that allegedly has a gain of 6.4 dBi. There is a 180 deg. phase reversing coil between the bottom 1/4WL and the top 1/2WL. The entire vertical should be less than one foot long. The 180 deg. phase reversing coil is the tricky part. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- Article: 217210 of rec.radio.amateur.antenna From: "Ron" References: <11htogetcauugb1@news.supernews.com> Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Message-ID: Date: Thu, 15 Sep 2005 20:46:12 -0500 Gee. I'm actually glad that my initial posting of this link (the one that was up before Charlie's by about 10 hours) didnt go out to all these other groups, only to alt.ham-radio.vhf-uhf. Far to many spastic individuals replying with unrelated and often inane comments. How come I'm not surprised. Ron "Charlie" wrote in message news:11htogetcauugb1@news.supernews.com... > 1. http://www.msnbc.msn.com/id/9228945/ > > -- > > Charlie - AD5TH > www.ad5th.com > > > > > > > Article: 217211 of rec.radio.amateur.antenna From: David Subject: Re: Open Stub fed J antenna References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <11ihidcala4s727@corp.supernews.com> <11ijfrs1plk1a5c@corp.supernews.com> <9ogji11j72vmidsbque5h0utjt7mgj40b2@4ax.com> <11ijvm28fliv45e@corp.supernews.com> <1126835197_2699@spool6-east.superfeed.net> Message-ID: Date: Fri, 16 Sep 2005 02:26:25 GMT Cecil, Thanks for the book reference. I searched amazon for it but they are charging $187 for it. Do you know where I might find a second hand copy ? Regards David Cecil Moore wrote: > David wrote: > >> Would anyone by chance have details of a whip antenna that is proven >> to work and is similar to what I am trying to construct that I could >> use as a starting point ? > > > In "Antennas For All Applications", by Kraus and Marhefka, third edition, > page 824, a 1/2WL over 1/4WL collinear array vertical is described that > allegedly has a gain of 6.4 dBi. There is a 180 deg. phase reversing coil > between the bottom 1/4WL and the top 1/2WL. The entire vertical should be > less than one foot long. The 180 deg. phase reversing coil is the tricky > part. Article: 217212 of rec.radio.amateur.antenna From: "J. Mc Laughlin" Subject: Re: best HF antenna system next to a trailer? Date: Thu, 15 Sep 2005 22:49:08 -0400 Message-ID: <11ikci8dunmjbdc@corp.supernews.com> References: <1126505259.234971.15970@f14g2000cwb.googlegroups.com> <9175-4326EEA5-1@storefull-3254.bay.webtv.net> <11if72vgu1uln04@corp.supernews.com> Dear Group: Long, long experience with angles above the horizon that are used by DX signals (at HF) indicates that the most useful angles are between 2 and 12 degrees. Comparing the expected gain of antennas at 6 degrees provides a good figure-of-merit. That said, if one has a low, horizontally polarized antenna with very little gain at 6 degrees, you might still work DX using more than an optimum number of hops (angle of more than ten degrees). However, you will work DX fewer days per month than someone who gets significant gain at angles smaller than ten degrees. I emphasize what Roy has said: the so-called take-off-angle (equal to the smallest angle at which peak gain occurs) of an antenna is not necessarily an indicator of DX performance. Another example is the case of a horizontally polarized antenna that is over 3 WL high: it has a small TOA but is likely to have a null at an important angle smaller than 12 degrees. In other words: the too-high-antenna works very well some of the time, but a lower antenna works better at other times. A useful goal for the (single) optimum (for DX) antenna is an antenna that has its second null (first null is at zero degrees) at an angle greater than 12 degrees and a first maximum (what is called by many the TOA) between 2 and 12 degrees. The actual angle used at the transmitter end of a DX circuit is sometimes quite different from that used at the receiver end. 73 Mac N8TT -- J. Mc Laughlin; Michigan U.S.A. Home: JCM@Power-Net.Net "Bill Turner" wrote in message news:xn0e78a5u2wg45000@cnews.newsguy.com... > Roy Lewallen wrote: > > > > > An antenna doesn't have a single "radiation angle". It radiates at > > all angles. The relevant question is how much does it radiate at the > > particular angle of interest, not at which angle does it radiate the > > most. > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > That's true, except few if any hams have a specific "angle of > interest", since different angles are used at different times. For > most of us, the angle of maximum radiation gives a general indication > of how the antenna will perform. A better indication would be a > graphical representation. It's always a problem when one tries to > reduce a complex situation like this down to a single number. > > 73, Bill W6WRT Article: 217213 of rec.radio.amateur.antenna From: richardharrison@webtv.net (Richard Harrison) Subject: Re: Open Stub fed J antenna Date: Thu, 15 Sep 2005 23:05:23 -0500 Message-ID: <24625-432A4483-301@storefull-3253.bay.webtv.net> References: <1126835197_2699@spool6-east.superfeed.net> Cecil, W5DXP wrote: "The 180 deg. phase reversing coil is the tricky part." For UHF, you might prefer to use a 1/4-wave short-circuited stub in place of a coil to reverse the phase. My 19th edition of the ARRL Antenna Book shows such an antenna, "the super J-pole on page 16-25. At other frequencies, this might be called a "Franklin Antenna". It`s a 1/2-wave in-phase with another 1/2-wave, one mounted directly over the other. The super J-pole is designed for 144 MHz, but can be scaled for any frequency with proper mechanical allowances. Gain is about 6 dB over a 1/4-wave whip. Best regards, Richard Harrison, KB5WZZI Article: 217214 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: Wooden I section pole Date: Fri, 16 Sep 2005 04:44:48 +0000 (UTC) Message-ID: References: "John N9JG" wrote > This is useful information to know. I don't know why the section about small > loops in the Antenna Handbook doesn't mention this. BTW, how far does the > near-field extend? > ====================================== It's because neither the authors nor the editors were aware of it. The near-field on the surface of an antenna's conductors starts off at a very high value. The far-field is zero at zero distance. The near-field fades into the distance just the same as the ar-field - only much faster. It also has a radiation pattern which depends on an antenna's structure. For argument's sake, for an isotropic antenna (which doesn't exist), at a distance of 1/2/Pi = 1/6 of a wavelength from the antenna, the near-fields and far-fields are equal to each other but differ in phase. They both exist together and their effects on foreign bodies are inseparable from a measurements point of view. They exist seperately at all distances only as a mathematical fiction. The near-field of open-wire transmission lines is sensibly zero at a distance of 4 or 5 times the wire spacing but the radiation field is finite and very small. The radiation field increases with wire spacing and is a maximum when spacing is about 1/2-wavelength which nobody ever uses. This accounts for the lack of use of low-loss open-wire lines at UHF and higher frequencies. Back to Magloops where the measurement unit is loop diameter rather than wavelength and the near-field is mainly magnetic. The magnetic field falls off at a rate proportional to the cube of distance. I would be very happy with a distance of 1/2 the loop diameter or more between the loop and large foreign bodies such as the ground. Highly conductive metallic bodies merely slightly detune the loop with little additional loss. ---- Reg. Article: 217215 of rec.radio.amateur.antenna From: David Subject: Re: Open Stub fed J antenna References: <1126835197_2699@spool6-east.superfeed.net> <24625-432A4483-301@storefull-3253.bay.webtv.net> Message-ID: Date: Fri, 16 Sep 2005 04:44:24 GMT Richard, I have the 20th edition. Looking at the picture, I would have difficulty building this into the end of a SMA plug to sit on top of the radio modem. Regards David Richard Harrison wrote: > Cecil, W5DXP wrote: > "The 180 deg. phase reversing coil is the tricky part." > > For UHF, you might prefer to use a 1/4-wave short-circuited stub in > place of a coil to reverse the phase. My 19th edition of the ARRL > Antenna Book shows such an antenna, "the super J-pole on page 16-25. At > other frequencies, this might be called a "Franklin Antenna". It`s a > 1/2-wave in-phase with another 1/2-wave, one mounted directly over the > other. > > The super J-pole is designed for 144 MHz, but can be scaled for any > frequency with proper mechanical allowances. Gain is about 6 dB over a > 1/4-wave whip. > > Best regards, Richard Harrison, KB5WZZI > Article: 217216 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: best HF antenna system next to a trailer? Date: Fri, 16 Sep 2005 06:23:47 +0000 (UTC) Message-ID: References: <1126505259.234971.15970@f14g2000cwb.googlegroups.com> <9175-4326EEA5-1@storefull-3254.bay.webtv.net> <11if72vgu1uln04@corp.supernews.com> <11ikci8dunmjbdc@corp.supernews.com> To Novices - It is use of the term "take off angle" which causes all the confusion surrounding DX and the "best" take off angles. It is a misnomer. The elevation angle of a radio path between two stations is purely a geometric function of their locations on the Earth's surface and the heights of ionospheric reflecting layers. It has nothing whatever to do with either of the antennas or ground conditions - except that it is the best elevation angle at which an antenna beam should be pointing. If, purely by coincidence, the "take off angle" indicated by Eznec happens to be the same as the exceedingly changeable "path elevation angle" then all is well and good. The true "take off angle" having maximum gain (another misnomer) for any vertical antenna is always zero degrees, ie., it corresponds to the always existent very strong groundwave. Whereas Eznec always reports the groundwave strength as being zero. It is of no use in the prediction of often-used ground waves between stations. Whenever a resistive ground is involved, programs like Eznec do not produce the true radiation pattern of an antenna. Not that there is anything incorrect with Eznec. It is just the confusing description of what it displays. ---- Reg. Article: 217217 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: best HF antenna system next to a trailer? Date: Fri, 16 Sep 2005 01:06:41 -0700 Message-ID: <11ikv8hhmvtlgd9@corp.supernews.com> References: <1126505259.234971.15970@f14g2000cwb.googlegroups.com> <9175-4326EEA5-1@storefull-3254.bay.webtv.net> <11if72vgu1uln04@corp.supernews.com> <11ikci8dunmjbdc@corp.supernews.com> Reg Edwards wrote: > . . . Whereas Eznec always > reports the groundwave strength as being zero. . . If you're using the strict definition of "groundwave" as being the field at an elevation angle of zero, only EZNEC's far field analysis reports it as zero, because (as the manual explains, and as I've explained here several times before) the far field results are valid at a distance beyond the point where the surface wave has decayed to essentially zero -- a few miles at HF. And at that distance, the field at zero elevation angle is zero if the ground conductivity is finite. If the surface wave strength is wanted, it can easily be found using EZNEC's near field calculation, which calculates the total field at any point in space -- including just above the ground surface. It is of no use in the > prediction of often-used ground waves between stations. Unless you use the near field results, which do give an accurate indication of the field at any point in space. I assume you've just forgotten the several times I've explained that to you. Maybe this will be the magic time it'll sink in. > Whenever a resistive ground is involved, programs like Eznec do not > produce the true radiation pattern of an antenna. . . For sure, the modeling of ground is the weakest point of all antenna modeling programs including EZNEC. But the pattern is generally a good representation of reality. Remembering, of course, that the far field pattern is just that -- the pattern at a distant point at which the surface wave has decayed to zero. A graphical pattern which includes the surface wave component would be different at every distance from the antenna up to the distance where the surface wave has decayed to essentially zero (a few miles at HF). The field strength at angles greater than zero would be of little interest to amateurs doing local communication by surface wave. Those who want to know the field strength at ground level at any distance can easily get this information from EZNEC's near field analysis (which reports the total field, not just the near field). Most amateurs who are interested in local communication over a few miles using surface waves don't need to see the overall elevation pattern, and they can get numerical results of the surface field strength from the near field analysis. Amateurs communicating by sky wave, by far the more common situation, can benefit from the graphical results afforded by EZNEC's far field elevation pattern. Not that there is > anything incorrect with Eznec. It is just the confusing description > of what it displays. It's interesting that in the 15 years EZNEC and its predecessor ELNEC have been available, and the thousands of users, no more than a half dozen people have expressed any confusion regarding its far and near field analysis. And none of the others has required repeated explanations. But some people are sure to have more trouble with the concept than others. It's explained in the EZNEC manual, and I always welcome questions and suggestions which would help me make it more clear. I am, however, resigned to the fact that some small number of people aren't capable of, and some simply aren't interested in, understanding. Because of your deep interest in surface wave propagation and field strength prediction, and your characterization of it as "often-used", you must do a lot of communication by this mode. What bands do you use, and what sort of range do you reliably communicate over? How many hams are within this radius whom you talk to? Roy Lewallen, W7EL Article: 217218 of rec.radio.amateur.antenna Subject: Re: Open Stub fed J antenna From: Cecil Moore Date: Fri, 16 Sep 2005 08:37:55 -0500 Message-ID: <1126878036_16053@spool6-east.superfeed.net> References: <1126835197_2699@spool6-east.superfeed.net> <24625-432A4483-301@storefull-3253.bay.webtv.net> Richard Harrison wrote: > Cecil, W5DXP wrote: > "The 180 deg. phase reversing coil is the tricky part." > > For UHF, you might prefer to use a 1/4-wave short-circuited stub in > place of a coil to reverse the phase. My 19th edition of the ARRL > Antenna Book shows such an antenna, "the super J-pole on page 16-25. At > other frequencies, this might be called a "Franklin Antenna". It`s a > 1/2-wave in-phase with another 1/2-wave, one mounted directly over the > other. The stub is a good idea and can be mechanically self-supporting at 920 MHz. However, making the bottom section 1/4WL (as Kraus suggests) instead of 1/2WL would make for a low feedpoint impedance > The super J-pole is designed for 144 MHz, but can be scaled for any > frequency with proper mechanical allowances. Gain is about 6 dB over a > 1/4-wave whip. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- Article: 217219 of rec.radio.amateur.antenna From: Walter Maxwell Subject: Re: Open Stub fed J antenna Message-ID: References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <11ihidcala4s727@corp.supernews.com> <11ijfrs1plk1a5c@corp.supernews.com> <9ogji11j72vmidsbque5h0utjt7mgj40b2@4ax.com> Date: Fri, 16 Sep 2005 10:22:07 -0400 Searching Maxwell on baluns on Google will turn up mostly baluns for sale by various dealers, not how they work. Searching Lewallen will turn up good data in answering your question on how does the current get onto the outside of the shield braid. If you want Maxwell's data on how the current gets there go to his web page at www.w2du.com, Click on 'Read Chapters from Reflections 2', and then click on Chapter 21, "Some Aspects of the Balun Problem." Walt, W2DU On Thu, 15 Sep 2005 17:57:11 -0400, "Fred W4JLE" wrote: >Suggest you do a google search for baluns coupled with each of the following >Maxwell, Cebik, and Lewellen. > >You will become enlightened grasshopper... Article: 217220 of rec.radio.amateur.antenna Subject: Re: Open Stub fed J antenna From: Cecil Moore Date: Fri, 16 Sep 2005 09:26:10 -0500 Message-ID: <1126880994_16131@spool6-east.superfeed.net> References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <11ihidcala4s727@corp.supernews.com> <11ijfrs1plk1a5c@corp.supernews.com> <9ogji11j72vmidsbque5h0utjt7mgj40b2@4ax.com> <11ijvm28fliv45e@corp.supernews.com> <1126835197_2699@spool6-east.superfeed.net> David wrote: > Do you know where I might find a second hand copy ? Google "used books". I've had good luck with www.abebooks.com I have also run across foreign published books that are about half priced and new. Don't recall the URL. But I've given you all the information in Kraus' book about that particular antenna. Laid on its side: | |----------/////-------------------- | 1/4WL coil 1/2WL The coil is a 180 deg. phase reversing coil. If I remember correctly, that means it is self-resonant. If that's right, it probably means that a trap would work instead of a coil. The impedance at the bottom and top of the coil is very high so it seems to me that instead of blocking the signal, like an ordinary trap, a trap would merely reverse the phase. -- 73, Cecil, http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- Article: 217221 of rec.radio.amateur.antenna Subject: Re: Open Stub fed J antenna From: Cecil Moore Date: Fri, 16 Sep 2005 09:43:35 -0500 Message-ID: <1126882039_16351@spool6-east.superfeed.net> References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <11ihidcala4s727@corp.supernews.com> <11ijfrs1plk1a5c@corp.supernews.com> <9ogji11j72vmidsbque5h0utjt7mgj40b2@4ax.com> <11ijvm28fliv45e@corp.supernews.com> <1126835197_2699@spool6-east.superfeed.net> <1126880994_16131@spool6-east.superfeed.net> Cecil Moore wrote: > I have also run across foreign published books that > are about half priced and new. Don't recall the URL. Doing a search on the following webpage for "John Kraus" and "Antennas for all Applications" yields an "as new" international soft cover version for $28.50. http://www.abebooks.com/ It would be nice if everyone on this newsgroup had one of these as a reference. -- 73, Cecil, http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- Article: 217222 of rec.radio.amateur.antenna From: John Ferrell Subject: Re: How to weather-seal an upside down Tailtwister rotor? Message-ID: References: <3op5feF73ibjU1@individual.net> <6pakv2-ti9.ln1@p400bob.personal.cox.net> Date: Fri, 16 Sep 2005 14:59:07 GMT I am not sure I understand the question. I think you have the rotator upside down on the tower at the moment. If it went through some weather, it is probably full of water now. The way I would handle the problem is to remove the rotator from the mount and hang it on the tower (clothes hanger wire) right side up. I would hang it there for a few days to drain & dry out. When it comes time to reinstall the antennas, test the rotator for proper operation. Chances are that it will be OK. If you seal it tight, the moisture will be sealed in. These things are intended to be able to breathe! If removing/replacing the rotator is a major hassle, I would either send it to one of the maintenance guys or put up a new one & sell the old one on ebay WITH the explanation. There are lots of us who have setups that are easy to change. If the rotator must be left in the inverted position outside for an extended time I would wrap it in black landscape plastic and duct tape to prevent more water from entering while leaving the bottom of the plastic open to dry out. On Tue, 13 Sep 2005 20:25:25 -0500, Bob Bob wrote: >One of the tricks I learnt early on with RTV sealant in medical >ultrasound water tanks is if you wet the surfaces with water and a >detergent wetting agent the sealant wont actually adhere to the >prewetted surface. Kind of handy if you wanted to force the sealant into >a clearance slot and remove it later. > >Or was it oil? Damn I cant remember! I know kerosene is used to pre the >surface for better adhesion... > >How about paper/masking tape over the gaps and spraying with that gluggy >sealant you use on sink drains? > >Probably not very useful thoughts, sorry! > >Cheers Bob W5/VK2YQA > >Dan/W4NTI wrote: > >> >> Maybe ... get some axle grease, or RTV sealant would be better, perhaps. >> Both should peal off reasonable well. >> >> One other thing I am concerned with tho. I always heard that the rotar >> must be kept in a vertical position or the grease would drain out of the >> bearings? Wives tale ??? I don't know. But I always keep mine vertical >> when stored. >> >> Dan/W4NTI >> >> Article: 217223 of rec.radio.amateur.antenna From: Ted Goldblatt Subject: Re: How to weather-seal an upside down Tailtwister rotor? Date: Fri, 16 Sep 2005 11:41:56 -0400 Message-ID: <3p07aaF7ublaU1@individual.net> References: <3op5feF73ibjU1@individual.net> <6pakv2-ti9.ln1@p400bob.personal.cox.net> John Ferrell wrote: > I am not sure I understand the question. I think you have the rotator > upside down on the tower at the moment. If it went through some > weather, it is probably full of water now. The way I would handle the > problem is to remove the rotator from the mount and hang it on the > tower (clothes hanger wire) right side up. I would hang it there for a > few days to drain & dry out. When it comes time to reinstall the > antennas, test the rotator for proper operation. Chances are that it > will be OK. If you seal it tight, the moisture will be sealed in. > These things are intended to be able to breathe! The tower is currently up (the mast broke above the rotor, so all the antennas are dangling by their feedlines, but the tower itself is OK) and the rotor is in its normal upright position. It will be upside down when the tower is folded over to work on. As far as I know, the rotor is fine right now. > If removing/replacing the rotator is a major hassle, I would either > send it to one of the maintenance guys or put up a new one & sell the > old one on ebay WITH the explanation. There are lots of us who have > setups that are easy to change. Don't understand this. Yes, removing/replacing the rotor is a hassle, largely because it has to be done with the unit upside down, and standing at the top of a ladder. But that isn't the issue here - in fact, there is no obvious reason to remove the rotor at all, since it seems intact. Just remove the stub of the broken mast from the thrust bearing and put a new one in. The issue is that while that is done, and the new antennas are mounted, and new (or repaired) feedlines are run, and all the antennas are tuned, the tower will need to be folded over, with the rotor mounted, and these steps will almost certainly take several days. Because of availability of helpers reasons, this will likely have to be on weekends, meaning the tower will be folded (and the rotor inverted) for a period of at least 1 to 2 weeks. > If the rotator must be left in the inverted position outside for an > extended time I would wrap it in black landscape plastic and duct tape > to prevent more water from entering while leaving the bottom of the > plastic open to dry out. I have done this in the past, but because of the way the rotor is mounted on the Rohn tower, it isn't possible to seal it very well this way - I was looking for suggestions for better ways of weatherproofing it for this period. Marshall Article: 217224 of rec.radio.amateur.antenna From: David Snyder Hale Subject: HD-73 vs. Ham-M rotors? Date: Fri, 16 Sep 2005 15:42:09 +0000 (UTC) Message-ID: Can anyone comment on a comparison between these two rotors? I'm looking to purchase one or the other, and need something to tip the scales. tnx, -- Dave * N3WTK (DM04xf) * http://isi.mtwilson.edu Article: 217225 of rec.radio.amateur.antenna From: Aaron Subject: Re: Question on car antenna (in-glass, rear windshield) References: <25ydndntds9xcoHeRVn-ow@rogers.com> Message-ID: <2HCWe.109780$G8.59772@text.news.blueyonder.co.uk> Date: Fri, 16 Sep 2005 16:47:58 GMT Frank wrote: > Hi all > > Let me preamble this by saying I am new at this, and need your > help. But I am a quick learner! > > I have a few specific questions and perhaps you can help. I am > trying to troubleshoot a Fm static problem > > 1) Is the car coax cable lead one or two wires? I am quite sure > it is two (one outer (the ground) and one inner wire) but I'll > ask to confirm > > 2) Should a "in-glass" rear winshield antenna be grounded to the > car's body? If so, from which end of the coax cable? (see Q 3) > > 3) Does the expression "grounding the antena" (in the case of a > glass mounted antenna) be as simple as soldering a grounding wire > from the outside coax lead end that plugs into the HU to a metal > ground of the car? Or should it be done closer to the actual > antena? SUch as at the junction of the end of the coax and where > the antenna starts... > > Here is more detail on my problem if this helps: inconsistent FM > reception (re: static) with in-glass antenna where I use to get > crystal clear reception with old car. However, there is a twist > to my problem: I noticed that the coax cable (inner cable) from > the HU is not truly connected to the antenna even if it looks > like it is. I tested it with a continuity tester and it is not. > When I try to connect the inner coax wire directly to the antenna > (using a wire and soldering), then I can test it and it is well > connected. In other words, the inner wire of the coax makes a > continuous circuit from the HU's to the end of the antenna. Yet, > I still get some static on some FM station (which is not induced > by the engine or the car's electrical systems). > > Any suggestion? It is an RSX 2004 (Acura). I changed the HU twice > (two models) and the problem persists (same issue with the OEM) > > TIA > > Have you deffinantly got the antenna power line connected to the head unit. On an ISO radio connector this is a blue wire which provides power to an antenna amplifier found on some cars. Make sure you've fitted the earth (ground?) bar from your radio to the car's body (for example the bolt that holds the radio cage in). Try using a different antenna to see if the problem re-occurs. -- Regards, Aaron. Article: 217226 of rec.radio.amateur.antenna From: richardharrison@webtv.net (Richard Harrison) Subject: Re: Open Stub fed J antenna Date: Fri, 16 Sep 2005 13:31:54 -0500 Message-ID: <15189-432B0F9A-307@storefull-3258.bay.webtv.net> References: <1126882039_16351@spool6-east.superfeed.net> Cecil, W5DXP wrote: "It would be nice if everyone on this newsgtoup had one of these as a refgerence." I second that motion. At $28.50, it is about 1/2 the cost of mine which was a bargain at that. Kraus` "Antennas" is without peer. As Kraus is now dead, there won`t likely be a new improved edition as in the past. Best regards, Richard Harrison, KB5WZI Article: 217227 of rec.radio.amateur.antenna From: lorentsonci@lycos.com Subject: antenna switch 'ground' how good/valueable?? Date: Fri, 16 Sep 2005 15:02:01 -0500 Message-ID: Last year I moved my antenna mast system to the 'south' side of my house. Right off lighting 'busted' a two meter/440 ground plane. The 'juice' came in the shack, by way of two antennas, a TV antenna/coax, and the coax for the 2/440. I had the coax un connected to the radios. The TV antenna's coax was connected, to a monitor/TV and VCR,,, ''they bit the dust''. I had almost this same system on the north side of the house for many years, with no apprent damage/problems. I have re purchased new antennas and installed them in the air, several months ago. We have had some 'near misses' since then, I no longer have the TV antenna on the main mast (75'), it is located nearby now at about 20'. I don't know why, after 'the move south 100' I have more problems with lighting. I want to add more assurances (gournds?) to the system, including a antenna switch, that has in it a swithch to "ground". But I don't feel really comfortable, putting some of my eggs in this 'ground switch basket'. I purchased some connectors that ''slip on, slip off'', and I am thinking of adding a panel with these slip connectors monted close at hand, and when there is "weather" I just pull the slip connectors lose, and then use the ''ground switch", switching, to ground. Soooo now my question, how many '''holes''' are there in my ideas/plans???? thanks in advance. cl 73 Article: 217228 of rec.radio.amateur.antenna From: "Steve Nosko" Subject: Re: Open Stub fed J antenna (long-ish) Date: Fri, 16 Sep 2005 14:11:39 -0500 Message-ID: References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <1126739764_407@spool6-east.superfeed.net> <11ihidcala4s727@corp.supernews.com> "David" wrote in message news:Si4We.47593$FA3.15680@news-server.bigpond.net.au... > Dave, > ... The article [Sperrtopf ] mentions the top part as 1/2 wave ... > If this is the case, how come the radiating element is 1480 > long ? Dave, If you read his shopping list you see that his drawing is wrong. The _TOTAL_ length of the small pipe is 1480. Still a vertical half wave radiator. I see no one took this part so I will address the question of what these antennas are, but second. I also read your later post describing your application very well and make this comment first. If you want to simply 'build' the antenna from physical dimensions derived from another frequency or antenna or just from "scratch", I see two significant problems. One is that if you have no measuring equipment for 915 MHz, you run a real risk of not getting the size close enough regardless which type of antenna you choose. This could wipe out all your desire to get "reasonable gain". While RF is commonly called "Black magic" there are strays that can be understood only to some extent and therefore they can easily get you off your target. The other is that the plastic "Radome" *will* have an effect on the resonant frequency (lowering the frequency), so comparing it to an "open air" version moves you off your target as well. A common issue relating to both of these is that as you make an antenna with more and more gain, the dimensions become more and more critical to get the best performance. As a conclusion to this I would recommend setting up the system with a simple, good old quarter wave ground plane and see if you really need "reasonable gain". Now, on to the "what-is-this-antenna" question you asked earlier. A "J-Pole" (or as I consider, more correctly) a "J" antenna is a vertical half wave antenna (radiating element). It is fed at the bottom (end fed) with an approximately quarter wave long, shorted line, or matching section, or matching stub - call it what you wish. This matching section is constructed of open, parallel wire transmission line. The match to 50 ohms is obtained by connecting the feed line to a point on the matching section closest to 50 ohms. As a simplification you can look at the classical quarter wave shorted stub. Where the impedance goes from zero at the shorted end to a very high value at the open end. Connecting the high impedance (end of the) half wave radiator to the high impedance end of the stub leads us to conclude that we ought to be able to find any impedance we want (between "high" and zero) somewhere along the length of the stub - and we basically do. . The length of the matching section and the point where the t-line connects both can be adjusted to get to the best match - though this may not be easy given the construction method used. It is called "J" because when you put the matching section in line with the radiator (and there is nothing requiring this) it has the physical shape of a "J". The matching section could be at right angles to the radiator destroying the "J" shape and the concepts described here are the same (there are antennas done this way). I described it as I did so I can replace the open wire matching section with a coax matching section of the same properties and get the Sperrtopf antenna exactly. So the Sperrtopf can be called a "Sleeve J-Pole" if you like. Or, for those enamored with the "pole", perhaps a "Sleeve-Pole". The "sleeve" antenna, or "sleeve dipole" I also a vertical half wave antenna, but it is center fed . Start with an ordinary half wave, center fed dipole. Turn it vertically. Feed it with coax (yes, I know there is a balanced to un-balanced issue, but stay with me). Now, convert one half of the dipole (one quarter wave length side) from a wire to a pipe. Make this the half which has the coax shield connected to it. Then, take the coax and rather than running it away at 90 degrees, stuff it down the center of the pipe, out the end and to the transmitter. This is the sleeve dipole. Some may consider the sleeve simply to be a "choke" keeping current off the t-line and there are usually several models which can be used to explain one configuration. The referenced Microwaves article shows one type of these, the ordinary sleeve dipole. Looking at Fig 3 and the Appendix B picture, Antenna 3 is clearly the classical vertical sleeve dipole. If I read this correctly, the sleeve dipole closely mimics the ordinary dipole as one would expect. The "spaced gap" antenna (#2) appears close with possibly a little less gain due to the flattened pattern (more radiation at 30 & 150 degrees). Either the #2 or #3 look like they are easy to construct, with the cautions I mentioned above. Finally, the antenna you described taking apart, looks to me like the #1 antenna (Extended Inner" with a choke 1/4 wave back from the shield end. Too bad the Microwave paper didn't try this. 73, Steve, K;9.D,C'I Article: 217229 of rec.radio.amateur.antenna From: "Steve Nosko" Subject: Re: Open Stub fed J antenna Date: Fri, 16 Sep 2005 14:25:38 -0500 Message-ID: References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <11ihidcala4s727@corp.supernews.com> <11ijfrs1plk1a5c@corp.supernews.com> <9ogji11j72vmidsbque5h0utjt7mgj40b2@4ax.com> <11ijvm28fliv45e@corp.supernews.com> <1126835197_2699@spool6-east.superfeed.net> <1126880994_16131@spool6-east.superfeed.net> "Cecil Moore" wrote in message news:1126880994_16131@spool6-east.superfeed.net... > ... > But I've given you all the information in Kraus' book > about that particular antenna. Laid on its side: > > | + - + > |----------/////-------------------- > | 1/4WL coil 1/2WL > > The coil is a 180 deg. phase reversing coil. [snip] > 73, Cecil, Yep and this makes it a "phasing" coil and the antenna a colinear. The phasing coil causes the current in the two sections of the antenna to be in phase. Note my addition of polarity indicators to the above diagram. The right end of both elements are the same = in phase currents. Now you have a half wave and a quarter wave in phase, yielding gain by a flatter pattern (whicn is vertical in this drawing). You can stack half waves up like this and this is done in common cellular gain antennas - probably WiMax as well. There are several ways to do the phasing... Coils like this, quarter-wave shorted stubs (parallel-line), reverse connecting alternate sections of coaxial t-line as elements, phasing harnesses on the feed line... Probably more. 73, Steve, K;9'D.C,I Article: 217230 of rec.radio.amateur.antenna From: David Subject: Re: Open Stub fed J antenna References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <11ihidcala4s727@corp.supernews.com> <11ijfrs1plk1a5c@corp.supernews.com> <9ogji11j72vmidsbque5h0utjt7mgj40b2@4ax.com> <11ijvm28fliv45e@corp.supernews.com> <1126835197_2699@spool6-east.superfeed.net> <1126880994_16131@spool6-east.superfeed.net> Message-ID: Date: Fri, 16 Sep 2005 23:15:47 GMT I would like to express my appreciation for all those who have taken the time to respond to my post. Being new to antenna design and construction I understand some of my questions and comments may seem a bit "silly" and it would be easy for people to suggest that I go learn more first or simply use trial and error. I have a practical requirement for a flexible whip antenna that results in "good" gain that works but at the same time I want to learn what I can because it is my intention to later experiment with other style of antenna (Yagi at 434MHz is next on my list). Now, back to the 1/4 wave, phasing coil, 1/2 wave design. Does this means for a practical antenna I could have... SMA plug centre pin -> 1/4 length of wire -> several turns of wire around the Radome -> 1/2 length of wire ? (ie. coax earth braid stops at SMA and rest of antenna is made up of inner conductor and dielectric only). Is it that "simple" ? If so, that would be easy to construct in a flexible whip (which is my aim) compared to many of the other suggestions. Is the gain the same as a dipole ? Also, I have EZNEC 4. but have not had a chance to learn it yet. Can you model the coil in the program or can you only enter segments ? Thanks. Steve Nosko wrote: > "Cecil Moore" wrote in message > news:1126880994_16131@spool6-east.superfeed.net... > >>... >>But I've given you all the information in Kraus' book >>about that particular antenna. Laid on its side: >> >>| + - + >>|----------/////-------------------- >>| 1/4WL coil 1/2WL >> >>The coil is a 180 deg. phase reversing coil. [snip] >>73, Cecil, > > > Yep and this makes it a "phasing" coil and the antenna a colinear. The > phasing coil causes the current in the two sections of the antenna to be in > phase. Note my addition of polarity indicators to the above diagram. The > right end of both elements are the same = in phase currents. Now you have a > half wave and a quarter wave in phase, yielding gain by a flatter pattern > (whicn is vertical in this drawing). > You can stack half waves up like this and this is done in common cellular > gain antennas - probably WiMax as well. There are several ways to do the > phasing... Coils like this, quarter-wave shorted stubs (parallel-line), > reverse connecting alternate sections of coaxial t-line as elements, phasing > harnesses on the feed line... Probably more. > > 73, Steve, K;9'D.C,I > > > Article: 217231 of rec.radio.amateur.antenna Date: Fri, 16 Sep 2005 19:27:06 -0500 From: Tom Ring Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com> <11ijakdlh2ucb26@corp.supernews.com> Message-ID: <432b62da$0$32203$39cecf19@news.twtelecom.net> David G. Nagel wrote: > If the poor people of New Orleans didn't have transportation out of town > it was because their elected Mayor refused to have them humiliated by > having to leave town in a school bus or city bus. He wanted Greyhound > busses with working air-conditioning for them. > > It's in the disaster plan to use busses for evacuation. Read it. > > Yep, I know I'd refuse to leave a doomed area if I couldn't go in an air conditioned vehicle. It would have to have leather seats, too. Can't have anybody dissing me. What B as in B, S as in S. tom K0TAR Article: 217232 of rec.radio.amateur.antenna From: Uncle Ted Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Date: Fri, 16 Sep 2005 23:01:22 -0400 Message-ID: References: <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com> <31f74$43299abf$471c63c6$12083@ALLTEL.NET> <1126821476.840433.194860@g49g2000cwa.googlegroups.com> On 15 Sep 2005 14:57:56 -0700, "an_old_friend" wrote: >Discounts I don't know but Chatholic dogma still provides for the sale >of Indulenges for sin, even allowing them to be purchased for yone >firend and relitives post mortem > >Luther thought the practice pro and so do most prods groups It's bad enough that people feel a need to believe in any deities at all, but when you have to listen to a bunch of old men in robes half a world away tell you how to live your life, you're pretty screwed up. Article: 217233 of rec.radio.amateur.antenna Subject: Re: Open Stub fed J antenna From: Cecil Moore Date: Fri, 16 Sep 2005 23:07:55 -0500 Message-ID: <1126930235_2245@spool6-east.superfeed.net> References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <11ihidcala4s727@corp.supernews.com> <11ijfrs1plk1a5c@corp.supernews.com> <9ogji11j72vmidsbque5h0utjt7mgj40b2@4ax.com> <11ijvm28fliv45e@corp.supernews.com> <1126835197_2699@spool6-east.superfeed.net> <1126880994_16131@spool6-east.superfeed.net> David wrote: > Is it that "simple" ? If so, that would be easy to construct in a > flexible whip (which is my aim) compared to many of the other suggestions. The non-simple part is designing the 180 deg. phase shifting coil. I think I have one of those on my Diamond mobile antenna. > Is the gain the same as a dipole ? Higher than a dipole - close to 6 dBi compared to the 1/4WL ground plane at *about* 0 dBi. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- Article: 217234 of rec.radio.amateur.antenna From: "Charlie" Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Date: Fri, 16 Sep 2005 23:41:03 -0500 Message-ID: <11in7j7e4fbgkf2@news.supernews.com> References: <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com> <31f74$43299abf$471c63c6$12083@ALLTEL.NET> <1126821476.840433.194860@g49g2000cwa.googlegroups.com> You tell em' Teddy Boy!!! -- Charlie "Uncle Ted" wrote in message news:ci1ni1dmf3cnhek0hggj3goetodbbns4qs@4ax.com... > On 15 Sep 2005 14:57:56 -0700, "an_old_friend" > wrote: > > >>Discounts I don't know but Chatholic dogma still provides for the sale >>of Indulenges for sin, even allowing them to be purchased for yone >>firend and relitives post mortem >> >>Luther thought the practice pro and so do most prods groups > > It's bad enough that people feel a need to believe in any deities at > all, but when you have to listen to a bunch of old men in robes half a > world away tell you how to live your life, you're pretty screwed up. Article: 217235 of rec.radio.amateur.antenna From: "Jerry Martes" References: <1126835197_2699@spool6-east.superfeed.net> <24625-432A4483-301@storefull-3253.bay.webtv.net> Subject: Re: Open Stub fed J antenna Message-ID: Date: Sat, 17 Sep 2005 05:40:23 GMT "Richard Harrison" wrote in message news:24625-432A4483-301@storefull-3253.bay.webtv.net... > Cecil, W5DXP wrote: > "The 180 deg. phase reversing coil is the tricky part." > > For UHF, you might prefer to use a 1/4-wave short-circuited stub in > place of a coil to reverse the phase. My 19th edition of the ARRL > Antenna Book shows such an antenna, "the super J-pole on page 16-25. At > other frequencies, this might be called a "Franklin Antenna". It`s a > 1/2-wave in-phase with another 1/2-wave, one mounted directly over the > other. > > The super J-pole is designed for 144 MHz, but can be scaled for any > frequency with proper mechanical allowances. Gain is about 6 dB over a > 1/4-wave whip. > > Best regards, Richard Harrison, KB5WZZI Richard I'd have expected the "gain" to be closer to 4 1/2 db over the 1/4 wave stub over a ground. is it easy to show where i've missed something? Jerry > Article: 217236 of rec.radio.amateur.antenna From: Ian Jackson Subject: Re: 73 Ohms, How do you get it? Date: Sat, 17 Sep 2005 08:24:36 +0100 Message-ID: References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> In message , Jim Kelley writes > > >Cecil Moore wrote: >> Ian Jackson wrote: >> >>> Just a quick question. >>> What is the impedance at the centre of an infinitely long dipole (in >>>free space)? >> Same as a terminated dipole in an anechoic chamber? 600-800 ohms? > >Not at zero Hz. > >ac6xg > What is a 'terminated dipole'? And why 600-800 ohms? No, Mine will be just a normal dipole (but long). I'll be in a spaceship, miles from anywhere, and I intend to put out a really long antenna so I can work the universe on all amateur bands. (I don't care about the polar diagram - there's bound to be someone out there in one of the major lobes). I intend to throw out an infinitely long wire either side of the ship, and use a balanced tuner connected directly to the antenna (no feeder required). Because of weight restrictions, I can only take one tuner, and I want to make sure that the one I do take will cope with the feed impedance of the antenna. I think the impedance will be the same at all frequencies (maybe even at 'zero Hz'). But what will it be? Ian. -- Article: 217237 of rec.radio.amateur.antenna From: David Subject: Re: Open Stub fed J antenna References: <1126835197_2699@spool6-east.superfeed.net> <24625-432A4483-301@storefull-3253.bay.webtv.net> Message-ID: <5_PWe.50333$FA3.17911@news-server.bigpond.net.au> Date: Sat, 17 Sep 2005 07:55:45 GMT I have constructed a 915 MHz 1/2 wave, end fed antenna that fits onto the end of a SMA plug based on help from you guys. I have some pics of the construction if anyone is interested in taking a look. Where is the appropriate place to post these jpg files ? I am accessing this newsgroup from my email client presently. I am not sure how I can optimize this yet. My antenna Analyzer is the MJF unit that only goes to 440MHz. I have a 1GHz spec analyzer, 1GHz Sig Gen and a Telonic VSWR kit that goes to 2.5GHz but I think the drive required to the VSWR "Rho-Tector" needs to be higher than the 10dBm from the sig gen. Could I optimize the design with this equipment, or maybe would I be better to use RSSI levels from a receiver placed say 3m away from Antenna under test ? If the antenna works I will be very excited as it is very simple to construct in around 10 minutes and at a cost of around $3 (no counting labour). Thanks for any help. Jerry Martes wrote: > "Richard Harrison" wrote in message > news:24625-432A4483-301@storefull-3253.bay.webtv.net... > >>Cecil, W5DXP wrote: >>"The 180 deg. phase reversing coil is the tricky part." >> >>For UHF, you might prefer to use a 1/4-wave short-circuited stub in >>place of a coil to reverse the phase. My 19th edition of the ARRL >>Antenna Book shows such an antenna, "the super J-pole on page 16-25. At >>other frequencies, this might be called a "Franklin Antenna". It`s a >>1/2-wave in-phase with another 1/2-wave, one mounted directly over the >>other. >> >>The super J-pole is designed for 144 MHz, but can be scaled for any >>frequency with proper mechanical allowances. Gain is about 6 dB over a >>1/4-wave whip. >> >>Best regards, Richard Harrison, KB5WZZI > > > Richard > > I'd have expected the "gain" to be closer to 4 1/2 db over the 1/4 wave > stub over a ground. is it easy to show where i've missed something? > > Jerry > > > Article: 217238 of rec.radio.amateur.antenna From: John Ferrell Subject: Re: antenna switch 'ground' how good/valueable?? Message-ID: <4q6oi15bjkdm4p5emvt76qgdeguaqjhm2b@4ax.com> References: Date: Sat, 17 Sep 2005 13:34:11 GMT Extra ground rods are good but they must ALL be tied together with at least #6 copper wire. A 300 foot roll of bare #6 copper wire costs about $69 at my local home improvement store. I am not an expert, but I have more than my share of bad experience! de W8CCW On Fri, 16 Sep 2005 15:02:01 -0500, lorentsonci@lycos.com wrote: >Last year I moved my antenna mast system to the 'south' side of my >house. Right off lighting 'busted' a two meter/440 ground plane. The >'juice' came in the shack, by way of two antennas, a TV antenna/coax, >and the coax for the 2/440. I had the coax un connected to the >radios. The TV antenna's coax was connected, to a monitor/TV and >VCR,,, ''they bit the dust''. > I had almost this same system on the north side of the house for >many years, with no apprent damage/problems. I have re purchased new >antennas and installed them in the air, several months ago. We have >had some 'near misses' since then, I no longer have the TV antenna on >the main mast (75'), it is located nearby now at about 20'. > I don't know why, after 'the move south 100' I have more problems >with lighting. I want to add more assurances (gournds?) to the >system, including a antenna switch, that has in it a swithch to >"ground". > But I don't feel really comfortable, putting some of my eggs in >this 'ground switch basket'. I purchased some connectors that >''slip on, slip off'', and I am thinking of adding a panel with these >slip connectors monted close at hand, and when there is "weather" I >just pull the slip connectors lose, and then use the ''ground switch", >switching, to ground. > Soooo now my question, how many '''holes''' are there in my >ideas/plans???? thanks in advance. cl 73 Article: 217239 of rec.radio.amateur.antenna Subject: Re: 73 Ohms, How do you get it? From: Cecil Moore Date: Sat, 17 Sep 2005 08:52:15 -0500 Message-ID: <1126965295_3165@spool6-east.superfeed.net> References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> <1126655181_28167@spool6-east.superfeed.net> <5MOAq4S9pIKDFwB+@g3ohx.demon.co.uk> <1126734334_299@spool6-east.superfeed.net> Ian Jackson wrote: > What is a 'terminated dipole'? In an anechoic chamber, the dipole has a resistor to chassis at both ends. When the value of the resistor equals the characteristic impedance of the dipole, the dipole becomes a traveling wave antenna instead of a standing wave antenna. Your infinite dipole in free space will be a traveling wave antenna, i.e. no reflections. > And why 600-800 ohms? That's a ballpark Z0 for traveling wave antennas not located near ground. It's the Z0 of a 1/2WL dipole during the transient state before the arrival of the first reflections from the ends. The resonant feedpoint impedance of a center-fed 1/2WL dipole is (the difference between the values of the forward voltage and the reflected voltage) divided by (the sum of the values of the forward current and reflected current). Note: the two voltages are out of phase and the two currents are in phase. This is the (B) definition of "impedance" in the "IEEE Dictionary", i.e. impedance as a *result*, not a cause. Destructive wave interference at the feedpoint of a center-fed 1/2WL dipole is what causes a Z0-match to a low resistive value, e.g. 50 ohms or 70 ohms. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- Article: 217240 of rec.radio.amateur.antenna Subject: Re: Open Stub fed J antenna From: Cecil Moore Date: Sat, 17 Sep 2005 09:00:27 -0500 Message-ID: <1126965787_3169@spool6-east.superfeed.net> References: <1126835197_2699@spool6-east.superfeed.net> <24625-432A4483-301@storefull-3253.bay.webtv.net> <5_PWe.50333$FA3.17911@news-server.bigpond.net.au> David wrote: > I have constructed a 915 MHz 1/2 wave, end fed antenna that fits onto > the end of a SMA plug based on help from you guys. How are you matching the very high feedpoint impedance? > I have some pics of > the construction if anyone is interested in taking a look. > Where is the appropriate place to post these jpg files ? Some of us have web pages from qsl.net for that purpose. There is also a netnews group for that purpose. I think it is alt.binaries. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- Article: 217241 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: 73 Ohms, How do you get it? Date: Sat, 17 Sep 2005 14:24:32 +0000 (UTC) Message-ID: References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> <1126655181_28167@spool6-east.superfeed.net> <5MOAq4S9pIKDFwB+@g3ohx.demon.co.uk> <1126734334_299@spool6-east.superfeed.net> > What is the impedance at the centre of an infinitely long dipole (in > free space)? =============================== Its not very different from - Zin = 120 * Ln( Wavelength / d ) ohms. where d = conductor diameter, both measured in metres. Thus, at wavelength = 80 metres with 14 gauge copper wire, input impedance = 1300 ohms approx. If you don't believe me, just measure it. ---- Reg. Article: 217242 of rec.radio.amateur.antenna From: "Fred W4JLE" References: <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com> <31f74$43299abf$471c63c6$12083@ALLTEL.NET> <1126821476.840433.194860@g49g2000cwa.googlegroups.com> Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Date: Sat, 17 Sep 2005 11:41:25 -0400 Message-ID: <17b21$432c3942$471c63c6$27597@ALLTEL.NET> Would someone put something in "Uncle Ted's" mouth, my zipper is stuck... Uncle Ted" wrote in message > It's bad enough that people feel a need to believe in any deities at > all, but when you have to listen to a bunch of old men in robes half a > world away tell you how to live your life, you're pretty screwed up. Article: 217243 of rec.radio.amateur.antenna From: aRKay Subject: Using a Fan Dipole for Six Meters Message-ID: Date: Sat, 17 Sep 2005 16:43:55 GMT I just purchased a Ten-Tec 1208 Transverter to get my feet wet on six meters. I would like to use my existing W9INN fan dipole if possible. At the present time the fan dipole has three sets of wires from the common feed point for 40/80, 10 MHz and 18 MHz. My plan is to add another short set of wires cut for 50.125 MHz. Since each of the new wires will only be 4.67 feet, I plan to use stand offs and run them close to the 40/80 dipoles. It will be interesting to see if this really works. Any suggestions for the short stand off insulators? Dick, AA5VU aa5vu at arrl.net Article: 217244 of rec.radio.amateur.antenna From: "Charlie" Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Date: Sat, 17 Sep 2005 11:46:58 -0500 Message-ID: <11ioi4diagii717@news.supernews.com> References: <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com> <31f74$43299abf$471c63c6$12083@ALLTEL.NET> <1126821476.840433.194860@g49g2000cwa.googlegroups.com> <17b21$432c3942$471c63c6$27597@ALLTEL.NET> Can't do it Fred..I'm not homosexual as apparently you are. -- Charlie "Fred W4JLE" wrote in message news:17b21$432c3942$471c63c6$27597@ALLTEL.NET... > Would someone put something in "Uncle Ted's" mouth, my zipper is stuck... > > Uncle Ted" wrote in message > >> It's bad enough that people feel a need to believe in any deities at >> all, but when you have to listen to a bunch of old men in robes half a >> world away tell you how to live your life, you're pretty screwed up. > > Article: 217245 of rec.radio.amateur.antenna From: aRKay Subject: Re: Using a Fan Dipole for Six Meters References: Message-ID: Date: Sat, 17 Sep 2005 16:55:52 GMT In article , aRKay wrote: > I just purchased a Ten-Tec 1208 Transverter to get my feet wet on six > meters. I would like to use my existing W9INN fan dipole if possible. > At the present time the fan dipole has three sets of wires from the > common feed point for 40/80, 10 MHz and 18 MHz. My plan is to add > another short set of wires cut for 50.125 MHz. Since each of the new > wires will only be 4.67 feet, I plan to use stand offs and run them > close to the 40/80 dipoles. It will be interesting to see if this > really works. Any suggestions for the short stand off insulators? > > Dick, AA5VU > aa5vu at arrl.net Any suggestions on how to keep the new six meter wires from wrapping around the 40 meter wire in the wind? My plan sounds good until the wind blows and I have visions of the short six meter wires getting tangled in the other wires. I would tie them off with additional tie ropes but it would wind up looking more like an extreme Inverted V antenna. AA5VU Article: 217246 of rec.radio.amateur.antenna Subject: Re: Using a Fan Dipole for Six Meters From: Cecil Moore Date: Sat, 17 Sep 2005 12:51:27 -0500 Message-ID: <1126979647_3729@spool6-east.superfeed.net> References: aRKay wrote: > I just purchased a Ten-Tec 1208 Transverter to get my feet wet on six > meters. I would like to use my existing W9INN fan dipole if possible. > At the present time the fan dipole has three sets of wires from the > common feed point for 40/80, 10 MHz and 18 MHz. My plan is to add > another short set of wires cut for 50.125 MHz. Since each of the new > wires will only be 4.67 feet, I plan to use stand offs and run them > close to the 40/80 dipoles. It will be interesting to see if this > really works. Any suggestions for the short stand off insulators? 18 MHz times three equals 54 MHz. The 18 MHz dipole is likely to detune the 6m dipole. See what the 6m SWR is now. You may not need any additional wires. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- Article: 217247 of rec.radio.amateur.antenna From: "Roger Conroy" Subject: Re: How to weather-seal an upside down Tailtwister rotor? Date: Sat, 17 Sep 2005 19:43:17 +0200 Message-ID: References: <3op5feF73ibjU1@individual.net> <6pakv2-ti9.ln1@p400bob.personal.cox.net> <3p07aaF7ublaU1@individual.net> "Ted Goldblatt" wrote in message news:3p07aaF7ublaU1@individual.net... > John Ferrell wrote: > >> I am not sure I understand the question. I think you have the rotator >> upside down on the tower at the moment. If it went through some >> weather, it is probably full of water now. The way I would handle the >> problem is to remove the rotator from the mount and hang it on the >> tower (clothes hanger wire) right side up. I would hang it there for a >> few days to drain & dry out. When it comes time to reinstall the >> antennas, test the rotator for proper operation. Chances are that it >> will be OK. If you seal it tight, the moisture will be sealed in. >> These things are intended to be able to breathe! > > The tower is currently up (the mast broke above the rotor, so all the > antennas are dangling by their feedlines, but the tower itself is OK) and > the rotor is in its normal upright position. It will be upside down when > the tower is folded over to work on. As far as I know, the rotor is fine > right now. > >> If removing/replacing the rotator is a major hassle, I would either >> send it to one of the maintenance guys or put up a new one & sell the >> old one on ebay WITH the explanation. There are lots of us who have >> setups that are easy to change. > > Don't understand this. Yes, removing/replacing the rotor is a hassle, > largely because it has to be done with the unit upside down, and standing > at the top of a ladder. But that isn't the issue here - in fact, there is > no obvious reason to remove the rotor at all, since it seems intact. Just > remove the stub of the broken mast from the thrust bearing and put a new > one in. The issue is that while that is done, and the new antennas are > mounted, and new (or repaired) feedlines are run, and all the antennas are > tuned, the tower will need to be folded over, with the rotor mounted, and > these steps will almost certainly take several days. Because of > availability of helpers reasons, this will likely have to be on weekends, > meaning the tower will be folded (and the rotor inverted) for a period of > at least 1 to 2 weeks. > >> If the rotator must be left in the inverted position outside for an >> extended time I would wrap it in black landscape plastic and duct tape >> to prevent more water from entering while leaving the bottom of the >> plastic open to dry out. > > I have done this in the past, but because of the way the rotor is mounted > on the Rohn tower, it isn't possible to seal it very well this way - I was > looking for suggestions for better ways of weatherproofing it for this > period. > > Marshall > LOTS of Heavy Grease "glooped" all over every conceivable (and inconceivable) opening. Then wrap it in plastic. 73 Roger ZR3RC Article: 217248 of rec.radio.amateur.antenna From: "Jerry Martes" References: <1126835197_2699@spool6-east.superfeed.net> <24625-432A4483-301@storefull-3253.bay.webtv.net> <5_PWe.50333$FA3.17911@news-server.bigpond.net.au> <1126965787_3169@spool6-east.superfeed.net> Subject: Re: Open Stub fed J antenna Message-ID: <38ZWe.1399$fb6.1163@trnddc08> Date: Sat, 17 Sep 2005 18:20:47 GMT "Cecil Moore" wrote in message news:1126965787_3169@spool6-east.superfeed.net... > David wrote: > >> I have constructed a 915 MHz 1/2 wave, end fed antenna that fits onto the >> end of a SMA plug based on help from you guys. > > How are you matching the very high feedpoint impedance? > >> I have some pics of the construction if anyone is interested in taking a >> look. >> Where is the appropriate place to post these jpg files ? > > Some of us have web pages from qsl.net for that purpose. > There is also a netnews group for that purpose. I think > it is alt.binaries. > -- > 73, Cecil http://www.qsl.net/w5dxp > > > ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet > News==---- > http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 > Newsgroups > ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- Cecil He is feeding the 1/2 wave antenna in the center, where the impedance will be somewhere around 70 ohms. His coax feed line is located within one half of the antenna and exits the 1/2 wave, center excited, dipole at the "high impedance" end of the dipole. David sent me some pictures. The antenna looks quite good. The effectiveness of the "choke" that attempts to disconnect the dipole >from the feed line may be less than ideal, but it is yet unknown how good this antenna needs to be. Jerry Article: 217249 of rec.radio.amateur.antenna From: aRKay Subject: Re: Using a Fan Dipole for Six Meters References: <1126979647_3729@spool6-east.superfeed.net> Message-ID: Date: Sat, 17 Sep 2005 19:17:10 GMT In article <1126979647_3729@spool6-east.superfeed.net>, Cecil Moore wrote: > aRKay wrote: > > I just purchased a Ten-Tec 1208 Transverter to get my feet wet on six > > meters. I would like to use my existing W9INN fan dipole if possible. > > At the present time the fan dipole has three sets of wires from the > > common feed point for 40/80, 10 MHz and 18 MHz. My plan is to add > > another short set of wires cut for 50.125 MHz. Since each of the new > > wires will only be 4.67 feet, I plan to use stand offs and run them > > close to the 40/80 dipoles. It will be interesting to see if this > > really works. Any suggestions for the short stand off insulators? > > 18 MHz times three equals 54 MHz. The 18 MHz dipole is likely to > detune the 6m dipole. See what the 6m SWR is now. You may not > need any additional wires. > -- > 73, Cecil http://www.qsl.net/w5dxp Good point. I may hold off until I get the Ten-Tec 1208 and see what I have with the existing mess of wires. HiHi I don't have an antenna analyser so will have to wait until I generate a six meter signal. Anyone ever tried six meters on an old Ringo Ranger 2 meter antenna? Dick AA5VU Article: 217250 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: Using a Fan Dipole for Six Meters Date: Sat, 17 Sep 2005 19:26:35 +0000 (UTC) Message-ID: References: It should work OK. You will need a little patience to prune the 50 Mhz antenna length to resonance. To reduce the coupling between antennas you could allow the 50 MHz dipole to droop a little in the form of a shallow inverted-V. Just progressivly increase the lemgth of the hanging insulating strings towards the end of the 50 MHz dipole. It doesn't matter if the dipole has curves in it. I hope I have correctly judged your setup. ---- Reg. Article: 217251 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Open Stub fed J antenna Date: Sat, 17 Sep 2005 12:46:24 -0700 Message-ID: <11ioskhlhnsrl9b@corp.supernews.com> References: <1126835197_2699@spool6-east.superfeed.net> <24625-432A4483-301@storefull-3253.bay.webtv.net> Jerry Martes wrote: > > I'd have expected the "gain" to be closer to 4 1/2 db over the 1/4 wave > stub over a ground. is it easy to show where i've missed something? > I think it should be more like 3 dB, but hadn't said anything until I had a chance to model it. The quarter wave stub doesn't radiate significantly, so it can be ignored. A half wavelength element should have about 1.5 dB gain over a quarter wave. Two of them would give another 3 dB if it weren't for mutual coupling, but the mutual coupling of collinear elements reduces the gain to about 1.5 dB over a single element. (See for example Fig. 39 on p. 8-35 of the ARRL Antenna Book, 20th Edition; look up Collinear, Gain and directivity in the index of other editions; or model it with your favorite program.) Roy Lewallen, W7EL Article: 217252 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: 73 Ohms, How do you get it? Date: Sat, 17 Sep 2005 20:00:02 +0000 (UTC) Message-ID: References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> <1126655181_28167@spool6-east.superfeed.net> <5MOAq4S9pIKDFwB+@g3ohx.demon.co.uk> <1126734334_299@spool6-east.superfeed.net> You had better go back to your old college days and start again with new teachers. The input impedance of an infinite dipole is as I have already simply mathematically described. It changes a little with frequency and wire diameter. Anything less than infinite length will be altogether different. Now you can stop trying to pull our legs. ---- Reg. Article: 217253 of rec.radio.amateur.antenna From: "Jerry Martes" References: <1126835197_2699@spool6-east.superfeed.net> <24625-432A4483-301@storefull-3253.bay.webtv.net> <11ioskhlhnsrl9b@corp.supernews.com> Subject: Re: Open Stub fed J antenna Message-ID: Date: Sat, 17 Sep 2005 20:03:43 GMT "Roy Lewallen" wrote in message news:11ioskhlhnsrl9b@corp.supernews.com... > Jerry Martes wrote: >> >> I'd have expected the "gain" to be closer to 4 1/2 db over the 1/4 wave >> stub over a ground. is it easy to show where i've missed something? >> > > I think it should be more like 3 dB, but hadn't said anything until I had > a chance to model it. The quarter wave stub doesn't radiate significantly, > so it can be ignored. A half wavelength element should have about 1.5 dB > gain over a quarter wave. Two of them would give another 3 dB if it > weren't for mutual coupling, but the mutual coupling of collinear elements > reduces the gain to about 1.5 dB over a single element. (See for example > Fig. 39 on p. 8-35 of the ARRL Antenna Book, 20th Edition; look up > Collinear, Gain and directivity in the index of other editions; or model > it with your favorite program.) > > Roy Lewallen, W7EL Thanks Roy Your posts always add alot to my understanding. I appreciate your taking time to evaluate this antenna and then pass the information on to the group. Jerry Article: 217254 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Open Stub fed J antenna Date: Sat, 17 Sep 2005 14:28:16 -0700 Message-ID: <11ip2ji5tbe343a@corp.supernews.com> References: <1126835197_2699@spool6-east.superfeed.net> <24625-432A4483-301@storefull-3253.bay.webtv.net> <11ioskhlhnsrl9b@corp.supernews.com> Jerry Martes wrote: > "Roy Lewallen" wrote in message >> >>I think it should be more like 3 dB, but hadn't said anything until I had >>a chance to model it. The quarter wave stub doesn't radiate significantly, >>so it can be ignored. A half wavelength element should have about 1.5 dB >>gain over a quarter wave. Two of them would give another 3 dB if it >>weren't for mutual coupling, but the mutual coupling of collinear elements >>reduces the gain to about 1.5 dB over a single element. (See for example >>Fig. 39 on p. 8-35 of the ARRL Antenna Book, 20th Edition; look up >>Collinear, Gain and directivity in the index of other editions; or model >>it with your favorite program.) >> >>Roy Lewallen, W7EL > > > Thanks Roy > > Your posts always add alot to my understanding. I appreciate your taking > time to evaluate this antenna and then pass the information on to the group. > > Jerry I'm sorry, I see I wasn't clear in saying that I haven't yet had a chance to model it. There might be a flaw in my reasoning, and the antenna might have more gain than I think. I'll try to get to it as soon as I can -- unless someone else wants to take it on. But I'm extremely busy just now. Roy Lewallen, W7EL Article: 217255 of rec.radio.amateur.antenna From: "Dan/W4NTI" References: <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com> <31f74$43299abf$471c63c6$12083@ALLTEL.NET> <1126821476.840433.194860@g49g2000cwa.googlegroups.com> <1126987193.132617.297010@g44g2000cwa.googlegroups.com> Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Message-ID: <3D0Xe.13382$_84.7807@newsread1.news.atl.earthlink.net> Date: Sat, 17 Sep 2005 22:18:39 GMT D A N G.....he posted without talking about Morse Code Testing. Hats off Lennie. Dan/W4NTI wrote in message news:1126987193.132617.297010@g44g2000cwa.googlegroups.com... > >>It has NEVER been the DOGMA of the Catholic Church to sell indulgences. >>PERIOD! A period of clerical abuse of indulgences, contrary to the >>Doctrinal position of the Church, did exist in history. Martin Luther >>was correct to cite this failure in clergy practice. The abuse was >>censured in the Council of Trent [ca 1545 - 1563]. > > > Did his karma run over your dogma? :-) > > > LenAnderson@ieee.org > Article: 217256 of rec.radio.amateur.antenna Subject: Re: 73 Ohms, How do you get it? From: Cecil Moore Date: Sat, 17 Sep 2005 17:35:50 -0500 Message-ID: <1126996710_4691@spool6-east.superfeed.net> References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> <1126655181_28167@spool6-east.superfeed.net> <5MOAq4S9pIKDFwB+@g3ohx.demon.co.uk> <1126734334_299@spool6-east.superfeed.net> Ham op wrote: > NOTE: an infinitely long wire in free space cannot be terminated. Doesn't need to be terminated. Reflections are eliminated without terminations. > A terminated wire in an anechoic chamber is not the same as a > free space model. Not exactly the same but close enough for government work. Reflections from the ends and from the walls are reduced to a negligible value. Been there, done that. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- Article: 217257 of rec.radio.amateur.antenna From: nospam@nouce.bellatlantic.net Subject: Re: Using a Fan Dipole for Six Meters Message-ID: References: <1126979647_3729@spool6-east.superfeed.net> Date: Sun, 18 Sep 2005 00:58:01 GMT On Sat, 17 Sep 2005 19:17:10 GMT, aRKay wrote: >In article <1126979647_3729@spool6-east.superfeed.net>, > Cecil Moore wrote: > >> aRKay wrote: >> > I just purchased a Ten-Tec 1208 Transverter to get my feet wet on six >> > meters. I would like to use my existing W9INN fan dipole if possible. >> > At the present time the fan dipole has three sets of wires from the >> > common feed point for 40/80, 10 MHz and 18 MHz. My plan is to add >> > another short set of wires cut for 50.125 MHz. Since each of the new >> > wires will only be 4.67 feet, I plan to use stand offs and run them >> > close to the 40/80 dipoles. It will be interesting to see if this >> > really works. Any suggestions for the short stand off insulators? >> >> 18 MHz times three equals 54 MHz. The 18 MHz dipole is likely to >> detune the 6m dipole. See what the 6m SWR is now. You may not >> need any additional wires. >> -- >> 73, Cecil http://www.qsl.net/w5dxp > >Good point. I may hold off until I get the Ten-Tec 1208 and see what I >have with the existing mess of wires. HiHi > >I don't have an antenna analyser so will have to wait until I generate a >six meter signal. > >Anyone ever tried six meters on an old Ringo Ranger 2 meter antenna? > >Dick AA5VU The ringo ranger is vertical and most 6m stuff is horizontal. On skip that may not hurt but for local it's very poor. Allison KB1GMX Article: 217258 of rec.radio.amateur.antenna From: "Ralph Mowery" References: <1126979647_3729@spool6-east.superfeed.net> Subject: Re: Using a Fan Dipole for Six Meters Message-ID: Date: Sun, 18 Sep 2005 00:58:02 GMT > Good point. I may hold off until I get the Ten-Tec 1208 and see what I > have with the existing mess of wires. HiHi > > I don't have an antenna analyser so will have to wait until I generate a > six meter signal. > > Anyone ever tried six meters on an old Ringo Ranger 2 meter antenna? > > Dick AA5VU I worked Canada on 6 meters with that transverter. Used a trapped dipole for 40 to 10 meters. I doube the ringo would work on 6 due to the way is fed. If it was just a baseloaded (matched) 5/8 wave 2 meter antenna, it might work fine. Article: 217259 of rec.radio.amateur.antenna From: nospam@nouce.bellatlantic.net Subject: Re: Using a Fan Dipole for Six Meters Message-ID: <5uepi1tmkb9qenqv47lpg5ch1oge9krf5l@4ax.com> References: Date: Sun, 18 Sep 2005 01:02:39 GMT On Sat, 17 Sep 2005 16:43:55 GMT, aRKay wrote: >I just purchased a Ten-Tec 1208 Transverter to get my feet wet on six >meters. I would like to use my existing W9INN fan dipole if possible. >At the present time the fan dipole has three sets of wires from the >common feed point for 40/80, 10 MHz and 18 MHz. My plan is to add >another short set of wires cut for 50.125 MHz. Since each of the new >wires will only be 4.67 feet, I plan to use stand offs and run them >close to the 40/80 dipoles. It will be interesting to see if this >really works. Any suggestions for the short stand off insulators? > >Dick, AA5VU >aa5vu at arrl.net That 17m (18mhz) antenna should do well. I run a bunch of antennas and for local work rather than turning a beam I use a `24ft EDZ with a stub tuning on each wire to match 50ohms. The oddity of that antenna is it looks like a plain dipole at 18mhz according to the MFJ269b. I'd drive that and see what the SWR looked like, it may be fair as is. Owing to the amount of wire it may offer some amout of gain over a plain dipole. Good luck, Allison KB1GMX Article: 217260 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: help requested for designing 4-square inverted L on 20 meters Date: Sat, 17 Sep 2005 19:59:24 -0700 Message-ID: <11ipm0ee3i0982@corp.supernews.com> References: <1126983316.093491.307380@g43g2000cwa.googlegroups.com> <1127010179.364313.192090@g14g2000cwa.googlegroups.com> The feedpoint SWR will depend heavily on the type of feed system used. The 4SqTL.EZ example model included with EZNEC, which uses one of the all-transmission line feed systems described by "The Simplest Phased Array Feed System - That Works", shows a 50-ohm SWR of 3.7 at the feedpoint. Other feed systems are possible using this method, each of which produces a different feedpoint impedance. The combination transmission line - L network method described in Chapter 8 of the ARRL Antenna book produces yet other feedpoint impedances, depending on the transmission line Z0s which are chosen. There's no need to settle for a feedpoint SWR in the thousands, and there's no need to alter your array elements as a means of improving it. If you use inverted-L elements for a four square array, it seems to me you'd get a different elevation pattern in the various directions, and that the azimuth pattern would be distorted by the directionality of the elements. Have you modeled the full four element array, with the currents phased as they would be for each of the four readily switchable directions? Roy Lewallen, W7EL eternalsquire@comcast.net wrote: > Take a look at the far-field pattern and you'll see why I want it. > Also, it seems that inverted L's rather than verticals lower the > SWR from the thousands to something more sensible. > > The Eternal Squire. > Article: 217261 of rec.radio.amateur.antenna From: aRKay Subject: Re: Using a Fan Dipole for Six Meters References: Message-ID: Date: Sun, 18 Sep 2005 03:55:02 GMT In article , aRKay wrote: > I just purchased a Ten-Tec 1208 Transverter to get my feet wet on six > meters. I would like to use my existing W9INN fan dipole if possible. > At the present time the fan dipole has three sets of wires from the > common feed point for 40/80, 10 MHz and 18 MHz. My plan is to add > another short set of wires cut for 50.125 MHz. Since each of the new > wires will only be 4.67 feet, I plan to use stand offs and run them > close to the 40/80 dipoles. It will be interesting to see if this > really works. Any suggestions for the short stand off insulators? > > Dick, AA5VU > aa5vu at arrl.net I have decided to hold off changing anything until I get the Transverter next week. I will then see if someone is close before I start messing with extra wires. The problem with adding another set of wires for 50.125 is how to keep them from getting tangled in the wind. I have visions of them wrapping around the 40/80 set of wires. Stay tuned for what happens. Half the fun of getting a new toy like the six meter transverter will be finding the right antenna. Dick aa5Vu Article: 217262 of rec.radio.amateur.antenna From: aRKay Subject: Re: Using a Fan Dipole for Six Meters References: <1126979647_3729@spool6-east.superfeed.net> Message-ID: Date: Sun, 18 Sep 2005 03:56:16 GMT In article , nospam@nouce.bellatlantic.net wrote: > The ringo ranger is vertical and most 6m stuff is horizontal. On skip > that may not hurt but for local it's very poor. > > Allison > KB1GMX Good response. I will not waste time messing with the old Ringo Ranger. Article: 217263 of rec.radio.amateur.antenna From: "Harold Burton" Subject: Re: Using a Fan Dipole for Six Meters Date: Sat, 17 Sep 2005 23:18:03 -0500 Message-ID: <11ipqjgbblu475f@corp.supernews.com> References: <1126979647_3729@spool6-east.superfeed.net> "aRKay" wrote in message news:REMOVEarkay-05A123.22561617092005@newsclstr02.news.prodigy.com... > In article , > nospam@nouce.bellatlantic.net wrote: > >> The ringo ranger is vertical and most 6m stuff is horizontal. On skip >> that may not hurt but for local it's very poor. >> >> Allison >> KB1GMX > > Good response. I will not waste time messing with the old Ringo Ranger. Don't give up on the vertical too quickly. I use both a 6 meter dipole and a 6 meter J-pole, 90% of my 6 meter contacts have been with the J-pole. Some of the more experienced Hams of my acquaintance have told me that DX sort of works outside of the normal vertical/horizontal polarization expectation. I rarely have any occasion for a local 6 meter contact. so am not able to speak about that aspect of the 6 meter band. Harold KD5SAK Article: 217264 of rec.radio.amateur.antenna From: David Subject: Re: Open Stub fed J antenna References: <1126835197_2699@spool6-east.superfeed.net> <24625-432A4483-301@storefull-3253.bay.webtv.net> <5_PWe.50333$FA3.17911@news-server.bigpond.net.au> <1126965787_3169@spool6-east.superfeed.net> Message-ID: Date: Sun, 18 Sep 2005 04:45:03 GMT Cecil, Using a 1/4 wave open stub. Cecil Moore wrote: > David wrote: > >> I have constructed a 915 MHz 1/2 wave, end fed antenna that fits onto >> the end of a SMA plug based on help from you guys. > > > How are you matching the very high feedpoint impedance? > >> I have some pics of the construction if anyone is interested in taking >> a look. >> Where is the appropriate place to post these jpg files ? > > > Some of us have web pages from qsl.net for that purpose. > There is also a netnews group for that purpose. I think > it is alt.binaries. Article: 217265 of rec.radio.amateur.antenna From: David Subject: Re: Open Stub fed J antenna References: <1126835197_2699@spool6-east.superfeed.net> <24625-432A4483-301@storefull-3253.bay.webtv.net> <11ioskhlhnsrl9b@corp.supernews.com> Message-ID: <7p6Xe.51542$FA3.8337@news-server.bigpond.net.au> Date: Sun, 18 Sep 2005 04:53:23 GMT Roy, I am using your EZNEC V4.019. Would you happen to have the ez description file for this antenna so I can see how it is modeled ? I had a "play" and set up 2 vertical have wave lengths and set the source at the centre I then placed a 1/4 wave wire near the lower 1/4 wave and connect them at the centre point with a horizontal wire but the program kept complaining that the wires were overlapping etc. I also tried modeling an open stub J-Pole and seemed to be able to get some plots that look ok but SWR was >100 across the band. Not sure what I did wrong here but I assume as I get more familiar with modeling techniques, I will get more meaningful results. Thanks Regards David Roy Lewallen wrote: > Jerry Martes wrote: > >> >> I'd have expected the "gain" to be closer to 4 1/2 db over the 1/4 >> wave stub over a ground. is it easy to show where i've missed something? >> > > I think it should be more like 3 dB, but hadn't said anything until I > had a chance to model it. The quarter wave stub doesn't radiate > significantly, so it can be ignored. A half wavelength element should > have about 1.5 dB gain over a quarter wave. Two of them would give > another 3 dB if it weren't for mutual coupling, but the mutual coupling > of collinear elements reduces the gain to about 1.5 dB over a single > element. (See for example Fig. 39 on p. 8-35 of the ARRL Antenna Book, > 20th Edition; look up Collinear, Gain and directivity in the index of > other editions; or model it with your favorite program.) > > Roy Lewallen, W7EL Article: 217266 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: help requested for designing 4-square inverted L on 20 meters Date: Sat, 17 Sep 2005 22:56:14 -0700 Message-ID: <11iq0c073np7le0@corp.supernews.com> References: <1126983316.093491.307380@g43g2000cwa.googlegroups.com> <1127010179.364313.192090@g14g2000cwa.googlegroups.com> <11ipm0ee3i0982@corp.supernews.com> <1127013267.286019.162340@g49g2000cwa.googlegroups.com> eternalsquire@comcast.net wrote: > Roy, > > Actually, I have modelled for a single direction, see my original post. > I am using 4nec2 for modelling the far field pattern. Would you be > interested in checking my work to see if anything better can be done? > > The Eternal Squire Sorry, I don't have the time just now. > > P.S: Do you have experience with 4-square arrays? > Yes. Article: 217267 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Open Stub fed J antenna Date: Sat, 17 Sep 2005 23:07:58 -0700 Message-ID: <11iq11vqieblm9a@corp.supernews.com> References: <1126835197_2699@spool6-east.superfeed.net> <24625-432A4483-301@storefull-3253.bay.webtv.net> <11ioskhlhnsrl9b@corp.supernews.com> <7p6Xe.51542$FA3.8337@news-server.bigpond.net.au> David wrote: > Roy, > > I am using your EZNEC V4.019. Would you happen to have the ez > description file for this antenna so I can see how it is modeled ? Sorry, I haven't had time to model it. But I dusted off a very old, originally ELNEC, model of a 3 element collinear, and uploaded it to my web site. It should give you the general idea. It's Collinear3.EZ at http://eznec.com/misc/. > . . . Roy Lewallen, W7EL Article: 217268 of rec.radio.amateur.antenna From: "pezSV7BAXdag" Subject: Re: 73 Ohms, How do you get it? Date: Sun, 18 Sep 2005 10:18:12 +0300 Message-ID: References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> <1126655181_28167@spool6-east.superfeed.net> <5MOAq4S9pIKDFwB+@g3ohx.demon.co.uk> <1126734334_299@spool6-east.superfeed.net> | "Reg Edwards" wrote in message | news:dghsk2$6cj$1@nwrdmz02.dmz.ncs.ea.ibs-infra.bt.com... | | You had better go back to your old college days | and start again with new teachers. | | The input impedance of an infinite dipole | is as I have already simply mathematically described. | It changes a little with frequency and wire diameter. | | Anything less than infinite length will be altogether different. | | Now you can stop trying to pull our legs. | ---- | Reg. Dear Mr. Reg Edwards, This is an interesting question indeed! Well, my wife yinSV7DMCdag has developed sometime an AVI movie [ in ZIP form: [ http://antennas.ee.duth.gr/ftp/visualantennas/thedipole/films/fu010100.zip [ 850 KB which deals among other properties of a filamentary dipole, with its Radiation Resistance relative to the Input Terminals (Driving Point) [ Please take a look if you like [ in the part D of the movie, [ at the bottom right of the screen This is actually the Input Resistance Rinp of a filamentary dipole of perfect conductivity in free space. The ratio of dipole length L to wavelength lambda takes values up to 10, but someone may maintain arguably that either the limit of Rinp exists in general as infinity or does not exist at all. Yours Sincerely, pezSV7BAXdag Article: 217269 of rec.radio.amateur.antenna From: Ian Jackson Subject: Re: 73 Ohms, How do you get it? Date: Sun, 18 Sep 2005 08:29:40 +0100 Message-ID: References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> In message , Reg Edwards writes >> What is the impedance at the centre of an infinitely long dipole >(in >> free space)? > >=============================== >Its not very different from - > >Zin = 120 * Ln( Wavelength / d ) ohms. > >where d = conductor diameter, both measured in metres. > >Thus, at wavelength = 80 metres with 14 gauge copper wire, input >impedance = 1300 ohms approx. > >If you don't believe me, just measure it. >---- >Reg. > > Are you sure it's as high as that, Reg? I once did a Smith Chart plot of the impedance at the centre of a dipole, the valued being taken from a table 'compiled by Wu' (LK Wu?). These only catered for a lengths up to a few wavelengths. As the plot progressed round and round the Smith Chart, it seemed to be heading for something around 350 to 400 ohms. I've just done a search on 'Wu+dipole+impedance', and one of the results is http://www.fars.k6ya.org/docs/antenna-impedance-models.pdf I'll have a read of it today. Cheers, Ian. -- Article: 217270 of rec.radio.amateur.antenna From: "SOMMERGIBILE" Subject: A lot of good diagrams Date: Sun, 18 Sep 2005 10:00:10 +0200 Message-ID: <432d21f4$0$8486$5fc30a8@news.tiscali.it> on: http://web.tiscali.it/am2zy/index.html Article: 217271 of rec.radio.amateur.antenna From: "Lee" Subject: E H Antenna Message-ID: Date: Sun, 18 Sep 2005 09:11:01 GMT Just heard mention of the EH Antenna and that it is rather small but equal radiation to a full size dipole !!!. If this is true, i am very interested as i only have a small garden (35x18 feet) and the EH sounds ideal so anyone with info , it would be greatly appreciated. I am using a homebrew helical for 80m and a sloping half size G5RV and i am really stuck for space :-/ Lee.....G6ZSG.. Article: 217272 of rec.radio.amateur.antenna Message-ID: <432d3141$0$980$626a14ce@news.free.fr> From: F8BOE Subject: Re: E H Antenna Date: Sun, 18 Sep 2005 11:20:03 +0200 References: Was interested too, but gave up. With so many different descriptions for one concept, there must bee something foolish. And I don't want to use my rig as an antenna! 73 de F8BOE Olivier ...-.- Lee wrote: > Just heard mention of the EH Antenna and that it is rather small but > equal radiation to a full size dipole !!!. > > If this is true, i am very interested as i only have a small garden (35x18 > feet) and the EH sounds ideal so anyone with info , it would be greatly > appreciated. > > I am using a homebrew helical for 80m and a sloping half size G5RV and i > am > really stuck for space :-/ > > Lee.....G6ZSG.. Article: 217273 of rec.radio.amateur.antenna From: "pezSV7BAXdag" Subject: Re: 73 Ohms, How do you get it? Date: Sun, 18 Sep 2005 12:30:11 +0300 Message-ID: References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> <1126655181_28167@spool6-east.superfeed.net> <5MOAq4S9pIKDFwB+@g3ohx.demon.co.uk> <1126734334_299@spool6-east.superfeed.net> | "Ian Jackson" | wrote in message news:LBpcZhCkdRLDFweH@g3ohx.demon.co.uk... | [...] | it seemed to be heading for something around 350 to 400 ohms. | [...] | Ian. 120*pi maybe ... pezSV7BAXdag Article: 217274 of rec.radio.amateur.antenna From: aRKay Subject: Re: Using a Fan Dipole for Six Meters References: <1126979647_3729@spool6-east.superfeed.net> <11ipqjgbblu475f@corp.supernews.com> Message-ID: Date: Sun, 18 Sep 2005 10:51:39 GMT In article <11ipqjgbblu475f@corp.supernews.com>, "Harold Burton" wrote: > "aRKay" wrote in message > news:REMOVEarkay-05A123.22561617092005@newsclstr02.news.prodigy.com... > > In article , > > nospam@nouce.bellatlantic.net wrote: > > > >> The ringo ranger is vertical and most 6m stuff is horizontal. On skip > >> that may not hurt but for local it's very poor. > >> > >> Allison > >> KB1GMX > > > > Good response. I will not waste time messing with the old Ringo Ranger. > > Don't give up on the vertical too quickly. I use both a 6 meter dipole and a > 6 meter J-pole, 90% of my 6 meter contacts have been with the J-pole. Some > of the more experienced Hams of my acquaintance have told me that DX sort of > works outside of the normal vertical/horizontal polarization expectation. I > rarely have any occasion for a local 6 meter > contact. so am not able to speak about that aspect of the 6 meter band. > > Harold > KD5SAK Thanks Harold. I forgot about the J-pole and I may try one while playing around with the new stuff. Dick - AA5VU Article: 217275 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: E H Antenna Date: Sun, 18 Sep 2005 11:46:33 +0000 (UTC) Message-ID: References: > Just heard mention of the EH Antenna and that it is rather small but equal > radiation to a full size dipole !!!. > =========================== Sucker! If you believe that then you'll believe anything. Article: 217276 of rec.radio.amateur.antenna Subject: Re: Open Stub fed J antenna From: Cecil Moore Date: Sun, 18 Sep 2005 07:14:39 -0500 Message-ID: <1127045838_7601@spool6-east.superfeed.net> References: <1126835197_2699@spool6-east.superfeed.net> <24625-432A4483-301@storefull-3253.bay.webtv.net> <11ioskhlhnsrl9b@corp.supernews.com> <7p6Xe.51542$FA3.8337@news-server.bigpond.net.au> David wrote: > I also tried modeling an open stub J-Pole and seemed to be able to get > some plots that look ok but SWR was >100 across the band. Not sure what > I did wrong here but I assume as I get more familiar with modeling > techniques, I will get more meaningful results. The open stub J-Pole (Zepp) is modeled as a shorted stub J-Pole with the source in the middle of the shorted segment. Mine is for 53.2 MHz. On edge it looks like this: 13.5 ft. +--------------------------------------------------- | (S) | +----------------- 4.5 ft. The sections are 0.1 ft. apart. The resonant frequency is 53.2 MHz and the feedpoint impedance is 25 ohms for an SWR of 2:1. The feedpoint is 30 ft. high over high-accuracy ground. The gain over ground is 6.2 dBi, omnidirectional. Free space gain is 3.4 dBi. Anyone who wants a copy of this 6m J-Pole EZNEC file, please send me an email to mycall@arrl.net. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- Article: 217277 of rec.radio.amateur.antenna From: "Lee" References: Subject: Re: E H Antenna Message-ID: Date: Sun, 18 Sep 2005 12:17:50 GMT "Reg Edwards" wrote in message news:dgjk2p$fck$1@nwrdmz03.dmz.ncs.ea.ibs-infra.bt.com... > > Just heard mention of the EH Antenna and that it is rather small > but equal > > radiation to a full size dipole !!!. > > > =========================== > > Sucker! If you believe that then you'll believe anything. > > Hi Reg......how so?, i regard you as among the knowlegeable and look forward to your thoughts on the EH that prompts your comment, `tho it does seem like something for nothing, i don`t wish to appear too dumb!!....i`m currently playing with a helical on 40 and am thinking of making a dipole with a matching helical, i can get that in my postage stamp garden......hi So you think the EH is a waste of time then??? ;-) Lee.....G6ZSG... Article: 217278 of rec.radio.amateur.antenna From: "John Ferrell" References: Subject: Re: Yet another grounding question Message-ID: <9RdXe.63$vw6.62@newsread1.news.atl.earthlink.net> Date: Sun, 18 Sep 2005 13:21:09 GMT You should have all grounds tied together with a minimum of # 6 copper. It is cheap. It is easy. It is code. It will save your equipment and you will never know the trouble you did not have! -- John Ferrell http://DixieNC.US "Joel" wrote in message news:e704c$43279dcb$943f9237$553@STARBAND.NET... .. > - I 'should' have the power entrance ground run over to the common ground. > But it's over 90 feet away and the house has plastic water pipes.. Does it > make sense to run a copper wire or strap that far? If so, should it be > berried all the way or run exposed. It seems to me the impedance would be > so high in the run, that it would be a waste of copper? > > TNX > Joe AG4QC > Article: 217279 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: E H Antenna Date: Sun, 18 Sep 2005 13:24:08 +0000 (UTC) Message-ID: References: "Lee" wrote > > > > Just heard mention of the EH Antenna and that it is rather small > > but equal > > > radiation to a full size dipole !!!. > > > > > Sucker! If you believe that then you'll believe anything. > > > > Hi Reg......how so?, ============================ Hello Lee, The EH antenna is a hoax perpetrated by somebody who hopes to make money by selling them. His sales description of how the thing works pretends to make use of the mathematical works of James Clerk Maxwell. It may sound good to novices but is just a load of nonsense. Actually, its performance is somewhat worse than other antennas of the same physical size. If it's claims are as marvellous as all that, ask yourself why every amateur doesn't have one, regardless of how big is his backyard. To a smaller extent, the G5RV falls into the same category. You did right to ask your question. ---- Reg. Article: 217280 of rec.radio.amateur.antenna Subject: Re: 73 Ohms, How do you get it? From: Cecil Moore Date: Sun, 18 Sep 2005 08:35:14 -0500 Message-ID: <1127050673_7845@spool6-east.superfeed.net> References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> <1126655181_28167@spool6-east.superfeed.net> <5MOAq4S9pIKDFwB+@g3ohx.demon.co.uk> <1126734334_299@spool6-east.superfeed.net> Ian Jackson wrote: > Are you sure it's as high as that, Reg? I once did a Smith Chart plot of > the impedance at the centre of a dipole, the valued being taken from a > table 'compiled by Wu' (LK Wu?). These only catered for a lengths up to > a few wavelengths. As the plot progressed round and round the Smith > Chart, it seemed to be heading for something around 350 to 400 ohms. Maybe 377 ohms? Remember that any finite length dipole is a standing wave antenna and the feedpoint impedance is (Vfor+Vref)/(Ifor+Iref) where Vfor is the forward voltage phasor, Vref is the reflected voltage phasor, Ifor is the forward current phasor, and Iref is the reflected current phasor. For a 1/2WL resonant dipole the feedpoint impedance is low: R = (|Vfor|-|Vref|)/(|Ifor|+|Iref|) ~ 73 ohms For a 1WL (anti)resonant dipole the feedpoint impedance is high: R = (|Vfor|+|Vref|)/(|Ifor|-|Iref|) ~ 5200 ohms (EZNEC) An infinite dipole would not be a standing wave antenna. It would be a traveling wave antenna (as in a terminated rhombic). So the feedpoint impedance of an infinite dipole would be Vfor/Ifor=Z0. Since the reflections modify the feedpoint impedance, we might suspect that Vfor/Ifor falls between the feedpoint impedance for a 1/2WL dipole and a one WL dipole. Seems to me, the Z0 of the dipole, i.e. Vfor/Ifor, must be in the ballpark of the square root of the product of those two feedpoint impedances. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- Article: 217281 of rec.radio.amateur.antenna Subject: Re: E H Antenna From: Cecil Moore Date: Sun, 18 Sep 2005 08:37:38 -0500 Message-ID: <1127050818_7851@spool6-east.superfeed.net> References: Reg Edwards wrote: >>Just heard mention of the EH Antenna and that it is rather small >> but equal radiation to a full size dipole !!!. > > Sucker! If you believe that then you'll believe anything. Now, now, Reg. He didn't say equal RF radiation. Heat is also radiation. :-) -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- Article: 217282 of rec.radio.amateur.antenna From: "Richard Fry" References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> <1126655181_28167@spool6-east.superfeed.net> <5MOAq4S9pIKDFwB+@g3ohx.demon.co.uk> <1126734334_299@spool6-east.superfeed.net> <1127050673_7845@spool6-east.superfeed.net> Subject: Re: 73 Ohms, How do you get it? Date: Sun, 18 Sep 2005 08:47:01 -0500 Message-ID: <432d6f9d_3@newsfeed.slurp.net> "Cecil Moore" > For a 1/2WL resonant dipole the feedpoint impedance is low: > R = (|Vfor|-|Vref|)/(|Ifor|+|Iref|) ~ 73 ohms _________________ The 73 ohm radiation resistance value applies to a physical 1/2-wave, thin-wire, linear dipole in free space, however a reactance term of + j42.5 ohms also applies to such a configuration (Kraus 3rd Edition, p. 182). The dipole length needs to be shorted by several percent in order to zero out the reactance term, at which time (according to Kraus), the resistance term will be about 65 ohms. RF Article: 217283 of rec.radio.amateur.antenna From: "Lee" References: Subject: Re: E H Antenna Message-ID: <5feXe.76569$2n6.48706@fe3.news.blueyonder.co.uk> Date: Sun, 18 Sep 2005 13:48:49 GMT "Reg Edwards" wrote in message news:dgjppo$55r$1@nwrdmz02.dmz.ncs.ea.ibs-infra.bt.com... > > "Lee" wrote snip< > > Hi Reg......how so?, > ============================ > Hello Lee, > > The EH antenna is a hoax perpetrated by somebody who hopes to make > money by selling them. His sales description of how the thing works > pretends to make use of the mathematical works of James Clerk Maxwell. > It may sound good to novices but is just a load of nonsense. > > Actually, its performance is somewhat worse than other antennas of the > same physical size. > > If it's claims are as marvellous as all that, ask yourself why every > amateur doesn't have one, regardless of how big is his backyard. Yes, it did cross my mind but i`ve only just heard of it and as i say, i`m dumb but not too dumb !!! ;-) > To a > smaller extent, the G5RV falls into the same category. Oh!, i`ve got one of those as a sloper........seems to work somewhat, not brilliant but i can hear stations..... LOL....(wish my garden was bigger :-/). > > You did right to ask your question. I have an enquiring mind ... ta!. Lee.. Article: 217284 of rec.radio.amateur.antenna Subject: Re: Open Stub fed J antenna From: Cecil Moore Date: Sun, 18 Sep 2005 08:55:56 -0500 Message-ID: <1127051915_7863@spool6-east.superfeed.net> References: <1126835197_2699@spool6-east.superfeed.net> <24625-432A4483-301@storefull-3253.bay.webtv.net> <11ioskhlhnsrl9b@corp.supernews.com> <7p6Xe.51542$FA3.8337@news-server.bigpond.net.au> <1127045838_7601@spool6-east.superfeed.net> Dan Richardson wrote: > You can vary the feedpoint impedance by changing (S). Moving the elements to one foot apart increases the feedpoint resistance to about 50 ohms at resonance but it decreases the gain and distorts the radiation pattern since one foot is an appreciable distance on 6 meters. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- Article: 217285 of rec.radio.amateur.antenna From: nospam@nouce.bellatlantic.net Subject: Re: Using a Fan Dipole for Six Meters Message-ID: References: <1126979647_3729@spool6-east.superfeed.net> <11ipqjgbblu475f@corp.supernews.com> Date: Sun, 18 Sep 2005 14:20:02 GMT On Sat, 17 Sep 2005 23:18:03 -0500, "Harold Burton" wrote: > >"aRKay" wrote in message >news:REMOVEarkay-05A123.22561617092005@newsclstr02.news.prodigy.com... >> In article , >> nospam@nouce.bellatlantic.net wrote: >> >>> The ringo ranger is vertical and most 6m stuff is horizontal. On skip >>> that may not hurt but for local it's very poor. >>> >>> Allison >>> KB1GMX >> >> Good response. I will not waste time messing with the old Ringo Ranger. > >Don't give up on the vertical too quickly. I use both a 6 meter dipole and a >6 meter J-pole, 90% of my 6 meter contacts have been with the J-pole. Some >of the more experienced Hams of my acquaintance have told me that DX sort of >works outside of the normal vertical/horizontal polarization expectation. I >rarely have any occasion for a local 6 meter >contact. so am not able to speak about that aspect of the 6 meter band. > >Harold >KD5SAK Experience is that my vertical beam hears far less DX than the horizontal. Occasionally I hear DX on the Vertical that is better but on confirming the other end is also vertical. So it goes. I do have vertical for those times where it may help. One thing I do notice is the noise level of the vertical beam is far worse. For local use the horizontal is usually 2-3 Sunits higher than the vertical. Allison KB1GMX Article: 217286 of rec.radio.amateur.antenna From: nospam@nouce.bellatlantic.net Subject: Re: Using a Fan Dipole for Six Meters Message-ID: <0utqi1toov2uefq3esvfma1gp53fhs12jc@4ax.com> References: Date: Sun, 18 Sep 2005 14:21:45 GMT On Sun, 18 Sep 2005 03:55:02 GMT, aRKay wrote: >In article >, > aRKay wrote: > >> I just purchased a Ten-Tec 1208 Transverter to get my feet wet on six >> meters. I would like to use my existing W9INN fan dipole if possible. >> At the present time the fan dipole has three sets of wires from the >> common feed point for 40/80, 10 MHz and 18 MHz. My plan is to add >> another short set of wires cut for 50.125 MHz. Since each of the new >> wires will only be 4.67 feet, I plan to use stand offs and run them >> close to the 40/80 dipoles. It will be interesting to see if this >> really works. Any suggestions for the short stand off insulators? >> I have one of those TT1208s and it's been a good tool for 6m. I have some impressive contacts off it and a 3 element beam. Enjoy it. Allison Article: 217287 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: E H Antenna Date: Sun, 18 Sep 2005 15:07:09 +0000 (UTC) Message-ID: References: "Lee" wrote - > i`m currently > playing with a helical on 40 and am thinking of making a dipole with a > matching helical, i can get that in my postage stamp garden ...... > ================================== A back-to-back horizontal helical dipole is a good proposition. Radiating efficiency is what matters with physically small antennas. The radiating pattern is whatever you happen to get. A 1/2-wave helical resonant dipole is considerably more efficient than a 1/4-wave vertical simply because of the absence of ground connection losses. A low dipole does have a small ground loss due to its proximity to ground. Ideally its height should be at least equal to its overall length but half that is a satisfactory compromise. A horizontal helical dipole is the same as a centre-loaded wire with a very long loading coil. It is easier to match to a feedline than a vertical and there is a choice of type of line and line impedance. Either coax or balanced line can be used. Make the loading coil continuous through the antenna centre and enclose the centre with a link coupling to the feedline. The number of turns on the coupling link is dependent on line impedance. The antenna itself is electrically isolated from the line and remains nicely balanced about ground. The greater the diameter of the loading coil former, a rigid plastic pipe, and the thicker the wire, the higher the efficiency. For 100 watts transmitters, close wound turns of thick enamelled wire are usually OK. Resonant frequency is adjusted by pruning the length of the wire or rods which extend beyond the ends of the coil. If essential due to space limitations, the end wires can be allowed to fall down towards the ground but not allowed to swing about in the wind. Short loaded antennas are essentially single frequency, very narrow bandwidth devices. Download program MIDLOAD from website below. It may be of assistance or at least provide you with something to think about. In postage-stamp backyards, size-for-size, Magloops are the most efficient of all very small antennas and can cover several adjacent bands, but are deceptively difficult/easy/expensive to construct depending on your ingenuity. Download program MAGLOOP4. ---- ........................................................... Regards from Reg, G4FGQ For Free Radio Design Software go to http://www.btinternet.com/~g4fgq.regp ........................................................... Article: 217288 of rec.radio.amateur.antenna From: Ian Jackson Subject: Re: 73 Ohms, How do you get it? Date: Sun, 18 Sep 2005 16:08:11 +0100 Message-ID: References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> In message <1127050673_7845@spool6-east.superfeed.net>, Cecil Moore writes >Ian Jackson wrote: >> Are you sure it's as high as that, Reg? I once did a Smith Chart plot >>of the impedance at the centre of a dipole, the valued being taken >>from a table 'compiled by Wu' (LK Wu?). These only catered for a >>lengths up to a few wavelengths. As the plot progressed round and >>round the Smith Chart, it seemed to be heading for something around >>350 to 400 ohms. > >Maybe 377 ohms? Remember that any finite length dipole is a standing >wave antenna and the feedpoint impedance is (Vfor+Vref)/(Ifor+Iref) >where Vfor is the forward voltage phasor, Vref is the reflected >voltage phasor, Ifor is the forward current phasor, and Iref is >the reflected current phasor. > >For a 1/2WL resonant dipole the feedpoint impedance is low: >R = (|Vfor|-|Vref|)/(|Ifor|+|Iref|) ~ 73 ohms > >For a 1WL (anti)resonant dipole the feedpoint impedance is high: >R = (|Vfor|+|Vref|)/(|Ifor|-|Iref|) ~ 5200 ohms (EZNEC) > >An infinite dipole would not be a standing wave antenna. It would >be a traveling wave antenna (as in a terminated rhombic). So the >feedpoint impedance of an infinite dipole would be Vfor/Ifor=Z0. >Since the reflections modify the feedpoint impedance, we might >suspect that Vfor/Ifor falls between the feedpoint impedance for >a 1/2WL dipole and a one WL dipole. Seems to me, the Z0 of the >dipole, i.e. Vfor/Ifor, must be in the ballpark of the square >root of the product of those two feedpoint impedances. Yes, I did think of 377 ohms (which I understand is 'the impedance of free space'), but I'm no expert in these matters. As you indicate, the impedance must lie somewhere between 73 and 5200 ohms. You suggest that this might be something like the square root of the product of those two feedpoint impedances (the geometric mean), which gives 616 ohms. However, you would see 600 ohms simply by looking into an infinite length of 600 ohm feeder, which has parallel, non-radiating conductors. If the length of the feeder was relatively short (compared with infinity!!), pulling the conductors apart would increase the impedance (probably to a lot more than 616 ohms). The question is, 'when does radiation start to influence the impedance?' If you look at K6OIK's paper at http://www.fars.k6ya.org/docs/antenna-impedance-models.pdf and look at, for example, page 22, you can see how the feed impedance at odd halfwaves increases, and at even halfwaves, decreases. I only found this paper this morning, and haven't had time to look to see which (if any) of the many formulas was used to obtain the plot. It must be possible to get close to the infinity condition by entering values for a very, very long dipole. Cheers, Ian. -- Article: 217289 of rec.radio.amateur.antenna From: Ian Jackson Subject: Re: E H Antenna Date: Sun, 18 Sep 2005 16:17:43 +0100 Message-ID: References: In message , Reg Edwards writes > >"Lee" wrote >> >> > > Just heard mention of the EH Antenna and that it is rather small >> > but equal >> > > radiation to a full size dipole !!!. >> > > >> > Sucker! If you believe that then you'll believe anything. >> > >> >> Hi Reg......how so?, >============================ >Hello Lee, > >The EH antenna is a hoax perpetrated by somebody who hopes to make >money by selling them. His sales description of how the thing works >pretends to make use of the mathematical works of James Clerk Maxwell. >It may sound good to novices but is just a load of nonsense. > >Actually, its performance is somewhat worse than other antennas of the >same physical size. > >If it's claims are as marvellous as all that, ask yourself why every >amateur doesn't have one, regardless of how big is his backyard. To a >smaller extent, the G5RV falls into the same category. > >You did right to ask your question. >---- >Reg. > > Didn't Radio 252 (252kHz) near Dublin start out using an E-H antenna? And wasn't there a new high-power SW station in Egypt which was supposed to use one too? I've feeling that with the latter, they pulled it down and used a conventional antenna. Ian. -- Article: 217290 of rec.radio.amateur.antenna From: "Lee" References: Subject: Re: E H Antenna Message-ID: <3NfXe.76646$2n6.18285@fe3.news.blueyonder.co.uk> Date: Sun, 18 Sep 2005 15:33:19 GMT "Reg Edwards" wrote in message news:dgjvqt$ksr$1@nwrdmz02.dmz.ncs.ea.ibs-infra.bt.com... > > "Lee" wrote - > > > i`m currently > > playing with a helical on 40 and am thinking of making a dipole with > a > > matching helical, i can get that in my postage stamp garden ...... > > > ================================== > > A back-to-back horizontal helical dipole is a good proposition. > Radiating efficiency is what matters with physically small antennas. > The radiating pattern is whatever you happen to get. > > A 1/2-wave helical resonant dipole is considerably more efficient than > a 1/4-wave vertical simply because of the absence of ground connection > losses. > > A low dipole does have a small ground loss due to its proximity to > ground. Ideally its height should be at least equal to its overall > length but half that is a satisfactory compromise. > > A horizontal helical dipole is the same as a centre-loaded wire with a > very long loading coil. It is easier to match to a feedline than a > vertical and there is a choice of type of line and line impedance. > > Either coax or balanced line can be used. Make the loading coil > continuous through the antenna centre and enclose the centre with a > link coupling to the feedline. The number of turns on the coupling > link is dependent on line impedance. > > The antenna itself is electrically isolated from the line and remains > nicely balanced about ground. > > The greater the diameter of the loading coil former, a rigid plastic > pipe, and the thicker the wire, the higher the efficiency. For 100 > watts transmitters, close wound turns of thick enamelled wire are > usually OK. > > Resonant frequency is adjusted by pruning the length of the wire or > rods which extend beyond the ends of the coil. If essential due to > space limitations, the end wires can be allowed to fall down towards > the ground but not allowed to swing about in the wind. > > Short loaded antennas are essentially single frequency, very narrow > bandwidth devices. > > Download program MIDLOAD from website below. It may be of assistance > or at least provide you with something to think about. > > In postage-stamp backyards, size-for-size, Magloops are the most > efficient of all very small antennas and can cover several adjacent > bands, but are deceptively difficult/easy/expensive to construct > depending on your ingenuity. Download program MAGLOOP4. Yes had a look at that one, gave me a few ideas as i like constructional projects.....You`ve given me a lot to think about Reg, it`s either a helical dipole or a magloop ..... there is a helical 40mtr beam in the ARRL handbook i`ve been looking at too.... Thanks . Lee. Article: 217291 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: E H Antenna Date: Sun, 18 Sep 2005 18:35:58 +0000 (UTC) Message-ID: References: <432d3141$0$980$626a14ce@news.free.fr> "F8BOE" wrote > Was interested too, but gave up. With so many different descriptions for one > concept, there must be something foolish. =================================== Hello Olivier, Nice to see a French contributor to this newsgroup. I am a foreigner myself but they make me feel at home provided I don't disagree too much with their technical opinions. ---- Reg, G4FGQ. Article: 217292 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: E H Antenna Date: Sun, 18 Sep 2005 19:25:48 +0000 (UTC) Message-ID: References: Professional radio engineers are disgraced and should be ashamed of being taken in by the bafflegab which would not have fooled cb-ers. Article: 217293 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: 73 Ohms, How do you get it? Date: Sun, 18 Sep 2005 13:50:46 -0700 Message-ID: <11irkp8rmnk0ta0@corp.supernews.com> References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> <1126655181_28167@spool6-east.superfeed.net> <5MOAq4S9pIKDFwB+@g3ohx.demon.co.uk> <1126734334_299@spool6-east.superfeed.net> <1127050673_7845@spool6-east.superfeed.net> In King and Harrrison's _Antennas and Waves_, they show a plot of calculated antenna feedpoint impedance as X vs R up to about 5 wavelengths. Antenna wire radius is 0.008496 wavelength. The Z of an infinite length antenna is indicated by locating the centers of the circles and noting that the center converges. The point of convergence for this particular wire radius is about 250 - j170 ohms. In the chapter on experimental measurements, there's a plot of the calculated admittance of an antenna of radius 0.000635 wavelength up to about 10 wavelengths. Superimposed are measured values from another source which show very good agreement. The theoretical values converge at 214 - j189 ohms, and the measured values at 218 - j174 ohms. Dervivation takes about a chapter of very heavy math, and numerical results were obtained with a computer. Roy Lewallen, W7EL Article: 217294 of rec.radio.amateur.antenna From: "Fred W4JLE" References: Subject: Re: E H Antenna Date: Sun, 18 Sep 2005 17:00:49 -0400 Message-ID: Don't hold back Reg, tell us what you really think. :>) "Reg Edwards" wrote in message news:dgkevs$29b$1@nwrdmz03.dmz.ncs.ea.ibs-infra.bt.com... > Professional radio engineers are disgraced and should be ashamed of > being taken in by the bafflegab which would not have fooled cb-ers. > > Article: 217295 of rec.radio.amateur.antenna From: richardharrison@webtv.net (Richard Harrison) Subject: Re: 73 Ohms, How do you get it? Date: Sun, 18 Sep 2005 15:57:41 -0500 Message-ID: <14168-432DD4C5-697@storefull-3257.bay.webtv.net> References: Ian Jackson wrote: "Maybe 377 ohms?" Arnold B. Bailey in "TV and Other Receiving Antennas" shows his calculations of radiation resistance at the current maximum point for a center-fed thin dipole at its various resonances: 1st--------------------------------72 ohms 2nd------------------------------200 ohms 3rd-------------------------------102 ohms 4th-------------------------------260 ohms 5th-------------------------------117 ohms 6th-------------------------------295 ohms 7th-------------------------------127 ohms 8th-------------------------------321 ohms 9th-------------------------------135 ohms 10th-----------------------------340 ohms He also shows the current distributions and feed point resistances which I can`t and won`t. The input resistance of the center-fed antenna at resonance never equals the surge resistance in value, but is related to it. Best regards, Richard Harrison, KB5WZI Article: 217296 of rec.radio.amateur.antenna From: Walter Maxwell Subject: Re: E H Antenna Message-ID: References: <432d3141$0$980$626a14ce@news.free.fr> Date: Sun, 18 Sep 2005 17:39:01 -0400 On Sun, 18 Sep 2005 18:35:58 +0000 (UTC), "Reg Edwards" wrote: > >"F8BOE" wrote >> Was interested too, but gave up. With so many different descriptions >for one >> concept, there must be something foolish. > >=================================== > >Hello Olivier, > >Nice to see a French contributor to this newsgroup. I am a foreigner >myself but they make me feel at home provided I don't disagree too >much with their technical opinions. >---- >Reg, G4FGQ. > And we'll keep you feeling right at home, Reg, as long as you continue to savor our California wine products and thus favor us with your dry witicisms. Walt Article: 217297 of rec.radio.amateur.antenna From: David Subject: Re: Open Stub fed J antenna References: <1126835197_2699@spool6-east.superfeed.net> <24625-432A4483-301@storefull-3253.bay.webtv.net> <11ioskhlhnsrl9b@corp.supernews.com> <7p6Xe.51542$FA3.8337@news-server.bigpond.net.au> <1127045838_7601@spool6-east.superfeed.net> Message-ID: Date: Sun, 18 Sep 2005 22:51:02 GMT Thanks for the model, I'll try it. What is the diameter of the elements. I understand you can also vary the feedpoint impedance by changing element diameter ? (Zo = 276 log(2S/d) Regards David Dan Richardson wrote: > On Sun, 18 Sep 2005 07:14:39 -0500, Cecil Moore > wrote: > > > >>The open stub J-Pole (Zepp) is modeled as a shorted stub >>J-Pole with the source in the middle of the shorted segment. >>Mine is for 53.2 MHz. On edge it looks like this: >> >> 13.5 ft. >> +--------------------------------------------------- >> | >>(S) >> | >> +----------------- >> 4.5 ft. >> >>The sections are 0.1 ft. apart. The resonant frequency is >>53.2 MHz and the feedpoint impedance is 25 ohms for an SWR >>of 2:1. The feedpoint is 30 ft. high over high-accuracy >>ground. The gain over ground is 6.2 dBi, omnidirectional. >>Free space gain is 3.4 dBi. > > > You can vary the feedpoint impedance by changing (S). > > 73, > Danny, K6MHE > > email: k6mhearrlnet > http://users.adelphia.net/~k6mhe/ Article: 217298 of rec.radio.amateur.antenna From: David Subject: Re: Open Stub fed J antenna References: <1126835197_2699@spool6-east.superfeed.net> <24625-432A4483-301@storefull-3253.bay.webtv.net> <11ioskhlhnsrl9b@corp.supernews.com> <7p6Xe.51542$FA3.8337@news-server.bigpond.net.au> <1127045838_7601@spool6-east.superfeed.net> Message-ID: Date: Sun, 18 Sep 2005 23:27:09 GMT That model seems to work fine in EZNEC. I tried a 918 MHz version with long length = 219mm, short length = 72mm, 24mm apart, 1.5mm solid aluminum construction. The results show excellent SWR and feedpoint impedance close to 50 Ohms.(50.29 -j0.0148), SWR = 1.006 The unit is not so omnidirectional showing a front/back ratio of 5.79dB.(Beamwidth 214.4 Degrees). The maximum gain was 4.74dB(ref) at 4 degrees (elevation). dB ref = 2.14dBi so I suppose this is saying gain is 4.74dBd. Dan Richardson wrote: > On Sun, 18 Sep 2005 07:14:39 -0500, Cecil Moore > wrote: > > > >>The open stub J-Pole (Zepp) is modeled as a shorted stub >>J-Pole with the source in the middle of the shorted segment. >>Mine is for 53.2 MHz. On edge it looks like this: >> >> 13.5 ft. >> +--------------------------------------------------- >> | >>(S) >> | >> +----------------- >> 4.5 ft. >> >>The sections are 0.1 ft. apart. The resonant frequency is >>53.2 MHz and the feedpoint impedance is 25 ohms for an SWR >>of 2:1. The feedpoint is 30 ft. high over high-accuracy >>ground. The gain over ground is 6.2 dBi, omnidirectional. >>Free space gain is 3.4 dBi. > > > You can vary the feedpoint impedance by changing (S). > > 73, > Danny, K6MHE > > email: k6mhearrlnet > http://users.adelphia.net/~k6mhe/ Article: 217299 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Open Stub fed J antenna Date: Sun, 18 Sep 2005 17:08:10 -0700 Message-ID: <11is0bc7ecfdd7d@corp.supernews.com> References: <1126835197_2699@spool6-east.superfeed.net> <24625-432A4483-301@storefull-3253.bay.webtv.net> <11ioskhlhnsrl9b@corp.supernews.com> <7p6Xe.51542$FA3.8337@news-server.bigpond.net.au> <1127045838_7601@spool6-east.superfeed.net> David wrote: > Thanks for the model, I'll try it. > > What is the diameter of the elements. I understand you can also vary the > feedpoint impedance by changing element diameter ? (Zo = 276 log(2S/d) Open the EZNEC file. In the main window, click the Wires line to open the Wires Window. Find the Diameter column, where you'll see the diameter of each conductor. The equation you give is approximately the characteristic impedance of a transmission line, not the feedpoint impedance of a J-pole. The relationship between the two is very tenuous and complex. Roy Lewallen, W7EL Article: 217300 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Open Stub fed J antenna Date: Sun, 18 Sep 2005 17:05:38 -0700 Message-ID: <11is06kpq8d7be4@corp.supernews.com> References: <1126835197_2699@spool6-east.superfeed.net> <24625-432A4483-301@storefull-3253.bay.webtv.net> <11ioskhlhnsrl9b@corp.supernews.com> <7p6Xe.51542$FA3.8337@news-server.bigpond.net.au> <1127045838_7601@spool6-east.superfeed.net> David wrote: > That model seems to work fine in EZNEC. > > I tried a 918 MHz version with long length = 219mm, short length = 72mm, > 24mm apart, 1.5mm solid aluminum construction. > > The results show excellent SWR and feedpoint impedance close to 50 > Ohms.(50.29 -j0.0148), SWR = 1.006 > The unit is not so omnidirectional showing a front/back ratio of > 5.79dB.(Beamwidth 214.4 Degrees). That's pretty strange. The only ready explanation is radiation from the transmission line section. Apparently it's significant with the 0.074 wavelength conductor spacing. > The maximum gain was 4.74dB(ref) at 4 degrees (elevation). dB ref = > 2.14dBi so I suppose this is saying gain is 4.74dBd. If the antenna is in free space, the currents in the elements are exactly in phase, and the transmission line radiation is negligible, the gain should be maximum broadside to the antenna, not at 4 degrees elevation. So one or more of those conditions isn't true. The horizontal directivity indicates that the transmission line section is radiating, but I wonder also if you might be modeling it over ground. The gain is 4.7 dB relative to a dipole in free space. If you're modeling it over ground, the gain isn't 4.7 dB over a dipole at the same height above ground, which is why I dislike the term "dBd". (But antenna manufacturers who can capitalize on the ambiguity love it.) If you're modeling it over ground and want to know the gain over a dipole at the same height, model a dipole at that height and compare gains. Roy Lewallen, W7EL Article: 217301 of rec.radio.amateur.antenna From: David Subject: Re: Open Stub fed J antenna References: <1126835197_2699@spool6-east.superfeed.net> <24625-432A4483-301@storefull-3253.bay.webtv.net> <11ioskhlhnsrl9b@corp.supernews.com> <7p6Xe.51542$FA3.8337@news-server.bigpond.net.au> <1127045838_7601@spool6-east.superfeed.net> <11is0bc7ecfdd7d@corp.supernews.com> Message-ID: Date: Mon, 19 Sep 2005 01:10:12 GMT Roy, The model I used for the open stub J-pole was not the same as your 3 element col. I used a vertical long element and vertical short element. They were joined by a horizontal element at the base. The source was set at 50% along the horizontal bar as per your diagram. I changed the model for free space rather than over real ground but this has not helped the directional aspects of the plot. The dimensions were scaled form those shown for a 150MHz open ended J-pole shown on Arrow Electronics site http://www.arrowantennas.com/j-pole.html Roy Lewallen wrote: > David wrote: > >> Thanks for the model, I'll try it. >> >> What is the diameter of the elements. I understand you can also vary >> the feedpoint impedance by changing element diameter ? (Zo = 276 >> log(2S/d) > > > Open the EZNEC file. In the main window, click the Wires line to open > the Wires Window. Find the Diameter column, where you'll see the > diameter of each conductor. > > The equation you give is approximately the characteristic impedance of a > transmission line, not the feedpoint impedance of a J-pole. The > relationship between the two is very tenuous and complex. > > Roy Lewallen, W7EL Article: 217302 of rec.radio.amateur.antenna From: "John N9JG" Subject: Re: Wooden I section pole Date: Sun, 18 Sep 2005 20:41:46 -0500 Message-ID: References: A wooden utility pole with a length of 40 feet above ground would do the job for me. It's just that I am not sure how the neighbors would react. A search of the web did show that there are fiber glass flag poles available that have sufficient height, but I don't know if they can support the weight of 100 feet of 3/4 in copper pipe and a 10-15 lb remotely tuned capacitor inside a weather-proof box. "Edward A. Feustel" wrote in message news:N9idnUMgF7L5LbfeRVn-1A@giganews.com... > > "John N9JG" wrote in message > news:dgc7u7$9h8$1@mailhub227.itcs.purdue.edu... >>I am in the planning stage for a 160 meters compact loop antenna. A loop >>antenna may not have metal nearby, so I am planning to use a wooden pole >>to support the top of the loop. In the ARRL Antenna handbook, it states >>that "W5QJR made a pole of 2 x 4-inch lumber with 1 x 4-inch boards on >>either side to form an I section. He held the boards together with >>1/4-inch bolts, 2 feet apart and tied rope guys to the top. This made an >>excellent mast up to 50 feet high." >> >> Does anyone have any comments on the feasibility of an unguyed pole using >> this same type of construction? Naturally, a portion of the pole would >> have to be underground, and perhaps set in concrete. What about a 50 feet >> pole, with 10 feet underground ,which would give you a 40 foot mast? >> >> An alternative would be to have a contractor install a 40 feet utility >> pole, but I assume the wooden pole described above would be less of an >> eyesore (to the neighbors) than a utility pole. >> >> Any comments and advice will be appreciated. >> John, N9JG >> > If you really want to have the "mast" unsupported, consider a 50-60' > telephone pole > properly installed (for your type of soil) with one end buried deeply. > Perhaps you could > use a fiberglass extension from its top to support the antenna. > > It would be worth your while to have a mechanical engineer calculate your > design's survival > characteristics in high wind and compare it with 100 year records for high > wind speed. Also you > might consider the prospect of icing if you live in a northern climb -- I > assume that the mast > is at a corner of the loop. > Regards, > Ed, N5EI > Article: 217303 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Open Stub fed J antenna Date: Sun, 18 Sep 2005 19:11:27 -0700 Message-ID: <11is7ii8shfs8fb@corp.supernews.com> References: <1126835197_2699@spool6-east.superfeed.net> <24625-432A4483-301@storefull-3253.bay.webtv.net> <11ioskhlhnsrl9b@corp.supernews.com> <7p6Xe.51542$FA3.8337@news-server.bigpond.net.au> <1127045838_7601@spool6-east.superfeed.net> <11is0bc7ecfdd7d@corp.supernews.com> Two other cautions for anyone modeling a J-pole with any NEC-2 based program: 1. Be sure to read the EZNEC manual section "Closely Spaced Wires" -- you'll find it in the index. 2. Run an Average Gain test. (See "Average Gain, Detecting source placement problems" in the manual index.) The small loop in closed-ended J-poles can be a problem for NEC-2. If the Average Gain test shows a problem, using the double precision calculating engine (available in EZNEC+) might help. Roy Lewallen, W7EL David wrote: > Roy, > > The model I used for the open stub J-pole was not the same as your 3 > element col. > > I used a vertical long element and vertical short element. They were > joined by a horizontal element at the base. The source was set at 50% > along the horizontal bar as per your diagram. > > I changed the model for free space rather than over real ground but this > has not helped the directional aspects of the plot. > > The dimensions were scaled form those shown for a 150MHz open ended > J-pole shown on Arrow Electronics site > > http://www.arrowantennas.com/j-pole.html Article: 217304 of rec.radio.amateur.antenna Message-ID: <432E206F.C8E0D41@russ.com> From: russ Subject: Re: How to weather-seal an upside down Tailtwister rotor? References: <3op5feF73ibjU1@individual.net> <3opd8pF71npnU1@individual.net> Date: Mon, 19 Sep 2005 02:20:33 GMT hi, A large sheet of 6 mil clear plastic should be able to cover the tower and the folded over section. Place a container of DampRid on the rotor shelf before you cover the tower with the plastic sheets. Two layer of sheet should do the trick. Drape the plastic 4 or 5 feet below the rotor, no way for any water to get inside the rotor. Tie it tiht with some good rope and your done. The damp rid will absorb any moisture that it trapped during the day from the hot sun heating up the top of the 'rotor bag' you just made. Or just take the rotor inside. good luck with the repairs. russ Article: 217305 of rec.radio.amateur.antenna Subject: Re: 73 Ohms, How do you get it? From: Cecil Moore Date: Sun, 18 Sep 2005 22:12:46 -0500 Message-ID: <1127099727_10687@spool6-east.superfeed.net> References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> <1126655181_28167@spool6-east.superfeed.net> <5MOAq4S9pIKDFwB+@g3ohx.demon.co.uk> <1126734334_299@spool6-east.superfeed.net> <1127050673_7845@spool6-east.superfeed.net> <11irkp8rmnk0ta0@corp.supernews.com> Roy Lewallen wrote: > The theoretical values converge > at 214 - j189 ohms, and the measured values at 218 - j174 ohms. Free space? As a data point, I pushed EZNEC to the limit on 40m with a 9000 ft. dipole. Resonant feedpoint resistance at 7.152 is 390 ohms. Anti-resonant feedpoint resistance at 7.092 is 1980 ohms. It appears that EZNEC would converge to something in between those two values for an infinite dipole in free space. I ran into the segment limit at 66 wavelengths. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- Article: 217306 of rec.radio.amateur.antenna Subject: Re: 73 Ohms, How do you get it? From: Cecil Moore Date: Sun, 18 Sep 2005 22:20:55 -0500 Message-ID: <1127100215_10699@spool6-east.superfeed.net> References: <14168-432DD4C5-697@storefull-3257.bay.webtv.net> Richard Harrison wrote: > Ian Jackson wrote: > "Maybe 377 ohms?" > > Arnold B. Bailey in "TV and Other Receiving Antennas" shows his > calculations of radiation resistance at the current maximum point for a > center-fed thin dipole at its various resonances: > > 1st--------------------------------72 ohms > 2nd------------------------------200 ohms > 3rd-------------------------------102 ohms > 4th-------------------------------260 ohms > 5th-------------------------------117 ohms > 6th-------------------------------295 ohms > 7th-------------------------------127 ohms > 8th-------------------------------321 ohms > 9th-------------------------------135 ohms > 10th-----------------------------340 ohms Note that those are not the feedpoint impedances. They are based on the current maximum points which often occur somewhere besides the feedpoint. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- Article: 217307 of rec.radio.amateur.antenna From: kashe@sonic.net Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Message-ID: References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com> <31f74$43299abf$471c63c6$12083@ALLTEL.NET> Date: Mon, 19 Sep 2005 05:30:15 GMT On Thu, 15 Sep 2005 12:00:29 -0400, "Fred W4JLE" wrote: >Perhaps you could show me where any of the offered definitions apply to an >HOA rule that prohibits non family members from residing in a home. > > The "wedded to ...." one >"Richard Clark" wrote in message >news:4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com... >> On Thu, 15 Sep 2005 10:41:17 -0400, "Fred W4JLE" >> wrote: >> >> >A few moments spent perusing a dictionary will show that simply refusing >to >> >take in a storm victim, while abhorrent to me, does not make one a bigot. >> > >> from the Oxford English Dictionary: >> >> Bigot. 1598. 1. A hypocrite. 2. A superstitious person - 1664. 3. A >> person obstinately and unreasonably wedded to a creed, opinion or >> ritual - 1661. Intolerant toward others - 1645. >> >> Hardly seems that the meaning has veered from this in the past 340 >> years. >> >> 73's >> Richard Clark, KB7QHC > Article: 217308 of rec.radio.amateur.antenna From: kashe@sonic.net Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Message-ID: References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com> <31f74$43299abf$471c63c6$12083@ALLTEL.NET> <1126810780_1703@spool6-east.superfeed.net> Date: Mon, 19 Sep 2005 05:32:16 GMT On Thu, 15 Sep 2005 13:55:56 -0500, Cecil Moore wrote: >Richard Clark wrote: >> Christian charity is not fulfilled by a shrug of the HOA committee, >> and members who enjoy the veil of these rules won't find it any easier >> getting through the eye of the needle. > >The small "eye of the needle" gate at the walls of a city >was sized for human beings. It was camels that couldn't >get through it. Camels had to enter through the main gate. But the reference was to it being as difficult for a rich man (as in dweller of the gated community type) as for the camel .... Article: 217309 of rec.radio.amateur.antenna From: kashe@sonic.net Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Message-ID: References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com> <31f74$43299abf$471c63c6$12083@ALLTEL.NET> Date: Mon, 19 Sep 2005 05:35:14 GMT On Thu, 15 Sep 2005 19:09:05 GMT, "KØHB" wrote: > >"Richard Clark" wrote > >> >> Christian charity is not fulfilled by a shrug of the HOA committee, >> and members who enjoy the veil of these rules won't find it any easier >> getting through the eye of the needle. >> > >How is "Christian charity" different from other charity, and do I need to be a >member of your cult in order to get through the eye of the needle (and why would >I want to?)? > >73, de Hans, K0HB It's (at the very least) expected to be the ideal of the Christian. Would youu care to expand on the ideals of "atheist charity" or whatever defined variety you prefer? Article: 217310 of rec.radio.amateur.antenna From: kashe@sonic.net Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Message-ID: References: <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com> <31f74$43299abf$471c63c6$12083@ALLTEL.NET> <1126821476.840433.194860@g49g2000cwa.googlegroups.com> Date: Mon, 19 Sep 2005 05:38:35 GMT On 15 Sep 2005 14:57:56 -0700, "an_old_friend" wrote: > >Richard Clark wrote: >> On Thu, 15 Sep 2005 19:09:05 GMT, "KØHB" >> wrote: >> >> >How is "Christian charity" different from other charity >> >> Hi Hans, >> >> I will leave that to other faiths to describe for themselves. One >> distinct difference between Christian charity and Islamic charity is >> that Muslims are commanded to give the expected portion of their >> charity directly to the afflicted. This means hand-to-hand. >> >> >, and do I need to be a >> >member of your cult in order to get through the eye of the needle (and why would >> >I want to?)? >> >> Complete the allusion and enlighten us to which cult offers fare >> discounts for buying the way to Heaven. Of course, if you have no >> interest in the destination, then the subject is rather transparent >> and hardly requires comment. > >Discounts I don't know but Chatholic dogma still provides for the sale >of Indulenges for sin Far from correct. Catholiic dogma in fact has a specific name for the sin of selling indulgences or objects which have been blessed -- it's called simony. Since at least the 40s, AFAIK. >, even allowing them to be purchased for yone >firend and relitives post mortem > >Luther thought the practice pro and so do most prods groups >> >> 73's >> Richard Clark, KB7QHC Article: 217311 of rec.radio.amateur.antenna From: kashe@sonic.net Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Message-ID: <5ujsi196c3dl0l0a7su4uqltnt4u0ql4ko@4ax.com> References: <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com> <31f74$43299abf$471c63c6$12083@ALLTEL.NET> <1126821476.840433.194860@g49g2000cwa.googlegroups.com> Date: Mon, 19 Sep 2005 05:41:38 GMT On Fri, 16 Sep 2005 23:01:22 -0400, Uncle Ted wrote: >On 15 Sep 2005 14:57:56 -0700, "an_old_friend" >wrote: > > >>Discounts I don't know but Chatholic dogma still provides for the sale >>of Indulenges for sin, even allowing them to be purchased for yone >>firend and relitives post mortem >> >>Luther thought the practice pro and so do most prods groups > >It's bad enough that people feel a need to believe in any deities at >all, but when you have to listen to a bunch of old men in robes half a >world away tell you how to live your life, you're pretty screwed up. Is this a slam against our Muslim brethren? A comment on the position of Saudi Arabian women? Article: 217312 of rec.radio.amateur.antenna From: kashe@sonic.net Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Message-ID: References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com> Date: Mon, 19 Sep 2005 05:56:51 GMT On Thu, 15 Sep 2005 10:28:40 -0700, Richard Clark wrote: >On Thu, 15 Sep 2005 12:01:35 -0400, Walter Maxwell >wrote: > >>In light of Colin Powell's position that the fate of the poorer people >>of New Orleans was not due to racism, but only failing to realize >>that those people had no means for transportation out of the city, it >>seems to me that racism and bigotry were not involved. To me it's >>significant that that position is held by a highly-respected person of >>color. > >Hi Walt, > >Being bigoted does not necessarily mean one is racist. Bigots can >focus their intolerance on many subjects and be perfectly race-free. >On the flip side being racist automatically carries the label bigot. > >Bigots are quite easily recognized, that is why there is the name to >denote the obvious. Certainly there is nothing subtle about this. I >cannot say that I have seen more than 20 minutes coverage on the >storm, especially when "news" is so evidently not informative as it is >salacious entertainment. They could have as easily run the movie >"Twister" to no different effect. > >Further, those 20 minutes were not watched here, but in England where >the world was astonished by the third world class of impoverished >action taken. > >As such, the folks at Fox would call me a bigot for being intolerant >of their coverage. However, it would be the Fox folks who serve the >American feed because their International feed was distinctly >different. None of you probably observed Rumsfield's visit, >un-edited, where the populace in a rage were yelling "Fuck YOU" at >him. I would suppose they were bigots too, given the inflexibility of >their opinion after rafting on the rooftops. > >Fox was content to satisfy any audience, and I suppose that makes them >most catholic. [For those who are short on dictionary skills, >catholic means liberal or tolerant, a most amusing irony applied to >the Fox organization that literally serves all masters.] Actually, at root, it means universal or "for all" (Greek kata and holos). > >73's >Richard Clark, KB7QHC Article: 217313 of rec.radio.amateur.antenna From: "pezSV7BAXdag" Subject: Re: 73 Ohms, How do you get it? Date: Mon, 19 Sep 2005 15:42:08 +0300 Message-ID: References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> <1126655181_28167@spool6-east.superfeed.net> <5MOAq4S9pIKDFwB+@g3ohx.demon.co.uk> <1126734334_299@spool6-east.superfeed.net> <1127050673_7845@spool6-east.superfeed.net> <11irkp8rmnk0ta0@corp.supernews.com> | "Roy Lewallen" | wrote in message news:11irkp8rmnk0ta0@corp.supernews.com... | [...] | The Z of an | infinite length antenna is indicated by locating the centers of the | circles and noting that the center converges. | [...] | Roy Lewallen, W7EL If we discuss here the impedance referenced to the input (base) current - and not to the maximum one - then IMHO: The quoted text above does not prove convergence. The convergence must be independent of the way the length goes to infinity. The centers of whatever circles may converge to a finite complex number but their radii have to simultaneously converge to zero, to have convergence. But the limit for Z exists if and only if both the limits for R and X exist. Therefore if the limit for R is dependent on the way the length goes to infinity then its limit does not exist. A guess for either a non-existent limit for R or an infinite one comes out from: http://antennas.ee.duth.gr/ftp/visualantennas/thedipole/films/fu010100.zip [850 KB] If either of the above is true for R then the corresponding is true for Z: The limit for Z does not exist or is (in general) the complex infinity. But always and only for the the impedance referenced to the input (base) current. Sincerely, pezSV7BAXdag Article: 217314 of rec.radio.amateur.antenna From: aRKay Subject: Re: Using a Fan Dipole for Six Meters References: <0utqi1toov2uefq3esvfma1gp53fhs12jc@4ax.com> Message-ID: Date: Mon, 19 Sep 2005 13:12:50 GMT In article <0utqi1toov2uefq3esvfma1gp53fhs12jc@4ax.com>, nospam@nouce.bellatlantic.net wrote: > > I have one of those TT1208s and it's been a good tool for 6m. I have > some impressive contacts off it and a 3 element beam. Enjoy it. > > Allison Allison, I have heard good things about the Ten Tec Transverter and figured it was time to give it a try. I am a RTTY Junkie and noticed a six meter RTTY spot yesterday. The 1208 should be here on Tuesday. Dick AA5VU