Article: 221875 of rec.radio.amateur.antenna From: Dot Subject: Re: nec simulation - unexpected result ?? Message-ID: References: <15631-43FF0DD8-401@storefull-3255.bay.webtv.net> <11vuv3l7thdn87@corp.supernews.com> <11vvku12b8t8398@corp.supernews.com> Date: Fri, 24 Feb 2006 23:13:49 -0500 On Fri, 24 Feb 2006 19:49:19 -0800, Roy Lewallen wrote: >> These days, resonance is described as either: >> >> a) the point at which Inductive Reactance and Capacitive Reactance are equal >> or >> b) the point at which a load impedence is purely resistive. > >The two points are exactly the same. Agreed, but the two definitions are used circumstantially so I thought it worth listing both for clarity. >The high-impedance full-wave resonant point (for a dipole; half-wave >resonant point for a monopole) is sometimes called "anti-resonance", but >not commonly, and mostly in older literature. It's a true point of >resonance, that is, where the reactance is zero. I don't believe I've >ever heard the term "anti-resonance" applied to other high-impedance >resonant circuits, such as a tank circuit. Exactly... the term amounts to a distinction without a difference and, far as I can tell, is of dubious worth. >> It would then be reasonable for a given wire perpendicular to a good ground >> plane to exhibit "resonance" at odd multiples of a quarter wavelength and >> "anti-resonance" at even multiples of a quarter wavelength... Translating >> gives low impedence at odds and high impedence at evens, which is where I >> started out in this discussion.... > >If you choose to call the high-impedance resonant points >"anti-resonance", that's true. Ummmm... please read again... I was explaining why I choose *not* to do that. >But again, they're points where the >reactance is zero, just like the points you're calling "resonant". The >only difference is that the impedance is high and the antenna acts more >like a parallel tuned circuit at nearby frequencies rather than a series >tuned circuit. Exactly... high voltage, low current... low voltage high current... both can dissipate the same wattage. 12v X 2a = 24w. 2v X 12a = 24w. >> Your semantics is correct if you are looking to define an antenna as "a >> current fed device", but that's not always the case. There are end fed half >> waves out there... they are voltage fed, they are resonant and they do work. >> (Ask anyone who owns a "Ringo Ranger".) > >No, the definition of resonance has nothing to do with how an antenna is >fed. Exactly... but to define anti-resonance at the high voltage low current point rather does betray a bias. >The impedance of the antenna doesn't change with the feed method >(assuming of course that it has a single feed point), and therefore its >resonant frequencies don't change with the feed method. This I can attest to from my own experience. What you do to the feedline seldom impacts the antenna, except for really messing up it's efficiency. >And an antenna doesn't have to >be resonant (that is, have a non-reactive feedpoint impedance) to >"work". But things do tend to run a lot cooler when it is. >Resonance is only an indication of the reactance of the input >impedance, and has nothing to do with an antenna's gain, pattern, >bandwidth, or other performance characteristics. Unless, of course you consider SWR a performance characteristic... I dunno, maybe I'm a bit odd but I kinda like antennas that don't blow up my transmitters. Article: 221876 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: nec simulation - unexpected result ?? References: <15631-43FF0DD8-401@storefull-3255.bay.webtv.net> <11vuv3l7thdn87@corp.supernews.com> <11vvku12b8t8398@corp.supernews.com> Message-ID: Date: Sat, 25 Feb 2006 05:21:52 GMT Roy Lewallen wrote: > The impedance of the antenna doesn't change with the feed method ... One feed method is center feed. Another feed method is off-center feed. The feedpoint impedance of the antenna changes with position since for 1/2WL, for instance, the net voltage is a sine wave referenced to the center, and the net current is a cosine wave referenced to the center. The feedpoint impedance is approximately sin(x)/cos(x)=tan(x) where 'x' is the number of degrees away from center. -- 73, Cecil http://www.qsl.net/w5dxp Article: 221877 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: nec simulation - unexpected result ?? References: <1K7Lf.15962$2O6.11668@newssvr12.news.prodigy.com> <43FD4A4F.9010209@comcast.net> <4wkLf.4207$vC4.1279@clgrps12> <43FE9C4F.3050104@comcast.net> <%lKLf.39590$H71.27479@newssvr13.news.prodigy.com> <6TLLf.13321$rL5.8593@newssvr27.news.prodigy.net> <1140826892.169941.137710@i40g2000cwc.googlegroups.com> <1140846944.072561.62710@z34g2000cwc.googlegroups.com> Message-ID: <6PSLf.16348$2O6.5443@newssvr12.news.prodigy.com> Date: Sat, 25 Feb 2006 06:29:22 GMT K7ITM wrote: > Geez, Cecil, I don't have an argument with either of you. The Devil made me do it. :-) -- 73, Cecil http://www.qsl.net/w5dxp Article: 221878 of rec.radio.amateur.antenna From: "Sal M. Onella" References: Subject: Re: ?? anyone have plans on how to build a usb gps antenna for laptop Message-ID: Date: Fri, 24 Feb 2006 22:58:57 -0800 "Lee" wrote in message news:KIzLf.48616$Q22.34001@fe1.news.blueyonder.co.uk... > > "Sal M. Onella" wrote in message > news:MebLf.968$Uc2.471@fed1read04... > > > > "Lee" wrote in message > > news:rXUKf.31812$Q22.24541@fe1.news.blueyonder.co.uk... > > > > > > "Sal M. Onella" wrote in message > > > news:RUSKf.130$Uc2.57@fed1read04... > > > > > > > > wrote in message > > > > news:IyQKf.18144$Ug4.11471@dukeread12... > > > > > > > > > > > > > > > > > > > http://64.71.184.220/eng/gpspatch.txt > > > > > > > > http://www.arrl.org/tis/info/pdf/0210036.pdf > > > > > > > > http://vancouver-webpages.com/peter/gpspatch.gif > > > > > > Any more designs to suit a Garmin 310 ??? > > > > > > Lee .....G6ZSG..... > > > > > > > > > > Lee, > > > > These are free-space antennas, intended for fitting with a length of coax > > terminated in the particular connector that mates with the connector on > your > > GPS rcvr. My Garmin GPS-III takes a BNC and I have my patch antenna > mounted > > on my van's luggage rack; Eight feet of coax brings the signal inside. > > Not too sure what i want, i`m a bit of a newb to GPS....just bought it!!!... > > > Not familiar with the 310 -- are you looking for an add-on antenna that > > physically mounts to your 310? ... or does the 310 require a special > > coupling technique (non-connector)? > > Same as the 320,330 and 340 series > > Lee.......G6ZSG....... > > My external antennas are all non-specific to the brand and model of consumer-grade GPS receivers (those using only the L1 signal). The connection method varies among receivers. If you are buying an antenna, here is Garmin's web link to the manual: http://www.garmin.com/manuals/StreetPilotc310_OwnersManual.pdf See page 26 for a mention of the GA27C antenna. Of course, it comes with the cable end being the right connector (MCX) for your receiver. Hunt in your manual if the pages don't match the one I found online. If you are making your own antenna from plans I linked to, you will need to also buy a type MCX connector for the cable end, as that is the connector type specified here: http://www.garmin.com/products/sp330/spec.html (which is the link from page 26 in the manual.) www.jameco.com sells MCX connectors, but if you google for "MCX connector" (with the quotes) you will get not only sources for the connector but also quite a few third-party vendors with ready-built GPS antennas using that connector. You are apparently in a large group of Garmin users who want an external antenna. Article: 221879 of rec.radio.amateur.antenna From: "John, N9JG" References: <4WJLf.1213$dg.9@clgrps13> <43FFC5C4.4010403@comcast.net> <6XQLf.5171$M52.5078@edtnps89> Subject: Re: 80 m compact loop - progress report Message-ID: Date: Sat, 25 Feb 2006 16:09:50 GMT Most people put the series tuning capacitor in the top side and the feed point at the bottom side. Since the capacitor, motor, and their mounting hardware is quite heavy, I am currently planning to do the reverse of the above, i.e., tuning capacitor at bottom and feed point at the top. It is not clear to me if there is any difference between these two configurations. John, N9JG "Frank" wrote in message news:6XQLf.5171$M52.5078@edtnps89... [snip] > Note that John mentioned he is using a gamma match, and tunes out the > reactance of the loop on the opposite side. The diameter of the loop is a > nominal 20 ft, so it would make the most sense to tune, and feed, the > antenna on the two vertical elements. My model is 30 ft at the top, and > 8.272 ft at the bottom, so even with the reduced height motorized tuning > makes a lot of sense. I am going to model a gamma match, and opposite > side tuning cap, so will update the code this weekend. [snip] Article: 221880 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: Cage Dipool Date: Sat, 25 Feb 2006 17:13:07 +0000 (UTC) Message-ID: References: <1140885963.957597.136480@v46g2000cwv.googlegroups.com> "John Minkjan" wrote > > Who can help on a usefull for a cage dipool on the 40 meter band? ========================================= You may find program DIPCAGE2 to be of interest. Download from website below in a few seconds and run immediately. ---- ........................................................... Regards from Reg, G4FGQ For Free Radio Design Software go to http://www.btinternet.com/~g4fgq.regp ........................................................... Article: 221881 of rec.radio.amateur.antenna From: "Frank's" References: <4WJLf.1213$dg.9@clgrps13> <43FFC5C4.4010403@comcast.net> <6XQLf.5171$M52.5078@edtnps89> Subject: Re: 80 m compact loop - progress report Message-ID: <3z0Mf.1838$dg.1085@clgrps13> Date: Sat, 25 Feb 2006 17:34:55 GMT "John, N9JG" wrote in message news:ij%Lf.797528$_o.574035@attbi_s71... > Most people put the series tuning capacitor in the top side and the feed > point at the bottom side. Since the capacitor, motor, and their mounting > hardware is quite heavy, I am currently planning to do the reverse of the > above, i.e., tuning capacitor at bottom and feed point at the top. It is > not clear to me if there is any difference between these two > configurations. > > John, N9JG I have not attempted to model the gamma match, but doubt it will change the current distribution. Feeding at the top places the minimum current at the loop base which seems to effect the high angle radiation only. The gain straight up is about + 2 dBi, and -3 dBi when reversed. Low angle radiation, for example at 10 deg elevation, is - 3 dBi in both cases. Removing the capacitor totally reverses the current distribution. Maximum gain occurs parallel to the loop plane. Frank, VE6CB Article: 221882 of rec.radio.amateur.antenna From: "Frank's" References: <4WJLf.1213$dg.9@clgrps13> <43FFC5C4.4010403@comcast.net> <6XQLf.5171$M52.5078@edtnps89> <3z0Mf.1838$dg.1085@clgrps13> Subject: Re: 80 m compact loop - progress report Message-ID: Date: Sat, 25 Feb 2006 17:56:47 GMT "Frank's" wrote in message news:3z0Mf.1838$dg.1085@clgrps13... > > "John, N9JG" wrote in message > news:ij%Lf.797528$_o.574035@attbi_s71... >> Most people put the series tuning capacitor in the top side and the feed >> point at the bottom side. Since the capacitor, motor, and their mounting >> hardware is quite heavy, I am currently planning to do the reverse of the >> above, i.e., tuning capacitor at bottom and feed point at the top. It is >> not clear to me if there is any difference between these two >> configurations. >> >> John, N9JG > > I have not attempted to model the gamma match, but doubt it will change > the current distribution. Feeding at the top places the minimum current > at the loop base which seems to effect the high angle radiation only. The > gain straight up is about + 2 dBi, and -3 dBi when reversed. Low angle > radiation, for example at 10 deg elevation, is - 3 dBi in both cases. > Removing the capacitor totally reverses the current distribution. Maximum > gain occurs parallel to the loop plane. > > Frank, VE6CB Also top feed increases the input impedance to 2.664 - j0.949, with the capacitive load 0.1 -j858 at 3.75 MHz. (NEC 4.1 double precision). Article: 221883 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: Q about balanced feed line Date: Sat, 25 Feb 2006 18:08:24 +0000 (UTC) Message-ID: References: "Ian White wrote > But the original questioner wants to measure what's *really* happening. ======================================== But the original questioner can tell what's *really* happening just by inspecting the antenna and feedline. He doesn't need any electrical measuring instruments. Of course, it may be in the middle of the night, in which case it would be best to wait till the sun comes up. Or he could rely on his memory of how he installed the antenna. The trouble with you experts is that you overcomplicate matters and make quite simple, obvious things appear to be mysterious. But you have to justify your existence in one way or another. ---- Reg. Article: 221884 of rec.radio.amateur.antenna From: Big Endian Subject: Re: Q about balanced feed line References: Message-ID: Date: Sat, 25 Feb 2006 18:18:35 GMT In article , "Reg Edwards" wrote: > "Ian White wrote > > But the original questioner wants to measure what's *really* > happening. > ======================================== > > But the original questioner can tell what's *really* happening just by > inspecting the antenna and feedline. He doesn't need any electrical > measuring instruments. > > Of course, it may be in the middle of the night, in which case it > would be best to wait till the sun comes up. > > Or he could rely on his memory of how he installed the antenna. > > The trouble with you experts is that you overcomplicate matters and > make quite simple, obvious things appear to be mysterious. > > But you have to justify your existence in one way or another. > ---- > Reg. Actually I want to monitor the antenna because I have a splice in the feedline and the feedpoint is subject to wx, snow ice and rain. Some times the feedline itself is covered with snow and ice. I would find it interesting to see what is happening when I see my SWR shoot up and retuning my matchbox. I also have a strange thing happen when I apply high power, I get a slight bump up in SWR suddenly. I often wonder if one of my end insulators are breaking down under 1KW of RF or if there is some imbalance on one leg due to ground or trees swaying in the wind. Article: 221885 of rec.radio.amateur.antenna From: "Ralph Mowery" References: Subject: Re: 50 Or 75 Ohm Coax For Receive Only Application ? Message-ID: Date: Sat, 25 Feb 2006 18:49:17 GMT "Robert11" wrote in message news:V_ednWRHBpRDPZ3Z4p2dnA@comcast.com... > Hello: > > Will be putting up a new HF atnenna for Receive-Only, to be used from 30 MHz > on down > > Trying to decide on a coax type for the radio to antenna run, about 150 > feet. > > As some will be buried in soil, want to have a PE jacket. > > It appears that when factoring in the PE requirement, and certainly price, I > can > do better, apparently, by picking a 75 ohm coax than a 50 ohm one. > > My receivers input is, of course, stamped 50 ohm. > > In a practical sense, do you experts believe I would see any difference > between > 50 or 75 ohm coax for a receive only situation at the 30 MHz and lower > listening freq's (150 foot coax run) ? > For receiving it will not make any differance. Even for transmitting it will only mater if youare using a 50 ohm swr or power meter and want to read it directly. Just use almost anyting but rg-58 or rg-59 is fine and those are not too bad. If you could handle the connection of the noncopper shield that most of the cable TV 70 ohm rg-6 has, that would probably be your best bet. Don't even go to the real high grade of the quad shielded stuff. While the receiver says 50 ohms, it is doubtful that it is actually 50 ohms except on a very few frequencies if even then. Article: 221886 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: 50 Or 75 Ohm Coax For Receive Only Application ? References: Message-ID: <512Mf.39813$H71.11535@newssvr13.news.prodigy.com> Date: Sat, 25 Feb 2006 19:15:13 GMT Robert11 wrote: > It appears that when factoring in the PE requirement, and certainly price, I > can do better, apparently, by picking a 75 ohm coax than a 50 ohm one. I use a lot of 75 ohm coax that I get for free from scrap ends from the local cable TV company. Can't beat that price. -- 73, Cecil http://www.qsl.net/w5dxp Article: 221887 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: Q about balanced feed line Date: Sat, 25 Feb 2006 19:23:16 +0000 (UTC) Message-ID: References: <0epuv1lpbqi5adut9qo1ijkp5k38hro11k@4ax.com> "Dot" wrote in message news:0epuv1lpbqi5adut9qo1ijkp5k38hro11k@4ax.com... > On Fri, 24 Feb 2006 19:39:31 GMT, Cecil Moore wrote: > > >What if one is broken and you don't know it? > > I one side of a dipole gets loose, you'll know all about it... the swr is > likely to go to 6 or higher. Your receiver would be mysteriously quiet and > you wouldn't be getting normal power from your transmitter. In the worst > case it could damage your equipment. > > Antenna failure is not trivial. ========================================== I quite agree. Of course, if there's anything the matter with the antenna then you will be aware of it long before you discover whether or not there's any need to get out your measuring instruments to find how much your feedline is unbalanced. Just go out into your back yard and see whether your antenna is still up in the air or not. Many years back I once had a neighbor who sabataged my inverted-L at 1am in the morning while I was on the air. I did NOT measure unbalance on the feedline - I was not equipped to do it - I just called the police! It turned out that my neighbor had very sensitive ears and could hear my microphone voice through the walls of our adjoining houses. ---- Reg. Article: 221888 of rec.radio.amateur.antenna From: John Ferrell Subject: Re: Technical vertical question Message-ID: <32d1025g3bhc6smmsu43gu2fu0gu5s0h6f@4ax.com> References: <1140841925.446621.18100@i39g2000cwa.googlegroups.com> Date: Sat, 25 Feb 2006 19:55:02 GMT A lot of questions in one post... You can get some of these answers by downloading the demo package of EZNEC. I dropped a radial from one of my test cases and found the pattern was less on that side of the azimuth display. Modeling buried radials is beyond my talents. In general, more is better and longer is better. The jury is still out in most cases. Most of your questions are addressed in the 20th Edition Arrl Antenna Handbook. You can use Google to search in the Groups and also find answers to most of your questions but that is the least reliable source that I use. Beware of experts who use assumed names, especially! Consider any advice from me as coming from a student in spite of old call and the Social Security Check! On 24 Feb 2006 20:32:05 -0800, "LiveToBe100.org" wrote: >If you have a Ground Mounted, or an Above Ground Mounted vertical, can >you create a lobe by placing your radials pointed in the direction you >want the lobe to occure? or, does the lobe occure in the opposite >direction from which you have the radials pointed? > >What is the optimum length for radials: > >1/10 wavelength? > >1/4 wavelength? > >1/4 wavelength plus 2%? > >1/2 wavelength? > >1 wavelength? > >2 wavelengths? > > >Is the optimum wavelength a function of where the vertical is mounted? >i.e. Ground Mounted or Above Grounded Mounted. > >Thanks for your help. > >William >http://LiveToBe100.org >- Retirement News - John Ferrell W8CCW Article: 221889 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: Q about balanced feed line Date: Sat, 25 Feb 2006 20:17:19 +0000 (UTC) Message-ID: References: "Big Endian" wrote > Actually I want to monitor the antenna because I have a splice in the > feedline and the feedpoint is subject to wx, snow ice and rain. Some > times the feedline itself is covered with snow and ice. I would find it > interesting to see what is happening when I see my SWR shoot up and > retuning my matchbox. I also have a strange thing happen when I apply > high power, I get a slight bump up in SWR suddenly. I often wonder if > one of my end insulators are breaking down under 1KW of RF or if there > is some imbalance on one leg due to ground or trees swaying in the wind. ======================================= Perhaps you should have mentioned all this in your original enquiry. The people you expect replies from are not mind readers! ---- Reg. Article: 221890 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: nec simulation - unexpected result ?? References: <15631-43FF0DD8-401@storefull-3255.bay.webtv.net> <11vuv3l7thdn87@corp.supernews.com> <11vvku12b8t8398@corp.supernews.com> Message-ID: Date: Sat, 25 Feb 2006 20:32:19 GMT Amos Keag wrote: > Feedpoint impedance does change. But, what has that to do with resonance?? > >> Roy Lewallen wrote: >>> The impedance of the antenna doesn't change with the feed method ... I may have inferred from Roy's posting what he didn't mean to imply. Here's what I assumed he said: "The *feedpoint* impedance of the antenna doesn't change with the feed method." I hope you agree that is a false statement but may not be the meaning that Roy intended. I apparently made the same mistake for the meaning of your posting. If you guys would just post in Texan, I could understand you. di-di-di-dit---di-dit If Roy had said, "The radiation resistance of an antenna doesn't change with the feed method", I wouldn't have questioned it. -- 73, Cecil http://www.qsl.net/w5dxp Article: 221891 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: Technical vertical question Date: Sat, 25 Feb 2006 20:34:31 +0000 (UTC) Message-ID: References: <1140841925.446621.18100@i39g2000cwa.googlegroups.com> There is no such thing as an 'optimum' length of radials. There is only an economic limit to what your bank balance can afford in terms of number of dollars per S-point. Most people's bank balance and lumbago problems run out when there are half a dozen radials of about 15 feet in length. ---- Reg. Article: 221892 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: 50 Or 75 Ohm Coax For Receive Only Application ? Date: Sat, 25 Feb 2006 21:03:37 +0000 (UTC) Message-ID: References: <512Mf.39813$H71.11535@newssvr13.news.prodigy.com> If you MUST use coax then prefer 75 ohms. Go for the greatest overall 75-ohm coaxial diameters. The greater the overall diameter the smaller the attenuation in terms of dB per 100 feet. There's no need to impedance match a 75ohm line to a 50-ohm receiver for receiving purposes. The mismatch loss is quite small. What matters is a severe mismatch between the antenna impedance and the line impedance which will occur on some of the higher frequency bands. ---- Reg. Article: 221893 of rec.radio.amateur.antenna From: Owen Duffy Subject: Re: 50 Or 75 Ohm Coax For Receive Only Application ? Message-ID: References: Date: Sat, 25 Feb 2006 21:07:10 GMT On Sat, 25 Feb 2006 18:49:17 GMT, "Ralph Mowery" wrote: >are not too bad. If you could handle the connection of the noncopper >shield that most of the cable TV 70 ohm rg-6 has, that would probably be >your best bet. Don't even go to the real high grade of the quad shielded >stuff. In this part of the world, some types of quad shield, and even some types of the dual sheild have one of the braids made from tinned copper and are solderable, check out the specs or get a sample and test it. Additionally, crimp BNC(M) connectors, F(M) connectors and F(F)-BNC(M) adapters are available. Owen -- Article: 221894 of rec.radio.amateur.antenna From: Owen Duffy Subject: Re: 75 And 50 Ohm Connectors In Same Listening Chain ? Message-ID: References: <_rOdndQpXOwhI53ZnZ2dnUVZ_sGdnZ2d@comcast.com> Date: Sat, 25 Feb 2006 21:22:06 GMT On Sat, 25 Feb 2006 15:32:06 -0500, "Robert11" wrote: >Hello, > >Should have asked this also in my previous post re 50 or 75 ohm coax, but >I guess it is probably better to start a different thread. >New at this, so please pardon these very basic type of questions. > >For a receiving only application, 30 MHz on down: >Putting up a new Inverted-L receiving antenna. > >Radio, Balun, Lightning Arrestor use the 259 type of plug which I guess is >nominally for 50 ohm systems. Firstly: Some types of connectors are designed to create a minimal characteristic impedance discontinuity, examples are N type and BNC. PL-259s are not so designed. Secondly, at HF, the impedance discontinuity of PL-259 or 50 ohm BNC in a nominally 75 ohm line for your intended use is insignificant. Beware of having 50 and 75 ohm versions of BNC and like around, incorrect pairing risk damage to the female connector. Most 75 ohms applications still use 50 ohm BNC connectors, even though 75 ohm versions are available. Owen > >I can go with 75 ohm BNC connectors for the main coax run, but am pretty >well stuck with the >259 type for the already purchased units I noted above. > >Intuitively, I guess I would like (all) 75 ohm connectors if I am using 75 >ohm coax. > See above re connector damage. >But, for 30 MHz and lower listening, would I even notice any difference, >probably ? > >Is any received signal lost, or reflected back, at these 75-50 ohm junctions >? Yes, we can readily calculate the effect of introducing a discontinuity, the effect is so small in your application that you are unlikely to be able to measure it, much less see the effect in receiver signal strength. Owen -- Article: 221895 of rec.radio.amateur.antenna From: Dot Subject: Re: Q about balanced feed line Message-ID: References: <0epuv1lpbqi5adut9qo1ijkp5k38hro11k@4ax.com> Date: Sat, 25 Feb 2006 16:06:06 -0500 On Sat, 25 Feb 2006 19:23:16 +0000 (UTC), "Reg Edwards" wrote: >It turned out that my neighbor had very sensitive ears and could hear >my microphone voice through the walls of our adjoining houses. And how much louder tha normal is your microphone voice that he would object to it but not your conversational voice? IOW... this sounds like a problem that'd been brewing for quite some time. Article: 221896 of rec.radio.amateur.antenna From: Dot Subject: Re: 75 And 50 Ohm Connectors In Same Listening Chain ? Message-ID: <5uh102pv7girsg2jv7rdjf7ue0ch9bl4om@4ax.com> References: <_rOdndQpXOwhI53ZnZ2dnUVZ_sGdnZ2d@comcast.com> Date: Sat, 25 Feb 2006 16:11:11 -0500 On Sat, 25 Feb 2006 15:32:06 -0500, "Robert11" wrote: >Radio, Balun, Lightning Arrestor use the 259 type of plug which I guess is >nominally for 50 ohm systems. >Intuitively, I guess I would like (all) 75 ohm connectors if I am using 75 >ohm coax. > >But, for 30 MHz and lower listening, would I even notice any difference, >probably ? > >Is any received signal lost, or reflected back, at these 75-50 ohm junctions >? >If meaningful, any way around the problem ? Yeah... spend a couple of bucks and get some 50 ohm coax. Article: 221897 of rec.radio.amateur.antenna From: The Benevolent dbu Subject: Re: Q about balanced feed line References: Message-ID: Date: Sat, 25 Feb 2006 21:31:17 GMT In article , Richard Clark wrote: > On Sat, 25 Feb 2006 18:18:35 GMT, Big Endian > wrote: > >> "Ian White wrote > >> > But the original questioner wants to measure what's *really* > >> happening. > >> ======================================== > >> But the original questioner can tell what's *really* happening just by > >> inspecting the antenna and feedline. He doesn't need any electrical > >> measuring instruments. > > > >Actually I want to monitor the antenna because I have a splice in the > >feedline and the feedpoint is subject to wx, snow ice and rain. Some > >times the feedline itself is covered with snow and ice. I would find it > >interesting to see what is happening when I see my SWR shoot up and > >retuning my matchbox. I also have a strange thing happen when I apply > >high power, I get a slight bump up in SWR suddenly. I often wonder if > >one of my end insulators are breaking down under 1KW of RF or if there > >is some imbalance on one leg due to ground or trees swaying in the wind. > > Hi OM, > > Reggie is particularly obtuse to this matter. Simple observation of a > dipole that is symmetrical to earth does not guarantee balance. When > that twin lead arrives at your gear, you can easily wipe that out (the > presumed balance) through an inappropriate connection to ground > (through any number of paths that are commonly overlooked in the > shack). > > Snow and ice on the line are not likely to impart a common mode > current, but as revealed by bench test by contributors here, the > characteristic Z of the line can change drastically, which then upsets > the tune, where it follows SWR begins to change - noticeably. If your > feedline is coaxial, then the ice is of no consequence, but that does > not remove the jeopardy of common mode current. There you need to > look at how you isolate the line from the drivepoint. > > 73's > Richard Clark, KB7QHC I am also concerned that the feedline may be causing unbalance condition because it is routed straight down perhaps 30 feet from the feedpoint then it makes a sharp turn to the shack and at that point it is parallel with one leg of the antenna for about 30 feet. It's the only way I can do it. I have thought of discarding the multiband doublet for a plain dipole with 52 ohm coax. I do like the doublet and my Johnson matchbox, besides I can use this antenna on 160 when I route the feedline via a knife switch over to my MN2700 and configure it to a inverted L. -- "Welcome to President Clinton, Mrs. Clinton, and my fellow astronauts." Al Gore Article: 221898 of rec.radio.amateur.antenna From: "Jim" Subject: need help with H antenna Date: Sun, 26 Feb 2006 04:43:07 -0500 Message-ID: I need help in building an H type of tracking antenna for use around 166-167 mhz. This is for wildlife tracking. I have a couple of handheld 3 element Yagi's that I built using YagiCad to do the math, and they work well, but they are big and clunky. There are times when I am willing to sacrifice the good f/b ratio of the yagi for convienience, for instance when working in brushy woods. I have used an H for tracking at 151 mhz, but of course, I can't use that one for 166. My tracking receiver, a King portable, has a BNC connector, so I can interchange antennas quickly. Is there a web page or magazine article that can help me design my H, or can someone share their experience? Thanks Jim Article: 221899 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: nec simulation - unexpected result ?? Date: Sat, 25 Feb 2006 14:47:47 -0800 Message-ID: <1201nkmsets01b7@corp.supernews.com> References: <15631-43FF0DD8-401@storefull-3255.bay.webtv.net> <11vuv3l7thdn87@corp.supernews.com> <11vvku12b8t8398@corp.supernews.com> I apologize for not being more clear. The context of my comment was in reply to a statement about the resonance somehow being different for "current fed" and "voltage fed" antennas. What I meant was that the antenna impedance is independent of the source impedance or other characteristics of the source. Of course, the feedpoint impedance will be different if you choose another feedpoint. I'm surprised that this topic has aroused so much commentary. It reveals a general lack of understanding about some of the most basic and fundamental characteristics of antennas and circuits in general. Hopefully, the discussion is helping some of the readers to gain a better grasp of the subject matter. Roy Lewallen, W7EL Amos Keag wrote: > Feedpoint impedance does change. But, what has that to do with resonance?? > > Cecil Moore wrote: > >> Roy Lewallen wrote: >> >>> The impedance of the antenna doesn't change with the feed method ... >> >> >> One feed method is center feed. Another feed method is off-center feed. >> The feedpoint impedance of the antenna changes with position since >> for 1/2WL, for instance, the net voltage is a sine wave referenced >> to the center, and the net current is a cosine wave referenced to the >> center. The feedpoint impedance is approximately sin(x)/cos(x)=tan(x) >> where 'x' is the number of degrees away from center. > Article: 221900 of rec.radio.amateur.antenna From: "Dan/W4NTI" References: Subject: Re: 20 Meter Dipole - instant DX!!! Message-ID: <8a5Mf.3299$F56.1837@newsread3.news.atl.earthlink.net> Date: Sat, 25 Feb 2006 22:49:40 GMT "Reg Edwards" wrote in message news:dtg0ij$1pr$1@nwrdmz03.dmz.ncs.ea.ibs-infra.bt.com... > > "Radio TexMex" wrote > >> Before someone beats me too it, I've already had somebody point out > the >> goofy flaw with my new super awesome 20M dipole. And after doing > some much >> needed reading on baluns, I've concluded that the 4:1 balun isn't > needed. >> >> Readers: Please be patient. Learning process taking place here. >> > ======================================== > > Reading about 4:1 baluns makes one imagine a 4:1 balun is > cessary - whereas most likely it isn't. > ---- > Reg. > > Times certainly have changed. I remember as a NOVICE being drilled that a coax fed 1/2 wave dipole will not work on EVEN multiples of the fundamental. Maybe I needed a ANTENNA TUNER, whatever that is. Not being critical OM, I applaud you for trying to learn instead of spouting garbage from CB. Keep up the good work. Dan/W4NTI Article: 221901 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Q about balanced feed line Date: Sat, 25 Feb 2006 14:59:51 -0800 Message-ID: <1201ob9bjmal91d@corp.supernews.com> References: Reg Edwards wrote: > . . . > The trouble with you experts is that you overcomplicate matters and > make quite simple, obvious things appear to be mysterious. > . . . I recently finished reading Richard Hofstadter's _Anti-Intellectualism in American Life_ (written in 1962, won a Pulitzer prize in 1964), where the author shows in great detail that a general disdain for education, sophistication, and complexity is a very deeply seated American tradition. That general outlook was virtually a basis of the founding of a number of now-mainstream religions, and has had lasting impacts on our educational and political systems. In short, it's a long and dearly held American tradition. So, Reg, that was a very American thing to say. You'd fit right in here. Roy Lewallen, W7EL Article: 221902 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Q about balanced feed line Date: Sat, 25 Feb 2006 15:09:48 -0800 Message-ID: <1201otu23v9lc6e@corp.supernews.com> References: Ian White GM3SEK wrote: > > It was clear enough to everyone else that he wanted to know how to make > measurements. It was also clear enough for you to declare that > measurements are not necessary. > > Maybe this is a good time to remind you of your own favourite quotation: > > >"When you can measure what you are speaking about and express > >it in numbers you know something about it. But when you cannot > >measure it, when you cannot express it in numbers, your knowledge > >is of a meagre and unsatisfactory kind. It may be the beginning of > >knowledge but you have scarcely in your thoughts advanced to > >the state of science." > > > >William Thomson, Lord Kelvin, 1824-1907. I recently came across some other notable quotes from Lord Kelvin: "Radio has no future." "Heavier than air flying machines are impossible." "X-rays will prove to be a hoax." -- quoted in _Unweaving the Rainbow: Science, Delusion, and the Appetite for Wonder_, by noted British writer Richard Dawkins. Dawkins also notes that "William Thompson, first Lord Kelvin, was one of the most distinguished and influential of nineteenth-century British physicists. He was a thorn in Darwin's side because he 'proved', with massive authority but, as we now know, even more massive error, that the earth was too young for evolution to have occurred." The value of Kelvin's contributions is unquestionable. But even he didn't get it right all the time. Roy Lewallen, W7EL Article: 221903 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: 50 Or 75 Ohm Coax For Receive Only Application ? Date: Sat, 25 Feb 2006 15:11:38 -0800 Message-ID: <1201p1brdalne7a@corp.supernews.com> References: Robert11 wrote: > . . . > In a practical sense, do you experts believe I would see any difference > between > 50 or 75 ohm coax for a receive only situation at the 30 MHz and lower > listening freq's (150 foot coax run) ? No. Roy Lewallen, W7EL Article: 221904 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: Q about balanced feed line References: <1201otu23v9lc6e@corp.supernews.com> Message-ID: Date: Sat, 25 Feb 2006 23:34:41 GMT Roy Lewallen wrote: > The value of Kelvin's contributions is unquestionable. But even he > didn't get it right all the time. And Roy, allow me to point out, in that respect, you don't get it right all the time either. I can prove to you that reflected waves contain joules but you simply refuse to listen and have "ploinked" me. What really aggravates me is that when an internet guru, such as yourself (or W8JI) appears to be on the verge of losing an argument, you simply kill-file the opponent and refuse to continue the thread. -- 73, Cecil http://www.qsl.net/w5dxp Article: 221905 of rec.radio.amateur.antenna Subject: Re: 50 Or 75 Ohm Coax For Receive Only Application ? From: Ed References: Message-ID: Date: 25 Feb 2006 23:38:53 GMT I'd recommend a good grade RG-6 cable (70ohms) also. Regarding the connectors, why not just use the standard TV F fittings all the way to the Rx. You can put an F to whatever adapter on your Rx. TV cable and fittings are not only cheap, but work quite well. Ed K7AAT Article: 221906 of rec.radio.amateur.antenna From: Dot Subject: Re: 75 And 50 Ohm Connectors In Same Listening Chain ? Message-ID: <76s1025kkhbcbscr4n3lvtmmmoutcbae9g@4ax.com> References: <_rOdndQpXOwhI53ZnZ2dnUVZ_sGdnZ2d@comcast.com> Date: Sat, 25 Feb 2006 19:05:55 -0500 On Sat, 25 Feb 2006 21:39:58 GMT, Cecil Moore wrote: >Simply forget about that worry. PL-259s are not 50 ohms. >That's why they are not used at VHF/UHF. Looked at the back of a 2 meter rig lately? Article: 221907 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: nec simulation - unexpected result ?? Date: Sat, 25 Feb 2006 16:32:35 -0800 Message-ID: <1201tp5bp9l5j4b@corp.supernews.com> References: <15631-43FF0DD8-401@storefull-3255.bay.webtv.net> <11vuv3l7thdn87@corp.supernews.com> <11vvku12b8t8398@corp.supernews.com> <1201nkmsets01b7@corp.supernews.com> Amos Keag wrote: > Agree! But, the radiation resistance ... ? > The topic of radiation resistance has been pretty much beaten to death on this newsgroup. A groups.google.com search should provide a good evening's reading and entertainment. In brief, "radiation resistance" is the part of an antenna's impedance which "absorbs" the power actually being radiated. It can be referred to any point on an antenna. At that point, wherever it is, the power radiated is I^2 * Rrad, where I is the current at that point. Kraus generally refers the radiation resistance to the feedpoint; that is, he calls the resistive part of the feedpoint impedance the radiation resistance. In AM broadcasting, where monopoles are often higher than a quarter wavelength, it's common to refer the radiation resistance to a point of maximum current. Either approach is perfectly valid. But it means that you have to be careful to say what you mean when you use the term, particularly if the antenna is longer than a quarter wavelength (monopole) or half wavelength (dipole). There's a common equation for efficiency, Eff = Rrad / (Rrad + Rloss). When using it, you have to make sure you're referring Rrad and Rloss to the same point. A common error when dealing with folded monopoles is to refer the radiation resistance to the high-impedance, transformed feedpoint, while neglecting to refer the loss resistance to the same point by transforming it. This leads to the erroneous conclusion that folding the element improves efficiency. It doesn't, except that the additional wire surface area reduces the wire loss -- but this isn't usually a significant contribution to the total loss. So to address the comment -- Changing the feedpoint location can change the current distribution on the antenna. This in turn will change the radiation resistance referred to some fixed point along the antenna, although in most common cases I can think of, it won't be a large change. You could contrive some cases where it would. If you refer the radiation resistance to the feedpoint, that is, define it as being the resistive part of the feedpoint impedance, then changing the feedpoint location can have a major impact on the radiation resistance. Again, if you want more about the topic, read some of the threads where it's been discussed in more detail. Roy Lewallen, W7EL > > Cecil Moore wrote: > >> Roy Lewallen wrote: >> >>> Of course, the feedpoint impedance will be different if you choose >>> another feedpoint. >> >> >> Here is the confusing quotation: >> >>> The impedance of the antenna doesn't change with the feed method >> >> > (assuming of course that it has a single feed point) >> >> A center-fed dipole has a "single feed point". An off-center-fed >> dipole has a "single feed point". The feedpoint impedance of the >> antenna does indeed change depending upon where that single >> feed point is located. > Article: 221908 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: 75 And 50 Ohm Connectors In Same Listening Chain ? Date: Sat, 25 Feb 2006 16:35:48 -0800 Message-ID: <1201tv5tdocjs8f@corp.supernews.com> References: <_rOdndQpXOwhI53ZnZ2dnUVZ_sGdnZ2d@comcast.com> Robert11 wrote: > Hello, > > Should have asked this also in my previous post re 50 or 75 ohm coax, but > I guess it is probably better to start a different thread. > New at this, so please pardon these very basic type of questions. > > For a receiving only application, 30 MHz on down: > Putting up a new Inverted-L receiving antenna. > > Radio, Balun, Lightning Arrestor use the 259 type of plug which I guess is > nominally for 50 ohm systems. > > I can go with 75 ohm BNC connectors for the main coax run, but am pretty > well stuck with the > 259 type for the already purchased units I noted above. > > Intuitively, I guess I would like (all) 75 ohm connectors if I am using 75 > ohm coax. > > But, for 30 MHz and lower listening, would I even notice any difference, > probably ? No. You wouldn't even if you were transmitting. > Is any received signal lost, or reflected back, at these 75-50 ohm junctions > ? No significant amount. The length of the discontinuity is extremely short compared to a wavelength, and it's not a terribly bad discontinuity. You'd be hard pressed to measure the difference at HF, even with very good equipment. (Of course, you could see it with a high speed TDR, but that's not an HF measurement.) Roy Lewallen, W7EL Article: 221909 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: 75 And 50 Ohm Connectors In Same Listening Chain ? Date: Sat, 25 Feb 2006 16:47:28 -0800 Message-ID: <1201ul29sgamu6b@corp.supernews.com> References: <_rOdndQpXOwhI53ZnZ2dnUVZ_sGdnZ2d@comcast.com> Owen Duffy wrote: > > Beware of having 50 and 75 ohm versions of BNC and like around, > incorrect pairing risk damage to the female connector. Most 75 ohms > applications still use 50 ohm BNC connectors, even though 75 ohm > versions are available. I keep reading this, and it puzzles me. I have a number of RG-59 patch cables which have 75 ohm BNC connectors fitted (and others with 50 ohm connectors). As far as I can tell with a magnified inspection, the center conductor of the 75 ohm male BNC is the same diameter as it is in a standard 50 ohm BNC. The only apparent difference is that the dielectric around the inside of the outer mating area is much thinner in the 75 ohm connector, and the diameter of the 50 ohm center pin steps up as it enters the solid dielectric at the bottom while the 75 ohm center pin doesn't. If some 75 ohm BNC connectors have a smaller center pin, then it looks to me like you can't even safely mate a male 75 ohm BNC (of the type I have) with a female 75 ohm BNC (which might be of this other type if it exists). Does anyone have a drawing or measurements showing that 50 and 75 ohm BNC connectors really have different pin diameters? I don't know about type N connectors -- I don't think I've ever seen a 75 ohm version. Roy Lewallen, W7EL Article: 221910 of rec.radio.amateur.antenna From: Owen Duffy Subject: Re: 50 Or 75 Ohm Coax For Receive Only Application ? Message-ID: References: Date: Sun, 26 Feb 2006 01:19:22 GMT On 25 Feb 2006 23:38:53 GMT, Ed wrote: > > > I'd recommend a good grade RG-6 cable (70ohms) also. Regarding the >connectors, why not just use the standard TV F fittings all the way to the >Rx. You can put an F to whatever adapter on your Rx. TV cable and >fittings are not only cheap, but work quite well. Agreed Ed. I did see another post that suggested 50 ohms was better and to spend the money. The matched line loss of 150' of RG6 at 30MHz is 1.6dB. the MLL of more expensive RG58C/U is 3.6dB, or the much more expensive RG213 is 1.6dB. The antenna will not be matched over the whole range, so mismatch losses will occur with both types of line, and there is no reason to think that overall spending more money on RG213 with the attendent loss of flexibility will actually be better. In this rx only application, especially below 15MHz, even if the RG6 was a few dB worse than 50 ohm line, it would not be worth spending the money on RG213. Robert, if you want to bury the RG6, buy the standard grade and fit it inside 13mm PE irrigation tube for better life. Owen -- Article: 221911 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: nec simulation - unexpected result ?? References: <15631-43FF0DD8-401@storefull-3255.bay.webtv.net> <11vuv3l7thdn87@corp.supernews.com> <11vvku12b8t8398@corp.supernews.com> <1201nkmsets01b7@corp.supernews.com> Message-ID: Date: Sun, 26 Feb 2006 01:25:44 GMT Amos Keag wrote: > Agree! But, the radiation resistance ... ? Nobody said anything about radiation resistance. -- 73, Cecil http://www.qsl.net/w5dxp Article: 221912 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: 75 And 50 Ohm Connectors In Same Listening Chain ? References: <_rOdndQpXOwhI53ZnZ2dnUVZ_sGdnZ2d@comcast.com> <76s1025kkhbcbscr4n3lvtmmmoutcbae9g@4ax.com> Message-ID: Date: Sun, 26 Feb 2006 01:27:54 GMT Dot wrote: > Cecil Moore wrote: >>Simply forget about that worry. PL-259s are not 50 ohms. >>That's why they are not used at VHF/UHF. > > Looked at the back of a 2 meter rig lately? I should have said they are not used at VHF/UHF by rational human beings. di-di-di-dit---di-dit. -- 73, Cecil http://www.qsl.net/w5dxp Article: 221913 of rec.radio.amateur.antenna From: Owen Duffy Subject: Re: 75 And 50 Ohm Connectors In Same Listening Chain ? Message-ID: References: <_rOdndQpXOwhI53ZnZ2dnUVZ_sGdnZ2d@comcast.com> <1201ul29sgamu6b@corp.supernews.com> Date: Sun, 26 Feb 2006 01:33:01 GMT On Sat, 25 Feb 2006 16:47:28 -0800, Roy Lewallen wrote: >Owen Duffy wrote: >> >> Beware of having 50 and 75 ohm versions of BNC and like around, >> incorrect pairing risk damage to the female connector. Most 75 ohms >> applications still use 50 ohm BNC connectors, even though 75 ohm >> versions are available. > >I keep reading this, and it puzzles me. I have a number of RG-59 patch Roy, I have clear recollection of 75 ohm BNCs (meaning a BNC connector desiged for 75 ohm through impedance) that were incompatible in days when I worked in communications facilities that used 75 ohms for IF (70MHz) and baseband, and 50 ohms for RF (GHz). However, I note on Amphenol's site: "Two distinct types of 75 ? BNC's are available, and both mate with each other and with 50 ? BNC's. Type 1 is designated 75 ? BNC-T1 and provides constant 75 ? performance with low VSWR DC – 4 GHz. Type 2 is designated 75 ? BNC-T2 and is usable with low reflection DC - 1 GHz. For applications above 1 GHz, Type 1 is recommended. " Though it is clear that Amphenol and probably some other manufacturers produce compatible connectors, I am mindfull of earlier experience, though I concede that it may have been the result of non standard 75 ohm BNCs. Owen -- Article: 221914 of rec.radio.amateur.antenna From: chuck Subject: Re: Q about balanced feed line References: <4%LLf.13325$rL5.10680@newssvr27.news.prodigy.net> Message-ID: Date: Sun, 26 Feb 2006 01:35:39 GMT If the antenna system can be satisfactorily matched to the transmitter output impedance, it would seem to matter little whether the feed line currents are balanced, or, if they are not, by how much. If there are no obvious common mode currents causing problems in the shack, then of what consequence would an imbalance be, other than to modify the radiation pattern, perhaps even beneficially? Chuck, NT3G Cecil Moore wrote: > Big Endian wrote: > >> An unbalanced condition would have a meter indication, like current >> flow? Balanced the meter needle would not move? > > > Yes, for a balanced condition, the meter needle should > not move. Article: 221915 of rec.radio.amateur.antenna From: Owen Duffy Subject: Re: 75 And 50 Ohm Connectors In Same Listening Chain ? Message-ID: <7h3202hofj05os221cd024hm2srjvjq160@4ax.com> References: <_rOdndQpXOwhI53ZnZ2dnUVZ_sGdnZ2d@comcast.com> <1201ul29sgamu6b@corp.supernews.com> Date: Sun, 26 Feb 2006 02:14:22 GMT On Sat, 25 Feb 2006 16:47:28 -0800, Roy Lewallen wrote: >I don't know about type N connectors -- I don't think I've ever seen a >75 ohm version. The 75 ohm version N-type uses a reduced centre pin and I believe they are incompatible. Owen -- Article: 221916 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: 75 And 50 Ohm Connectors In Same Listening Chain ? Date: Sat, 25 Feb 2006 18:15:14 -0800 Message-ID: <12023pjnigrsldf@corp.supernews.com> References: <_rOdndQpXOwhI53ZnZ2dnUVZ_sGdnZ2d@comcast.com> <76s1025kkhbcbscr4n3lvtmmmoutcbae9g@4ax.com> Dot wrote: > On Sat, 25 Feb 2006 21:39:58 GMT, Cecil Moore wrote: > >> Simply forget about that worry. PL-259s are not 50 ohms. >> That's why they are not used at VHF/UHF. > > Looked at the back of a 2 meter rig lately? I used to have a Motorola UHF (450 MHz) ex-taxicab radio. It used UHF (PL-259/SO-239) connectors. At very high frequencies where the impedance discontinuity might become noticeable, the resulting reactance can usually be compensated for by slight readjustment of matching networks which are usually present anyway. UHF connectors are poor for a number of mechanical reasons, but the impedance discontinuity is seldom a problem. Roy Lewallen, W7EL Article: 221917 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: 50 Or 75 Ohm Coax For Receive Only Application ? Date: Sat, 25 Feb 2006 18:22:39 -0800 Message-ID: <120247hee085k77@corp.supernews.com> References: Owen Duffy wrote: > . . . > In this rx only application, especially below 15MHz, even if the RG6 > was a few dB worse than 50 ohm line, it would not be worth spending > the money on RG213. >. . . I think Owen means, "even if the RG6 was a few dB *lossier*". In receiving applications at HF, added loss (within reason) doesn't translate to any reduction in signal/noise ratio. So one line can be considerably lossier than another without making it even one little bit worse in this application. There's no point in spending extra money on line which won't make any improvement at all on your ability to receive signals. It might, on the other hand, be worthwhile to pay extra for line which will last longer or is more physically rugged. Or it might not. Roy Lewallen, W7EL Article: 221918 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Q about balanced feed line Date: Sat, 25 Feb 2006 18:30:34 -0800 Message-ID: <12024mc203qch0f@corp.supernews.com> References: <4%LLf.13325$rL5.10680@newssvr27.news.prodigy.net> chuck wrote: > If the antenna system can be satisfactorily matched to the transmitter > output impedance, it would seem to matter little whether the feed line > currents are balanced, or, if they are not, by how much. > > If there are no obvious common mode currents causing problems in the > shack, then of what consequence would an imbalance be, other than to > modify the radiation pattern, perhaps even beneficially? You have to remember that the common mode feedline current doesn't stop at the rig. It continues to the Earth by whatever means are available. So your house wiring, appliance cords, and other odd conductors often become part of your antenna system. These aren't likely to be very efficient radiators. People often go to a lot of trouble to put their antennas high and in the clear. That doesn't make much sense if you're going to have your house do a good part of the radiating. But you can still talk to lots of stations even if some of your radiating is being done by your feedline and house wiring. And that's enough for a lot of folks. Roy Lewallen, W7EL Article: 221919 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: Q about balanced feed line Date: Sun, 26 Feb 2006 02:50:44 +0000 (UTC) Message-ID: References: <4%LLf.13325$rL5.10680@newssvr27.news.prodigy.net> > If the antenna system can be satisfactorily matched to the transmitter > output impedance, it would seem to matter little whether the feed line > currents are balanced, or, if they are not, by how much. > > If there are no obvious common mode currents causing problems in the > shack, then of what consequence would an imbalance be, other than to > modify the radiation pattern, perhaps even beneficially? > > Chuck, NT3G ========================================== I agree with what you say. But antenna (or line) unbalance and line-to-antenna impedance mismatch are not entirely independent of each other. An unbalanced line or antenna causes a small impedance mismatch. Because it is small is the reason why it very often happens it doesn't matter very much whether or not a balanced feedline is used. For example, a coax line can be used quite successfully to feed a balanced dipole. And, in practice, no antenna is perfectly balanced about ground. ---- Reg. Article: 221920 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: nec simulation - unexpected result ?? Date: Sun, 26 Feb 2006 02:59:15 +0000 (UTC) Message-ID: References: <15631-43FF0DD8-401@storefull-3255.bay.webtv.net> <11vuv3l7thdn87@corp.supernews.com> <11vvku12b8t8398@corp.supernews.com> <1201nkmsets01b7@corp.supernews.com> "Roy Lewallen" wrote > Hopefully, the discussion is helping some of the readers to gain a > better grasp of the subject matter. ====================================== What a forlorn hope! Novices learn next to nothing. They are unable to sort out a very small amount of simple wheat from a great amount of over-complicated chaff. ---- Reg. Article: 221921 of rec.radio.amateur.antenna From: Owen Duffy Subject: Re: 50 Or 75 Ohm Coax For Receive Only Application ? Message-ID: References: <120247hee085k77@corp.supernews.com> Date: Sun, 26 Feb 2006 03:09:27 GMT On Sat, 25 Feb 2006 18:22:39 -0800, Roy Lewallen wrote: >Owen Duffy wrote: >> . . . >> In this rx only application, especially below 15MHz, even if the RG6 >> was a few dB worse than 50 ohm line, it would not be worth spending >> the money on RG213. > >. . . > >I think Owen means, "even if the RG6 was a few dB *lossier*". In >receiving applications at HF, added loss (within reason) doesn't >translate to any reduction in signal/noise ratio. So one line can be >considerably lossier than another without making it even one little bit >worse in this application. There's no point in spending extra money on >line which won't make any improvement at all on your ability to receive >signals. It might, on the other hand, be worthwhile to pay extra for >line which will last longer or is more physically rugged. Or it might not. Quite. The chart at http://www.vk1od.net/bpl/AreYouReady.htm shows that for a good HF receiver, the ambient galactic noise is more than 10dB above the rx noise floor. For an older receiver, the rx noise floor might be 10 to 15dB higher. The ambient noise due to man made and atmospheric sources would be even higher than the galactic noise plotted in the chart. Owen -- Article: 221922 of rec.radio.amateur.antenna From: richardharrison@webtv.net (Richard Harrison) Subject: Re: nec simulation - unexpected result ?? Date: Sat, 25 Feb 2006 21:17:03 -0600 Message-ID: <12985-44011DAF-575@storefull-3254.bay.webtv.net> References: <1140826892.169941.137710@i40g2000cwc.googlegroups.com> Rom, KC7ITM wrote: "I don`t think I`ve EVER heard anyone call a parallel-tuned circuit antiresonant." There are many synonyms I am unfamiliar with also, but I`ve heard of antiresonance and used the word. My "Dictionary of Electronics" says: "Antiresonance - A type of resonance in which a system offers maximum impedance at its resonant frequency." An antiresonant circuit is defined: "Antiresonant circuit - A parallel-resonant circuit offering maximum impedance to the series passage of the resonant frequenccy." A parallel-tuned resonant circuit fits the dictionary definition. It`s a synonym for antiresonant circuit. Best regards, Richard Harrison, KB5WZI Article: 221923 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: Q about balanced feed line References: <4%LLf.13325$rL5.10680@newssvr27.news.prodigy.net> Message-ID: Date: Sun, 26 Feb 2006 04:43:05 GMT chuck wrote: > If there are no obvious common mode currents causing problems in the > shack, then of what consequence would an imbalance be, other than to > modify the radiation pattern, perhaps even beneficially? The purpose of the antenna is to radiate. The purpose of the transmission line is to transfer the energy from the transmitter to the antenna with as little loss as feasible. How much an antenna system is allowed to deviate from its purpose is up to the individual. When I was in high school, I didn't much care about the purpose of an antenna system and burned a hole in my lip. -- 73, Cecil http://www.qsl.net/w5dxp Article: 221924 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: nec simulation - unexpected result ?? References: <1140826892.169941.137710@i40g2000cwc.googlegroups.com> <12985-44011DAF-575@storefull-3254.bay.webtv.net> Message-ID: <0qaMf.35360$Jd.33591@newssvr25.news.prodigy.net> Date: Sun, 26 Feb 2006 04:47:56 GMT Richard Harrison wrote: > An antiresonant circuit is defined: > "Antiresonant circuit - A parallel-resonant circuit offering maximum > impedance to the series passage of the resonant frequenccy." The traps in a trapped dipole are antiresonant. -- 73, Cecil http://www.qsl.net/w5dxp Article: 221925 of rec.radio.amateur.antenna From: "Sal M. Onella" References: <0epuv1lpbqi5adut9qo1ijkp5k38hro11k@4ax.com> Subject: Re: Q about balanced feed line Message-ID: Date: Sat, 25 Feb 2006 22:56:07 -0800 "Dot" wrote in message news:rjh10251g328fp0l057uj3nj3jm0402f25@4ax.com... > On Sat, 25 Feb 2006 19:23:16 +0000 (UTC), "Reg Edwards" > wrote: > > >It turned out that my neighbor had very sensitive ears and could hear > >my microphone voice through the walls of our adjoining houses. > > And how much louder tha normal is your microphone voice that he would object > to it but not your conversational voice? > > IOW... this sounds like a problem that'd been brewing for quite some time. > Some guy in Florida killed a noisy neighbor this week. http://www.wftv.com/irresistible/7359552/detail.html Digital modes are so-o-o nice and quiet! Article: 221926 of rec.radio.amateur.antenna From: "Sal M. Onella" References: Subject: Re: 50 Or 75 Ohm Coax For Receive Only Application ? Message-ID: Date: Sat, 25 Feb 2006 23:33:38 -0800 "Robert11" wrote in message news:V_ednWRHBpRDPZ3Z4p2dnA@comcast.com... > Hello: > > Will be putting up a new HF atnenna for Receive-Only, to be used from 30 MHz > on down > > Trying to decide on a coax type for the radio to antenna run, about 150 > feet. > > As some will be buried in soil, want to have a PE jacket. > > It appears that when factoring in the PE requirement, and certainly price, I > can > do better, apparently, by picking a 75 ohm coax than a 50 ohm one. > > My receivers input is, of course, stamped 50 ohm. > > In a practical sense, do you experts believe I would see any difference > between > 50 or 75 ohm coax for a receive only situation at the 30 MHz and lower > listening freq's (150 foot coax run) ? > > Thanks, > Bob > > 1. The 50-ohm rating is nominal. I suspect it's all over the map as you tune around. 2. The mismatch loss going from 75 to 50 ohm impedance is only about a dB. So, unless you're doing FM, there's little chance that you could ever hear 1dB (and you'd only hear it on FM if you were right at the "edge"). Article: 221927 of rec.radio.amateur.antenna From: "Lee" References: Subject: Re: ?? anyone have plans on how to build a usb gps antenna for laptop Message-ID: Date: Sun, 26 Feb 2006 08:47:11 GMT "Sal M. Onella" wrote in message news:beTLf.1206$Uc2.194@fed1read04... > > "Lee" wrote in message > news:KIzLf.48616$Q22.34001@fe1.news.blueyonder.co.uk... > > > > "Sal M. Onella" wrote in message > > news:MebLf.968$Uc2.471@fed1read04... > > > > > > "Lee" wrote in message > > > news:rXUKf.31812$Q22.24541@fe1.news.blueyonder.co.uk... > > > > > > > > "Sal M. Onella" wrote in message > > > > news:RUSKf.130$Uc2.57@fed1read04... > > > > > > > > > > wrote in message > > > > > news:IyQKf.18144$Ug4.11471@dukeread12... > > > > > > > > > > > > > > > > > > > > > > > http://64.71.184.220/eng/gpspatch.txt > > > > > > > > > > http://www.arrl.org/tis/info/pdf/0210036.pdf > > > > > > > > > > http://vancouver-webpages.com/peter/gpspatch.gif > > > > > > > > Any more designs to suit a Garmin 310 ??? > > > > > > > > Lee .....G6ZSG..... > > > > > > > > > > > > > > Lee, > > > > > > These are free-space antennas, intended for fitting with a length of > coax > > > terminated in the particular connector that mates with the connector on > > your > > > GPS rcvr. My Garmin GPS-III takes a BNC and I have my patch antenna > > mounted > > > on my van's luggage rack; Eight feet of coax brings the signal inside. > > > > Not too sure what i want, i`m a bit of a newb to GPS....just bought > it!!!... > > > > > Not familiar with the 310 -- are you looking for an add-on antenna that > > > physically mounts to your 310? ... or does the 310 require a special > > > coupling technique (non-connector)? > > > > Same as the 320,330 and 340 series > > > > Lee.......G6ZSG....... > > > > > My external antennas are all non-specific to the brand and model of > consumer-grade GPS receivers (those using only the L1 signal). The > connection method varies among receivers. > > If you are buying an antenna, here is Garmin's web link to the manual: > http://www.garmin.com/manuals/StreetPilotc310_OwnersManual.pdf > > See page 26 for a mention of the GA27C antenna. Of course, it comes > with the cable end being the right connector (MCX) for your receiver. > Hunt in your manual if the pages don't match the one I found online. > > If you are making your own antenna from plans I linked to, you will need > to also buy a type MCX connector for the cable end, as that is the connector > type specified here: > http://www.garmin.com/products/sp330/spec.html (which is the link from > page 26 in the manual.) > > www.jameco.com sells MCX connectors, but if you google for "MCX connector" > (with the quotes) you will get not only sources for the connector but also > quite > a few third-party vendors with ready-built GPS antennas using that > connector. > You are apparently in a large group of Garmin users who want an external > antenna. Thanks. Lee.......G6ZSG...... Article: 221928 of rec.radio.amateur.antenna From: Big Endian Subject: Re: Q about balanced feed line References: <4%LLf.13325$rL5.10680@newssvr27.news.prodigy.net> <12024mc203qch0f@corp.supernews.com> Message-ID: Date: Sun, 26 Feb 2006 09:21:35 GMT In article <12024mc203qch0f@corp.supernews.com>, Roy Lewallen wrote: > chuck wrote: > > If the antenna system can be satisfactorily matched to the transmitter > > output impedance, it would seem to matter little whether the feed line > > currents are balanced, or, if they are not, by how much. > > > > If there are no obvious common mode currents causing problems in the > > shack, then of what consequence would an imbalance be, other than to > > modify the radiation pattern, perhaps even beneficially? > > You have to remember that the common mode feedline current doesn't stop > at the rig. It continues to the Earth by whatever means are available. > So your house wiring, appliance cords, and other odd conductors often > become part of your antenna system. These aren't likely to be very > efficient radiators. People often go to a lot of trouble to put their > antennas high and in the clear. That doesn't make much sense if you're > going to have your house do a good part of the radiating. > > But you can still talk to lots of stations even if some of your > radiating is being done by your feedline and house wiring. And that's > enough for a lot of folks. > > Roy Lewallen, W7EL I'm always concerned about TVI and telephone I. and that is another reason I hope to have my feeders balanced, so they radiate minimum RF. I was using a field strength meter while I had the transmitter going the other day and working the antenna along some table lamps and the electrical wire I found the F.S. meter would jump up quite a bit. So what you say about re-radiating house wiring is surely true. Article: 221929 of rec.radio.amateur.antenna From: "oli" Subject: The DELTA LOOP Antenna calculator is now online ! Date: Sun, 26 Feb 2006 12:31:50 +0100 Message-ID: <440191af$0$20142$8fcfb975@news.wanadoo.fr> Good morning to all, I am happy to announce you that I have put online the DELTA LOOP Antenna calculator on the antenna web site. You just have to give the work frequency between 26 to 30 MHz and the number of elements that you want and the site calculate automatiquely all dimensions and spacings. I invite you to try it at : http://www.antenna-street.com/delta-loop-1en.php If you have questions or want to speake about, you could use the dedicated forum : http://www.antenna-street.com/viewtopic.php?t=16 best regards Oli004 www.antenna-street.com www.photomontages.org Article: 221930 of rec.radio.amateur.antenna From: chuck Subject: Re: Q about balanced feed line References: <4%LLf.13325$rL5.10680@newssvr27.news.prodigy.net> Message-ID: Date: Sun, 26 Feb 2006 16:06:16 GMT Thanks for the responses. Put differently, I guess the purpose of the entire station is to radiate and intercept radiated waves containing information. I was trying to explore the benefits and consequences of preventing transmission line radiation as they relate to this more global purpose. While it is clear that maintaining balance in the line will prevent radiation from the line, some (maybe all) of the radiation prevented might have contributed to the global purpose of the station. For example, radiation from common-mode currents in a vertical transmission line could produce beneficial low-angle, omnidirectional radiation, as has been pointed out often on the group. It would seem that for the common-mode transmission line currents the antenna system would look like a top-loaded vertical, ignoring the balanced line currents and their interaction with the horizontal portion of the antenna. The efficiency of the vertically polarized radiation from the line would depend heavily on the station's RF ground system. But basically we would have (for the common-mode currents) a conventional vertical antenna with all its attendant plusses and minuses. To the extent the AC grounding conductor in the house presents a lower impedance than the station's RF grounding system, we would expect to see displacement currents in the AC system, just as with an "ordinary" vertical using a poor RF ground. Coupling to the telephone wires also would seem to be a consequence of a vertical radiator with a poor RF ground, rather than a consequence of transmission line imbalance (which I understand is the cause of the radiation in the first place). So here is my main question: do we object to the vertical radiation per se (i.e., if we wanted vertically polarized radiation, we would have put up a vertical in the first place), or is radiation from an unbalanced line somehow more insidious in that it causes other problems that "ordinary" verticals do not cause? In other words, why do we really care about imbalance? Reg has called attention to another of my shortcomings: I have no idea how the common-mode line currents that enter a link in the tuner are seen and "processed" by the tuner. It would seem that the link appears as one plate of a capacitor for those currents. Thanks again for everyone's patience. Chuck, NT3G Cecil Moore wrote: > chuck wrote: > >> If there are no obvious common mode currents causing problems in the >> shack, then of what consequence would an imbalance be, other than to >> modify the radiation pattern, perhaps even beneficially? > > > The purpose of the antenna is to radiate. The purpose > of the transmission line is to transfer the energy from > the transmitter to the antenna with as little loss as > feasible. How much an antenna system is allowed to > deviate from its purpose is up to the individual. When > I was in high school, I didn't much care about the purpose > of an antenna system and burned a hole in my lip. Article: 221931 of rec.radio.amateur.antenna From: chuck Subject: Re: Q about balanced feed line References: <4%LLf.13325$rL5.10680@newssvr27.news.prodigy.net> Message-ID: Date: Sun, 26 Feb 2006 17:09:02 GMT Please change my reference to a "link" in the tuner to the symmetrical taps on the inductor in the tuner. Sorry. I still have the same conceptual problem with common-mode currents entering that inductor. Chuck, NT3G Article: 221932 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: Q about balanced feed line References: <4%LLf.13325$rL5.10680@newssvr27.news.prodigy.net> Message-ID: Date: Sun, 26 Feb 2006 17:48:03 GMT chuck wrote: > So here is my main question: do we object to the vertical radiation per > se ...? Maybe an example would help. I model a dipole until I am happy with the results predicted by EZNEC. The take-off-angle is perfect for my schedule to AZ. EZNEC assumes no feedline radiation. I am sloppy about putting my dipole in the air and lots of feedline radiation results which goes off in directions not predicted by EZNEC. Murphey's Law predicts that the unknown directions will be bad (entropy never decreases). Besides, half of my feedline is routed horizontal under the eaves of my house. So would you rather deal with the devil you know or trust the angel that you don't know? Does the angel that you are trusting really understand entropy? -- 73, Cecil http://www.qsl.net/w5dxp Article: 221933 of rec.radio.amateur.antenna From: "Old Ed" References: <4%LLf.13325$rL5.10680@newssvr27.news.prodigy.net> Subject: Re: Alternatives... Message-ID: Date: Sun, 26 Feb 2006 19:17:42 GMT Bottom posted... "Cecil Moore" wrote in message news:nRlMf.16689$2O6.11340@newssvr12.news.prodigy.com... > chuck wrote: > > So here is my main question: do we object to the vertical radiation per > > se ...? > > Maybe an example would help. I model a dipole until > I am happy with the results predicted by EZNEC. The > take-off-angle is perfect for my schedule to AZ. > EZNEC assumes no feedline radiation. I am sloppy > about putting my dipole in the air and lots of feedline > radiation results which goes off in directions not > predicted by EZNEC. Murphey's Law predicts that the > unknown directions will be bad (entropy never > decreases). Besides, half of my feedline is routed > horizontal under the eaves of my house. > > So would you rather deal with the devil you know or > trust the angel that you don't know? Does the angel > that you are trusting really understand entropy? > -- > 73, Cecil http://www.qsl.net/w5dxp That's a fair question; but here are a few more: If you have X amount of time available to fuss around trying to minimize feedline radiation, might you rather spend that time: 1. Having more or longer QSOs with your AZ friend? 2. Working a little DX? 3. Improving your audio? 4. Watching a movie? 5. Making whoopie with the XYL? 6. Any number of other possibilities? Disclaimer: Nothing should be inferred from the (more-or-less random) order of the above list. ;-) 73, Ed Article: 221934 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: Alternatives... References: <4%LLf.13325$rL5.10680@newssvr27.news.prodigy.net> Message-ID: Date: Sun, 26 Feb 2006 21:24:00 GMT Old Ed wrote: > That's a fair question; but here are a few more: > > If you have X amount of time available to fuss around trying to > minimize feedline radiation, might you rather spend that time: If one follows good engineering practice, it becomes second nature after awhile and consumes only a negligible amount of time which is usually more than worth it. If it takes someone more time to learn about feedline radiation than they are willing to spend, well then what-the-hell, ignorance is bliss. > 1. Having more or longer QSOs with your AZ friend? We run out of things to talk about as it is. > 2. Working a little DX? Most of them don't speak Texan. > 3. Improving your audio? I'm already famous for my audio. I do a mean Johnny Cash. I'm also not bad at Elvis. I'm lead bass in the church choir. They call me the "largemouth bass". > 4. Watching a movie? The last movies that I really enjoyed were "Patton" and "Alien". Most movies put me to sleep (which is not a bad thing). If you enjoy homosexual sheephearders - well, it takes all kinds. > 5. Making whoopie with the XYL? Divorced in 1984 - I wish it had been sooner. > 6. Any number of other possibilities? I do have a part time teaching job and I like riding my Harley. I also just spent about three hours getting my birdhouse ready for the Purple Martins that are returning from Brazil to nest in East Texas. The fact that I am posting to this newsgroup at this time means that I don't have anything interesting or productive to do. :-) -- 73, Cecil http://www.qsl.net/w5dxp Article: 221935 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Q about balanced feed line Date: Sun, 26 Feb 2006 19:43:20 -0800 Message-ID: <1204taq72kips40@corp.supernews.com> References: <4%LLf.13325$rL5.10680@newssvr27.news.prodigy.net> chuck wrote: > . . . > So here is my main question: do we object to the vertical radiation per > se (i.e., if we wanted vertically polarized radiation, we would have put > up a vertical in the first place), or is radiation from an unbalanced > line somehow more insidious in that it causes other problems that > "ordinary" verticals do not cause? In other words, why do we really care > about imbalance? >. . . Would you intentionally load up your house wiring an use it as an antenna? Roy Lewallen, W7EL Article: 221936 of rec.radio.amateur.antenna From: W2RAC Subject: Re: HAM II Rotor Template ? Message-ID: References: <_V5Mf.3682$S25.3399@newsread1.news.atl.earthlink.net> Date: Mon, 27 Feb 2006 04:46:41 GMT try this address bama.sbc.edu/downloads/cde There is a copy of the owners manual. If you cant get to it I email me and I will zip it to you. On Sat, 25 Feb 2006 23:40:42 GMT, "DOUGLAS SNOWDEN" wrote: >Anyone have a template for drilling for a Ham II rotor? >Probably the same as the Ham IV rotor. > >Doug N4IJ > Article: 221937 of rec.radio.amateur.antenna From: "Frank" References: Subject: Re: antenna impedance - calculated 10 - 20 Ohms - measured 36 Ohms?? Message-ID: <8ywMf.8215$vC4.4087@clgrps12> Date: Mon, 27 Feb 2006 05:58:28 GMT "dansawyeror" wrote in message news:WJ-dnc6gp48L7Z_Z4p2dnA@comcast.com... > All, > > This is an attempt to add loaded radials to a loaded vertical. The plan is > to make a large efficient loading coil for the radials and offset the > variable coil in a 'screwdriver' vertical segment. > > The antenna is about 4 meters overall with about an load at about 1.5 > meters from the base. The antenna is raised about a meter. > > The loaded radials are two 1 inch copper tubes about 1.67 meters long. The > radial loading coil is connected from the coax shield to the radial coil. > > The feed is 50 Ohm coax, the shield is connected to the loading coil and > the center to the base. > > 4nec2 predicts an impedance of between 10 and 20 ohms depending of the > assumed values of R in the impedance loads. The actual antenna measures 36 > Ohms at the feed. > > The question is: What is the basis of the difference between predicted and > measured values? > > Below is a representation of the nec code used to simulate the antenna. > > Thanks - Dan > > CM 75 m Vertical 12 ft high > CM base 3 ft up - two radials > CM copper conductivity > CE > GW 1 11 0 0 1 0 0 5 > 0.025 > GW 2 7 0 0 1 0 1.67 1 > 0.025 > GW 3 7 0 0 1 0 -1.67 1 > 0.025 > GE 0 > LD 4 1 1 1 5 1500 > LD 4 1 6 6 8 600 > EX 0 1 2 0 1 0 > GN 2 0 0 0 13 5.e-3 > FR 0 1 0 0 3.74 0 > EN Interesting Dan, I get the same results as you, using your code. At 3.74 MHz the input z is 16.8 +j133. The antenna is resonant at about 3.55 MHz. With your average ground the gain is about -9 dBi. The only question I have is how certain are you of the accuracy of your test equipment? Did you use a 1:1 balun at the feed point? You may be getting a large current on the outside of the coax. Frank Article: 221938 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: antenna impedance - calculated 10 - 20 Ohms - measured 36 Ohms?? Date: Sun, 26 Feb 2006 22:58:27 -0800 Message-ID: <12058okq4o35l22@corp.supernews.com> References: dansawyeror wrote: > . . . > The question is: What is the basis of the difference between predicted > and measured values? 1. Have you decoupled your feedline? If you're not using a feedline, have you decoupled your measurement device? 2. Have you substituted a lumped impedance of about 16 + j133 ohms for the antenna and observed what your measurement equipment indicates? Roy Lewallen, W7EL Article: 221939 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: antenna impedance - calculated 10 - 20 Ohms - measured 36 Ohms?? References: Message-ID: <80CMf.35606$Jd.5433@newssvr25.news.prodigy.net> Date: Mon, 27 Feb 2006 12:11:48 GMT dansawyeror wrote: > 4nec2 predicts an impedance of between 10 and 20 ohms depending of the > assumed values of R in the impedance loads. The actual antenna measures > 36 Ohms at the feed. > > The question is: What is the basis of the difference between predicted > and measured values? Does 4nec2 include the ground losses in the feedpoint impedance? -- 73, Cecil http://www.qsl.net/w5dxp Article: 221940 of rec.radio.amateur.antenna From: Eskay Subject: Ladder line supports. Message-ID: <7ekv2ysr2oel.1tn134dbykemn.dlg@40tude.net> Date: Mon, 27 Feb 2006 13:58:43 GMT In another newsgroup mention is made of a handy ladderline support. Would like to know where these items were originally made for? Farm electric fencing? http://www.dxengineering.com/images/examples/LL_Insulator_Install.jpg Thanks,,,Eskay. Article: 221941 of rec.radio.amateur.antenna From: chuck Subject: Re: Q about balanced feed line References: <4%LLf.13325$rL5.10680@newssvr27.news.prodigy.net> <1204taq72kips40@corp.supernews.com> Message-ID: Date: Mon, 27 Feb 2006 14:29:47 GMT Of course not, Roy. I sure hope what I wrote did not suggest otherwise. But I am trying to learn exactly which properties of an antenna system cause house wiring to be "loaded up." In particular, I am trying to establish whether a top-loaded vertical with the same wire geometry and RF ground as the open-wire transmission line-fed dipole would be just as likely to cause undesirable coupling to the house wiring. It seems to me that it is. If it is not, I'm trying to understand why not. In other words, is the problem transmission line unbalance, or simply having a radiator with undesirable proximity to house wiring? One more way to word the question: if you tie the open-wire lines together at the tuner/transmitter and feed the antenna as a vertical, all of the current in the line will be common-mode. Would that be less likely to cause undesirable coupling than the exact same antenna with transmission line unbalance. I am not advocating unbalanced transmission lines, verticals, or the pursuit of radiation patterns one knows in advance to be undesirable. I apologize for my prolix and obtuse approach, but I'm not sure how to pose the question properly. I'll try to work on that. Thanks again. Chuck Roy Lewallen wrote: > chuck wrote: > >> . . . >> So here is my main question: do we object to the vertical radiation >> per se (i.e., if we wanted vertically polarized radiation, we would >> have put up a vertical in the first place), or is radiation from an >> unbalanced line somehow more insidious in that it causes other >> problems that "ordinary" verticals do not cause? In other words, why >> do we really care about imbalance? > > >. . . > > Would you intentionally load up your house wiring an use it as an antenna? > > Roy Lewallen, W7EL Article: 221942 of rec.radio.amateur.antenna From: chuck Subject: Re: Q about balanced feed line References: Message-ID: Date: Mon, 27 Feb 2006 14:39:49 GMT As a follow-up, is there a practical way to determine how much current unbalance will cause a one dB reduction in power delivered to the antenna, the "lost power" being that power radiated by the transmission line? It seems like a rather complex modeling problem. Thanks! Chuck, NT3G ig Endian wrote: > How does one check the balance between two parallel feed wires into a > doublet antenna. Neon bulbs or some sort of meter gizmo? > > tnx > > d Article: 221943 of rec.radio.amateur.antenna From: "Frank's" References: <12058okq4o35l22@corp.supernews.com> <44031031.9050905@comcast.net> Subject: Re: antenna impedance - calculated 10 - 20 Ohms - measured 36 Ohms?? Message-ID: <8eFMf.6418$dg.3208@clgrps13> Date: Mon, 27 Feb 2006 15:51:32 GMT "dansawyeror" wrote in message news:44031031.9050905@comcast.net... > Roy, > > No I have not decoupled the feed from the antenna. I will try that > tonight. I have wound a 2:1 balun for testing. (anticipating at least a 25 > ohm input impedance) > > I have measured the antenna with two different instruments. One is an > Autek analyzer at the antenna, the second is with an 8405a at the end of > 100+ feed of cable. They both show the same results. > > Thanks - Dan Dan, I notice the Autek analyzer only measures the magnitude of the impedance. With any of these lower cost instruments it is impossible to find any accuracy specifications. The 8405A is an excellent instrument, but assume you calibrated it -- short/open/load -- at the end of the 100 ft cable. This calibration should also be carried out on the antenna side of your isolation transformer when you install it. Curious as to what kind of directional coupler you are using for HF. I remember using a small HP coupler for HF, but cannot remember its model number. Frank Article: 221944 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: antenna impedance - calculated 10 - 20 Ohms - measured 36 Ohms?? Date: Mon, 27 Feb 2006 10:44:07 -0800 Message-ID: <1206i3qqmrurb42@corp.supernews.com> References: <12058okq4o35l22@corp.supernews.com> <44031031.9050905@comcast.net> The first thing I'd try, then, would be to put a 1:1 balun (common mode choke) at the feedpoint and, when using feedline, a second one about a quarter wave down the line. The balun can be constructed by winding the coax (if you're using RG-58 or smaller) 8 - 10 turns on a type 43 ferrite core. Or you can clamp or thread a few large cores over the coax. You can use the Autek to measure the core impedance -- shoot for 500 - 1000 ohms total -- the angle of the impedance isn't important. Unlike the 2:1 balun, this won't disturb your basic measurement in any way, it'll just reduce any common mode current. If you still get the same result, then there are only two other possible causes I can think of. One is the modeling of the inductors. I've found that a lumped model of an inductor isn't good if there's any appreciable current change in the real inductor from one end to the other due to its physical length. The solution is to model the inductor as a helix. You'll have to add some extra R to the model, however, if the turns are spaced closer than a couple of wire diameters, since the program doesn't account for proximity effect. The other possible cause is that there's some source of loss you're not accounting for in your model. The inductors and coupling to nearby lossy objects are the most obvious candidates. Roy Lewallen, W7EL dansawyeror wrote: > Roy, > > No I have not decoupled the feed from the antenna. I will try that > tonight. I have wound a 2:1 balun for testing. (anticipating at least a > 25 ohm input impedance) > > I have measured the antenna with two different instruments. One is an > Autek analyzer at the antenna, the second is with an 8405a at the end of > 100+ feed of cable. They both show the same results. > > Thanks - Dan > > Roy Lewallen wrote: >> dansawyeror wrote: >> >>> . . . >>> The question is: What is the basis of the difference between >>> predicted and measured values? >> >> >> 1. Have you decoupled your feedline? If you're not using a feedline, >> have you decoupled your measurement device? >> >> 2. Have you substituted a lumped impedance of about 16 + j133 ohms for >> the antenna and observed what your measurement equipment indicates? >> >> Roy Lewallen, W7EL Article: 221945 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: antenna impedance - calculated 10 - 20 Ohms - measured 36 Ohms?? Date: Mon, 27 Feb 2006 10:47:59 -0800 Message-ID: <1206ib348gjnb4@corp.supernews.com> References: <12058okq4o35l22@corp.supernews.com> <44031031.9050905@comcast.net> <8eFMf.6418$dg.3208@clgrps13> Frank's wrote: > > Dan, I notice the Autek analyzer only measures the magnitude of the > impedance. With any of these lower cost instruments it is impossible to > find any accuracy specifications. The 8405A is an excellent instrument, but > assume you calibrated it -- short/open/load -- at the end of the 100 ft > cable. This calibration should also be carried out on the antenna side of > your isolation transformer when you install it. Curious as to what kind of > directional coupler you are using for HF. I remember using a small HP > coupler for HF, but cannot remember its model number. > > Frank Hm, if the Autek measures only the magnitude of the impedance, how does Dan know the resistance? The model shows about 133 ohms of reactance, which is much greater than the resistance. Roy Lewallen, W7EL Article: 221946 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Q about balanced feed line Date: Mon, 27 Feb 2006 11:04:04 -0800 Message-ID: <1206j98slafj4a@corp.supernews.com> References: <4%LLf.13325$rL5.10680@newssvr27.news.prodigy.net> <1204taq72kips40@corp.supernews.com> chuck wrote: > Of course not, Roy. I sure hope what I wrote did not suggest > otherwise. But I am trying to learn exactly which properties of an > antenna system cause house wiring to be "loaded up." > > In particular, I am trying to establish whether a top-loaded vertical > with the same wire geometry and RF ground as the open-wire > transmission line-fed dipole would be just as likely to cause > undesirable coupling to the house wiring. It seems to me that it is. > If it is not, I'm trying to understand why not. When you have common mode current, it not only flows on the feedline, but continues to ground via whatever path it can. And this is usually the house wiring. So your antenna now consists of the "antenna", the feedline, and the house wiring. The problem here is current in house wiring due to conduction, not coupling. If you properly feed a vertical, no RF current is conducted to the house wiring. Either a properly fed vertical or a radiating feedline can induce current in the house wiring by coupling, but the amount will depend on (among other things) proximity of the antenna or feedline to the house. Most of us can put a vertical at least a little distance from the house, but the feedline has to come right in. > In other words, is the problem transmission line unbalance, or simply > having a radiator with undesirable proximity to house wiring? Again, the problems are twofold. One is conducted current, and the other is coupled current due to proximity. > One more way to word the question: if you tie the open-wire lines > together at the tuner/transmitter and feed the antenna as a vertical, > all of the current in the line will be common-mode. Would that be > less likely to cause undesirable coupling than the exact same antenna > with transmission line unbalance. You would have exactly the same problems in either case, assuming a worst case of imbalance when feeding the antenna normally (which isn't likely). Whatever current leaves the rig via the connected-together feedline conductors (or via common mode current in a normally fed antenna), an equal amount of current has to leave the rig via its chassis or "ground" connection. In a properly fed vertical, this current ends up in the ground system at the base of the antenna. In the tied-together feed, it'll end up getting to ground however it can, radiating and inducing other currents along the way. > . . . Roy Lewallen, W7EL Article: 221947 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Q about balanced feed line Date: Mon, 27 Feb 2006 11:16:01 -0800 Message-ID: <1206jvk3rsclp55@corp.supernews.com> References: chuck wrote: > As a follow-up, is there a practical way to determine how much current > unbalance will cause a one dB reduction in power delivered to the > antenna, the "lost power" being that power radiated by the transmission > line? > > It seems like a rather complex modeling problem. > > Thanks! > > Chuck, NT3G Nope. You can't generally say that one part of an antenna is radiating a particular amount of the total power. Each part of the antenna creates a field, and it interacts with the fields from all other parts of the antenna. The total power radiated has to equal the total power input less loss, but that's all you can say for sure. An example will help illustrate the problem. Consider a parasitic element in a Yagi. It has considerable current and contributes a great deal to the overall pattern. Yet the total power input to the Yagi element is zero. With zero power input, it can't, by itself, be radiating any power. What it does is intercept some of the power radiated by the driven element and re-radiates it with a different phase and amplitude. So how would you apportion the power radiated by the driven element and the parasitic element? You might take a look at the current in the driven element and note that it increases or decreases as you put the parasitic element in place and remove it. But the current can either increase or decrease, depending on the length and spacing of the parasitic element. So has the parasitic element increased or decreased the power radiated by the driven element? There's no answer. You can look at the change in pattern in some idealized cases by modeling. This can tell you what range of effects you might expect in a real situation. Roy Lewallen, W7EL Article: 221948 of rec.radio.amateur.antenna From: Bob Miller Subject: Re: Ladder line supports. Message-ID: <7jk602tjuddh9g6683r151skaj4qs4oill@4ax.com> References: <7ekv2ysr2oel.1tn134dbykemn.dlg@40tude.net> Date: Mon, 27 Feb 2006 19:29:27 GMT On Mon, 27 Feb 2006 13:58:43 GMT, Eskay wrote: >In another newsgroup mention is made of a handy ladderline support. >Would like to know where these items were originally made for? >Farm electric fencing? >http://www.dxengineering.com/images/examples/LL_Insulator_Install.jpg >Thanks,,,Eskay. Dunno about the other group's idea... ...but cut a short section of plastic or rubber hose. Slit one side of it. Screw it to a support. Insert ladderline into the slit. bob k5qwg Article: 221949 of rec.radio.amateur.antenna From: Big Endian Subject: Re: Q about balanced feed line References: <4%LLf.13325$rL5.10680@newssvr27.news.prodigy.net> <1204taq72kips40@corp.supernews.com> <1206j98slafj4a@corp.supernews.com> Message-ID: Date: Mon, 27 Feb 2006 19:33:09 GMT In article <1206j98slafj4a@corp.supernews.com>, Roy Lewallen wrote: > chuck wrote: > > Of course not, Roy. I sure hope what I wrote did not suggest > > otherwise. But I am trying to learn exactly which properties of an > > antenna system cause house wiring to be "loaded up." > > > > In particular, I am trying to establish whether a top-loaded vertical > > with the same wire geometry and RF ground as the open-wire > > transmission line-fed dipole would be just as likely to cause > > undesirable coupling to the house wiring. It seems to me that it is. > > If it is not, I'm trying to understand why not. > > When you have common mode current, it not only flows on the feedline, > but continues to ground via whatever path it can. And this is usually > the house wiring. So your antenna now consists of the "antenna", the > feedline, and the house wiring. The problem here is current in house > wiring due to conduction, not coupling. > > If you properly feed a vertical, no RF current is conducted to the house > wiring. Either a properly fed vertical or a radiating feedline can > induce current in the house wiring by coupling, but the amount will > depend on (among other things) proximity of the antenna or feedline to > the house. Most of us can put a vertical at least a little distance from > the house, but the feedline has to come right in. > > > In other words, is the problem transmission line unbalance, or simply > > having a radiator with undesirable proximity to house wiring? > > Again, the problems are twofold. One is conducted current, and the other > is coupled current due to proximity. > > > One more way to word the question: if you tie the open-wire lines > > together at the tuner/transmitter and feed the antenna as a vertical, > > all of the current in the line will be common-mode. Would that be > > less likely to cause undesirable coupling than the exact same antenna > > with transmission line unbalance. > > You would have exactly the same problems in either case, assuming a > worst case of imbalance when feeding the antenna normally (which isn't > likely). Whatever current leaves the rig via the connected-together > feedline conductors (or via common mode current in a normally fed > antenna), an equal amount of current has to leave the rig via its > chassis or "ground" connection. In a properly fed vertical, this current > ends up in the ground system at the base of the antenna. In the > tied-together feed, it'll end up getting to ground however it can, > radiating and inducing other currents along the way. > > > . . . > > Roy Lewallen, W7EL Here is something strange I discovered this weekend. While using a F.S. meter as a RF sniffer, I was probing along some lamp cords that are plugged into one of those extention outlet strips. I have a split block ferrite core which measures one inch square and a 1/2 inch ID hole. So while monitoring the FS meter I placed the core on the 115 to the house outlet thinking that I will see a decrease in FS reading, much to my surprise just the opposite happened, the FS meter pegged out. Why would adding the core cause the FS reading to increase? Article: 221950 of rec.radio.amateur.antenna From: "David G. Nagel" Subject: Re: antenna impedance - calculated 10 - 20 Ohms - measured 36 Ohms?? Date: Mon, 27 Feb 2006 13:36:55 -0600 Message-ID: <1206l6vgcp658bd@corp.supernews.com> References: dansawyeror wrote: > All, > > This is an attempt to add loaded radials to a loaded vertical. The plan > is to make a large efficient loading coil for the radials and offset the > variable coil in a 'screwdriver' vertical segment. > > The antenna is about 4 meters overall with about an load at about 1.5 > meters from the base. The antenna is raised about a meter. > > The loaded radials are two 1 inch copper tubes about 1.67 meters long. > The radial loading coil is connected from the coax shield to the radial > coil. > > The feed is 50 Ohm coax, the shield is connected to the loading coil and > the center to the base. > > 4nec2 predicts an impedance of between 10 and 20 ohms depending of the > assumed values of R in the impedance loads. The actual antenna measures > 36 Ohms at the feed. > > The question is: What is the basis of the difference between predicted > and measured values? > > Below is a representation of the nec code used to simulate the antenna. > > Thanks - Dan > > CM 75 m Vertical 12 ft high > CM base 3 ft up - two radials > CM copper conductivity > CE > GW 1 11 0 0 1 0 0 5 > 0.025 > GW 2 7 0 0 1 0 1.67 1 > 0.025 > GW 3 7 0 0 1 0 -1.67 1 > 0.025 > GE 0 > LD 4 1 1 1 5 1500 > LD 4 1 6 6 8 600 > EX 0 1 2 0 1 0 > GN 2 0 0 0 13 5.e-3 > FR 0 1 0 0 3.74 0 > EN > > Dan; I can't answer you question except to note that this is why they call antenna design an ART not a SCIENCE. Other comm enters have good suggestions. Let us know what happens. Dave WD9BDZ Article: 221951 of rec.radio.amateur.antenna From: dplatt@radagast.org (Dave Platt) Subject: Re: Ladder line supports. Date: Mon, 27 Feb 2006 20:25:22 -0000 Message-ID: <1206o1iiurrsv40@corp.supernews.com> References: <7ekv2ysr2oel.1tn134dbykemn.dlg@40tude.net> In article <7ekv2ysr2oel.1tn134dbykemn.dlg@40tude.net>, Eskay wrote: >In another newsgroup mention is made of a handy ladderline support. >Would like to know where these items were originally made for? >Farm electric fencing? >http://www.dxengineering.com/images/examples/LL_Insulator_Install.jpg That could well be, although I can't match this photo to a specific electric-fence insulator brand. It resembles some of the "pinlock" insulators which can be used to hold wire, polywire, and polyrope (the latter two being wire- or rope-thick strands of a woven plastic, with very-fine-gauge copper wire woven in among it to provide the current carrying capability). http://electric-deer-fence.com/electricdeerfences/electricfenceinsulators/woodposts.htm shows one such, about halfway down the page. Another possibility for retaining ladder line would be the insulators made for "polytape" (sort of like polyrope, but formed into a flat woven tape anywhere from .5" to 2" wide). Polytape clips seem to be designed to "clamp down" on the tape, to keep it from sliding back and forth and cutting the insulator (or the tape itself), and this clamping arrangement might or might not be compatible with any given variety of ladder line... the line's conductors might turn out to be too thick for some types of insulator clip. The electric-fence insulators seem to be be modestly priced - anywhere form $6 to $8 per bag of 25 - and so experimentation might be worthwhile. Another variant I see at several vendors' sites is the "Isoline New Generation Line Insulator" (seems to have a manufacturer part number of 653.002). It's a single-piece nail-on insulator for wire or polyrope. Looks as if it'd take a ladder line turned sideways and hold it quite securely. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! Article: 221952 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Q about balanced feed line Date: Mon, 27 Feb 2006 12:39:37 -0800 Message-ID: <1206oscg5noap5f@corp.supernews.com> References: <4%LLf.13325$rL5.10680@newssvr27.news.prodigy.net> <1204taq72kips40@corp.supernews.com> <1206j98slafj4a@corp.supernews.com> Big Endian wrote: > > Here is something strange I discovered this weekend. While using a F.S. > meter as a RF sniffer, I was probing along some lamp cords that are > plugged into one of those extention outlet strips. I have a split block > ferrite core which measures one inch square and a 1/2 inch ID hole. So > while monitoring the FS meter I placed the core on the 115 to the house > outlet thinking that I will see a decrease in FS reading, much to my > surprise just the opposite happened, the FS meter pegged out. Why would > adding the core cause the FS reading to increase? There are at least three possible explanations. The first is one I've come across many times in doing EMI work, and is probably the most likely. What happens is that you've got two or more radiating sources whose fields cancel or partially cancel at the field strength meter. When you reduce the radiation from one of those sources, the field at the meter increases. The second can be a bit subtle. Suppose you have a wire near an antenna and that wire is, say, 3/4 wavelength long. Very little current will be induced in this wire because it's far from self-resonance. Now put a choke in the wire 1/4 wavelength from one end. Presto, a lot of induced current in the now-isolated 1/2 wavelength portion. This phenomenon can cause common mode current to increase when you add a common mode choke on the feedline, if the current is being induced in the feedline (as opposed to conducted) and the wire length and choke position are favorable for this to happen. The third is that the core you're using is a high frequency ferrite. If it is, it will act as a loading coil, which could make a previously non-resonant system resonant. I don't think this is likely, though, because most clamp-on cores are made from ferrites suitable for EMI suppression. A common type of material for this purpose is type 43 ferrite, which has a Q of 1 at a few MHz. So this type of ferrite won't cause resonant effects like a high frequency ferrite (e.g., type 61) would. Roy Lewallen, W7EL Article: 221953 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: antenna impedance - calculated 10 - 20 Ohms - measured 36 Ohms?? References: <12058okq4o35l22@corp.supernews.com> <44031031.9050905@comcast.net> Message-ID: Date: Mon, 27 Feb 2006 23:47:00 GMT dansawyeror wrote: > I have measured the antenna with two different instruments. One is an > Autek analyzer at the antenna, the second is with an 8405a at the end of > 100+ feed of cable. They both show the same results. Are you aware that a coax cable will change the impedance >from the antenna feedpoint impedance in a spiral to 50 ohms in the limit? -- 73, Cecil http://www.qsl.net/w5dxp Article: 221954 of rec.radio.amateur.antenna From: "Frank" References: <12058okq4o35l22@corp.supernews.com> <44031031.9050905@comcast.net> <8eFMf.6418$dg.3208@clgrps13> <4403C93F.2040700@comcast.net> Subject: Re: antenna impedance - calculated 10 - 20 Ohms - measured 36 Ohms?? Message-ID: Date: Tue, 28 Feb 2006 04:34:54 GMT "dansawyeror" wrote in message news:4403C93F.2040700@comcast.net... > Frank, > > The Autek is remarkably close. I have used it to checkout 50 and 25 Ohm > loads. For these two values it is very close. (It is battery level > sensitive.) > > The couplers are a pair of M-C ZFDC 20-4's. > > Dan Thanks Dan, I had forgotten about Mini-Circuits. Their price is hard to beat. I may pick up one of the "PDC" series dual directional couplers. Incidentally your code indicates resonance occurs at 3.54 MHz. I wonder how the Autek behaves when subjected to a reactive load does it actually get close to the magnitude? Frank Article: 221955 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: antenna impedance - calculated 10 - 20 Ohms - measured 36 Ohms?? Date: Mon, 27 Feb 2006 21:44:55 -0800 Message-ID: <1207oqqsdjk4eab@corp.supernews.com> References: <12058okq4o35l22@corp.supernews.com> <44031031.9050905@comcast.net> <8eFMf.6418$dg.3208@clgrps13> <1206ib348gjnb4@corp.supernews.com> <4403BF4F.80702@comcast.net> dansawyeror wrote: > Roy, > > Several weeks back, and confirmed by frequency sweep model runs, you > indicated that minimum impedance is close or equal to the resonance > point. I tuned the antenna to the frequency of interest and then used > the Autek to verify the resonance point. That minimum value was 36 Ohms. > I am assuming this is or is very close to the resonance point for the > antenna system. Yes, that should be correct. > What does your running of the model show for resonance frequency? At > resonance my running of the model shows close to 20 Ohms for the > relatively large values of R used in the model. NEC-2 shows resonance (and minimum SWR) at 3.55 MHz, where R = 16.12 ohms; NEC-4 says resonance is at 3.51 MHz., where R is 16.08 ohms. (I'm using EZNEC implementations of both.) Although small, I don't usually see that much difference between NEC-2 and NEC-4. I suspect it's because of the very low height above ground -- the two programs implement the Sommerfeld ground somewhat differently. An average gain test shows good average gain, indicating that NEC isn't having numerical difficulties. I'm getting pretty convinced that the problem is the use of lumped loads for the inductors. With this short an antenna, I'd expect the inductor currents to be quite different at the ends(*), making the lumped load models inadequate. This can lead to pretty severe errors. (*) due to inductor radiation and unsymmetrical coupling of the inductor to the rest of the antenna and to ground. Roy Lewallen, W7EL Article: 221956 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: antenna impedance - calculated 10 - 20 Ohms - measured 36 Ohms?? Date: Tue, 28 Feb 2006 00:31:33 -0800 Message-ID: <12082j8tknvfi05@corp.supernews.com> References: <12058okq4o35l22@corp.supernews.com> <44031031.9050905@comcast.net> <8eFMf.6418$dg.3208@clgrps13> <1206ib348gjnb4@corp.supernews.com> <4403BF4F.80702@comcast.net> <1207oqqsdjk4eab@corp.supernews.com> <4403EA1D.4090802@comcast.net> dansawyeror wrote: > Thanks - I will try to figure you how to create a non lumped model for > the inductors. Right now that is 'undiscovered country'. EZNEC v. 4.0 users should use Wires Window/Create/Create Helix. You'll get many choices, including position, orientation, various ways of specifying the pitch and number of turns, twist direction, and so forth. (EZNEC demo users can create any size helix to see how it works, but won't be able to run a calculation unless the helix is extremely simple.) In NEC, use a GH 'card'. There should be at least a wire diameter of air space between turns, preferably several. (That is, the center-center distance between the wires in one turn and the wires in adjacent turns should be at least two wire diameters, preferably more.) If air spacing is less than 2 or 3 wire diameters, the calculated loss will be somewhat lower than reality because NEC (or EZNEC) doesn't account for proximity effect. Roy Lewallen, W7EL Article: 221957 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Q about balanced feed line Date: Tue, 28 Feb 2006 04:00:37 -0800 Message-ID: <1208er7msvro839@corp.supernews.com> References: <4%LLf.13325$rL5.10680@newssvr27.news.prodigy.net> <1204taq72kips40@corp.supernews.com> <1206j98slafj4a@corp.supernews.com> <1206oscg5noap5f@corp.supernews.com> Big Endian wrote: > > I suppose the right thing to do is to place ferrite cores on all the > conductors in the area. Could get expensive. I have so many wires all > over the place the job seems a bit hopeless. >. . . Well, that's one way to solve the problem. Like the sign over my desk says, "Anyone can design a bridge that will stand up. It takes an engineer to design a bridge that will barely stand up." Roy Lewallen, W7EL Article: 221958 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: antenna impedance - calculated 10 - 20 Ohms - measured 36 Ohms?? References: <12058okq4o35l22@corp.supernews.com> <44031031.9050905@comcast.net> <8eFMf.6418$dg.3208@clgrps13> <1206ib348gjnb4@corp.supernews.com> <4403BF4F.80702@comcast.net> <1207oqqsdjk4eab@corp.supernews.com> Message-ID: Date: Tue, 28 Feb 2006 13:49:42 GMT Roy Lewallen wrote: > I'm getting pretty convinced that the problem is the use of lumped loads > for the inductors. With this short an antenna, I'd expect the inductor > currents to be quite different at the ends(*), making the lumped load > models inadequate. This can lead to pretty severe errors. > > (*) due to inductor radiation and unsymmetrical coupling of the inductor > to the rest of the antenna and to ground. Over on qrz.com, W8JI reported that he measured a 60 degree phase shift through a 100 uH coil at 1 MHz. He also asserted that the flux density is highest in the middle of a coil. Since the current is proportional to flux density, that means the current in the middle of the coil is higher than at the ends. These things are perfectly consistent with what EZNEC reports when the distributed network helical coil inductor is used instead of the lumped circuit load inductor. Essentially the only time the currents at each end of the coil are equal is when it is installed near a standing-wave current maximum point where the slope of the current is already close to zero whether it be in a wire or in a coil. The phase of the standing- wave current is relatively constant whether it be in a wire or in a coil. (The standing-wave current doesn't rotate like a normal phasor.) The phase shift caused by the coil happens in the forward and reflected currents, not in the standing wave current which is the sum of the forward current and reflected current. Not much changes when part of a wavelength of wire is replaced by a large loading coil. The current waveform, though warped somewhat by the high fields inside the coil, still very roughly follows the classic cosine shape of a wire. After all, no matter what, the current at the tip of an antenna is zero whether it be a wire or a coil. If a coil is placed at a standing-wave current node, the phase at each end of the coil will be opposite, i.e. current is either flowing in both ends at the same time or out both ends at the same time. Such is the nature of distributed networks. -- 73, Cecil http://www.qsl.net/w5dxp Article: 221959 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: antenna impedance - calculated 10 - 20 Ohms - measured 36 Ohms?? References: <12058okq4o35l22@corp.supernews.com> <44031031.9050905@comcast.net> <8eFMf.6418$dg.3208@clgrps13> <1206ib348gjnb4@corp.supernews.com> <4403BF4F.80702@comcast.net> <1207oqqsdjk4eab@corp.supernews.com> <4403EA1D.4090802@comcast.net> <12082j8tknvfi05@corp.supernews.com> Message-ID: Date: Tue, 28 Feb 2006 13:51:53 GMT Roy Lewallen wrote: > EZNEC v. 4.0 users should use Wires Window/Create/Create Helix. And the detailed results are quite different from the lumped circuit load inductor. -- 73, Cecil http://www.qsl.net/w5dxp Article: 221960 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Q about balanced feed line Date: Tue, 28 Feb 2006 12:06:33 -0800 Message-ID: <1209back4d2on5a@corp.supernews.com> References: <1204taq72kips40@corp.supernews.com> <1206j98slafj4a@corp.supernews.com> <1206oscg5noap5f@corp.supernews.com> <1208er7msvro839@corp.supernews.com> <4ms802ppu9r432gkopvfdlkltdkfigtaiu@4ax.com> Wes Stewart wrote: > On Tue, 28 Feb 2006 04:00:37 -0800, Roy Lewallen > wrote: > >> Big Endian wrote: >>> I suppose the right thing to do is to place ferrite cores on all the >>> conductors in the area. Could get expensive. I have so many wires all >>> over the place the job seems a bit hopeless. >>> . . . >> Well, that's one way to solve the problem. Like the sign over my desk >> says, "Anyone can design a bridge that will stand up. It takes an >> engineer to design a bridge that will barely stand up." > > Or not [g] > > http://www.ketchum.org/bridgecollapse.html Ah, yes, the Tacoma Narrows bridge. That movie played continuously in the lobby of the Engineering Building at the U. of Colorado most of the time I was going there. For anyone interested in this topic, I recommend _To Engineer is Human: The Role of Failure in Successful Design_ by Henry Petroski. The whole trick, of course, is to stay on the right side of "barely". Roy Lewallen, W7EL Article: 221961 of rec.radio.amateur.antenna From: Bob Bob Subject: About dipoles and current/voltage nodes Message-ID: Date: Tue, 28 Feb 2006 14:25:32 -0600 Yes I should know this.. However an issue has come up in my place of work I am trying to get my head around. On a 10GHz microwave TX there is a stripline parallel to the output track that is suppose to detect forward power. Nothing strange about that. What is weird is that it appears to be roughly a half wave length (or more). The question is this. If one hangs a 1/2 wave dipole in free space I assume it receives such that current maximums are at the centre and voltage maxiums at the ends. Is this the case whether a feedline is connected or not? If I then take a stripline cct terminated at one end with a 50r resistor and a detect diode at the other and is a half wave long, what is the current/voltage distribution in this configuration. What I wonder is if it is a halfwave there may be no voltage at the detect diode input. (It could be 3/4 wavelength when one factors in pcb dielectric and end loading) Thoughts? Cheers Bob VK2YQA Article: 221962 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: Q about balanced feed line References: <1204taq72kips40@corp.supernews.com> <1206j98slafj4a@corp.supernews.com> <1206oscg5noap5f@corp.supernews.com> <1208er7msvro839@corp.supernews.com> <4ms802ppu9r432gkopvfdlkltdkfigtaiu@4ax.com> <1209back4d2on5a@corp.supernews.com> Message-ID: Date: Tue, 28 Feb 2006 21:10:58 GMT Roy Lewallen wrote: > The whole trick, of course, is to stay on the right side of "barely". Why not the left side? :-) -- 73, Cecil http://www.qsl.net/w5dxp Article: 221963 of rec.radio.amateur.antenna From: cmwlbh@shaw.ca Subject: Younger Sister Caught In BathTub With Hidden Cam... 4295 [1/2] Message-ID: Date: Tue, 28 Feb 2006 21:27:45 GMT Hi im trying to get into filming porn so i setup a hiddem camera in our bathroom and caught my younger sister (hot) playin with herself, get her pics here. Enjoy hehe rjnvhrpwsigncgqeemulifevsgmcvosxbipbqwbnchzfivrnrbpmqqlzegsizqxupyuzxryvpbsgpsdvprkwiiiqkxhzcdextc Article: 221964 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: About dipoles and current/voltage nodes References: Message-ID: Date: Tue, 28 Feb 2006 21:34:09 GMT Bob Bob wrote: > If I then take a stripline cct terminated at one end with a 50r resistor > and a detect diode at the other and is a half wave long, what is the > current/voltage distribution in this configuration. Since the ends of the 1/2WL conductor are open circuits, standing waves on the conductor are the result. The standing wave(s) consists of the superposition of the forward wave(s) and the reflected wave(s). This is exactly why the forward and reflected waves cannot be ignored (as some gurus advise) if understanding is the goal. For a 1/2WL conductor, the standing wave has a cosine envelope with a phase near zero all along the line because the forward and reflected phasors are rotating in opposite directions. The current is obviously zero at the ends and maximum in the center. The resistor termination at one end dissipates either the forward wave or reflected wave depending upon which end it is located. The dipole at the other end rectifies the other wave. If you are measuring the forward power, the forward wave is rectified by the diode and the reflected wave is dissipated/attenuated by the resistor. I have an old Heathkit SWR meter that operates the same way. There's two pickup conductors, one for forward power and one for reflected power. In short, the resistor dissipates one of the component traveling waves thus preventing reflections while the diode rectifies the other traveling wave, thus providing a voltage proportional to that other traveling wave. Which wave is dissipated and which wave is rectified depends upon which end of the conductor the resistor and diode are located. -- 73, Cecil http://www.qsl.net/w5dxp Article: 221965 of rec.radio.amateur.antenna From: "F5AD" References: Subject: Re: About dipoles and current/voltage nodes Date: Tue, 28 Feb 2006 22:35:02 +0100 Message-ID: <4404c2d0$0$8250$636a55ce@news.free.fr> With 50 Ohms at the end, I suppose the line is producing progressive waves and not standing waves, and no matter its length 73 André F5AD http://f5ad.free.fr Article: 221966 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: About dipoles and current/voltage nodes References: <1141162560.167190.40830@i40g2000cwc.googlegroups.com> Message-ID: Date: Tue, 28 Feb 2006 21:45:26 GMT K7ITM wrote: > Clearly in a center-fed half-wave dipole, if there is no load at the > center, the current there is quite low, and depends on the capacitance > from wire end to wire end. If you short across the feedpoint, it will > be resonant and the center will be a current node. Maybe you would like to rethink that, Tom. Consider a parasitic 1/2WL element on a Yagi. The currents at the ends are obviously zero. The current 1/4WL away from the zero points are the maximum current points. If you short across the feedpoint of a 1/2WL dipole, it will be resonant but the center will be a current loop (antinode), i.e. a maximum current point. The center of a *one wavelength* dipole will be a current node. -- 73, Cecil http://www.qsl.net/w5dxp Article: 221967 of rec.radio.amateur.antenna From: "Ron H" References: Subject: Re: Younger Sister Caught In BathTub With Hidden Cam... 4295 [1/2] Message-ID: Date: Tue, 28 Feb 2006 16:11:45 -0600 I certainly hope everyone in this list is smart enough to NEVER open a file with the .scr extension! Carry On! K3PID Ron H. Article: 221968 of rec.radio.amateur.antenna From: bytyhe@shaw.ca Subject: TEEN SISTER WITH DILDO XXX 7396 [1/2] Message-ID: Date: Tue, 28 Feb 2006 22:20:07 GMT See hiden cam pics of my teen sister (hot) in her bedroom playing with her dildo, see what you think ! i know im sick but hey shes hot ! ixegdwntxrxtwjkzimrkprdcyuqewvjmosbuvsdwxmsjxlejgyoqigqzrebrhonkvrsiwvbhjjsqivjtfpilohwziygy Article: 221969 of rec.radio.amateur.antenna From: Al Klein Subject: Re: Question regarding MFJ-1714 antenna Message-ID: References: <1141163079.201800.133290@v46g2000cwv.googlegroups.com> Date: Tue, 28 Feb 2006 20:38:48 -0500 On 28 Feb 2006 13:44:39 -0800, junjunius@yahoo.com wrote: >I hope that someone might be able to answer a question for me: does >the MFJ-1714 have any coil in it which would serve to attenuate >frequencies below the 2m amateur band for which it's apparently >designed? The 2 meter band is 144-148, not 440. The coil is a loading coil - it manes the antenna electrically longer, it doesn't cut off any frequencies. >Or would this antenna serve well for frequencies below 440 MHz on a >handheld scanner? It's a bit long (cumbersome), but it should work.