Article: 220661 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: Standing Waves (and Impedance) References: <1135102751.103538.224970@g47g2000cwa.googlegroups.com> <5Uoqf.43886$6e1.2147@newssvr14.news.prodigy.com> <43ab7ab2@kcnews01> Message-ID: Date: Sun, 25 Dec 2005 22:31:09 GMT Crazy George wrote: > Those antennas aren't flat, and > there are 2 transmitters, visual and aural. The audio is not mixed with the main carrier? -- 73, Cecil http://www.qsl.net/w5dxp Article: 220662 of rec.radio.amateur.antenna From: dplatt@radagast.org (Dave Platt) Subject: Re: Shorting out a transmission line Date: Sun, 25 Dec 2005 23:06:32 -0000 Message-ID: <11qu9fossjcp3a7@corp.supernews.com> References: <11qu3cv7eu6t505@corp.supernews.com> >If I can find a scrap BNC male connector, and make a shorting-plug out >of it, I'll run the coax-and-T experiment I suggested, and post some >actual numbers for the systems's behavior at those frequencies I can >coerce out of my MFJ-269. OK, I ran the test, and the results are pretty much as I had anticipated. Although the test arrangement and gear isn't lab-standard, I think it's good enough to confirm the basic principles. Test equipment: MFJ-259 antenna analyzer, with an N-to-BNC adapter. Transmission line and load: 12' length of RG-58 coax, with a 50-ohm Ethernet terminator attached to the end. Shorting insertion: an additional 6' length of RG-58, with a couple of BNC "T" adapters, which can be inserted between the analyzer and the T-line-and-load. If the shorting plug is inserted it'll be 6' from the analyzer and 12' from the load. Short circuit: a male BNC plug, with a short inserted between center pin and shell as far down inside the shell as possible. First test: check quality of T-line and load, using only the 12' section of RG-58 between analyzer and load. Note that the Imag(load) numbers do not indicate the sign of the reactance... the MFJ won't do that, alas. Frequency Real(load) Imag(load) Indicated SWR 2.5 52 4 1.0 5 58 6 1.2 10 57 7 1.2 15 49 1 1.0 20 56 6 1.1 50 54 2 1.1 144 51 4 1.0 166 59 8 1.2 440 1.4 Impression: either the RG-58 or the Ethernet terminator isn't exactly 50 ohms (not unexpected) or the MFJ's calibration isn't perfect (likewise) but the figures are good enough to let us draw some reasonable conclusions. Second test: insert the 6' RG-58 and its T connectors between the analyzer and the 12' section. See how much this additional length of line, and the parasitics of the T connectors, affect the load and SWR. Frequency Real(load) Imag(load) Indicated SWR 2.5 54 4 1.1 5 59 5 1.2 10 50 10 1.2 15 49 1 1.0 20 51 8 1.1 50 48 5 1.1 144 50 4 1.0 166 40 2 1.2 440 1.1 Impression: the measured values change a bit, but the SWRs are close or identical (save for the 440 measurement). The additional length of line, and the parasitics from the T connectors, are shifting things around a bit (especially at 440)... not unexpected. Third test: connect the shorting plug to one of the T connectors. See what "pinning the line" does to the analyzer's view of the load. Frequency Real(load) Imag(load) Indicated SWR 2.5 0 6 >31 5 0 12 >31 10 1 26 >31 15 1 43 >31 20 2 70 >31 50 0 44 28.7 144 7 33 15.4 166 166 353 13.0 440 >5 Impression: yeah, that looks like a short circuit, transformed via a feedline. Nothing close to a 50-ohm-resistive load shows up at any of the test frequencies. Fourth test: disconnect the 50-ohm load from the end of the 12' line, creating an abrupt change in the load impedance. See what this does to the figures from the third test - how much of the antenna load change gets back "around" the short? Frequency Real(load) Imag(load) Indicated SWR 2.5 0 6 >31 5 0 12 >31 10 1 25 >31 15 1 43 >31 20 2 70 >31 50 6 44 29.0 144 6 30 18.5 166 133 317 14.1 440 >5 Impression: changing the antenna load from 50-ohms-resistive to near-infinite made a slight change in the impedance seen by the analyzer, but not much at all at any frequency. The presence of the short circuit 6 feet from the analuzer is still dominating the load that the analyzer "sees". Special-distance test: with the short, and the 50-ohm load both in place, sweep the analyzer frequency around the ranges at which the analyzer-to-short distance is around 1/4 and 1/2 wavelength. See if we can "see past" the short under these conditions. Measurements: with the short circuit in place, and a 50-ohm load at the end of the 12' line, an impedance peak (Z>1500 ohms) is noted when sweeping between 32.14 MHz and 32.94 MHz. An impedance minimum (Real(load) of 2-3 ohms, Imag(load) of 0 ohms) is noted between 65.7 MHz and 65.85 MHz. The indicated SWR remains high (22 or above) at all frequencies between the impedance maximum and impedance minimum... there's no point at which the load resembles anything like "50 ohms resistive, little reactive component". Removing the 50-ohm load, and thus open-circuiting the antenna feedline, has no significant effect on the impedance as seen at the quarter-wavelength maximum, at the half-wavelength minimum, or at points in between. Impression: we cannot "see past" the short circuit, no matter whether it's a quarter-wavelength from the transmitter, a half-wavelength, or some distance in between these two. The analyzer "sees" only what would be expected for a short circuit, transformed by 6' of coax. Short-circuit quality test: measure impedance of the shorted BNC plug. At 16 MHz and below, the MFJ-269 shows it as 0+0j. Above 16 MHz, some reactance shows up... 2 ohms at 28 MHz, 3 ohms at 42 MHz, 4 ohms and 55 MHz, 8 ohms at 112 MHz, 10 ohms at 144 MHz, 12 ohms at 169 MHz. The inductance of the shorted plug itself, and/or the length of the N-to-BNC adapter on the analyzer, is having some effect. SWR remains unreadably high: >31 up through VHF and >5 on 440. It's not the highest-quality "short circuit" in the world, for certain, but at HF and VHF it's close enough for our purposes here. So... what do I conclude from this? I conclude that at HF and VHF frequencies, if you accidentally short your transmitter-to-antenna coaxial feedline (with a pin, nail, or a loose strand of coax braid which "gets loose" inside a connector), you're going to present your transmitter with an unrealistic load (high, low, or nastily reactive) and that the power flow up the feedline is going to stop at the short circuit. Since no "short circuit" in the real world is going to have 0+0j impedance, this isn't *absolutely* true, but you can probably consider it to be *practically* true and correct at these frequencies, with this sort of shorting. I further conclude that with respect to the above, there's no 'magic' about shorts which happen to occur at a quarter-wavelength distance >from the transmitter. In this situation, the transmitter will 'see' something which behaves like a quarter-wavelength shorted stub... the load further up the transmission line at the antenna remains 'invisible' to the transmitter. At high-UHF and SHF/microwave frequencies, where a direct "short" is likely to be a significant fraction of a wavelength, then the additional reactance of the "short" will certainly affect how the undesired connection affects what the transmitter "sees". It may hurt, or help (helping to "tune out" reactance from the antenna itself), or may be completely invisible. Allison is entirely correct on this point, under these particular conditions. -- 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: 220663 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: Standing Waves (and Impedance) References: <1135102751.103538.224970@g47g2000cwa.googlegroups.com> <5Uoqf.43886$6e1.2147@newssvr14.news.prodigy.com> <43ab7ab2@kcnews01> <43AF3FFC.8060502@comcast.net> Message-ID: Date: Mon, 26 Dec 2005 01:05:48 GMT dansawyeror wrote: > No. They are separate. Audio is FM and video is AM. Dan I can receive the commercial FM band just fine on my IC-706. Why can't I receive TV audio on it? -- 73, Cecil http://www.qsl.net/w5dxp Article: 220664 of rec.radio.amateur.antenna From: Eskay Subject: Re: An Antenna for the FT-857D References: Message-ID: <1mt9zb9sv88uk$.1eijiyl6g2au3$.dlg@40tude.net> Date: Sun, 01 Jan 2006 13:49:51 GMT On Sat, 31 Dec 2005 21:09:53 GMT, west wrote: > Been away from Ham Radio for over 20 years and am ready to buy a Yaesu > FT-857D (160-6 & 2; .7m, also 60m). I have a relatively small lot and was > wondering with all those bands, what am I going to use for a good DX > antenna(s). I have a dear friend in Australia that it would be great if I > could hook up with him. Any thoughts? Thank you. > > Cordially, > west > AF4GC (Tampa Bay, Florida) HI You might consider the Hexbeam, It is a five band antenna and very compact and light. Google for it and you will find all kinds of info. Eskay. Article: 220665 of rec.radio.amateur.antenna From: larry d clark Subject: Re: minimum Z on a center loaded vertical? References: Message-ID: Date: Mon, 26 Dec 2005 02:06:20 GMT dansawyeror wrote: > Is minimum Z, across a frequency scan, 'resonance' on a 1/4 wave vertical? > > Is it resonance on a center loaded vertical? > > Thanks - Dan kb0qil resonance is defined as XL = XC Article: 220666 of rec.radio.amateur.antenna From: Owen Duffy Subject: Re: Standing Waves (and Impedance) Message-ID: <1aruq1hvfibcbanikv8vs5cfbv00fkn01n@4ax.com> References: <5Uoqf.43886$6e1.2147@newssvr14.news.prodigy.com> <43ab7ab2@kcnews01> <43AF3FFC.8060502@comcast.net> Date: Mon, 26 Dec 2005 04:15:22 GMT On Sun, 25 Dec 2005 22:59:49 -0500, "Fred W4JLE" wrote: >You can if you tune to the audio offset. > >"Cecil Moore" wrote in message >news:MlHrf.45274$tV6.281@newssvr27.news.prodigy.net... >> dansawyeror wrote: >> > No. They are separate. Audio is FM and video is AM. Dan >> >> I can receive the commercial FM band just fine on my IC-706. >> Why can't I receive TV audio on it? Fred, is the correct answer because although analogue TV sound in frequency modulated on a sub carrier of the composite signal, the sub carrier is not transmitted in the "commercial FM band". Cecil's IC-706 may not cover the entire TV broadcast bands, he only asked why, when he can receive the commercial fm band just fine, can he not receive TV sound in general. Cecil probably knows the answer. Owen >> -- >> 73, Cecil http://www.qsl.net/w5dxp > -- Article: 220667 of rec.radio.amateur.antenna From: "n9zle" Subject: No link attitude! Message-ID: Date: Mon, 26 Dec 2005 04:22:04 GMT No link attitude! http://www.n9zle.com/forum/ What is it with this no-link to other site attitude? Years ago when the internet was in its infancy just about any site would add your site as a link from theirs. In return you would do the same. But now it has come to NO-LINKS. Not even in the forums. I have had a website located on tripod for about 9 years over those nine years I had a link to qrz dot com That site received over a million hits. And many users went from that site to qrz and on-to Icomamerica dot com. I have always supported Icom. They have never given a link on their site to mine. I have always supported qrz. But of course he(AA7BQ) never put a link on his site to mine. Well you may say that "I never asked". And that is true. But recently I have noticed he has been deleting my posts. ALL OF THEM. He never contacted me telling me why. AA7BQ just deleted them. I build CIV cables and sell a few of them every week to amateur operators who want them. When I posted one on his site. I found he deleted the post soon after it was placed there. My beliefs are. 1. QRZ AKA AA7BQ no longer has the amateur radio attitude. 2. AA7BQ has gone fully commercial but calls his site "The Ham Radio Super Site" 3. AA7BQ does not have your best interest in mind. I can also prove what I am writing here. For one if he claims he is nothing but a commercial site then why does he ask for donations? If he is not a commercial site than why will he not allow me to post my CIV cables on his site? That takes care of number 2 Now for number 1 and 3. If some one knows the truth about something but keeps it from you he is a liar. No mater how you put it, he is a liar. On the QRZ site Fred is there to help you renew your license. Or so he leads you to believe so. He charges you for it. Mr. Lloyd has never revealed it to any amateurs that you can renew your license or do an address change at the fcc.gov web site for FREE. Yes TOTAL FREE at the FCC web site. The forms at the FCC web site or no harder to fill out than his. His CD. He charges 24.95 plus tax and shipping. On that CD is data he obtained from the FCC and got it for FREE, he sales it to you. Also he has software, created by programmers like MYSELF. And MODS that have been made available from the manufactures and other HAMS like ME! I have been contributing to Amateur Radio community for greater than 10 years, and have received very little for software I created. Never complained when it was copied. I have performed and created several of the MODS for various transceivers. Never asked a penny for it. I never commercialized HAM RADIO. And NEVER took money from some one for something they could get FREE else where. I am sure many of you would like to ask me "what I am going to do about it?" Here is my answer. I have created an open forum on my web site http://www.n9zle.com/forum/ There you can post a link to your own site even if it is a commercial site. You can post any ham radio equipment you have for sell on the site. You can do a callsign lookup at my site from the FCC database, not that stupid qrz thing. I will soon put together an open source database that I will sell for the price of the CD plus the true cost of shipping. About two bucks total. Once you install the database on your system, you will be able to download updates for FREE. I will make drivers available to programmers to access the database in several different languages and operating systems. I will also attempt to make the database available on the internet for FREE to download. I only ask for a little help from other HAMS like myself. I need a few elmers that are willing to moderate some of the forums. It is easy and you will find it fun. If you have any suggestions on new forums or sections please logon to my site and make a post. 73s N9ZLE Article: 220668 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: using an HP 8405A to measure SWR ? References: <1ZmdnY0padRtpyreRVn-sQ@comcast.com> <1cjer19bq1ivqfusjudsf4e4oqnr1b71ar@4ax.com> Message-ID: <5eStf.60511$tV6.26377@newssvr27.news.prodigy.net> Date: Sun, 01 Jan 2006 15:06:41 GMT dansawyeror wrote: > Where are these equations? I have searched the ARRL handbook for Gamma > and did not find it. This is also the first reference to rho. Some texts, like ITT's "Reference Data for Radio Engineers" simply define rho to be complex as does Ramo and Whinnery. rho = Eref/Efor = -Iref/Ifor = (Z-Z0)/(Z+Z0) = (Y0-Y)/(Y0+Y) = |rho| /_ 2*psi where psi is the electrical angle to the nearest voltage maximum looking back toward the generator from the load. Walter C. Johnson uses 'k' for the reflection coefficient. -- 73, Cecil http://www.qsl.net/w5dxp Article: 220669 of rec.radio.amateur.antenna From: 'Doc Subject: Re: No link attitude! References: Message-ID: Date: Mon, 26 Dec 2005 05:57:31 GMT ...or maybe he's just tired of all the garbage being linked to his site (intentionally or not). Not a 'ham' attitude anymore, or just maybe not the same kind of ham you are? Get over it... - 'Doc Article: 220670 of rec.radio.amateur.antenna From: 'Doc Subject: Re: Harry E. Landsberg, Jr., CIA Maltese Falcon: Kennedy assassination, References: <1135568241.709698.30700@o13g2000cwo.googlegroups.com> Message-ID: Date: Mon, 26 Dec 2005 05:58:45 GMT > Laura Landsberg > 305 Linden St., Apt. B > Fond du Lac, WI 54935 > (920) 922-2599 > You just made the 'junk' list. - 'Doc Article: 220671 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: Standing Waves (and Impedance) References: <1135102751.103538.224970@g47g2000cwa.googlegroups.com> <5Uoqf.43886$6e1.2147@newssvr14.news.prodigy.com> <43ab7ab2@kcnews01> <43AF3FFC.8060502@comcast.net> Message-ID: Date: Mon, 26 Dec 2005 06:06:08 GMT Fred W4JLE wrote: > You can if you tune to the audio offset. I have run the IC-706 all up and down the channel 3 60-66 MHz frequencies while in College Station, TX and cannot hear the audio anywhere. -- 73, Cecil http://www.qsl.net/w5dxp Article: 220672 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: Standing Waves (and Impedance) References: <5Uoqf.43886$6e1.2147@newssvr14.news.prodigy.com> <43ab7ab2@kcnews01> <43AF3FFC.8060502@comcast.net> <1aruq1hvfibcbanikv8vs5cfbv00fkn01n@4ax.com> Message-ID: Date: Mon, 26 Dec 2005 06:24:33 GMT Owen Duffy wrote: > Cecil probably knows the answer. Actually, I don't. My IC-706 certainly covers 60-66 MHz which is channel 3 in College Station, TX. I jumped to the conclusion that since I couldn't hear WFM audio anywhere on that band, that the audio wasn't detectable until down-converted to the intercarrier. It is possible that I hit some dead air time and gave up too soon. I just cracked open my TV reference book and it indicates there are two ways to detect the sound, split IF reception and intercarrier reception. What now seems most likely is that I didn't tune high enough up to the 65.75 MHz sound carrier frequency or if I did tune that high, I hit some dead air time with no modulation. Next time I'm over there, I will try again. -- 73, Cecil http://www.qsl.net/w5dxp Article: 220673 of rec.radio.amateur.antenna From: Owen Duffy Subject: Re: Standing Waves (and Impedance) Message-ID: References: <5Uoqf.43886$6e1.2147@newssvr14.news.prodigy.com> <43ab7ab2@kcnews01> <43AF3FFC.8060502@comcast.net> Date: Mon, 26 Dec 2005 06:24:58 GMT On Mon, 26 Dec 2005 06:06:08 GMT, Cecil Moore wrote: >Fred W4JLE wrote: >> You can if you tune to the audio offset. > >I have run the IC-706 all up and down the channel 3 >60-66 MHz frequencies while in College Station, TX >and cannot hear the audio anywhere. Is the sound subcarrier supposed to be at 65.75MHz for your Ch3? -- Article: 220674 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: minimum Z on a center loaded vertical? References: Message-ID: <1cMrf.46192$tV6.28306@newssvr27.news.prodigy.net> Date: Mon, 26 Dec 2005 06:36:45 GMT dansawyeror wrote: > Is minimum Z, across a frequency scan, 'resonance' on a 1/4 wave vertical? The Xc=XL frequency is not always minimum Z and is also not always minimum SWR according to my MFJ-259B. -- 73, Cecil http://www.qsl.net/w5dxp Article: 220675 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: Standing Waves (and Impedance) References: <5Uoqf.43886$6e1.2147@newssvr14.news.prodigy.com> <43ab7ab2@kcnews01> <43AF3FFC.8060502@comcast.net> Message-ID: Date: Mon, 26 Dec 2005 06:39:53 GMT Owen Duffy wrote: > Is the sound subcarrier supposed to be at 65.75MHz for your Ch3? I think that's a valid assumption. It's possibly a cockpit error of some kind. I will have to try again. -- 73, Cecil http://www.qsl.net/w5dxp Article: 220676 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: Standing Waves (and Impedance) References: <11qv3fbeossj9cb@corp.supernews.com> Message-ID: Date: Mon, 26 Dec 2005 06:41:40 GMT Dave Platt wrote: > It's possible that your IC-706 isn't willing/able to lock onto a > carrier with such a high deviation, perhaps? or perhaps it needs to > be switched manually to a "wide FM" mode to do so in this frequency > range? It's also possible that I am senile and need to try again. -- TNX & 73, Cecil http://www.qsl.net/w5dxp Article: 220677 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: Standing Waves (and Impedance) References: <11qv3fbeossj9cb@corp.supernews.com> Message-ID: Date: Mon, 26 Dec 2005 06:51:57 GMT Dave Platt wrote: > It's possible that your IC-706 isn't willing/able to lock onto a > carrier with such a high deviation, perhaps? I just drug out the IC-706 manual. It receives channel 2 on the HF antenna and channel 3 on the VHF antenna. :-) -- 73, Cecil http://www.qsl.net/w5dxp Article: 220678 of rec.radio.amateur.antenna Message-ID: <43B805F2.1BA1A294@r2d2.com> From: Ronald Subject: Re: Tri-Ex vs US Towers References: <1135791976.986773.247810@g47g2000cwa.googlegroups.com> <8bedneexiqBYQC_eRVn-oQ@comcast.com> <1135797989.127934.42730@f14g2000cwb.googlegroups.com> Date: Sun, 01 Jan 2006 16:40:19 GMT I agree, do it right the first time and enjoy the tower ! on the other side, take a look at this installation ! http://deepsouthnet.net/tower.html 73 ron Article: 220679 of rec.radio.amateur.antenna From: dplatt@radagast.org (Dave Platt) Subject: Re: using an HP 8405A to measure SWR ? Date: Sun, 01 Jan 2006 19:15:12 -0000 Message-ID: <11rgai07jv1clc6@corp.supernews.com> References: <1ZmdnY0padRtpyreRVn-sQ@comcast.com> In article , Wes Stewart wrote: >>The measuring setup is a standard signal generator feeding a tee. One branch >>feeds the A input of the 8405A and the other a 20 db directional configured in >>reverse, that is feeding the out port. The assumption is the reflected signal >>will be read correctly on the in port. The in port is then terminated or >>connected to an antenna. > >It would also be nice it you had a 6 - 10 dB pad between the generator >and the directional coupler (DC); located right at the DC. You want >the source match to be set right there and the A probe to sample right >there. The 8405A manual indicates the use of a power divider, and then a pair of equal-value pads. One side goes to the probe T for the A (reference) probe and thence to the termination, and the other goes to the probe T for the B probe and thence to the device-under-test. The manual is quite clear that the A and B probes need to be connected to points which are isolated from one another. You really don't want the oddities of the load connected to the B side to affect the voltage/phase of the reference signal seen by the "A" probe - it'd certainly wreck the measurement. Using a power divider, and resistive pads for isolation is one way to do this. Using a pad followed by a dual directional coupler (as in the experiment page to which Owen posted a link - thanks!) is another. -- 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: 220680 of rec.radio.amateur.antenna From: richardharrison@webtv.net (Richard Harrison) Subject: Re: Recommendation for 915MHz omni antenna Date: Sun, 1 Jan 2006 13:39:28 -0600 Message-ID: <21513-43B82FF0-476@storefull-3258.bay.webtv.net> References: David wrote: "In addition to coms between the sheds and house, there are links between sheds (hence require omni-directional)." The benefit of simple and directional 915 MHz antennas is so significant that you might consider making one site a repeater and all other sites directional, communicating through the repeater. A small antenna can have much gain at 915 MHz. You could conveniently use full-duplex (2 frequencies) for simplicity.. Best regards, Richard Harrison, KB5WZI Article: 220681 of rec.radio.amateur.antenna From: "west" References: <52adr190uivec9du680b4hd7olru6rqbl6@4ax.com> Subject: Re: 2nd Floor grounding Message-ID: Date: Sun, 01 Jan 2006 20:10:08 GMT "Bill Turner" wrote in message news:52adr190uivec9du680b4hd7olru6rqbl6@4ax.com... > > ORIGINAL MESSAGE: > > On Sat, 31 Dec 2005 10:16:19 -0500, jawod wrote: > > >Several articles referred to long grounding lines being close to 1/4 > >wavelength as being a problem. Is this eliminated with balanced feedline? > > > >Thanks, > > > >john > > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > No. You can not "ground" your station for RF, at least not in the > sense of running a wire to ground. Don't bother because it isn't > necessary anyway. You do need two kinds of ground, one for the AC > mains for safety, and one for lightning. > > RF energy is expensive to generate. Don't waste it by running part of > it into a lossy "ground". Keep it up in the air where it belongs. > Baluns are your friend. > > 73, Bill W6WRT Bill, I like your answer but it leaves me to want a bit more. Would you mind expanding on your 2 paragraphs? Thanks. west AF4GC Article: 220682 of rec.radio.amateur.antenna From: Owen Duffy Subject: Re: using an HP 8405A to measure SWR ? Message-ID: References: <1ZmdnY0padRtpyreRVn-sQ@comcast.com> Date: Sun, 01 Jan 2006 21:45:17 GMT On Sun, 01 Jan 2006 03:25:23 GMT, Owen Duffy wrote: >On Sat, 31 Dec 2005 18:14:04 -0800, dansawyeror > wrote: > >why the tee as described, doesn't the 8405A have a tee probe? Dan, my reason for this question is that you do not seem to have a load independent sample of the forward wave (if you are referencing measurements to the A probe). Ideally you would use a dual directional coupler, otherwise, you need to isolate the A sample from load impedance variations and reflections using a largish attenuator for example. If you are working the ratios out entirely from the B probe, eg B probe measurements on s/c and unknown load, then the A measurement becomes unimportant. Note that while this approach can give you enough info to measure rho and calculate SWR, it will not permit phase measurements. This approach dumbs the instrument down to a single channel RF voltmeter. Owen -- Article: 220683 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Dipoles and the rig's RF ground... Date: Sun, 01 Jan 2006 13:45:36 -0800 Message-ID: <11rgjc3pu8roqe9@corp.supernews.com> References: <1136148463.132269.164130@g49g2000cwa.googlegroups.com> billcalley wrote: > I realize that dipoles are balanced antennas, but does the rig > itself still need an RF ground too? If your feedline is balanced, that is it has equal and opposite currents on the two conductors, then there's no current left over to flow to or >from ground and no need for an RF ground connection. All the current >from one conductor goes back on the other. Feedlines can be balanced even if they're coax and/or the antenna is unsymmetrical; they can be unbalanced even if the antenna and feedline are symmetrical. If the feedline isn't balanced, the difference current (that is, the difference between the currents on the two feedline conductors) will find its way to ground however it can. This often creates undesirable effects. But if you can't avoid it, it's better to provide a low impedance path for the ground current if possible. And that can sometimes be difficult to do. (I know the radio always needs a DC > ground, of course). No, it doesn't. It needs an AC safety ground if connected to the mains, and a lightning ground if that's a possible hazard. But DC isn't important. How about if the dipole is being used as a > non-loaded "all band" antenna (IE: RIG--TRANSMATCH--LADDER > LINE--DIPOLE) -- would this affect the need for an RF ground on the rig > for operation in the dipole's non-resonant bands? Or is no RF ground > _at all_ required with a dipole; unlike when using random wires or > verticals, and other such un-balanced antennas? The trick is to get the feedline balanced on all bands. That requires either a truly balanced tuner, or a combination of a good balun and impedances on all bands at the balun which the balun can handle. Roy Lewallen, W7EL Article: 220684 of rec.radio.amateur.antenna From: dplatt@radagast.org (Dave Platt) Subject: Re: using an HP 8405A to measure SWR ? Date: Sun, 01 Jan 2006 22:10:09 -0000 Message-ID: <11rgkq1ppamdce@corp.supernews.com> References: <1ZmdnY0padRtpyreRVn-sQ@comcast.com> <11rgai07jv1clc6@corp.supernews.com> In article , Wes Stewart wrote: >>>The 8405A manual indicates the use of a power divider, and then a pair >>>of equal-value pads. One side goes to the probe T for the A >>>(reference) probe and thence to the termination, and the other goes to >>>the probe T for the B probe and thence to the device-under-test. >> >>Actually, my manual does not show this. Although I have the full kit >>of a resistive tee, two 50 ohm "N" sampling tees and appropriate >>terminations, I don't believe Dan does. >>> >>>The manual is quite clear that the A and B probes need to be connected >>>to points which are isolated from one another. >> >>I've read this someplace, but again my version of the manual (unless >>I'm really missing something) doesn't say it. The BAMA copy mentions it in paragraph 3-14. Later text indicates that attaching the two probes to a single point is an appropriate way to set phase-zero. >> Nevertheless, the >>directional coupler provides the isolation between probes. I see the issue, and I think I was conflating two different sorts of measurement regimes. The splitter/isolator/pad arrangement I was referring to appears on page 3-3 of the 8405A manual available at BAMA. It's what's appropriate for doing an in-line test of a transmission line or other network, where you want to see the effect of the network itself and can measure (via probe B) at the network's output. Page 3-4 shows a somewhat similar hookup, which doesn't include the resistive pads... I presume because the device-under-test (an amplifier) is assumed to have high isolation as part of its design. Neither of these hookups wouldn't work for measuring an antenna, since you can't measure at the antenna's output. Instead, using a directional coupler provides the necessary isolation, and (as you point out) lets you determine the incident and reflected signals accurately. >I've got to clarify this a bit if I can... > >If you have the full set of parts per figure 11 in AN77-3 and you are >using them as shown, then with equal loads on the two ends, the >circuit is essentially a resistive Wheatstone bridge in balance with >the null detected by the difference between probes A and B. > >In this case, the "incident" signal -is- measured by the A probe and >the effects to the source by a changing load are incorporated into the >measurement. > >In the case at hand, at least as I imagine it, there is no longer an >nice tidy resistive Wheatstone bridge, but some cabling and a >directional coupler in the mix. In this case, the generator is no >longer the "source", the source is the signal at the input to the >coupler. It is my belief (unless I change my mind later) that a >sample derived from a resistive divider remote from the input to the >directional coupler is not a true measure of the incident signal. Hmmm. In the general case, I believe you're correct. I suspect that the setup shown in the 8405A manual sets up a specific special case, though. The diagrams and text seem to be defining a case in which: - there is a physical and electrical symmetry in the T arrangement - that is, the power splitter is symmetrical, and the pair of attenuator pads between the splitter and the (A probe tap) and (device under test) are matched. The manual makes a point of this issue. - The pads being used are matched to the system's transmission line impedance, so that any reflected signal coming back from the DUT/coupler sees a proper termination by the source (the pad and signal generator, in this case) and is not re-reflected. In this particular situation, I believe that the incident signals reaching the DUT (the input to the coupler, in this case) and the "A" probe, would be identical... would they not? The proper termination of the reflected wave will mean that it won't re-reflect off of the generator and alter the incident wave. The "A" probe signal (off on its side of the "T") and a signal read out via the incident-wave tap on the directional coupler ought to be the same, once the coupling coefficient is taken into account... no? -- 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: 220685 of rec.radio.amateur.antenna From: Bill Turner Subject: Re: 2nd Floor grounding Date: Sun, 01 Jan 2006 14:44:30 -0800 Message-ID: References: <52adr190uivec9du680b4hd7olru6rqbl6@4ax.com> ORIGINAL MESSAGE: On Sun, 01 Jan 2006 20:10:08 GMT, "west" wrote: > >"Bill Turner" wrote in message >news:52adr190uivec9du680b4hd7olru6rqbl6@4ax.com... >> >> ORIGINAL MESSAGE: >> >> On Sat, 31 Dec 2005 10:16:19 -0500, jawod wrote: >> >> >Several articles referred to long grounding lines being close to 1/4 >> >wavelength as being a problem. Is this eliminated with balanced >feedline? >> > >> >Thanks, >> > >> >john >> >> >> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ >> >> No. You can not "ground" your station for RF, at least not in the >> sense of running a wire to ground. Don't bother because it isn't >> necessary anyway. You do need two kinds of ground, one for the AC >> mains for safety, and one for lightning. >> >> RF energy is expensive to generate. Don't waste it by running part of >> it into a lossy "ground". Keep it up in the air where it belongs. >> Baluns are your friend. >> >> 73, Bill W6WRT > >Bill, > >I like your answer but it leaves me to want a bit more. Would you mind >expanding on your 2 paragraphs? Thanks. > >west >AF4GC > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ OK. 1. Running a wire from your rig to ground will not do what you think it will. Any wire is a significant portion of a wavelength at HF and may be many wavelengths at VHF and UHF. On ten meters, for example, eight feet is almost exactly 1/4 wavelegth. If you recall your basic transmission line theory, whatever condition is present at one end of a 1/4 wave line has just the opposite at the other end. If you really do have a good ground connection at the grounded end of the wire, the other is an open circuit. Not very effective for grounding, is it? The effect becomes less as you lower the frequency, but never completely disappears. It is possible to tune out this effect with a suitable coil and capacitor combination, but it really isn't needed anyway. MFJ makes a "ground tuner" or whatever they call it, and I suppose it does work, but think about this: If getting a good RF ground actually improves your signal, you have a SERIOUS problem in your antenna. More on this in the next paragraph. 2. RF does no good flowing through the earth. None at all. Dirt is a poor conductor at any ham frequency and you should do your best to keep your RF out of it. I suspect the idea that "ground" helps your signal came from the very early days of radio when frequencies were very low and wavelenghts were very long... miles long in fact. At those frequencies there are two factors which might make use of ground desireable: The earth is much more conductive at very low frequencies, and miles of wire for an antenna is not easily done. Under those circumstances, working a long wire against ground might actually be a good idea. None of that applies to ham frequencies, of course. At ham frequencies, RF works best when it's up in the air, all of it. Not in the ground, not in your shack, up in the air. Keep that in mind and you can't go wrong. 73, Bill W6WRT Article: 220686 of rec.radio.amateur.antenna From: Bill Turner Subject: Re: Dipoles and the rig's RF ground... Date: Sun, 01 Jan 2006 14:49:33 -0800 Message-ID: References: <1136148463.132269.164130@g49g2000cwa.googlegroups.com> ORIGINAL MESSAGE: On 1 Jan 2006 12:47:43 -0800, "billcalley" wrote: >Or is no RF ground >_at all_ required with a dipole; unlike when using random wires or >verticals, and other such un-balanced antennas? ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Any antenna which requires a connection to ground should be shown the trash can immediately. Ground (earth) is a lousy conductor and does nothing to help your signal. RF belongs up in the air, not down in the dirt. If you find that connecting a ground wire actually improves your signal, you have a SERIOUS problem in your antenna. 73, Bill W6WRT Article: 220687 of rec.radio.amateur.antenna From: David Subject: Re: Recommendation for 915MHz omni antenna References: <21513-43B82FF0-476@storefull-3258.bay.webtv.net> Message-ID: Date: Sun, 01 Jan 2006 23:52:12 GMT Richard, If I was to use directional antennas. What would your recommendation be ? What about a vertically polarized Yagi ? other ? Thanks Regards David Richard Harrison wrote: > David wrote: > "In addition to coms between the sheds and house, there are links > between sheds (hence require omni-directional)." > > The benefit of simple and directional 915 MHz antennas is so significant > that you might consider making one site a repeater and all other sites > directional, communicating through the repeater. A small antenna can > have much gain at 915 MHz. You could conveniently use full-duplex (2 > frequencies) for simplicity.. > > Best regards, Richard Harrison, KB5WZI > -- Kind Regards David Huisman General Manager ----------------------------------------------------------------------- ORBIT COMMUNICATIONS Pty Ltd - Wireless Solutions that Work (Telemetry, Control, Monitoring, Security, HVAC ...) A.C.N. 107 441 869 Website : http://www.orbitcoms.com PO Box 4474 Lakehaven NSW 2263, AUSTRALIA Phone: 61-2-4393-3627 Fax : 61-2-4393-3685 Mobile: 61-413-715-986 Article: 220688 of rec.radio.amateur.antenna From: "Jerry Martes" References: <1ZmdnY0padRtpyreRVn-sQ@comcast.com> Subject: Re: using an HP 8405A to measure SWR ? Message-ID: <9f%tf.17696$zJ3.11265@trnddc04> Date: Mon, 02 Jan 2006 01:22:13 GMT "dansawyeror" wrote in message news:vIadnfqrOM6B5CXenZ2dnUVZ_tWdnZ2d@comcast.com... > Owen, > > Yes, you are right. The single coupler doesn't isolate the channels. > Putting a 10 dbm attenuator between the tee and the coupler changes the 50 > Ohm reading. I think a dual directional coupler is required. I will have > to put this on hold until that problem is solved. > > Thanks - Dan Dan Are you open to trying to assemble something to measure the reflection coefficient rather than to put the project on hold? The HP 41952A Transmission/Reflection Test Set uses only one directional coupler. It uses a power splitter at the input with a pad to level the outputs from the "Fwd" and "Rev" ports. I can scan some info from the HP 41952 and E-mail them to you if you have interest in building something. I would think it would be fairly easy to build devices for HF if you already have a decent directional coupler. Jerry Article: 220689 of rec.radio.amateur.antenna From: Bill Turner Subject: Re: 2nd Floor grounding Date: Sun, 01 Jan 2006 17:59:37 -0800 Message-ID: <632hr11s5ogf0n25s5if48242t5n87j44g@4ax.com> References: ORIGINAL MESSAGE: On Mon, 02 Jan 2006 00:17:00 +0000, Dan Andersson wrote: >Forget about balun's and other widgetry! > >Get a virtual earth! They are easy to build for all ham bands! > >It's basically a phasing unit for the earth connection which can null the >voltage on the earth at the RF Rig! > >If you don't want to build one, MFJ sells one! > >Cheers > >M0DFI ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ They're great if you like your antenna two feet above ground. The way you "null out the voltage" is by making that wire resonant and resonant wires love to radiate. Nobody would intentionally install an antenna below knee level, but that's what you're doing. Busted any pileups lately? :-) 73, Bill W6WRT Article: 220690 of rec.radio.amateur.antenna From: Bill Turner Subject: Re: Dipoles and the rig's RF ground... Date: Sun, 01 Jan 2006 18:01:41 -0800 Message-ID: References: <1136148463.132269.164130@g49g2000cwa.googlegroups.com> ORIGINAL MESSAGE: On Mon, 02 Jan 2006 00:12:21 +0000, Dan Andersson wrote: >This is best solved by a short ground cable to a proper ground rod. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ No it isn't. It's best solved by keeping the RF out of the shack in the first place. Even if you could "ground" your RF, why would you want to run your RF through dirt? Is dirt a good antenna? 73, Bill W6WRT Article: 220691 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: 2nd Floor grounding Date: Sun, 01 Jan 2006 18:45:57 -0800 Message-ID: <11rh4v9gdjsm65c@corp.supernews.com> References: <632hr11s5ogf0n25s5if48242t5n87j44g@4ax.com> Bill Turner wrote: > > They're great if you like your antenna two feet above ground. > > The way you "null out the voltage" is by making that wire resonant and > resonant wires love to radiate. Nobody would intentionally install an > antenna below knee level, but that's what you're doing. > . . . I don't agree entirely with some of the recent short postings. And making a wire resonant doesn't make it radiate any better or worse than a non-resonant one. But if you have an unbalanced feedline (and by this I don't mean a symmetrical feedline like ladder line, but one of any construction with imbalanced currents) and consequential current from your rig to ground, that conductive path to ground will radiate just like an antenna -- any current flowing on a conductor causes radiation, regardless of whether we consider it to be an "antenna", a "ground wire", or a "transmission line". And as Bill points out, the location of a ground wire isn't usually what you'd choose for an antenna. Other consequential effects are that an unbalanced feedline has a net (common mode) current and so it radiates, too. The feedline and ground wire are also part of the antenna when receiving, so they'll be good at receiving noise that's generated in the house or radiating from mains wiring. All in all, it's not an ideal situation, although quite a number of people manage to get away with it. Roy Lewallen, W7EL Article: 220692 of rec.radio.amateur.antenna From: richardharrison@webtv.net (Richard Harrison) Subject: Re: Recommendation for 915MHz omni antenna Date: Sun, 1 Jan 2006 20:47:59 -0600 Message-ID: <26048-43B8945F-1005@storefull-3251.bay.webtv.net> References: Dave wrote: "What would your recommendation be?" I would use a vertical collinear omni antenna for the repeater and vertically polarized Yagis for each of the "sheds". To avoid stimulation of argument, I`ll say no more. You mainly need a line-of-sight path at 915 MHz between all remote sites and the repeater. Best regards, Richard Harrison, KB5WZI Article: 220693 of rec.radio.amateur.antenna Date: Sun, 01 Jan 2006 22:42:53 -0500 From: jawod Subject: Practical "ideal" antenna Message-ID: What would you recommend for a wire antenna if there was enough room for an 80 dipole? Assume use for 80M , 40M and 20M, Thanks Article: 220694 of rec.radio.amateur.antenna From: "Ralph Mowery" References: Subject: Re: Practical "ideal" antenna Message-ID: Date: Mon, 02 Jan 2006 04:01:18 GMT "jawod" wrote in message news:f23fd$43b8a13e$42a1bfc2$2968@FUSE.NET... > What would you recommend for a wire antenna if there was enough room for > an 80 dipole? Assume use for 80M , 40M and 20M, > Use either an 80 meter dipole fed by open wire or one of the off center fed dipoles, often called a Windom. Article: 220695 of rec.radio.amateur.antenna From: dplatt@radagast.org (Dave Platt) Subject: Re: using an HP 8405A to measure SWR ? Date: Mon, 02 Jan 2006 04:11:52 -0000 Message-ID: <11rha08kqa1cb85@corp.supernews.com> References: <1ZmdnY0padRtpyreRVn-sQ@comcast.com> <11rgkq1ppamdce@corp.supernews.com> In article , Wes Stewart wrote: >Bingo. Didn't seem like an "Electrical feature" to me :-) Yeah. I'm not sure just why there would be substantial interaction if the two points are connected to the same test point, since the rated impedance is pretty high even without 10:1 isolators. >But I still submit that when you separate the bridge, insert a DC and >some cabling, you lose the symmetry and the signal measured by the A >probe is not necessarily the same as the signal incident at the input >to the DC. Close maybe, but not something I would rely on. The signal on the other side of the T-and-attenuator setup wouldn't be the same as the signal at the input to the DC, certainly, since the signal at the input of the DC would be affected by the reflected signal. I don't disagree with you there. What I suggest, though, is that the signal on the "A" probe (at the other side of the T from the DC), and a signal as seen at the output of the DC's "forward" coupler line, ought to be very closely correlated. They'd differ by the coupler's coupling factor, of course, and there's be a bit of phase shift from the coupler (dependent on the coupler line length and the frequency). However, the loading at the coupler output from the load (or the calibration short) ought not to affect the signal appearing at the 'forward' tap on the coupler. >Remember, when doing the calibration there is a 100% reflection. This >can have a huge perturbing effect on the incident signal at the >coupler input if the source is not well matched. Agreed, and I don't suggest that measuring the incident at the coupler input is a good idea. > That's why I >originally suggested a pad right at the coupler input, especially if >there is some cabling between the generator (or power splitting tee) >and the DC. Agreed. >No. The B probe, in the single directional coupler arrangement, is >not measuring -incident-, but reflected signal. True. I was assuming a double directional coupler, and asserting that the "forward" output on the coupler will produce a signal equivalent (except for scaling and perhaps a tad of phase shift) to a signal taken from the far side of the splitter-and-pads "T". >In any event, Dan has stated that he doesn't have all of this stuff >and is stuck using the DC only. My suggestion holds, put a pad at the >DC input, measure the incident at the DC input and of course, the >reflected at the coupled port. Yes, that should work quite well, and I think it'd give results pretty much equivalent to [1] a dual directional coupler or [2] the splitter-and-two-pads isolation arrangement. -- 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: 220696 of rec.radio.amateur.antenna Date: Sun, 01 Jan 2006 22:02:07 -0700 From: BKR Subject: Re: Practical "ideal" antenna References: Message-ID: <43b8b3c6$1@nntp.zianet.com> jawod wrote: > What would you recommend for a wire antenna if there was enough room for > an 80 dipole? Assume use for 80M , 40M and 20M, > > Thanks I would use a fan dipole because of the harmonic relationship between the frequencies you wish to operate on. Others might use a trap dipole but traps always have some loss involved and may fail due to moisture. KD5RPO Article: 220697 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: measurement error or bad coax?? Date: Mon, 26 Dec 2005 22:53:36 -0800 Message-ID: <11r1p7hf402smbd@corp.supernews.com> References: <11r15cu46m2rc9e@corp.supernews.com> <43B0BDEB.5090203@comcast.net> I agree with Owen, something here doesn't compute. The only way I can make sense out of it is if your line length is really an odd number of quarter waves, and it's exceptionally lossy. As a first thing to do in resolving the matter, I recommend measuring the velocity factor of the main coax. For best accuracy, short circuit the far end of the line with a low-inductance short circuit, and look for a low Z at the input. (You can even use a scope or diode detector for this.) At low frequencies, a single wire will do for the short; at higher frequencies, use multiple wires radially extending from the center to the shield, or a metal plate. At very low frequencies, the impedance will be low, increasining with frequency. At some point it'll rise and become very high, then drop again as frequency increases. Find the frequency where it's the lowest -- this is the frequency where the line is exactly a half wavelength. Physically measure the line and calculate the velocity factor. For line constructed like you describe, the velocity factor should be around 84%. A significantly lower factor probably means it has water in it. If it comes out about right, let us know and we'll go from there. Roy Lewallen, W7EL Article: 220698 of rec.radio.amateur.antenna From: Bill Turner Subject: Re: 2nd Floor grounding Date: Sun, 01 Jan 2006 22:10:43 -0800 Message-ID: References: <632hr11s5ogf0n25s5if48242t5n87j44g@4ax.com> <11rh4v9gdjsm65c@corp.supernews.com> ORIGINAL MESSAGE: On Sun, 01 Jan 2006 18:45:57 -0800, Roy Lewallen wrote: > >I don't agree entirely with some of the recent short postings. And >making a wire resonant doesn't make it radiate any better or worse than >a non-resonant one. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ You are correct of course. I should have said a resonant antenna (or ground wire) is easier to couple energy into, and in that sense, it radiates better. 73, Bill W6WRT Article: 220699 of rec.radio.amateur.antenna From: Bill Turner Subject: Re: Practical "ideal" antenna Date: Sun, 01 Jan 2006 22:17:38 -0800 Message-ID: References: ORIGINAL MESSAGE: On Sun, 01 Jan 2006 22:42:53 -0500, jawod wrote: >What would you recommend for a wire antenna if there was enough room for > an 80 dipole? Assume use for 80M , 40M and 20M, > >Thanks ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ I use the W9INN trap dipole and I love it. The "traps" are not the conventional coil/capacitor kind. Rather, they are a self-resonant inductor with no separate capacitor, and they are rated at full legal power as a result. I run the antenna at 1500 watts on RTTY, probably the toughest working conditions possible. It's been up five years through more than 40,000 contest QSOs and not a minute's problem. W9INN is now an SK and I don't know if they are still in production, but they are simple enough to homebrew if you have a grid dip meter. The ARRL antenna book has more info on building this type of antenna. 73, Bill W6WRT Article: 220700 of rec.radio.amateur.antenna From: Owen Duffy Subject: Re: using an HP 8405A to measure SWR ? Message-ID: References: <1ZmdnY0padRtpyreRVn-sQ@comcast.com> Date: Mon, 02 Jan 2006 07:15:57 GMT On Sun, 01 Jan 2006 16:51:37 -0800, dansawyeror wrote: >Owen, > >Yes, you are right. The single coupler doesn't isolate the channels. Putting a >10 dbm attenuator between the tee and the coupler changes the 50 Ohm reading. I >think a dual directional coupler is required. I will have to put this on hold >until that problem is solved. > Dan, it seems to me that you should be able to make measurements with a single directional coupler (DC) You could connect your signal generator to the directional coupler via a 40dB attenuator, and put the chan A probe T on the sig gen end of the attenuator. This sample should be fairly independent of the reflection from the unknown load (to the extent of the 40dB attenuator), and so approximately proportional to the incident wave alone. The sample from the DC "reflected" port (properly terminated) is fairly independent of the incident wave (depending on the F/B ratio of the coupler) and so is approximately proportional to the reflected wave alone. Calibration of the B channel magnitude with a s/c and o/c taken as rho=1 provides the basis for measurement of Gamma. The angle of Gamma should be calibrated to 180 and o deg respectively. BTW, the angle of Gamma for a 50 ohm termination is unimportant if rho is very small. The angle of Gamma is real important for s/c and o/c and ought be almost exactly 180 deg difference (if not, you have a instrument problem). Following this procedure, if the magnitude of the B channel on the unknown load measures for example 9.5dB below the B chan magnitude on a s/c, then the return loss is 9.5dB and the VSWR is 2:1. rho (the magnitude of Gamma) is 0.333 and you could measure the phase offset >from the o/c angle to determine the angle of Gamma. Why won't this work? Owen -- Article: 220701 of rec.radio.amateur.antenna From: David Subject: Use of MJF-269 Analyzer help Message-ID: Date: Mon, 02 Jan 2006 08:45:39 GMT Hi, I am wanting to check the match efficiency or return loss of a C-Tap matching network that matches 50 Ohms in to 4500 Ohm load with 2.5pF in parallel. Match at single Freqency = 45 MHz. Using a 134nH inductor with Q of approx. 85 My calculations result in Cap to ground = 864pF, Cap to inductor = 102pF I tried the match on the front end of my IF circuit and it appears to tune smoothly and peak ok at 45MHz. I then wanted to measure the return loss to see how good the match is. Using the MJF-269, I get a lousey reading of 0.9dB. (almost everything reflected). Either my calculations are way off base, or I am not using the MJF-269 correctly. I also get lousey SWR (16.5), match efficiency below 5%. I purchased the analyzer ages ago and have only used it to measure Vp of coax till now. Any help appreciated. Thanks Article: 220702 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: vertload.exe versus loadcoil.exe ?? Date: Tue, 27 Dec 2005 12:31:58 +0000 (UTC) Message-ID: References: <43B066A6.908@comcast.net> "dansawyeror" wrote in message news:43B066A6.908@comcast.net... > Thank you very much. > > Can you speak to the calculated ATU value in VertLoad? Is it the value to match > to a 50 Ohm coax? > > One of the program set simulates a dipole with a base coil centered between the > elements. Is there a program to simulate a dipole with each of the arms center > loaded? I was trying to approximate this by vertload/loadcoil simulations. They > should be pretty close. > > Thanks - Dan kb0qil > =============================== Yes, it's 50-ohm coax. Somewhere the program tells you that. Two 1/4-wave resonant coil-loaded verticals, back to back, make one 1/2-wave resonant coil-loaded dipole. But the dipole is more efficient. There is no ground loss resistance. ---- Reg. Article: 220703 of rec.radio.amateur.antenna From: "Richard Fry" References: <1135422926.082522.168780@o13g2000cwo.googlegroups.com> <43afeda5_4@newsfeed.slurp.net> Subject: Re: If the ideal lenght of an antenna is 1/4 Wave lenght then way are the Car Cellular antennas are longer then this ? Date: Tue, 27 Dec 2005 07:39:04 -0600 Message-ID: <43b1433b_4@newsfeed.slurp.net> "Hal Rosser" wrote: > Right you are. > Like I said - using a 5/8 wave vertical flattens out the "doughnut of > propogation." > And using two - back-to-back as a dipole will exhibit gain as well - > over a dipole. ______________ If you mean gain over a _ 1/2-wave _ dipole, then all of the single verticals > 90 degrees in the plots I posted earlier (with their "image" components) already have greater peak gain than that. The peak, intrinsic gain of the 90 degree vertical and its image in my plots exactly matches the free-space peak gain of a self-resonant, 1/2-wave dipole (2.15 dBi). The fact that all of the radiation from these verticals is confined to a 1/2 hemisphere adds 3 dB h-plane gain to all of the plots. RF Article: 220704 of rec.radio.amateur.antenna From: Bill Turner Subject: Re: Crimp, Clamp or Solder? Date: Tue, 27 Dec 2005 06:21:59 -0800 Message-ID: <0bj2r15i9iic4td11aejgpe330g8b07efe@4ax.com> References: <76fsq1hrdjvdt82p798efnk9iui6jv4vlo@4ax.com> <113sf.16964$wq.9439@bignews7.bellsouth.net> ORIGINAL MESSAGE: On Mon, 26 Dec 2005 23:04:44 -0500, "Hal Rosser" wrote: >crimps can 'work loose' >Same reason you have 5 lug nuts on your wheel instead of 2 or 3. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Nonsense. Properly crimped, the wire will break before the crimp "works loose". Your tire has multiple lug nuts to spread the stress, not because a smaller number will "work loose". 73, Bill W6WRT Article: 220705 of rec.radio.amateur.antenna From: "Richard Fry" References: <1135422926.082522.168780@o13g2000cwo.googlegroups.com> <43afeda5_4@newsfeed.slurp.net> <43b1433b_4@newsfeed.slurp.net> Subject: Re: If the ideal lenght of an antenna is 1/4 Wave lenght then way are the Car Cellular antennas are longer then this ? Date: Tue, 27 Dec 2005 09:43:23 -0600 Message-ID: <43b1605d_5@newsfeed.slurp.net> "Reg Edwards" wrote > Just to start an argument, why is it that EZNEC shows zero gain for a > vertical antenna in the horizontal plane? Whereas, all your diagrams > show maximum gain along the horizontal. ____________ EZNEC shows the same patterns/gains as in the plots I posted, when its models are set up correctly. RF Article: 220706 of rec.radio.amateur.antenna From: Jim Higgins Subject: Re: More BPL rollout. sigh... Message-ID: References: <43AA4CDA.46CD92EB@nobplforme.com> Date: Tue, 27 Dec 2005 16:23:50 GMT On Sun, 25 Dec 2005 20:32:45 -0500, Roger wrote: >On Thu, 22 Dec 2005 13:57:06 GMT, Jim Higgins > wrote: > >>On Thu, 22 Dec 2005 06:51:08 GMT, bpl_just_say_NO >> wrote: >> >>>150 Million for ten years. that is a lot of money for nothing. >>> >>>DQE will also have a pilot program in Monroeville PA >>> >>>http://biz.yahoo.com/prnews/051215/cgth037.html?.v=44 >>> >>>I don't think they can compete with the newer intel and >>>motorola technology for wireless. >> >>If the common folk play their cards right BPL can't compete with >>anyone anywhere. If rollout is inevitable it's time (past time > >The PUCs want it for grid control and monitoring. The BPL marketers >have made it look like they can do that (which they can) plus have an >revenue stream from their costomers. The power companies already have control systems using low frequency carriers over the distribution lines. BPL brings nothing new to that game. >>actually) to go to the PUC and ask that everything related to BPL only >>be paid for from revenue gained from BPL. No shifting of revenue from >>power sales to support BPL - strictly separate. Also ask that service > >They will just state they are running the service for monitoring and >control anyway so it'll be handy if any one wants to sign up. That nonsense won't stand up to knowledgeable public comment if hams will get involved with their local PUCs rather than depending on the ARRL to continue dry humping the FCC's leg in hopes of getting their attention. I don't recommend giving up on demanding that the FCC enforce the rules against interference, but it's time to broaden the attack on BPL. >>be provided promptly to anyone asking for it and everyone at the same >>price regardless of whether in a large city or one with a population >>of 22 at the end of 150 miles of dead-end power line. After all, BPL >>promises high speed Internet access to EVERYONE and you can be sure > >Some implented forms of BPL can't even deliver high speed with very >many customers before running into packet collisions which means wider >bandwidth or slower service. Exactly. The power lines will saturate rather quickly in any BPL implementation that gains a meaningful number of customers. The trick to killing BPL completely is to - via the PUC - force the power companies that implement it to provide the service to all customers promptly. Faced with a requirement to provide service to far flung customers - many of those who currently can't get cable will almost surely want to at least try BPL - makes the implementation a money loser. Faced with that choice, few will implement it. And based on the results of trials, few are implementing it anyhow. I think any who do go ahead will soon become posterchildren for why BPL is a bad idea. The regulatory environment as far as the FCC goes looks good at the moment from some perspectives, but the FCC is ignoring law and regulations and that can't go on forever. Imagine the utility that implements BPL based on a dependence on the FCC continuing to flout their duties to enforce. Figuratively speaking, they wouldn't be able to sleep at night because that favorable environment can shift overnight to a very hostile one. The promise of BPL is high speed access for the masses who can't get cable, but the economic success of BPL depends on subscribership in densely populated areas and ignoring the far flung areas. Force them to meet the promises and it isn't viable economically. >>that at some point that was said. Hold them to it now, not 20 years >>from now. The result? BPL economics absolutely cannot support the >>promises made for it. If they have to fulfill the promises it's dead >>before it starts. > >If they can be held off just two years regular broad band will be >widely available and cheaper. Rather than out in the country where >it's expensive to implement, they are finding the prime candidate are >offices and apartment buildings. OTOH once those offices and >apartments are up and running I wonder what kind of track record >they'll have? Add a few real time gamers, VoIP, and some streaming >video. Exactly. And I don't think it will even support web browsing of today's typical high bandwidth web sites at an acceptable speed once the subscribership in an area becomes significant... or if many use the services you mention above. My take on it is that BPL is well suited - technically, but completely ignoring the problem of interference - to the promise of making broadband available to those who are too far out to get cable. But it isn't suited to that task economically because the cost to implement it to serve far flung customers will exceed any revenue projections from that potential subscriber base. When it comes to servicing densely populated areas the economics are there - today - but the bandwidth will fill quickly and customers will be unhappy with the service. Even the first customer will see speeds well below those available from cable and the price difference - which you suggest and I agree will only last a few more years - will not entice knowledgeable cable customers to switch to BPL, and of those who do, most will switch back. Ensuring the predicted price crunch develops requires preventing any subsidy of BPL services from revenue from sales of power. That's why I say we need to start on our PUCs now. Article: 220707 of rec.radio.amateur.antenna From: "Charlie" Subject: 6M stacked loops - best height above ground? Date: Tue, 27 Dec 2005 10:52:54 -0600 Message-ID: <11r2sc828n5ri78@news.supernews.com> Currently the top loop is at only 20ft but I am making many contacts. Soon however they will be placed off a sidearm on the tower. The top loop could then be as high as 80 ft. I have read and read about this topic. Does anyone have any first hand knowledge of 6M height above ground comparisons especially for stacked loops? Thanks.... -- Charlie-AD5TH Article: 220708 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Why use s balanced tuner? Date: Mon, 2 Jan 2006 14:56:49 +0000 (UTC) Message-ID: Why use a balanced tuner when a less expensive, easier to operate, unbalanced tuner, in conjunction with a simple choke-balun, will do just as well? Insert the 2-wire choke-balun between the unbalanced tuner and the balanced transmission line. ---- Reg. Article: 220709 of rec.radio.amateur.antenna From: "n9zle" References: Subject: Re: No link attitude! Message-ID: Date: Tue, 27 Dec 2005 17:50:34 GMT Happy New year to all. N9ZLE.COM forum a success!, this is where every one is going. http://www.n9zle.com/forum After one day up there was 8 registered users, and 38 posts. We have had 36 guests come by and take a look at the postings. This forum is slightly different than most internet forums because of the following. We are holding to the Amateur Radio ideals and principles. We have a section for anonymous posts. You may post a link to your personal or commercial site. All opinions are appreciated and accepted as long as they are not slanderous or unclean. There is a callsign lookup at the top of the forum on every page. We are dedicated to helping our fellow HAM in what ever his/her needs are. Please stop by and make a suggestion on any additional forums you believe the BBS may need, 73s and 88s N9ZLE "'Doc" wrote in message news:fDLrf.4483$4o7.4087@newssvr24.news.prodigy.net... > ...or maybe he's just tired of all the garbage being linked to his site > (intentionally or not). Not a 'ham' attitude anymore, or just maybe not > the same kind of ham you are? Get over it... > - 'Doc Article: 220710 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: If the ideal lenght of an antenna is 1/4 Wave lenght then way References: <1135422926.082522.168780@o13g2000cwo.googlegroups.com> <43afeda5_4@newsfeed.slurp.net> <43b1433b_4@newsfeed.slurp.net> Message-ID: <3nfsf.47706$6e1.36320@newssvr14.news.prodigy.com> Date: Tue, 27 Dec 2005 18:04:47 GMT Reg Edwards wrote: > Just to start an argument, why is it that EZNEC shows zero gain for a > vertical antenna in the horizontal plane? Whereas, all your diagrams > show maximum gain along the horizontal. Sometimes the maximum gain is zero dBi? -- 73, Cecil http://www.qsl.net/w5dxp Article: 220711 of rec.radio.amateur.antenna From: "west" References: Subject: Re: 2nd Floor grounding Message-ID: <6zbuf.1589$bd.604@tornado.tampabay.rr.com> Date: Mon, 02 Jan 2006 15:22:42 GMT "Dan Andersson" wrote in message news:YpWcnfnxDahj7SXeSa8jmw@karoo.co.uk... > jawod wrote: > > > After reading the archive regarding 2nd floor grounding, a couple of > > questions. > > > > Outside of sufficiently thick gauge wire and proper depth to grounding > > rod. Are there any ELECTRICAL (nonRF) issues left to resolve for a 2nd > > floor ground? > > > > Several articles referred to long grounding lines being close to 1/4 > > wavelength as being a problem. Is this eliminated with balanced feedline? > > > > Thanks, > > > > john > > > Forget about balun's and other widgetry! > > Get a virtual earth! They are easy to build for all ham bands! > > It's basically a phasing unit for the earth connection which can null the > voltage on the earth at the RF Rig! > > If you don't want to build one, MFJ sells one! > > Cheers > > M0DFI Ok Dan, How about a follow up and give us a link or a schematic to build one? west > > > > Article: 220712 of rec.radio.amateur.antenna From: "west" References: <52adr190uivec9du680b4hd7olru6rqbl6@4ax.com> Subject: Re: 2nd Floor grounding Message-ID: Date: Mon, 02 Jan 2006 15:26:49 GMT "Bill Turner" wrote in message news:gtlgr15u5hipup2i413f12nrd7jca4b5gs@4ax.com... > > ORIGINAL MESSAGE: > > On Sun, 01 Jan 2006 20:10:08 GMT, "west" > wrote: > > > > >"Bill Turner" wrote in message > >news:52adr190uivec9du680b4hd7olru6rqbl6@4ax.com... > >> > >> ORIGINAL MESSAGE: > >> > >> On Sat, 31 Dec 2005 10:16:19 -0500, jawod wrote: > >> > >> >Several articles referred to long grounding lines being close to 1/4 > >> >wavelength as being a problem. Is this eliminated with balanced > >feedline? > >> > > >> >Thanks, > >> > > >> >john > >> > >> > >> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > >> > >> No. You can not "ground" your station for RF, at least not in the > >> sense of running a wire to ground. Don't bother because it isn't > >> necessary anyway. You do need two kinds of ground, one for the AC > >> mains for safety, and one for lightning. > >> > >> RF energy is expensive to generate. Don't waste it by running part of > >> it into a lossy "ground". Keep it up in the air where it belongs. > >> Baluns are your friend. > >> > >> 73, Bill W6WRT > > > >Bill, > > > >I like your answer but it leaves me to want a bit more. Would you mind > >expanding on your 2 paragraphs? Thanks. > > > >west > >AF4GC > > > > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > OK. > > 1. Running a wire from your rig to ground will not do what you think > it will. Any wire is a significant portion of a wavelength at HF and > may be many wavelengths at VHF and UHF. On ten meters, for example, > eight feet is almost exactly 1/4 wavelegth. If you recall your basic > transmission line theory, whatever condition is present at one end of > a 1/4 wave line has just the opposite at the other end. If you really > do have a good ground connection at the grounded end of the wire, the > other is an open circuit. Not very effective for grounding, is it? > > The effect becomes less as you lower the frequency, but never > completely disappears. It is possible to tune out this effect with a > suitable coil and capacitor combination, but it really isn't needed > anyway. MFJ makes a "ground tuner" or whatever they call it, and I > suppose it does work, but think about this: If getting a good RF > ground actually improves your signal, you have a SERIOUS problem in > your antenna. More on this in the next paragraph. > > 2. RF does no good flowing through the earth. None at all. Dirt is a > poor conductor at any ham frequency and you should do your best to > keep your RF out of it. I suspect the idea that "ground" helps your > signal came from the very early days of radio when frequencies were > very low and wavelenghts were very long... miles long in fact. At > those frequencies there are two factors which might make use of ground > desireable: The earth is much more conductive at very low frequencies, > and miles of wire for an antenna is not easily done. Under those > circumstances, working a long wire against ground might actually be a > good idea. None of that applies to ham frequencies, of course. At ham > frequencies, RF works best when it's up in the air, all of it. Not in > the ground, not in your shack, up in the air. > > Keep that in mind and you can't go wrong. > > 73, Bill W6WRT That makes a lot of sense, Bill. It takes talent to take a rather technical concept and put it into an easy to understand explanation. This post is going in my Ham archive. Thanks again. Cordially, west AF4GC Article: 220713 of rec.radio.amateur.antenna From: Registered User Subject: Re: Practical "ideal" antenna Date: Mon, 02 Jan 2006 10:28:27 -0500 Message-ID: References: On Sun, 01 Jan 2006 22:42:53 -0500, jawod wrote: >What would you recommend for a wire antenna if there was enough room for > an 80 dipole? Assume use for 80M , 40M and 20M, > How wide is the area that can fit an 80M dipole? You should consider a large horizontal loop aka Loop Skywire. I also use my loop on 6 and 2 meters with HB balanced tuners. 73 de n4jvp Fritz Article: 220714 of rec.radio.amateur.antenna Subject: Re: FA: 1-Day-Left: Book: SPREAD SPECTRUM SYSTEMS: An Advanced Electronics/Math Book From: "John E. Golden" References: <020120060925139207%clifford@acjkjowimak.com> Message-ID: Date: Mon, 02 Jan 2006 16:12:11 GMT Auctions should be listed in [alt.marketplace.online.ebay]...NOT here! Article: 220715 of rec.radio.amateur.antenna From: Allodoxaphobia Subject: Re: Antenna spacing Date: 2 Jan 2006 16:11:35 GMT Message-ID: References: On Mon, 02 Jan 2006 14:33:18 GMT, Dave Oldridge wrote: > Chris W <1qazse4@cox.net> wrote in news:IT3tf.45644$ih5.19066@dukeread11: > >> I want to put a short 2 meter yagi and a long 70cm yagi on the same >> vertical mast. The 70cm will be a horizontally polarized, center >> mounted 17' boom and the 2 meter will be a vertically polarized, end >> mounted 6 foot boom. How far apart do they need to be? I will only be >> transmitting with one at a time but one could be receiving and the other >> transmitting, the 70cm will be for ATV receive only for now. > > A good rule of thumb is to separate them by at least a half-wave at the > lowest frequency. In this case that means about a meter (39") apart. Not when they are orthogonally polarized. They can be 0.000 wavelengths apart. I.e., in the OP's case, the 2M elements can be _mounted_ on the 70cm's boom. I have a 6-el, close-spaced 2m vertical mounted on the forward boom of my CC A3S. (Not that I give a crap much about 2M vert. propagation...) HNY es 73 Jonesy -- Marvin L Jones | jonz | W3DHJ | linux Pueblo, Colorado | @ | Jonesy | OS/2 __ 38.24N 104.55W | config.com | DM78rf | SK Article: 220716 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Why ground the transmitter? Date: Mon, 2 Jan 2006 17:09:08 +0000 (UTC) Message-ID: Transmitters, like any other 50/60 Hz AC power operated equipment, should be grounded for safety reasons. This is done automatically via the AC power cable regardless of what floor level the transmitter is located. If a balanced feedline is used to the antenna then no other grounding is needed. If the antenna is an endfed wire then, for good RF radiating efficiency, there should be a low impedance connection between the TUNER and ground. The transmitter can still be left to its own devices. If the transmitter and tuner are in the same box then the low impedance ground connection and the AC power ground are in parallel with each other. This results in an even lower impedance RF ground connection. On whatever floor the transmitter + tuner is located, to obtain a low impedance ground, connect everything in sight together via the shortest reasonably possible wires, including hot and cold metal water pipes, the domestic plumbing system, central heating system, not forgetting the incoming water and gas mains. The more the merrier! But only 2 or 3 distributed wires can be very effective. Running a copper strip down an outside wall to a set of shallow buried radial wires in your back yard will be useful provided the length of the copper strip is NOT 1/4-wavelength at your favourite operating frequency. A single ground rod is wasted time, money and labour. But, in general, if you live several floors up in a block of flats, a centre-fed dipole of random length, fed via a 450-ohm ladder-line, plus a tuner plus ckoke-balun, will be the more convenient and RF power-efficient option. Any objections from the experts and Guru's? ---- Reg, G4FGQ. Article: 220717 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: Why use s balanced tuner? Date: Mon, 2 Jan 2006 17:29:42 +0000 (UTC) Message-ID: References: "Tim Wescott" wrote in message news:MOKdnXMrI8I7yiTeRVn-og@web-ster.com... > Reg Edwards wrote: > > > Why use a balanced tuner when a less expensive, easier to operate, > > unbalanced tuner, in conjunction with a simple choke-balun, will do > > just as well? > > > > Insert the 2-wire choke-balun between the unbalanced tuner and the > > balanced transmission line. > > ---- > > Reg. > > > > > Because a balun particularly lossy at high SWR -- with a balanced tuner > followed by a balun you present the balun with the correct impedance, so > it's at its best. > > -- > > Tim Wescott > Wescott Design Services > http://www.wescottdesign.com ======================================== Tim! I don't know what design services you offer but you are WRONG. You must have been reading the wrong comical magazines. A choke balun is amongst the most power-efficient devices. It consists only of a pair of wires wound around a ferrite ring. It is just a very short transmission line of the same length as the wire and has the same very low loss. It has a phase shift of the same length of line. Which is immaterial insofar as the tuner is concerned. It merely changes the tuner L and C settings. ---- Reg. Article: 220718 of rec.radio.amateur.antenna Subject: Re: Why use s balanced tuner? From: Ed References: Message-ID: Date: 02 Jan 2006 17:58:31 GMT > > I don't know what design services you offer but you are WRONG. > > You must have been reading the wrong comical magazines. > > A choke balun is amongst the most power-efficient devices. > I don't know where you get your balun information, but you really need to do more homework, apparently. BALUNs can become quite lossy, depending on the impedence characteristics of the antenna you are trying to match at a particular frequency. There are hundreds of sites where you can find this information.... http://www.cebik.com/a10/ant48.html is just one, for example. Do some homework. Ed K7AAT Article: 220719 of rec.radio.amateur.antenna From: fmmck@aol.com (Fred McKenzie) Subject: Re: measurement error or bad coax?? Date: Mon, 02 Jan 2006 13:02:12 -0500 Message-ID: References: <11r15cu46m2rc9e@corp.supernews.com> <43B0BDEB.5090203@comcast.net> <11r1p7hf402smbd@corp.supernews.com> In article <11r1p7hf402smbd@corp.supernews.com>, Roy Lewallen wrote: > Physically measure the line and calculate the velocity factor. For line > constructed like you describe, the velocity factor should be around 84%. > A significantly lower factor probably means it has water in it. Roy- Is this correct? As described, the "dielectric" is mostly air with some plastic used as a spacer. I would have expected something over 90%. Back to the question of how to get the water out. If there is a large quantity, you might be able to pour it out. Beyond that, is there a common technique used to dry-out cable? (I suppose a shop-vac could be connected to one end and run for a while, on a day with low humidity.) Fred Article: 220720 of rec.radio.amateur.antenna From: "johan aeq" References: Subject: Re: Why use s balanced tuner? Date: Mon, 2 Jan 2006 18:52:55 +0100 Message-ID: <7679a$43b96aae$52ad139c$8967@news.versatel.nl> So a simple "pi filter" withe a bulun will do the same? I always thought that the wide impedancerange of open wire made a currentbalun or voltagebalun unusable. I was just gathering parts to build my own balanced tuner.... Greetings Johan PE1AEQ "Reg Edwards" schreef in bericht news:dpbevh$sd4$1@nwrdmz03.dmz.ncs.ea.ibs-infra.bt.com... > Why use a balanced tuner when a less expensive, easier to operate, > unbalanced tuner, in conjunction with a simple choke-balun, will do > just as well? > > Insert the 2-wire choke-balun between the unbalanced tuner and the > balanced transmission line. > ---- > Reg. > > Article: 220721 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: measurement error or bad coax?? Date: Mon, 2 Jan 2006 18:59:58 +0000 (UTC) Message-ID: References: <11r15cu46m2rc9e@corp.supernews.com> <43B0BDEB.5090203@comcast.net> <11r1p7hf402smbd@corp.supernews.com> To dry out a cable which is partially air-spaced, get a cylinder of dry air or nitrogen and allow the gas to seep through it under a pressure of two or three times atmospheric. It may take several days or more for a length of 100 metres. Measure capacitance at intervals for stability. It speeds things up if the cable can be warmed in an oven at about 60 degrees C. You don't want to melt the polyethylene. The foregoing is based on a vague memory of an episode about 50 years back. ========================================== Article: 220722 of rec.radio.amateur.antenna From: Bill Turner Subject: Re: Why ground the transmitter? Date: Mon, 02 Jan 2006 11:41:10 -0800 Message-ID: References: ORIGINAL MESSAGE: On Mon, 2 Jan 2006 17:09:08 +0000 (UTC), "Reg Edwards" wrote: >If the antenna is an endfed wire then, for good RF radiating >efficiency, there should be a low impedance connection between the >TUNER and ground. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ End fed wires should only be used for transmitting when people are bleeding and the phone is out. 73, Bill W6WRT Article: 220723 of rec.radio.amateur.antenna From: Bill Turner Subject: Re: Why ground the transmitter? Date: Mon, 02 Jan 2006 11:44:19 -0800 Message-ID: References: <1136229473.837565.47960@g44g2000cwa.googlegroups.com> ORIGINAL MESSAGE: Previously posted: >>On whatever floor the transmitter + tuner is located, to obtain a low >impedance ground, connect everything in sight together via the >shortest reasonably possible wires, including hot and cold metal water >pipes, the domestic plumbing system, central heating system, not >>forgetting the incoming water and gas mains. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Yep, those things radiate reeeeeely good, don'tcha know. Busted any pileups lately? 73, Bill W6WRT Article: 220724 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: Why use s balanced tuner? Date: Mon, 2 Jan 2006 20:21:55 +0000 (UTC) Message-ID: References: <7679a$43b96aae$52ad139c$8967@news.versatel.nl> "johan aeq" wrote > So a simple "pi filter" withe a bulun will do the same? > I always thought that the wide impedancerange of open wire made a > currentbalun or voltagebalun unusable. > I was just gathering parts to build my own balanced tuner.... > Greetings Johan PE1AEQ > ========================================== All kinds of peculiar things can happen with voltage baluns and current baluns which have a definite impedance ratio. But my comments apply to a CHOKE balun, the most simple form of balun. It is a pair of wires wound together on a ferrite ring. It is just a very short 2-wire transmission line. For longitudinal currents it is an RF choke, the 2 wires being effectively connected in parallel. The impedances between which it can work are indeterminate. There is no impedance ratio. When connected between a balanced line and an unbalanced tuner, the tuner can be an ordinary simple L, Pi or T network. If you happen to have a balanced tuner, lying around doing nothing, then by all means use it without a balun. But if you don't have a balanced tuner, as is very likely, there's no need to make one. Just use a common or garden unbalanced tuner, which nearly everybody has already got, with a CHOKE balun. The hardest part of making a choke balun is obtaining the ferrite ring. 50mm outside diameter, 30mm inside diameter, permeability 200-400, about 16 turns of twin, flexible, stranded, speaker cable, will be OK for the HF bands. Or similar. All the very best for 2006. ---- Reg, G4FGQ. Article: 220725 of rec.radio.amateur.antenna From: mcalhoun@ksu.edu Subject: Re: Why use s balanced tuner? Date: 2 Jan 2006 15:06:03 -0600 Message-ID: References: <7679a$43b96aae$52ad139c$8967@news.versatel.nl> >....[snip].... >The hardest part of making a choke balun is obtaining the ferrite ring.... Use a TV-set flyback transformer core; see: "another balun design", by Fred Brown, W6HPH, in Ham Radio magazine of May, 1982, pp. 54-57 "Three Baluns for a Buck" by Donald E. Lively, W6SJQ, from a magazine which didn't print either its name or the date on the pages I saved! but it basically says the same thing as the HR article. A hint on p. 37 of the August, 1987, QST describes "The Baby-Bottle Balun", an air-core balun based on DeMaw's article "Simple Coreless Baluns" (QST, Oct. 1980, p. 47; which I apparently didn't appreciate enough to keep). -- --Myron A. Calhoun. Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge PhD EE (retired). "Barbershop" tenor. CDL(PTXS). W0PBV. (785) 539-4448 NRA Life Member and Certified Instructor (Home Firearm Safety, Rifle, Pistol) Article: 220726 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: If the ideal lenght of an antenna is 1/4 Wave lenght then way Date: Tue, 27 Dec 2005 13:12:12 -0800 Message-ID: <11r3bhdh1gfja72@corp.supernews.com> References: <1135422926.082522.168780@o13g2000cwo.googlegroups.com> <43afeda5_4@newsfeed.slurp.net> <43b1433b_4@newsfeed.slurp.net> Reg Edwards wrote: > Just to start an argument, Things are even duller than usual in Rowley Regis, I see. why is it that EZNEC shows zero gain for a > vertical antenna in the horizontal plane? Whereas, all your diagrams > show maximum gain along the horizontal. C'mon Reg, it's only been three months since you last asked this and got it answered(1). The time before that was four years earlier(2), and before that multiple times going back at least to 1998(3). At the rate you're going, you'll be asking it weekly before long. Getting tired of promoting "TLI"s, grumping at "Gurus" (while carefully excluding yourself, of course), grousing about Americans, and asking "Who's Kraus"? C'mon, be original. Surely you can think of a new topic to keep you awake on those long, boring evenings. I've got an idea -- maybe you can use your knowledge to actually help some of the folks who ask serious questions on this newsgroup. For anyone who wants an answer to Reg's perennial question, use groups.google.com to look up the following threads on this newsgroup, where Reg has asked the same question and where it's been answered: (1) "best HF antenna system next to a trailer?", Sept. 2005 (2) "40M Delta Loop Advice Needed:", May 2001 (3) "Raised V's burried ground systems." [sic], Feb. 2000 "Ground Radial system comparisons", April 1999 "Is there", Aug. 1998 "Better for DXing: Beam or vertical?", Aug. 1998 Roy Lewallen, W7EL Article: 220727 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Standing Waves (and Impedance) Date: Tue, 27 Dec 2005 13:22:19 -0800 Message-ID: <11r3c4d6j8il978@corp.supernews.com> References: <5Uoqf.43886$6e1.2147@newssvr14.news.prodigy.com> <43ab7ab2@kcnews01> <43AF3FFC.8060502@comcast.net> <527e$43b0776a$97d55fa7$15010@ALLTEL.NET> <18j2r1htui6k0q8en625ouj51jft58v5o6@4ax.com> <43b16164$1_4@newsfeed.slurp.net> Richard Fry wrote: > > If you are still thinking of the broadcast television signal, the audio > portion is not a subcarrier -- it is a discrete carrier whose modulation > can be detected by any receiver capable of FM demodulation, and able to > tune to its r-f center frequency. > You've described how it's commonly generated. But is the end result any different than if it were generated instead by modulation of the main carrier by an ideal modulation system not having the practical problem of intermodulation distortion? That is, isn't the end result identical to a subcarrier? When I worked in radio broadcasting in the '60s, we generated an FM (SCA) subcarrier in addition to the stereo subcarrier by modulating the transmitter. Some stations had multiple SCA subcarriers. Roy Lewallen, W7EL Article: 220728 of rec.radio.amateur.antenna From: "F4DRH" References: Subject: Re: Practical "ideal" antenna Date: Mon, 2 Jan 2006 22:45:16 +0100 Message-ID: <43b99eec$0$20169$8fcfb975@news.wanadoo.fr> Hello If you want to operate on several bands .... I recommand you the center feeded dipole. I use en 2 x 20 m in inverted V configuration. It works fine. Antenna: http://www.barbaxoops.com/modules/xcgal/displayimage.php?pid=4&album=7&pos=3 Antenna tuner: http://www.barbaxoops.com/modules/xcgal/displayimage.php?pid=46&album=7&pos=0 The home made 300 ohms feeder: http://www.barbaxoops.com/modules/xcgal/displayimage.php?pid=57&album=7&pos=2 Good luck and happy new year. Jean-Marc F4DRH www.barbaxoops.com "jawod" a écrit dans le message de news: f23fd$43b8a13e$42a1bfc2$2968@FUSE.NET... > What would you recommend for a wire antenna if there was enough room for > an 80 dipole? Assume use for 80M , 40M and 20M, > > Thanks Article: 220729 of rec.radio.amateur.antenna From: Owen Duffy Subject: Re: using an HP 8405A to measure SWR ? Message-ID: References: <1ZmdnY0padRtpyreRVn-sQ@comcast.com> <7sSdnWELDbgfASTenZ2dnUVZ_tGdnZ2d@comcast.com> Date: Mon, 02 Jan 2006 21:56:37 GMT On Mon, 02 Jan 2006 13:34:54 -0800, dansawyeror wrote: >Owen, > >That idea seems to work. I set it up and then looked and the 'interference', the >change in phase based on changing the pad. Zero pad showed several degrees phase >shift from -40 dbm, 10 dbm showed small shift, and 20, 30, and 40 were all about >equal. I decided on 20 dbm as a practical base. This doesn't make sense... are you using "dbm" to mean decibels of attenuation, usually written "dB". The units "dBm" are usually written to qualify a power level with respect to one milliwatt. The attenuator on your sig gen might be marked in dBm, but that applies to the combination of the oscillator, possibly its level meter, and the attenuator as a system. Using the wrong terms for things is often a result of a concept gap! A 20dB attenuator will reduce the effect of the reflected component to about the same level as you would expect from a practical directional coupler, more attenuation is better if you have the power from the sig gen and the VVM probe chan can operate at the higher input level. Owen -- Article: 220730 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Dipoles and the rig's RF ground... Date: Mon, 02 Jan 2006 14:23:25 -0800 Message-ID: <11rj9uu7bkogd37@corp.supernews.com> References: <1136148463.132269.164130@g49g2000cwa.googlegroups.com> Dave Oldridge wrote: > > If the antenna is TRULY balanced and the feedline dressed well away from it > at right angles you should have no common-mode currents on the feedline. >. . . That only prevents one of the two ways common mode current can be created, by coupling. It can also be created by conduction. A common example is a coax-fed dipole, where the current in the outer feedline conductor splits between the antenna conductor and the outside of the coax. An equivalent problem can occur when a dipole is fed with symmetrical line such as ladder line, and one conductor of the line is connected to the rig's chassis at the rig end. The current on the inside of the chassis is equal to the current from the "hot" conductor, and this splits between the transmission line conductor and the outside of the chassis. A detailed explanation of conducted common mode current can be found at http://eznec.com/Amateur/Articles/Baluns.pdf. Roy Lewallen, W7EL Article: 220731 of rec.radio.amateur.antenna From: 'Doc Subject: Re: Why ground the transmitter? References: <1136229473.837565.47960@g44g2000cwa.googlegroups.com> Message-ID: Date: Mon, 02 Jan 2006 22:23:22 GMT MK, Unfortunately, grounds are sometimes necessary (neighbor, TVI/RFI), even with dipoles/loops. Wish it weren't, I'm lazy... 'Doc Article: 220732 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: measurement error or bad coax?? Date: Mon, 02 Jan 2006 14:31:04 -0800 Message-ID: <11rjad95v7gfj8f@corp.supernews.com> References: <11r15cu46m2rc9e@corp.supernews.com> <43B0BDEB.5090203@comcast.net> <11r1p7hf402smbd@corp.supernews.com> Fred McKenzie wrote: > In article <11r1p7hf402smbd@corp.supernews.com>, Roy Lewallen > wrote: > > >>Physically measure the line and calculate the velocity factor. For line >>constructed like you describe, the velocity factor should be around 84%. >>A significantly lower factor probably means it has water in it. > > > Roy- > > Is this correct? As described, the "dielectric" is mostly air with some > plastic used as a spacer. I would have expected something over 90%. I was going by the manufacturer's specifications. I've never used this stuff myself. I think if you look at the construction you'll find more plastic and less air than you might expect. > Back to the question of how to get the water out. If there is a large > quantity, you might be able to pour it out. Beyond that, is there a > common technique used to dry-out cable? (I suppose a shop-vac could be > connected to one end and run for a while, on a day with low humidity.) Hopefully someone else can help you there. Roy Lewallen, W7EL Article: 220733 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: using an HP 8405A to measure SWR ? Date: Mon, 02 Jan 2006 14:35:42 -0800 Message-ID: <11rjalv5c4p4n4a@corp.supernews.com> References: <1ZmdnY0padRtpyreRVn-sQ@comcast.com> <1cjer19bq1ivqfusjudsf4e4oqnr1b71ar@4ax.com> <8e2fr1dbcoajchpl8ehg6j4od0od8mg7f1@4ax.com> <7sSdnWALDbhwASTenZ2dnUVZ_tGdnZ2d@comcast.com> dansawyeror wrote: > Now that the setup is reading consistently I will 'test' a loaded 2m > monopole over a 1 m**2 ground plane. I suggest that you start with an unloaded monopole or some very simple antenna with a well known impedance. (You will of course have to know and allow for the effect of the finite ground plane.) You also need to take measures to prevent coupling between the antenna and the outside of the feedline. The ground plane you mention will help, but there can still be substantial coupling. Some high impedance ferrite beads at the feedpoint and another set about a quarter wavelength down should reduce the coupling to a small value. Roy Lewallen, W7EL Article: 220734 of rec.radio.amateur.antenna From: "Paul P" References: <8eednR8-kb5f4CzeRVn-sw@comcast.com> Subject: Re: OT HX-50 schematic please. Message-ID: Date: Tue, 27 Dec 2005 22:23:52 GMT "Amos Keag" wrote in message news:8eednR8-kb5f4CzeRVn-sw@comcast.com... > rec.radio.amateur.boatanchors ??? Cool thanks, Paul Article: 220735 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: using an HP 8405A to measure SWR ? Date: Mon, 02 Jan 2006 16:21:48 -0800 Message-ID: <11rjgst2n8hun49@corp.supernews.com> References: <1ZmdnY0padRtpyreRVn-sQ@comcast.com> <1cjer19bq1ivqfusjudsf4e4oqnr1b71ar@4ax.com> <8e2fr1dbcoajchpl8ehg6j4od0od8mg7f1@4ax.com> <7sSdnWALDbhwASTenZ2dnUVZ_tGdnZ2d@comcast.com> <11rjalv5c4p4n4a@corp.supernews.com> <43B9C0DA.6010305@comcast.net> dansawyeror wrote: > I proceeded before reading this note. The procedure was to zero the > phase meter on an short and then to test the loaded 2m vertical. The > result was +10 dbm forward (before the 20 dbm pad) and -50 dbm > reflected. The coupler measures about -14 dbm. The total was about -60 > dbm, with 34 db of that due to the pad and coupler. The net is -26 db > forward - reflected. > > (The phase angle and reflected ware very touchy. It was almost > impossible to adjust by changing frequency. It was easier to 'adjust' it > by sitting very still and moving my arm.) > > The antenna is a copy from the ARRL handbook. It is a 4 inch segment, a > 1 inch long by 3/4 inch diameter 5 turn coil, and a 4 inch tip. It is > mounted over a 2 foot square aluminum plate. This antenna should have an > input impedance less then 20 Ohms. How did you arrive at this figure? I wouldn't hazard a guess without modeling it. > How can it measure very close to 50 Ohms? 1. Inductor loss. 2. Effect of finite size ground plane. 3. Coupling to feedline. 4. Measurement error. Is there something wrong with > this analysis? I don't know. What should the impedance really be? Roy Lewallen, W7EL Article: 220736 of rec.radio.amateur.antenna From: "Richard Fry" References: <5Uoqf.43886$6e1.2147@newssvr14.news.prodigy.com> <43ab7ab2@kcnews01> <43AF3FFC.8060502@comcast.net> <527e$43b0776a$97d55fa7$15010@ALLTEL.NET> <18j2r1htui6k0q8en625ouj51jft58v5o6@4ax.com> <43b16164$1_4@newsfeed.slurp.net> <11r3c4d6j8il978@corp.supernews.com> Subject: Re: Standing Waves (and Impedance) Date: Tue, 27 Dec 2005 17:04:50 -0600 Message-ID: <43b1c7d3$1_4@newsfeed.slurp.net> "Roy Lewallen" wrote > Richard Fry wrote: > You've described how it's commonly generated. But is the end result any > different than if it were generated instead by modulation of the main > carrier by an ideal modulation system not having the practical problem of > intermodulation distortion? That is, isn't the end result identical to a > subcarrier? ____________ No, in that an aural subcarrier would disappear without a visual carrier to convey it. TV aural via a standalone r-f transmission system would not. RF Article: 220737 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Current and voltage distribution on an antenna. Date: Mon, 02 Jan 2006 18:28:17 -0800 Message-ID: <11rjoa2qen3k216@corp.supernews.com> References: <7Ahuf.287$WY5.73@newsread2.news.pas.earthlink.net> W. Watson wrote: > There's a figure at the bottom of > that shows current > distribution on > an antenna. Is there some book or source that describes how figures B and C > and produced? A lot of authors of antenna and electromagnetics texts avoid the issue. There's a decent analysis in King, Mimno, and Wing, _Transmission Lines, Antennas, and Waveguides_. The problem is much more difficult when the antenna is longer than a half wavelength or when the wire diameter becomes significant. In those cases, a much more complex calculation is necessary, with only approximate results being available from closed form solutions. Numerical solution of a triple integral equation is the method usually used. That approach is necessary when there are nearby current-carrying conductors, since that alters the current distribution in ways which are usually too complex for other methods. A brief discussion of several methods of approaching the problem can be found in Sec. 14.11, "The Cylindrical Antenna Problem", in Jordan and Balmain, _Electromagnetic Waves and Radiating Systems". > I'm guessing that one starts with an open ended transmission line, and > looks > at how the E and B fields are distributed along it. Then one peels the open > end back until the two lines are pointing away from one another. One then > ends up with E fields pretty much in a plane directed from one point on one > side of the wire to the similar point on the other wire. Similarly the B > fields encircle each wire. On one side they have a CC direction and the > other a CC direction (looking in the direction of the current). Using a transmission line as an analogy for antenna operation works just well enough to be dangerous. While it's a way to get an intuitive understanding of antenna operation, taking it too far can lead to some erroneous conclusions. One fundamental limitation is that classical analysis of a transmission line depends on the assumption that no radiation occurs, and that's certainly not the case for an antenna. > As a separate item, it would also seem that for a transmission line that is > open ended the current flowing in one wire induces a current to flow in the > opposite direction in the other wire. That is the current flows in the one > wire because it does so by induction rather than it being physically > part of > the other wire. Yes, that's correct. If you assume that the entire field from one wire couples to the other, which is strictly true for coax and approximately true for twinlead, it follows from Ampere's law that the current on one wire must be equal and opposite that on the other. This assumption of field coupling isn't true for an antenna, although coupling does indeed exist and it does have a profound effect on the currents. Roy Lewallen, W7EL Article: 220738 of rec.radio.amateur.antenna From: David Subject: Still have problems reading MJF-269 Analyzer Message-ID: Date: Tue, 03 Jan 2006 02:45:50 GMT Hi, I have a matching circuit that matches 50 Ohms to 4500 Ohms in parallel with 2.5pF at 45MHz. The coil was measured at 147nH with a Q of 50 at 45 MHz. The circuit is a C-Tap typology with following values. Tap input to ground = 784pF Tap to hot side of coil = 92pF Par inductor = 147nH My design calculations predict Loaded Q = 26 and BW = 1.7 MHz. I used a 50p trimmer in par with 68pF cap for top of tap to fine tune. A 4k7 resistor and 2p2 cap were placed across the output to simulate the correct load. The test results show BW = 1.7 MHz and Loaded Q = 24.7 (agree with calculated values). When installed on the IF front end, the expected sensitivity is achieved when tuned. This would indicate most of the signal must be getting through or sensitivity would be effected due to mismatch. All seems to look ok but when I attach the MJF-269 Analyzer I get impedance of 280 angle 35 degrees (240 -j 179) for the impedance, I get SWR = 6.1 , return loss of 2.8dB and match efficiency of 48%. I cannot understand why there is such a discrepency between the design values and tested results (using sig gen, spectrum analyzer and power meter) compared to the MJF-269. Is there something I am doing wrong here or is it a mis-interpretation of displayed values ? Thanks for any help. Article: 220739 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: using an HP 8405A to measure SWR ? Date: Tue, 3 Jan 2006 03:25:40 +0000 (UTC) Message-ID: References: <1ZmdnY0padRtpyreRVn-sQ@comcast.com> <7sSdnWELDbgfASTenZ2dnUVZ_tGdnZ2d@comcast.com> "Owen Duffy" wrote > Using the wrong terms for things is often a result of a concept gap! > =========================================== . . . . . and using the wrong name for an SWR meter often results in a concept gap. ---- Reg. Article: 220740 of rec.radio.amateur.antenna From: Bill Turner Subject: Re: Why ground the transmitter? Date: Mon, 02 Jan 2006 20:30:21 -0800 Message-ID: References: ORIGINAL MESSAGE: On Tue, 03 Jan 2006 00:45:45 GMT, Mike wrote: >Why is that? I use them all the time with excellent results. >Mike ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Your results are "excellent' because you've never used anything better. Put up a modest yagi and prepare to be amazed. Even a good dipole will beat a longwire worked against ground. 73, Bill W6WRT Article: 220741 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: Current and voltage distribution on an antenna. References: <7Ahuf.287$WY5.73@newsread2.news.pas.earthlink.net> Message-ID: Date: Tue, 03 Jan 2006 06:00:07 GMT W. Watson wrote: > I'm guessing that one starts with an open ended transmission line, and > looks at how the E and B fields are distributed along it. It's a standing-wave antenna. That means there is a forward wave and a reflected wave. The forward current adds to the reflected current all up and down the dipole. The magnitude of the reflected current arriving back at the feedpoint is approximately 90% of the forward current and are assumed to be approximately equal by Kraus. The forward current and reflected current are very close to being in phase at the feedpoint. The forward and reflected current are equal in magnitude and 180 degrees out of phase at the tip of the dipole. The feedpoint impedance of a 1/2WL dipole is approximately (|Vfor|-|Vref|)/(|Ifor|+|Iref|). The angle of the reflected current is close to equal in magnitude and opposite in sign to the forward current at any point along the dipole so the angle of the net current is very close to zero degrees. The net current pictured on that web page is a standing current wave with the same basic shape as in a 1/4WL open-circuit stub. That current distribution is illustrated in any antenna book, including Kraus and Balanis. It's also in my 15th edition ARRL Antenna Book. -- 73, Cecil http://www.qsl.net/w5dxp Article: 220742 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: building an antenna from midload ?? Date: Tue, 3 Jan 2006 05:54:44 +0000 (UTC) Message-ID: References: <11r15cu46m2rc9e@corp.supernews.com> <43B0BDEB.5090203@comcast.net> <11r1p7hf402smbd@corp.supernews.com> <43B9ADEC.3030209@comcast.net> Dan, To read the notes again, it is necessary to "go back to the start of program" from the 'results' screen. The loading coil is always continuous from one end to the other. There are no breaks or cuts in it. The coax line can have its braid attached directly to the centre of the coil with the inner coaxial conductor tapped into the coil a few turns away from the centre. But this is not recommended. It is much easier to construct and adjust the number of link-turns by using a link-coupling coil. The link-coupling coil is wound over the top of the center of the main coil and is well insulated from it. You can use the same type of wire for both main and coupling coils. Close-wound enamelled magnet wire is suitable except at the higher frequencies where not many turns are needed. With link coupling either coax or balanced-twin feedline can be used. It is easier to change the number of turns on a link coil. It may be necessary to change the number of turns on the link coil to provide an impedance match with the feedline impedance. The computed number of turns on the link coil is approximate. Only a whole number of turns is possible in practice. When the feedline is directly tapped into the main coil, a soldering iron and other work is needed to change the number of tap turns. Don't forget the antenna is a one-frequency, one-band, very narrow bandwidth antenna. To resonate the antenna exactly to a particular frequency it is necesary to prune the length of the loading wires or loading rods at each end of the main coil. The antenna is easier to construct and adjust for use in a confined space such as an attic, at frequencies between 1.8 and 10 MHz. Good DX in 2006. ---- Reg, G4FGQ. ============================================ I am planning on building an antenna based on midload.exe. For some reason the > 'notes' do not appear so I cannot read them. > > I plan to feed the antenna with coax. What are the hookup instructions? Is the > coil actually cut? What does link coupling refer to? > > There is a similar antenna in the ARRL handbook, however it does not appear to > be cut. The shield is connected to a center tap and the coax center is tapped a > few turns out. > > The program predicts 40 turns with a coil tap of .8 turns. Which connection is > this? > > Thanks - Dan > Article: 220743 of rec.radio.amateur.antenna From: Owen Duffy Subject: Re: using an HP 8405A to measure SWR ? Message-ID: References: <1ZmdnY0padRtpyreRVn-sQ@comcast.com> <1cjer19bq1ivqfusjudsf4e4oqnr1b71ar@4ax.com> <8e2fr1dbcoajchpl8ehg6j4od0od8mg7f1@4ax.com> <7sSdnWALDbhwASTenZ2dnUVZ_tGdnZ2d@comcast.com> <11rjalv5c4p4n4a@corp.supernews.com> <43B9C0DA.6010305@comcast.net> Date: Tue, 03 Jan 2006 06:42:53 GMT On Mon, 02 Jan 2006 16:10:02 -0800, dansawyeror wrote: > The coupler measures >about -14 dbm. What does this mean? Are you trying to tell us that the power on the coupler port is 14dB less than the through power? What has dBm got to do with it? You didn't report the power in the coupler port with a s/c and / or o/c at the measurement plane. Did you perform this cal? >(The phase angle and reflected ware very touchy. It was almost impossible to >adjust by changing frequency. It was easier to 'adjust' it by sitting very still >and moving my arm.) That is understandable. How much coax between the A probe and the load, and the B probe and the load... how many degress does this total electrical length change for a 1% change in frequency? Does that explain some of the phase sensitivity? > >The antenna is a copy from the ARRL handbook. It is a 4 inch segment, a 1 inch >long by 3/4 inch diameter 5 turn coil, and a 4 inch tip. It is mounted over a 2 >foot square aluminum plate. This antenna should have an input impedance less >then 20 Ohms. Don't you need to measure some "known" loads. Why not try a 50 ohm load tee'd to a s/c stub (quarter wave at a known frequency) and see if you get the predictable results at different frequencies around resonance. Then try two 50 ohm loads in parallel with the stub. (339mm of RG58C/U should have a Z of around 6000+j0 ohms at around 146MHz, at half that frequency it should be 0.85+j50, etc... > >How can it measure very close to 50 Ohms? Is there something wrong with this >analysis? See if you can trust your measurements on known loads before wondering why the unknown load isn't what you expect when using unknown measurement technology... too many unknowns. Owen -- Article: 220744 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Why ground the transmitter? Date: Mon, 02 Jan 2006 23:19:15 -0800 Message-ID: <11rk9bkpb525lfa@corp.supernews.com> References: <1136229473.837565.47960@g44g2000cwa.googlegroups.com> <1136269078.138519.170020@g49g2000cwa.googlegroups.com> nm5k@wt.net wrote: >> Unfortunately, grounds are sometimes necessary (neighbor, TVI/RFI), >>even with dipoles/loops. Wish it weren't, I'm lazy... >> 'Doc > > > Hummmm...Maybe, but I'm having a hard time of thinking > of the uses of a ground to cure said problems... Most > of those problems would seem to be better cured using chokes, > etc. If the problem is fundamental overload to their gear, any > grounding on your end won't cure that. > MK If you have an imbalance current trying to find its way to ground, it'll take the path of least resistance (technically, impedance). If that path is the mains wiring, you have a lot of potential for RFI. If you can convince some of that current to go elsewhere by "grounding" your station, you're likely to cut down the RFI. But a better solution is to get those feedline currents balanced so you won't have any imbalance or "ground" current to deal with in the first place. It brings the added benefit of putting the power into your antenna to be radiated rather than being radiated from the conductors carrying the imbalance current. Roy Lewallen, W7EL Article: 220745 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: Why ground the transmitter? Date: Tue, 3 Jan 2006 08:32:47 +0000 (UTC) Message-ID: References: <1136229473.837565.47960@g44g2000cwa.googlegroups.com> <1136269078.138519.170020@g49g2000cwa.googlegroups.com> <11rk9bkpb525lfa@corp.supernews.com> Radiation from the feedline is usually the least of one's problems. 99 % of RFI is due to radiation from the very nearby antenna. ========================================== Article: 220746 of rec.radio.amateur.antenna From: Owen Duffy Subject: Re: using an HP 8405A to measure SWR ? Message-ID: References: <1ZmdnY0padRtpyreRVn-sQ@comcast.com> <1cjer19bq1ivqfusjudsf4e4oqnr1b71ar@4ax.com> <8e2fr1dbcoajchpl8ehg6j4od0od8mg7f1@4ax.com> <7sSdnWALDbhwASTenZ2dnUVZ_tGdnZ2d@comcast.com> <11rjalv5c4p4n4a@corp.supernews.com> <43B9C0DA.6010305@comcast.net> Date: Tue, 03 Jan 2006 08:36:41 GMT On Mon, 02 Jan 2006 23:06:43 -0800, Richard Clark wrote: >On Tue, 03 Jan 2006 06:42:53 GMT, Owen Duffy wrote: > >>>(The phase angle and reflected ware very touchy. It was almost impossible to >>>adjust by changing frequency. It was easier to 'adjust' it by sitting very still >>>and moving my arm.) >> >>...Does that >>explain some of the phase sensitivity? > >Hi Owen, > >Being very touchy, especially to the specifics of sitting very still, >sounds like classic common mode problems. Yes it does Richard. I saw Roy's response regarding isolation of the feedline, and it is a valid comment. My comment was towards the reported frequency sensitivity... until the effect of the propagation delay is removed from the results, the underlying impedance is obsured. Owen -- Article: 220747 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Why ground the transmitter? Date: Tue, 03 Jan 2006 02:02:28 -0800 Message-ID: <11rkitl79f70v56@corp.supernews.com> References: <1136229473.837565.47960@g44g2000cwa.googlegroups.com> <1136269078.138519.170020@g49g2000cwa.googlegroups.com> <11rk9bkpb525lfa@corp.supernews.com> That's an interesting statistic. How did you arrive at it? Roy Lewallen, W7EL Reg Edwards wrote: > Radiation from the feedline is usually the least of one's problems. > > 99 % of RFI is due to radiation from the very nearby antenna. > > ========================================== > > Article: 220748 of rec.radio.amateur.antenna Date: Tue, 03 Jan 2006 10:15:14 +0000 From: cut this out <""lionelcarter\"@(cut this out)lineone.net"> Subject: Re: Ideas for Inside 144/440 Mhz antenna References: <11rdteenct18p09@corp.supernews.com> Message-ID: <43ba4d7f$1_2@mk-nntp-1.news.uk.worldonline.com> If it works for you OK, but I would be very wary of putting a mag mount too close to my rig in case the innards are not effectively shielded. Butch Magee wrote: > I have a dualbander with a magmount stuck to the rig itself. It works > just fine. > > KF5DE > > Gary KW4Z wrote: > >> I am not looking to punch any holes in the walls or ceiling to get a coax >> from an outdoor 144/440 Mhz antenna. I'm setting up a mobile rig powered >> off an Astron Power Supply in order to allow my wife to communicate on >> some >> of the local repeaters so she can talk to and follow me into work. >> >> The antenna can be simple as something that has a magnetic mount that >> sets >> on top of the power supply or something that might present some >> measure of >> gain. If any of you have eny experience with either building >> antennas or >> have one you purchased that you really like I would love to know what >> it is >> and consider it to fit my needs. >> >> Thanks in advance >> >> Gary >> Article: 220749 of rec.radio.amateur.antenna From: "David G. Nagel" Subject: Re: More BPL rollout. sigh... Date: Tue, 27 Dec 2005 17:26:59 -0600 Message-ID: <11r3jeeg3fqhsa0@corp.supernews.com> References: <43AA4CDA.46CD92EB@nobplforme.com> Jim Higgins wrote: > On Thu, 22 Dec 2005 14:41:03 +0000 (UTC), gsm@mendelson.com (Geoffrey > S. Mendelson) wrote: > > >>Jim Higgins wrote: >> >> >>>The result? BPL economics absolutely cannot support the >>>promises made for it. If they have to fulfill the promises it's dead >>>before it starts. >> >>The flaw in your logic is that Google invested $100,000,000 on Current >>Communications. If the trial flops economicaly, they can just keep >>pouring money into it until they corner the market. >> >>The way I figure it is they just raised $4b in a stock offering. If the >>$3b left over after buying part of AOL isn't enough, they will just >>sell more stock. > > > > And the flaw in your analysis is that they'll make up for a losing > proposition with sheer volume. > > The thing is that BPL doesn't scale up all that well. The power line > bandwidth is eaten up far faster than cable bandwidth and they can't > get more by just adding some new transducers using a different > wavelength and keep going. BPL will slow down quickly as subscribers > are added and it won't be as fast as cable even with only one > subscriber. The BPL industry has sold the power companies a bill of > goods and the few who aren't simply abandoning it after initial trials > need to be fought at a level that doesn't require FCC involvement. > > I'm sick and tired of seeing the ARRL humping the FCC's leg over BPL > and being ignored. It's time to add another weapon to the arsenal. If > not an approach involving regulating BPL to death thru the state PUCs, > what do you suggest? > > > >>Every time you click on an "ads by google", you are supporting BPL. >>Every time you vist a web site with "ads by google" you are supporting BPL. >>If you bought Google stock, or invested in a mutual fund that did, >>you are supporting BPL. > > > > I don't believe for a second that a call to not use Google will have > any effect on BPL. It will take millions of people cooperating to > make that approach effective and you'll never get that many to > cooperate. Getting the attention of state PUCs takes far fewer people > to accomplish. > Unless you have one like Indiana's. They have stated that if the FCC is happy there is no reason for them to get involved. Dave N Article: 220750 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: Why ground the transmitter? Date: Tue, 3 Jan 2006 12:52:55 +0000 (UTC) Message-ID: References: <1136229473.837565.47960@g44g2000cwa.googlegroups.com> <1136269078.138519.170020@g49g2000cwa.googlegroups.com> <11rk9bkpb525lfa@corp.supernews.com> "Ian White GM3SEK" wrote > Reg Edwards wrote: > >Radiation from the feedline is usually the least of one's problems. > > > >99 % of RFI is due to radiation from the very nearby antenna. > > > > That's rubbish - have you ever *measured* the RF currents in your > station wiring? > ========================================== No, but I HAVE measured RF current in the antenna - from where most RFI originates. Have you ever run 400 watts from an 80 meter 1/2-wave dipole a few feet above your roof and not far from the TV aerial? ---- Reg. Article: 220751 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: Why ground the transmitter? Date: Tue, 3 Jan 2006 14:07:11 +0000 (UTC) Message-ID: References: <1136229473.837565.47960@g44g2000cwa.googlegroups.com> <1136269078.138519.170020@g49g2000cwa.googlegroups.com> <11rk9bkpb525lfa@corp.supernews.com> <11rkitl79f70v56@corp.supernews.com> Roy! Just a legitimate crude guess - perhaps biassed a little in the opposite direction to the normal excessive bias. If I remember correctly, you, your very good self, used Eznec to demonstrate that even under the most adverse worst-case conditions you could think of, power radiated from the feedline is only a fraction of that radiated from the antenna. . . . . . and the equipment being interfered with is in the near-field of the antenna just as it is in the near-field of the feedline. That, for most people, includes your next-door neighbors. Especially if your next-door neighbors happen to be within the antenna beam. ---- Reg. ============================================ "Roy Lewallen" wrote > That's an interesting statistic. How did you arrive at it? > > Roy Lewallen, W7EL > > Reg Edwards wrote: > > Radiation from the feedline is usually the least of one's problems. > > > > 99 % of RFI is due to radiation from the very nearby antenna. Article: 220752 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: Why ground the transmitter? References: <1136229473.837565.47960@g44g2000cwa.googlegroups.com> <1136269078.138519.170020@g49g2000cwa.googlegroups.com> <11rk9bkpb525lfa@corp.supernews.com> Message-ID: <6hwuf.51316$6e1.21830@newssvr14.news.prodigy.com> Date: Tue, 03 Jan 2006 14:57:06 GMT Reg Edwards wrote: > Radiation from the feedline is usually the least of one's problems. > > 99 % of RFI is due to radiation from the very nearby antenna. In some cases, that nearby antenna is a counterpoise laid across the floor which some people consider to be a "ground" of sorts. :-) -- 73, Cecil http://www.qsl.net/w5dxp Article: 220753 of rec.radio.amateur.antenna Subject: Re: Dipoles and the rig's RF ground... From: Dave Oldridge References: <1136148463.132269.164130@g49g2000cwa.googlegroups.com> <11rj9uu7bkogd37@corp.supernews.com> Message-ID: Date: Tue, 03 Jan 2006 15:49:42 GMT Roy Lewallen wrote in news:11rj9uu7bkogd37@corp.supernews.com: > Dave Oldridge wrote: >> >> If the antenna is TRULY balanced and the feedline dressed well away >> from it at right angles you should have no common-mode currents on >> the feedline. > >. . . > > That only prevents one of the two ways common mode current can be > created, by coupling. It can also be created by conduction. A common > example is a coax-fed dipole, where the current in the outer feedline > conductor splits between the antenna conductor and the outside of the > coax. An equivalent problem can occur when a dipole is fed with > symmetrical line such as ladder line, and one conductor of the line is > connected to the rig's chassis at the rig end. The current on the > inside of the chassis is equal to the current from the "hot" > conductor, and this splits between the transmission line conductor and > the outside of the chassis. A detailed explanation of conducted common > mode current can be found at > http://eznec.com/Amateur/Articles/Baluns.pdf. > > Roy Lewallen, W7EL Still, if the antenna is TRULY balanced (a situation that only rarely actually happens), you won't get common-mode currents. I've never had a problem with them with well-grounded (from an RF standpoint) ground- mounted verticals either. Essentially this is why I recommend using open wire or twinlead and feeding it through a proper balanced-line tuner. Years ago, I built an amplifier that literally had a balanced line output and fed a 600-ohm feeder direct off two taps on its output coil. That feedline was only ten feet long and I worked a TON of 80m DX an the inverted vee that it connected to. And I could always tap the coil so as to have ZERO RF in the shack (though my landlady's little 7.5 watt light bulbs used to light on some frequencies when the house wiring picked up direct from the antenna). -- Dave Oldridge+ ICQ 1800667 Article: 220754 of rec.radio.amateur.antenna From: chuck Subject: Re: Dipoles and the rig's RF ground... References: <1136148463.132269.164130@g49g2000cwa.googlegroups.com> <11rj9uu7bkogd37@corp.supernews.com> Message-ID: Date: Tue, 03 Jan 2006 16:24:01 GMT Is it not true that if the currents on the transmission line are unbalanced (i.e., unequal on the two conductors) then the transmitter must already be connected to ground? If not, what is the path of the differential current? Chuck Dave Oldridge wrote: > Roy Lewallen wrote in > news:11rj9uu7bkogd37@corp.supernews.com: > >> Dave Oldridge wrote: >>> >>> If the antenna is TRULY balanced and the feedline dressed well away >>> from it at right angles you should have no common-mode currents on >>> the feedline. >> >. . . >> >> That only prevents one of the two ways common mode current can be >> created, by coupling. It can also be created by conduction. A common >> example is a coax-fed dipole, where the current in the outer feedline >> conductor splits between the antenna conductor and the outside of the >> coax. An equivalent problem can occur when a dipole is fed with >> symmetrical line such as ladder line, and one conductor of the line is >> connected to the rig's chassis at the rig end. The current on the >> inside of the chassis is equal to the current from the "hot" >> conductor, and this splits between the transmission line conductor and >> the outside of the chassis. A detailed explanation of conducted common >> mode current can be found at >> http://eznec.com/Amateur/Articles/Baluns.pdf. >> >> Roy Lewallen, W7EL > > Still, if the antenna is TRULY balanced (a situation that only rarely > actually happens), you won't get common-mode currents. I've never had a > problem with them with well-grounded (from an RF standpoint) ground- > mounted verticals either. > > Essentially this is why I recommend using open wire or twinlead and > feeding it through a proper balanced-line tuner. Years ago, I built an > amplifier that literally had a balanced line output and fed a 600-ohm > feeder direct off two taps on its output coil. That feedline was only > ten feet long and I worked a TON of 80m DX an the inverted vee that it > connected to. And I could always tap the coil so as to have ZERO RF in > the shack (though my landlady's little 7.5 watt light bulbs used to light > on some frequencies when the house wiring picked up direct from the > antenna). > > Article: 220755 of rec.radio.amateur.antenna From: "Richard Fry" References: <43AF3FFC.8060502@comcast.net> <527e$43b0776a$97d55fa7$15010@ALLTEL.NET> <18j2r1htui6k0q8en625ouj51jft58v5o6@4ax.com> <6383f$43b18c3e$471d2513$27459@ALLTEL.NET> <6bo3r1d3cpu9a81illbs9np90n4sldib3j@4ax.com> Subject: Re: Standing Waves (and Impedance) Date: Tue, 27 Dec 2005 20:53:54 -0600 Message-ID: <43b1fd83_3@newsfeed.slurp.net> "Gary Schafer" wrote > However if the TV video signal was an FM modulated signal rather than > AM then the sound sub carrier would not be visible without the main > video carrier if it was generated as a sub carrier. > The same happens with an FM broadcast SCA sub carrier or the stereo > sub carrier on the main signal. The main signal must first be > demodulated in order to demodulate any sub carrier. _____________ The r-f spectra of TV aural signals and FM SCAs are standalone entities. Each may be fully demodulated by a suitable FM receiver capable of tuning to that r-f spectrum. No "main" carrier is needed. Given, this isn't the conventional practice -- however it would be possible to do. Likewise, the L-R audio information of an FM stereo transmission is a standalone entity, and given a suitable r-f receiver and detector, it can be fully demodulated back to L-R without needing the main carrier. Not conventional or cost-effective, but possible. Of course, the L+R waveform conveyed by the main carrier is necessary to matrix with L-R to produce the L&R channels needed for stereo reproduction by the receiver system. RF Article: 220756 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: Why use s balanced tuner? Date: Tue, 3 Jan 2006 16:37:40 +0000 (UTC) Message-ID: References: Tim! I was out of order confusing your design services with baluns. Please accept my apologies. But I did make it clear that CHOKE baluns were involved. You may see elsewhere what a choke balun actually is. If you already have a balanced tuner then by all means use it. But if you don't have one there's no need to make one or buy one. It is more convenient to use an ordinary unbalanced tuner plus a very simple to make choke balun which has no particular impedance matching properties apart from being a very short length of transmission line of predictable Zo and predictable phase shift which don't matter very much. It seems my rhetorical question has inadvertently stirred up quite a discussion the newsgroup. I wish you much success with Wescott Design Services in 2006. ---- Reg, just a radio amateur, G4FGQ. Article: 220757 of rec.radio.amateur.antenna From: richardharrison@webtv.net (Richard Harrison) Subject: Re: converting dBm to uV/m Date: Tue, 3 Jan 2006 11:10:19 -0600 Message-ID: <7296-43BAAFFB-517@storefull-3254.bay.webtv.net> References: <1hjdr1ta0t4bnu9pprsqmh0itgq03nb6k3@4ax.com> Richard Clark wrote: "---where dBm is frequently a short hand for dB (re1 mW into 600 Ohms)---." I agree, but I`ve worked with communicatiobs systems in which the builder specified signal (test-tone) levels throughout in dBm regardless of the impedance at the particular point. Incinvenient, maybe, but often the conversion factor is specified for reading with a dB meter calibrated for 600 Ohms. dB is a power ratio. dBm is a power level for which the 0 dBm reference is 1 milliwatt. The impedance is not specified. 2 milliwatts is approximately +3 dBm and 1/2 milliwatt is approximately -3 dBm. The a-c voltmeter which reads in dB is likely calibrated at 600 Ohms impedance. Volts vary as the square root of the power. +6 dB is 4X the power but only double the voltage. dBm is frequently specified as a test-tone level at various points throughout a communications system. The dB meter will only be correct when the impedance at the measurement point imatches the impedance for which the meter is calibrated. When the impedance is different, The system builder will often give a correction factor to be used with a 600-Ohm dB meter. Knowing the power level in milliwatts, the a-c volts are easily calculated from the square toot of PR. Best regards, Richard Harrison, KB5WZI Article: 220758 of rec.radio.amateur.antenna From: Bill Turner Subject: Re: 6M stacked loops - best height above ground? Date: Tue, 27 Dec 2005 19:31:29 -0800 Message-ID: References: <11r2sc828n5ri78@news.supernews.com> ORIGINAL MESSAGE: On Tue, 27 Dec 2005 10:52:54 -0600, "Charlie" wrote: >Currently the top loop is at only 20ft but I am making many contacts. Soon >however they will be placed off a sidearm on the tower. > The top loop could then be as high as 80 ft. > >I have read and read about this topic. Does anyone have any first hand >knowledge of 6M height above ground comparisons especially for stacked >loops? Thanks.... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ I'm not that sure about loops, but for yagis working DX, the optimum height seems to be about 35 feet. Higher is better for ground wave, but for DX, 35 is best, believe it or not. This has been proven with crank up towers many times. It may well be the same for loops. 73, Bill W6WRT Article: 220759 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: Why use s balanced tuner? Date: Tue, 3 Jan 2006 17:32:41 +0000 (UTC) Message-ID: References: wrote > My link coupled tuner (Johnson Matchbox) cost me less than 60 USD, I > can tuner faster than a T-type tuner, doesn't need nor use a balun. > (Read one less component and its associated loss). So why would I want > to replace it with something that works almost as good? > > Danny, > K6MHE ========================================== Danny Boy, If you are happy with your link-coupled tuner, which can be either balanced or unbalanced, then by all means stick with it. I must admit it is something I forgot about. Many years back I had a similar commercial tuner. It didn't cover enough bands for me. So I dismantled it. The only parts worth recovering were the slow-motion variable capacitor drives and the nice skirted tuning knobs. Which I still have. They are of sentimental value. Ever since then I have used only home-brewed tuners with coils and capacitors connected with universal alligator clips. But never of the balanced variety. I wish you the very best of DX for 2006. ---- Reg, G4FGQ. Article: 220760 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: Why use s balanced tuner? Date: Tue, 3 Jan 2006 17:58:02 +0000 (UTC) Message-ID: References: Hi Richard (Clark)! As usual you contribute nothing towards the technical knowledge of the readers. Who cares about them anyway? But I'm pleased you are still reading my stuff and am gratified to receive your seasonal greetings. May I, in return, wish You personally, Your Family and Friends, a Prosperous and Peaceful 2006. And while I'm about it, 2007, 2008, 2009 . . . . . ! ---- Yours, Punchinello Article: 220761 of rec.radio.amateur.antenna From: Owen Duffy Subject: Re: coaxpair reflection coeff angle is 'zero' Message-ID: <2h74r1l7553gsr3o2j1rapa5rb9ugvci82@4ax.com> References: Date: Wed, 28 Dec 2005 05:12:54 GMT On Tue, 27 Dec 2005 20:05:37 -0800, dansawyeror wrote: >The program coaxpair does not seem to compute the reflection angle. Is this an >error? Is the cause known? Works allright for me (WAFM). (coaxpair.exe dated 5/10/98) Reflection seem to be at the load end of the line, is that your issue? > >Thanks - Dan -- Article: 220762 of rec.radio.amateur.antenna From: Chris W <1qazse4@cox.net> Subject: Re: Antenna spacing References: Message-ID: Date: Tue, 03 Jan 2006 13:01:32 -0600 Dave Oldridge wrote: >Allodoxaphobia wrote in >news:slrndrik5n.2p1i.bit-bucket@shell.config.com: > > > >>On Mon, 02 Jan 2006 14:33:18 GMT, Dave Oldridge wrote: >> >> >>>Chris W <1qazse4@cox.net> wrote in >>>news:IT3tf.45644$ih5.19066@dukeread11: >>> >>> >>> >>>>I want to put a short 2 meter yagi and a long 70cm yagi on the same >>>>vertical mast. The 70cm will be a horizontally polarized, center >>>>mounted 17' boom and the 2 meter will be a vertically polarized, end >>>>mounted 6 foot boom. How far apart do they need to be? I will only >>>>be transmitting with one at a time but one could be receiving and >>>>the other transmitting, the 70cm will be for ATV receive only for >>>>now. >>>> >>>> >>>A good rule of thumb is to separate them by at least a half-wave at >>>the lowest frequency. In this case that means about a meter (39") >>>apart. >>> >>> >>Not when they are orthogonally polarized. They can be 0.000 >>wavelengths apart. I.e., in the OP's case, the 2M elements can be >>_mounted_ on the 70cm's boom. >> >> > >You're right. I didn't catch the polarization thing. In fact, building >them on the same boom would be quite workable. > > > What if they are 2 different antennas and you can't put them on the same boom, how close can I put them? -- Chris W KE5GIX Gift Giving Made Easy Get the gifts you want & give the gifts they want One stop wish list for any gift, >from anywhere, for any occasion! http://thewishzone.com Article: 220763 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: coaxpair reflection coeff angle is 'zero' Date: Wed, 28 Dec 2005 06:06:24 +0000 (UTC) Message-ID: References: "dansawyeror" wrote in message news:mrmdnRrhheeJki_enZ2dnUVZ_tadnZ2d@comcast.com... > The program coaxpair does not seem to compute the reflection angle. Is this an > error? Is the cause known? > > Thanks - Dan ===================================== Dan, I don't know what you mean by "reflection angle". The program DOES compute the angle of the reflection coefficient. The answer is in the bottom left-hand corner of the screen. When the terminating impedance, Rt+jXt, equals line impedance, Ro+jXo, the magnitude of the reflection coefficient is zero. But zero magnitude cannot have an angle. Its a mathematical impossibility. But when RC = zero the program is obliged to print something for the angle, so it prints an indeterminate angle which can lie randomly anywhere between +180 and -180 degrees. Actually, you can't set the RC exactly to zero because the program only works to 14 decimal places. The randomly generated angle can't be used for anything because when the RC is zero there's nowhere in an equation to insert it. Just forget about it. It's meaningless. And even for a very small magnitude of RC the value of the angle doesn't matter very much. It has little effect on what is being calculated. ---- Reg. Article: 220764 of rec.radio.amateur.antenna From: 'Doc Subject: Re: Why ground the transmitter? References: <1136229473.837565.47960@g44g2000cwa.googlegroups.com> <1136269078.138519.170020@g49g2000cwa.googlegroups.com> Message-ID: Date: Tue, 03 Jan 2006 19:34:04 GMT MK, The 'problem' wasn't completely on my end (neighbor's defective devices), but a good grounding did help cure the a RFI. Is grounding a 'sure thing' as a cure? Nope, but it certainly doesn't hurt if it's at all possible, which isn't always a 'sure thing'. Also used to use a fence around the place as a ground. Very BAD idea since the fence was connected to the neighbor's fence too. Just 'took' the RF closer to the neighbor, probably a 'sort' of direct connection to his 'stuff'. Always a 'bad' idea? No, but something to think about. 'Doc Article: 220765 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: If the ideal lenght of an antenna is 1/4 Wave lenght then way are the Car Cellular antennas are longer then this ? Date: Wed, 28 Dec 2005 06:36:16 +0000 (UTC) Message-ID: References: <1135422926.082522.168780@o13g2000cwo.googlegroups.com> <43afeda5_4@newsfeed.slurp.net> <43b1433b_4@newsfeed.slurp.net> <11r3bhdh1gfja72@corp.supernews.com> Roy, you'll just have to accept the fact that I'm peculiar. But no more peculiar than other frequenters of this newsgroup. I don't think I do much damage. ---- Reg. Article: 220766 of rec.radio.amateur.antenna From: Owen Duffy Subject: Re: using an HP 8405A to measure SWR ? Message-ID: <2jllr1d3bgiod019673n1b00vnfcagj91u@4ax.com> References: <1ZmdnY0padRtpyreRVn-sQ@comcast.com> <7sSdnWELDbgfASTenZ2dnUVZ_tGdnZ2d@comcast.com> Date: Tue, 03 Jan 2006 20:04:02 GMT On Tue, 03 Jan 2006 08:25:48 -0700, Wes Stewart wrote: ... >Owen > >Let me pick a nit or two. > >More attenuation is not necessarily better. In theory the improvement >in source match is two times the attenuation, so a 10 dB pad improves >the return loss to no less than 20 dB, even with a zero ohm source, >and with a decent source match of RL = 10 dB or so, is as good as you >need. (I know you know this already) > >I say this because it's very likely that the return loss of the >attenuator isn't any better than 25-30 dB, regardless of its >attenuation. For example Narda makes a "precision" Type N attenuator: > >http://www.nardamicrowave.com/east/PassiveComponents/pdf/attenuators/FixedPrecision.pdf > >Note the VSWR spec, 1.15 at low frequency. That's a 23 dB RL. So >although a 20 dB pad in theory provides a minimum 40 dB RL, the actual >RL can be as little as 23 dB. > >Manufacturers have to work really hard and typically use a precision >connector like 3.5mm or 7mm to build a 40 dB RL termination although >Anritsu will sell you a 40 dB RL type N termination for -only- $650 >USD. > >Also, and this goes back a post or two, where you suggested that if a >pad is used between the generator and the input to the coupler, the >"A" probe (reference/incident) should be between the generator and the >pad. > >This is contrary to what I tried to recommend earlier when I said: > >"It would also be nice it you had a 6 - 10 dB pad between the >generator and the directional coupler (DC); located right at the DC. >You want the source match to be set right there and the A probe to >sample right there." > >Let me offer this thought experiment: > >If you had two directional couplers, such that one could be used to >sample the forward signal and the other the reflected, would you place >a pad between them to isolate the generator from the effects of the >load? No, of course not... it just adds another source of error, and increases the gap between the measurements being made on both probes. But Dan does not have two directional couplers. To my mind, if the A probe is sampling the main transmission line, the sample is of the resultant of the algebraic sum of the forward and reflected waves rather than a sample of the forward wave alone (well, nearly alone) as you would get with a directional coupler. My suggestion of placing the A probe on the source side of the attenuator is to reduce the contribution of the reflected wave to the A probe measurement. The attenuator was proposed mainly for isolation of the forward wave component for measurement, rather than a source matching issue... which also exists. Have I got this wrong? All comments on practical limits of RL from pads / attenuators noted, and understood. Owen > > -- Article: 220767 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Dipoles and the rig's RF ground... Date: Tue, 03 Jan 2006 13:19:25 -0800 Message-ID: <11rlqiv2po14n6d@corp.supernews.com> References: <1136148463.132269.164130@g49g2000cwa.googlegroups.com> <11rj9uu7bkogd37@corp.supernews.com> Dave Oldridge wrote: > > Still, if the antenna is TRULY balanced (a situation that only rarely > actually happens), you won't get common-mode currents. That's true only if by "balanced" you mean that the two feedline conductors carry equal and opposite currents. In that case, common mode current is zero by definition. But if you really mean symmetrical, as most amateurs do when they say "balanced", you certainly can have common mode current. A detailed explanation of how that happens is in the article at http://eznec.com/Amateur/Articles/Baluns.pdf, and the article by Walt Maxwell, W2DU at http://www.w2du/r2ch21.pdf which is referenced at the end of the first article? Note particularly figures 3 and 4 of the Baluns.pdf article. > I've never had a > problem with them with well-grounded (from an RF standpoint) ground- > mounted verticals either. The reason this provides balanced feedline currents is that the impedance to ground at the base of the antenna is much less than the impedance looking back from the feedpoint down along the outside of the feedline. Consequently, the large majority of the current from the inside of the coax shield flows to ground rather than down the outside of the coax. And laying the coax on the ground keeps coupled common mode current down. > > Essentially this is why I recommend using open wire or twinlead and > feeding it through a proper balanced-line tuner. That combination will produce a truly balanced system with no common mode current. But it's not the only way. >. . . Years ago, I built an > amplifier that literally had a balanced line output and fed a 600-ohm > feeder direct off two taps on its output coil. That feedline was only > ten feet long and I worked a TON of 80m DX an the inverted vee that it > connected to. And I could always tap the coil so as to have ZERO RF in > the shack (though my landlady's little 7.5 watt light bulbs used to light > on some frequencies when the house wiring picked up direct from the > antenna). > > Article: 220768 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Dipoles and the rig's RF ground... Date: Tue, 03 Jan 2006 13:26:34 -0800 Message-ID: <11rlr0cabfufv8c@corp.supernews.com> References: <1136148463.132269.164130@g49g2000cwa.googlegroups.com> <11rj9uu7bkogd37@corp.supernews.com> chuck wrote: > Is it not true that if the currents on the transmission line are unbalanced > (i.e., unequal on the two conductors) then the transmitter must already be > connected to ground? If not, what is the path of the differential current? Your thinking is correct. If you had a small, battery operated rig, you could theoretically force current balance by completely isolating it >from ground. You might burn yourself when you touch it, though. In practice, differential current can flow to ground via capacitive coupling from the rig to ground, or by flowing onto any connecting wires such as power supply, speaker, or key leads, which will radiate. Common mode feedline current is generally sinusoidally distributed. So you can have a relatively small common mode current at the rig but a much larger one at places on the feedline, if the rig happens to fall at a common mode current node. When the current is due to coupling, a single balun will be ineffective if placed at a natural current node, or in some other cases will only change the distribution by moving the node, rather than reducing the overall current. In those cases, two baluns placed about a quarter wavelength apart are effective. Roy Lewallen, W7EL Article: 220769 of rec.radio.amateur.antenna From: "johan aeq" References: <7679a$43b96aae$52ad139c$8967@news.versatel.nl> Subject: Re: Why use s balanced tuner? Date: Tue, 3 Jan 2006 22:46:22 +0100 Message-ID: <1abf5$43baf2df$52ad139c$24330@news.versatel.nl> Thanks Reg, i already have such a tuner but never thought it would be usful with varying impedances. I hope 2006 will be good for you too... Greetings Johan PE1AEQ "Reg Edwards" schreef in bericht news:dpc213$gqd$1@nwrdmz01.dmz.ncs.ea.ibs-infra.bt.com... > > "johan aeq" wrote > > So a simple "pi filter" withe a bulun will do the same? > > I always thought that the wide impedancerange of open wire made a > > currentbalun or voltagebalun unusable. > > I was just gathering parts to build my own balanced tuner.... > > Greetings Johan PE1AEQ > > > ========================================== > All kinds of peculiar things can happen with voltage baluns and > current baluns which have a definite impedance ratio. > > But my comments apply to a CHOKE balun, the most simple form of balun. > It is a pair of wires wound together on a ferrite ring. It is just a > very short 2-wire transmission line. For longitudinal currents it is > an RF choke, the 2 wires being effectively connected in parallel. > > The impedances between which it can work are indeterminate. There is > no impedance ratio. > > When connected between a balanced line and an unbalanced tuner, the > tuner can be an ordinary simple L, Pi or T network. > > If you happen to have a balanced tuner, lying around doing nothing, > then by all means use it without a balun. But if you don't have a > balanced tuner, as is very likely, there's no need to make one. Just > use a common or garden unbalanced tuner, which nearly everybody has > already got, with a CHOKE balun. > > The hardest part of making a choke balun is obtaining the ferrite > ring. 50mm outside diameter, 30mm inside diameter, permeability > 200-400, about 16 turns of twin, flexible, stranded, speaker cable, > will be OK for the HF bands. Or similar. > > All the very best for 2006. > ---- > Reg, G4FGQ. > > Article: 220770 of rec.radio.amateur.antenna From: David Subject: Re: Still have problems reading MJF-269 Analyzer References: <96ydncE65IOaCCfeRVn-tw@comcast.com> Message-ID: <3rCuf.167640$V7.100747@news-server.bigpond.net.au> Date: Tue, 03 Jan 2006 21:57:19 GMT Amos, The circuit is passive (R/L/C) only. I would not expect any non-linearity. I suspect the previous post may have been correct. The match was over a large ratio of impedance (50 Ohms to 4500 Ohms). I expect the small value of inductor and reasonably low Q was limiting the performance of the circuit. I tried the match again from 50 Ohms to 800 Ohms as a test and found the MJ-269 showed match efficiency of 90% with SWR dropping to 1.8. These results are much better. Regards David Amos Keag wrote: > Have you considered that there may be non-linear effects in the test set > up? > > The MFJ uses several to ten milliwatts in it's circuitry [+10 dBm]. > Sensitivity is generally measured at the pico-watt [~ -130 dBm] level. > > AK > > David wrote: > >> Hi, >> >> I have a matching circuit that matches 50 Ohms to 4500 Ohms in >> parallel with 2.5pF at 45MHz. >> >> The coil was measured at 147nH with a Q of 50 at 45 MHz. >> >> The circuit is a C-Tap typology with following values. >> >> Tap input to ground = 784pF >> Tap to hot side of coil = 92pF >> Par inductor = 147nH >> >> My design calculations predict Loaded Q = 26 and BW = 1.7 MHz. >> >> I used a 50p trimmer in par with 68pF cap for top of tap to fine tune. >> >> A 4k7 resistor and 2p2 cap were placed across the output to simulate >> the correct load. >> >> The test results show BW = 1.7 MHz and Loaded Q = 24.7 (agree with >> calculated values). >> >> When installed on the IF front end, the expected sensitivity is >> achieved when tuned. This would indicate most of the signal must be >> getting through or sensitivity would be effected due to mismatch. >> >> All seems to look ok but when I attach the MJF-269 Analyzer I get >> impedance of 280 angle 35 degrees (240 -j 179) for the impedance, I >> get SWR = 6.1 , return loss of 2.8dB and match efficiency of 48%. >> >> I cannot understand why there is such a discrepency between the design >> values and tested results (using sig gen, spectrum analyzer and power >> meter) compared to the MJF-269. >> >> Is there something I am doing wrong here or is it a mis-interpretation >> of displayed values ? >> >> Thanks for any help. > > Article: 220771 of rec.radio.amateur.antenna From: David Subject: Re: Still have problems reading MJF-269 Analyzer References: <96ydncE65IOaCCfeRVn-tw@comcast.com> Message-ID: Date: Tue, 03 Jan 2006 22:02:21 GMT Tam, I believe you are correct. The 147nH inductor is the largest "can" that I have. The inductor really needs to be larger to get the loaded Q of the match down for this ration of impedance transform. When trying 50 Ohms to 800 Ohms (instead of the original 4500 Ohms), the match works. The actual loaded Q was about 8. Seems a good rule of thumb would be to go for loaded Q around 10% of unloaded Q. Thanks Tam/WB2TT wrote: > "Amos Keag" wrote in message > news:96ydncE65IOaCCfeRVn-tw@comcast.com... > >>Have you considered that there may be non-linear effects in the test set >>up? >> >>The MFJ uses several to ten milliwatts in it's circuitry [+10 dBm]. >>Sensitivity is generally measured at the pico-watt [~ -130 dBm] level. >> >>AK >> >>David wrote: >> >> >>>Hi, >>> >>>I have a matching circuit that matches 50 Ohms to 4500 Ohms in parallel >>>with 2.5pF at 45MHz. >>> >>>The coil was measured at 147nH with a Q of 50 at 45 MHz. >>> >>>The circuit is a C-Tap typology with following values. >>> >>>Tap input to ground = 784pF >>>Tap to hot side of coil = 92pF >>>Par inductor = 147nH >>> > > > These seem like horrendously large capacitors to use at 45 MHz. > > > >>>My design calculations predict Loaded Q = 26 and BW = 1.7 MHz. >>> >>>I used a 50p trimmer in par with 68pF cap for top of tap to fine tune. >>> >>>A 4k7 resistor and 2p2 cap were placed across the output to simulate the >>>correct load. >>> >>>The test results show BW = 1.7 MHz and Loaded Q = 24.7 (agree with >>>calculated values). > > > For an unloaded Q of 50, I would shoot for a loaded Q of around 5. If you > plan to put any power through this, try getting the unloaded Q up to around > 200, with a loaded Q of around 8. > > My guess is that if you remove the 4.7K, the impedance at the other end of > the network will not change all that much. > > Tam/WB2TT > > Article: 220772 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: Impedance question References: <1136325640.479701.9580@g49g2000cwa.googlegroups.com> Message-ID: Date: Tue, 03 Jan 2006 22:47:04 GMT pdrunen@aol.com wrote: > I have a MFJ-269 and I measured a value of 65 and j16 for my 6-meter > dipole, the dipole is a little long so I assume that the j16 is > inductive and I need to add a cap of equal reactive value. > Also, The measurement was taken directly at the antenna feedpoint > without any coax. How did you keep your body from affecting the measurement? Why do you think an SWR of 1.5:1 is enough to worry about? > Once I back calculate the cap value ,should I place this cap across the > antenna input at the feed point or in series with the signal line of > the feed point to cancel out the j16 and leave me with 65 ohm > resistive? The impedance displayed by the MFJ-269 is a series impedance. If the feedpoint impedance is indeed 65+j16, two caps of -j8, one to each side of the dipole on the antenna side of a 1:1 choke-balun will tend to keep the currents balanced. But here's another approach for your consideration. A little less than 1/2WL of 300 ohm or 450 ohm line will bring the antenna to resonance, assuming a 65+j16 feedpoint impedance. That's about 8.5 feet on 6m. A series section of ladder-line is usually easier to install than discrete components. And if you did make an error in your measurement, trimming the ladder-line to resonance is a pretty easy task. -- 73, Cecil http://www.qsl.net/w5dxp Article: 220773 of rec.radio.amateur.antenna From: Allodoxaphobia Subject: Re: Antenna spacing Date: 3 Jan 2006 22:53:02 GMT Message-ID: References: On Tue, 03 Jan 2006 13:01:32 -0600, Chris W wrote: > Dave Oldridge wrote: >>Allodoxaphobia wrote: >>>On Mon, 02 Jan 2006 14:33:18 GMT, Dave Oldridge wrote: >>>>Chris W <1qazse4@cox.net> wrote: >>>> >>>>>I want to put a short 2 meter yagi and a long 70cm yagi on the same >>>>>vertical mast. The 70cm will be a horizontally polarized, center >>>>>mounted 17' boom and the 2 meter will be a vertically polarized, end >>>>>mounted 6 foot boom. How far apart do they need to be? I will only >>>>>be transmitting with one at a time but one could be receiving and >>>>>the other transmitting, the 70cm will be for ATV receive only for >>>>>now. >>>>> >>>>A good rule of thumb is to separate them by at least a half-wave at >>>>the lowest frequency. In this case that means about a meter (39") >>>>apart. >>>> >>>Not when they are orthogonally polarized. They can be 0.000 >>>wavelengths apart. I.e., in the OP's case, the 2M elements can be >>>_mounted_ on the 70cm's boom. >> >>You're right. I didn't catch the polarization thing. In fact, building >>them on the same boom would be quite workable. >> > What if they are 2 different antennas and you can't put them on the same > boom, how close can I put them? OK, if we're still talking about one vertically polarized and one horizontally polarized, I'd slap'em together so that the vertical elements are at least 1/4 wavelength from the horizontal's boom. Or, you could do what some fellers seem to do: Spend all your time in rraa, anguishing and arguing about antenna installation choices. After all, which propagates best: The antenna on the floor of the garage, or the one up in the air? HI!HI! JONESY'S AXIOM: You never put an antenna up just once. Good Luck and Happy New Year! 73 Jonesy -- Marvin L Jones | jonz | W3DHJ | linux Pueblo, Colorado | @ | Jonesy | OS/2 __ 38.24N 104.55W | config.com | DM78rf | SK Article: 220774 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Impedance question Date: Tue, 03 Jan 2006 15:14:04 -0800 Message-ID: <11rm19vhgq87647@corp.supernews.com> References: <1136325640.479701.9580@g49g2000cwa.googlegroups.com> pdrunen@aol.com wrote: > Hi de KJ4UO, > > I have a MFJ-269 and I measured a value of 65 and j16 for my 6-meter > dipole, the dipole is a little long so I assume that the j16 is > inductive and I need to add a cap of equal reactive value. > Also, The measurement was taken directly at the antenna feedpoint > without any coax. > > Once I back calculate the cap value ,should I place this cap across the > antenna input at the feed point or in series with the signal line of > the feed point to cancel out the j16 and leave me with 65 ohm > resistive? There's no point in adding a capacitor at all. Assuming you're using a 50 ohm feedline, it would only change the SWR from about 1.5 to 1.3. I can't see where that would be worth the trouble. But you haven't measured the dipole impedance. One terminal of the MFJ-269 is connected to one side of the dipole. The other terminal is connected to the dipole in parallel with the outside of the MFJ-269 itself and, if you were holding it, your body also. So you're measuring the impedance of an antenna having a wire for one leg, and a combination of a wire, box, and body for the other. If you really had measured the dipole impedance and if the reactance was enough to bother with, the answer to your question would be to put it in series. Roy Lewallen, W7EL Article: 220775 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Current and voltage distribution on an antenna. Date: Tue, 03 Jan 2006 15:23:52 -0800 Message-ID: <11rm1s9q3tbhj43@corp.supernews.com> References: <7Ahuf.287$WY5.73@newsread2.news.pas.earthlink.net> <11rjoa2qen3k216@corp.supernews.com> W. Watson wrote: > > How about that? I read further into the book and found a whole chapter > on the software on the CD. Another quick romp through the book tells me > that (I'm inferring this.) that what most of it is about is describing > antennas and where they might be used. It looks like a potential catalog > of such designs to try out on the software. I don't think that's > necessarily the reason why the book was written, but it makes it > appealing. I don't see anywhere that all the designs offered could be > investigated with the software on the CD. > > Roy, perhaps you have an answer for the last statement. I see that one > of your programs is included. Sorry, I know nothing of the book, except I vaguely recall Joe mentioning that he was including the EZNEC demo program with a book. If you're interested in modeling various antenna designs, consider the _ARRL Antenna Book_. On its CD are several hundred EZNEC models of various antennas discussed in the book, plus a special version of EZNEC which can be used to analyze them (http://eznec.com/eznec_arrl.htm). The Antenna Book models can also be used with any standard (non-demo) version of EZNEC. Roy Lewallen, W7EL Article: 220776 of rec.radio.amateur.antenna From: Registered User Subject: Re: Why use s balanced tuner? Date: Tue, 03 Jan 2006 18:16:02 -0500 Message-ID: References: On Mon, 02 Jan 2006 10:20:30 -0800, Dan Richardson <> wrote: >On Mon, 2 Jan 2006 14:56:49 +0000 (UTC), "Reg Edwards" > wrote: > >>Why use a balanced tuner when a less expensive, easier to operate, >>unbalanced tuner, in conjunction with a simple choke-balun, will do >>just as well? >> >>Insert the 2-wire choke-balun between the unbalanced tuner and the >>balanced transmission line. >>---- >>Reg. >> > >My link coupled tuner (Johnson Matchbox) cost me less than 60 USD, I >can tuner faster than a T-type tuner, doesn't need nor use a balun. >(Read one less component and its associated loss). So why would I want >to replace it with something that works almost as good? > I use my 500+ foot horizontal loop on 6 and 2 meters with homebrew balanced tuners from the '63 ARRL Handbook. On HF a balanced double-L tuner does the trick. The balanced-L tuner does use a balun but it is between the rig and the matching device. The only problem with using the Johnson Matchbox is 30M 73 de n4jvp Fritz Article: 220777 of rec.radio.amateur.antenna From: "Ralph Mowery" References: Subject: Re: Antenna spacing Message-ID: Date: Wed, 04 Jan 2006 00:31:11 GMT "Dave Oldridge" wrote in message news:Xns973F42AD4851doldridgsprintca@64.59.135.159... > Chris W <1qazse4@cox.net> wrote in news:IT3tf.45644$ih5.19066@dukeread11: > > > I want to put a short 2 meter yagi and a long 70cm yagi on the same > > vertical mast. The 70cm will be a horizontally polarized, center > > mounted 17' boom and the 2 meter will be a vertically polarized, end > > mounted 6 foot boom. How far apart do they need to be? I will only be > > transmitting with one at a time but one could be receiving and the other > > transmitting, the 70cm will be for ATV receive only for now. > > A good rule of thumb is to separate them by at least a half-wave at the > lowest frequency. In this case that means about a meter (39") apart. > > Sofar all the answers are assuming the question is will one antenna affect the other antenna. One other thing to look at is will the transmitter 'kill' the receiver of the other rig ? Article: 220778 of rec.radio.amateur.antenna Date: Tue, 03 Jan 2006 18:59:13 -0600 From: Tom Ring Subject: Re: Recommendation for 915MHz omni antenna References: <26048-43B8945F-1005@storefull-3251.bay.webtv.net> Message-ID: <43bb1dfe$0$3759$39cecf19@news.twtelecom.net> Richard Harrison wrote: > Dave wrote: > "What would your recommendation be?" > > I would use a vertical collinear omni antenna for the repeater and > vertically polarized Yagis for each of the "sheds". To avoid stimulation > of argument, I`ll say no more. You mainly need a line-of-sight path at > 915 MHz between all remote sites and the repeater. > > Best regards, Richard Harrison, KB5WZI > Motorola 900 Mhz Canopys are advertised as "non line of site", so you may get more mileage than you'd expect when running at this relatively low frequency. If you are looking at paths that can be well defined, try a program called "Radio Mobile" for a very good simulation of the situation. It is freeware, and the databases it uses are also free (courtesy of the US taxpayer and some hardworking US Shuttle astronauts and groundcrew). tom K0TAR Article: 220779 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: Impedance question Date: Wed, 4 Jan 2006 01:17:46 +0000 (UTC) Message-ID: References: <1136325640.479701.9580@g49g2000cwa.googlegroups.com> <11rm19vhgq87647@corp.supernews.com> <1136335461.975240.53730@g47g2000cwa.googlegroups.com> Try suspending the measuring instrument in mid-air to remove your body capacitance and see if it makes any difference to the measured impedance. ---- Reg Article: 220780 of rec.radio.amateur.antenna From: David Subject: Scaling of Yagi design Message-ID: Date: Wed, 04 Jan 2006 01:30:59 GMT Hi, I have a design for a Yagi antenna at 436MHz and would like to scale it to 921 MHz. The calculations I used from the understanding I have obtained from reading various articles appears below. Would someone be kind enough to advise me if this procedure and values look correct ? Thanks in advance. The original dimensions(mm) were Boom = 15 or 20mm square aluminum, 350mm long Element Length Spacing Diameter RE 336 0 8 DE 316 80 10 D1 300 190 8 D2 292 330 8 My scaled values to 921MHz Boom = 12mm x 12mm aluminum 166mm long Element Length Spacing Diameter RE 158.9 0 3.78 DE 149.5 38 4.73 D1 141.9 90 3.78 D2 138.2 142 3.78 Now I scaled the tubing to 6mm diameter that I have in stock Element Length Spacing Diameter RE 158.5 0 6 DE 148.7 38 6 D1 139.4 90 6 D2 135.3 142 6 Regards David Huisman Article: 220781 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: If the ideal lenght of an antenna is 1/4 Wave lenght then way References: <1135422926.082522.168780@o13g2000cwo.googlegroups.com> <43afeda5_4@newsfeed.slurp.net> <43b1433b_4@newsfeed.slurp.net> <11r3bhdh1gfja72@corp.supernews.com> Message-ID: <3Iysf.47963$tV6.36131@newssvr27.news.prodigy.net> Date: Wed, 28 Dec 2005 16:04:15 GMT Reg Edwards wrote: > Roy, you'll just have to accept the fact that I'm peculiar. But no > more peculiar than other frequenters of this newsgroup. How's this for peculiar? :-) "The movement of energy within the line is complex; in the abbreviated analysis I've had time to do so far, it sloshes back and forth in regions within the line." -- 73, Cecil http://www.qsl.net/w5dxp Article: 220782 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Impedance question Date: Tue, 03 Jan 2006 18:05:11 -0800 Message-ID: <11rmbaoo5n5tk1f@corp.supernews.com> References: <1136325640.479701.9580@g49g2000cwa.googlegroups.com> <11rm19vhgq87647@corp.supernews.com> <1136335461.975240.53730@g47g2000cwa.googlegroups.com> Reg Edwards wrote: > Try suspending the measuring instrument in mid-air to remove your body > capacitance and see if it makes any difference to the measured > impedance. Suspending the analyzer might be adequate for 6 meters, which is the antenna under discussion. But I should mention for the benefit of the general audience that it isn't adequate for 2 meters. Not too long ago I heard from an EZNEC user who found a substantial difference between modeled and measured results from a simple antenna. On my suggestion, he added a simple wire frame representation of the MFJ 269 to his model, and it made the model results much closer to his measurement. So in that case the antenna analyzer itself was enough to substantially skew the measurement. Roy Lewallen, W7EL Article: 220783 of rec.radio.amateur.antenna Date: Tue, 03 Jan 2006 20:17:34 -0600 From: Tom Ring Subject: Re: Scaling of Yagi design References: Message-ID: <43bb303e$0$47666$39cecf19@news.twtelecom.net> David wrote: > Hi, > > I have a design for a Yagi antenna at 436MHz and would like to scale it > to 921 MHz. The calculations I used from the understanding I have > obtained from reading various articles appears below. > > Would someone be kind enough to advise me if this procedure and values > look correct ? > > Thanks in advance. > > The original dimensions(mm) were > > Boom = 15 or 20mm square aluminum, 350mm long > > Element Length Spacing Diameter > RE 336 0 8 > DE 316 80 10 > D1 300 190 8 > D2 292 330 8 > > My scaled values to 921MHz > Boom = 12mm x 12mm aluminum 166mm long > > Element Length Spacing Diameter > RE 158.9 0 3.78 > DE 149.5 38 4.73 > D1 141.9 90 3.78 > D2 138.2 142 3.78 > > Now I scaled the tubing to 6mm diameter that I have in stock > Element Length Spacing Diameter > RE 158.5 0 6 > DE 148.7 38 6 > D1 139.4 90 6 > D2 135.3 142 6 > > Regards > > David Huisman Are these through the boom, and if so, insulated, or uninsulated? If not through the boom, give specifics on the mounting. Please do this for both the original antenna, and how you propose to build the scaled one. tom K0TAR Article: 220784 of rec.radio.amateur.antenna From: David Subject: Re: Scaling of Yagi design References: <43bb303e$0$47666$39cecf19@news.twtelecom.net> Message-ID: Date: Wed, 04 Jan 2006 02:33:21 GMT The elements are mounted approximately 3mm off the boom by nylon insulator blocks on the original design. The scaled design will use same construction. http://www.qsl.net/dk7zb/start1.htm Tom Ring wrote: > David wrote: > >> Hi, >> >> I have a design for a Yagi antenna at 436MHz and would like to scale >> it to 921 MHz. The calculations I used from the understanding I have >> obtained from reading various articles appears below. >> >> Would someone be kind enough to advise me if this procedure and values >> look correct ? >> >> Thanks in advance. >> >> The original dimensions(mm) were >> >> Boom = 15 or 20mm square aluminum, 350mm long >> >> Element Length Spacing Diameter >> RE 336 0 8 >> DE 316 80 10 >> D1 300 190 8 >> D2 292 330 8 >> >> My scaled values to 921MHz >> Boom = 12mm x 12mm aluminum 166mm long >> >> Element Length Spacing Diameter >> RE 158.9 0 3.78 >> DE 149.5 38 4.73 >> D1 141.9 90 3.78 >> D2 138.2 142 3.78 >> >> Now I scaled the tubing to 6mm diameter that I have in stock >> Element Length Spacing Diameter >> RE 158.5 0 6 >> DE 148.7 38 6 >> D1 139.4 90 6 >> D2 135.3 142 6 >> >> Regards >> >> David Huisman > > > Are these through the boom, and if so, insulated, or uninsulated? > > If not through the boom, give specifics on the mounting. > > Please do this for both the original antenna, and how you propose to > build the scaled one. > > tom > K0TAR -- Kind Regards David Huisman General Manager ----------------------------------------------------------------------- ORBIT COMMUNICATIONS Pty Ltd - Wireless Solutions that Work (Telemetry, Control, Monitoring, Security, HVAC ...) A.C.N. 107 441 869 Website : http://www.orbitcoms.com PO Box 4474 Lakehaven NSW 2263, AUSTRALIA Phone: 61-2-4393-3627 Fax : 61-2-4393-3685 Mobile: 61-413-715-986 Article: 220785 of rec.radio.amateur.antenna From: "Charlie" Subject: Re: 6M stacked loops - best height above ground? Date: Wed, 28 Dec 2005 04:40:00 -0600 Message-ID: <11r4qt5p297c9c2@news.supernews.com> References: <11r2sc828n5ri78@news.supernews.com> Hi Bill...this is also what I have found to be the crux of my dilemma. If I should strive to optimize height for DX or terrestrial contacts. I have need for both so I am going to need to compromise a bit. TY again for your input. -- Charlie "Bill Turner" wrote in message news:bj14r193j2vigo77et4ohq6ki077v339q6@4ax.com... > > ORIGINAL MESSAGE: > > On Tue, 27 Dec 2005 10:52:54 -0600, "Charlie" > wrote: > >>Currently the top loop is at only 20ft but I am making many contacts. >>Soon >>however they will be placed off a sidearm on the tower. >> The top loop could then be as high as 80 ft. >> >>I have read and read about this topic. Does anyone have any first hand >>knowledge of 6M height above ground comparisons especially for stacked >>loops? Thanks.... > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > I'm not that sure about loops, but for yagis working DX, the optimum > height seems to be about 35 feet. Higher is better for ground wave, > but for DX, 35 is best, believe it or not. This has been proven with > crank up towers many times. It may well be the same for loops. > > 73, Bill W6WRT Article: 220786 of rec.radio.amateur.antenna Date: Tue, 03 Jan 2006 21:05:59 -0600 From: Tom Ring Subject: Re: Scaling of Yagi design References: <43bb303e$0$47666$39cecf19@news.twtelecom.net> Message-ID: <43bb3bb0$0$3767$39cecf19@news.twtelecom.net> David wrote: > The elements are mounted approximately 3mm off the boom by nylon > insulator blocks on the original design. > > The scaled design will use same construction. > http://www.qsl.net/dk7zb/start1.htm > Ok, I'll try to run a scaled version for you in the next one or two days. tom K0TAR Article: 220787 of rec.radio.amateur.antenna From: David Subject: Re: Scaling of Yagi design References: <43bb303e$0$47666$39cecf19@news.twtelecom.net> <43bb3bb0$0$3767$39cecf19@news.twtelecom.net> Message-ID: Date: Wed, 04 Jan 2006 03:27:49 GMT Thanks Tom. The smallest aluminum I have is 12mm square for the boom and 6mm round for elements. I would like to stick with the aluminum rod as I think this will be easier to secure than welding rod etc. Tom Ring wrote: > David wrote: > >> The elements are mounted approximately 3mm off the boom by nylon >> insulator blocks on the original design. >> >> The scaled design will use same construction. >> http://www.qsl.net/dk7zb/start1.htm >> > > Ok, I'll try to run a scaled version for you in the next one or two days. > > tom > K0TAR Article: 220788 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: Impedance question Date: Wed, 4 Jan 2006 03:38:51 +0000 (UTC) Message-ID: References: <1136325640.479701.9580@g49g2000cwa.googlegroups.com> <11rm19vhgq87647@corp.supernews.com> <1136335461.975240.53730@g47g2000cwa.googlegroups.com> <11rmbaoo5n5tk1f@corp.supernews.com> The Autec Analyser is a better instrument than the MFJ for suspended-in-mid-air measurements. It is much smaller and is lighter in weight and has a smaller capacitance. The Autec case has a self-capacitance of the order of 3 pF corresponding to a reactance of 1768 ohms at 30 MHz which can be ignored when measuring 50 ohms with zero lead length. The Autec's highest frequency is 35 MHz. The MFJ's highest frequency is at VHF. With a self-capacitance of 7 pF at VHF substantial errors can occur. To estimate capacitance, the DC capacitance of a sphere is - pF = 55.55 * Diameter in metres. ---- Reg. Article: 220789 of rec.radio.amateur.antenna From: David Subject: Re: Impedance question References: <1136325640.479701.9580@g49g2000cwa.googlegroups.com> <1136345393.622949.34840@g43g2000cwa.googlegroups.com> Message-ID: Date: Wed, 04 Jan 2006 04:23:39 GMT Are these antennas all in parallel for have you posted the identical request multiple times ? pdrunen@aol.com wrote: > Hi again all, > > the dipole was suspensed on a pole and the MFJ-269 was connected to it, > no body effects here. After adjusting frequency then I move away from > the setup. > > I do understand that 65 + j16 is not really a bad match, if I did add a > capacitive reactance, then would I have to place two caps, each of > equal value in series with coax? > > If I wanted to do a shunt capacitor, would I find the admittance of the > above and then determine a shunt from the resulting reactance? > > de KJ4UO > Article: 220790 of rec.radio.amateur.antenna From: Bill Turner Subject: Re: Why ground the transmitter? Date: Tue, 03 Jan 2006 23:53:32 -0800 Message-ID: References: <1136229473.837565.47960@g44g2000cwa.googlegroups.com> <1136269078.138519.170020@g49g2000cwa.googlegroups.com> <11rk9bkpb525lfa@corp.supernews.com> ORIGINAL MESSAGE: On Mon, 02 Jan 2006 23:19:15 -0800, Roy Lewallen wrote: > But a better solution is to >get those feedline currents balanced so you won't have any imbalance or >"ground" current to deal with in the first place. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Not only that, but whenever the neighbor plugs in a different appliance, uses an extension cord or otherwise rearranges his AC mains, your problem may be right back. 73, Bill W6WRT Article: 220791 of rec.radio.amateur.antenna From: David Subject: Re: Scaling of Yagi design References: Message-ID: <9vLuf.169769$V7.114119@news-server.bigpond.net.au> Date: Wed, 04 Jan 2006 08:16:05 GMT Ian, Thanks for that. I did previously look at your site and bookmarked it. I am going to make up the element cutting jig and bending jig (for when I want to experiment with folded dipoles). Great site. Regards David Ian White GM3SEK wrote: > David wrote: > >> Hi, >> >> I have a design for a Yagi antenna at 436MHz and would like to scale >> it to 921 MHz. The calculations I used from the understanding I have >> obtained from reading various articles appears below. >> >> Would someone be kind enough to advise me if this procedure and values >> look correct ? > > [...] > >> >> Regards >> >> David Huisman > > > > The basic principle of scaling antennas according to wavelength is that > you must make an *exact* scale model. That means scaling every > dimension, and not adding any new or different 'features'. > > Often that isn't practical for mechanical engineering reasons, so then > you need to apply corrections. However, you should still aim to keep > those corrections as small as possible. For example, simple scaling is > likely to produce odd, unavailable values for the element diameter, so > it's OK to use corrections to change to the nearest commercially > available diameter. But if you also decide to double the diameter, the > correction is more risky - you're entering the territory of a completely > new design. > > Sorry that I don't have time to check your particular dimensions in > detail, David, but you can find resources for scaling and constructional > techniques on my 'VHF/UHF Long Yagi Workshop' pages. There is a > downloadable program which leads you through the relevant questions, and > also a link to an online Javascript version. > > (From about 1200utc I will not have access to this newsgroup for the > next few days, so I hope the above will keep you going.) > > Article: 220792 of rec.radio.amateur.antenna From: "David J Windisch" References: Subject: Re: Why use a balanced tuner? Message-ID: Date: Wed, 04 Jan 2006 12:16:34 GMT Put a 500-pF variable capacitor in series with the link inside or, outside the enclosure in series with the center conductor of the coax line feeding the JMBox. Gives you an extra degree of freedom in tuning. 73, Dave, N3HE SNIP > between the rig and the matching device. The only problem with using > the Johnson Matchbox is 30M > > 73 de n4jvp > Fritz Article: 220793 of rec.radio.amateur.antenna From: richardharrison@webtv.net (Richard Harrison) Subject: Re: Recommendation for 915MHz omni antenna Date: Wed, 4 Jan 2006 09:23:19 -0600 Message-ID: <25145-43BBE867-1164@storefull-3255.bay.webtv.net> References: <43bb1dfe$0$3759$39cecf19@news.twtelecom.net> Tom Ring wrote: "Motorola 900 MHz Canopys are advertised as "non line of sight"... so you may get more mileage than you`d expect when running at the relatively low frequency." It`s true that radio does not always take a direct path. Part of ham radio fun is in anomalous propagation. It`s also true that the higher the frequency, the smaller the obstruction that can block propagation. 900 MHz is more reliable than frequencies in the GHz. A point to multipoint system may require more reliability than a single point to point system, and more reliability than: "Can You believe it? I`ve contacted DX!" I`ve engineered and installed several 900 MHz systems which proved to provide, with their path clearances and fade margins, 24-7 reliability of very nearly 100%. Line of sight is defined as: "The distance to the horizon from an elevated point, including the effects of atmospheric refraction." Another definition is: "The propagation characteristic of microwave radio." 900 MHz is on the border between UHF and microwaves. It shares some of the characteristics of both. Best regards, Richard Harrison, KB5WZI Article: 220794 of rec.radio.amateur.antenna From: Owen Duffy Subject: Re: using an HP 8405A to measure SWR ? Message-ID: References: <1ZmdnY0padRtpyreRVn-sQ@comcast.com> <7sSdnWELDbgfASTenZ2dnUVZ_tGdnZ2d@comcast.com> Date: Wed, 04 Jan 2006 21:35:40 GMT On Tue, 03 Jan 2006 08:25:48 -0700, Wes Stewart wrote: >Owen > >Let me pick a nit or two. ... Firstly, thanks for posting AN 77-3, it is a long time since I read it, and have little recollection of the recommended low frequency test setup. The HP 11549A is described as a power splitter, so I am guessing that it is some kind of hybrid (ie as in hybrid transformer) that in that role, whilst splitting the power to the "output" ports, will prevent power flow between "output" ports, so isolating the A probe to some extent from the reflected wave on the unknown load side. Additionally, the 8491 attenuator in the load path will improve the return loss at the B side 11549A port, so that combination seems to be stabilising the loads presented to the splitter (which if it is a hybrid, improves is cross port isolation), and improving the RL by the action of the attenuator and splitter. Without knowing the loss in the 8491 (I know they were available in 10dB, but I think there were -3, -6, -10 and -20s), or the isolation across the splitter, it is hard to quantify the total isolation of reflected wave from the A probe. It may be that Dan should consider constructing a hybrid or Return Loss Bridge, whatever you want to call it, it will be cheaper and have less loss that a dual directional coupler for HF measurements. IIRC, the ARRL has some simple designs. Owen -- Article: 220795 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Transmission Line Reflections Date: Wed, 04 Jan 2006 13:45:52 -0800 Message-ID: <11roggi5f4i1h3a@corp.supernews.com> References: W. Watson wrote: > It seems reasonable that if I have an open ended transmission line that > the current would reflect back and change phase. After all, the > electrons at the end have nowhere to go but back down the line. However, > the voltage is a different matter. There is no phase reversal (or > polarization change) There doesn't seem to be an intuitive reason for > this. However, if one examines the equations for current and capacitive > voltage, then it falls out of the math. Still, where is the non-math > that indicates this is true? > > Now suppose instead the line is short circuited. The voltage returns > down the line, and the current does not. That's not true. Both are totally reflected. > In this case, there doesn't > seem to be any non-math or intuitive feel for why the short should cause > this--either for voltage or current. Can one clue me in on what's really > happening above (voltage) and here (voltage and current)? Inquiring > minds want to know. The math is dictated by the boundary conditions, and those can be used to gain an intuitive feel for what's happening. When both forward and reflected waves are present, the voltage and current at any point on the line are the sum of the forward and reverse waves. When the line is open circuited, the current at the end of the line is of course zero. So the sum of the forward and reverse current wave is zero at the end, and the only way that can be is for the forward and reverse waves to be equal in magnitude and out of phase. Likewise, when the line is shorted, the voltage is zero, and the only way that can happen is for the reverse voltage wave to be equal in magnitude and opposite in phase to the forward voltage wave. Some confusion can result when discussing the reverse wave. The reverse current wave can be, and usually is, defined as positive in the same direction as the forward wave. If you use this definition, the current changes phase at a shorted end, since the sum of the two current waves has to equal zero when both are defined as being positive in the same direction. However, you can also say that the current simply reverses direction and remains the same in phase. Those two viewpoints are equivalent. I've been using, and will continue to use, the convention that the direction of positive current is toward the load for both waves, for this discussion. At an open end, the forward and reverse voltages are equal and in phase, and at a shorted end, the forward and reverse currents are equal and in phase. This can be seen by realizing that the voltage/current ratio of the forward wave is the same as for the reverse wave -- both equal the line Z0, but because of the current convention, the sign of the current reverses for the reflected wave. So we know that Vf/If = -Vr/Ir, where If and Ir are defined as positive when flowing toward the load. Now let's apply what we know about shorted ends to find what happens at an open end. At an open end, we know that If = -Ir. Since Vf/If = -Vr/Ir, it follows that Vr = Vf. Likewise, at an open end, we know that Vf = -Vr, so from the same equation If = Ir. Roy Lewallen, W7EL Article: 220796 of rec.radio.amateur.antenna From: richardharrison@webtv.net (Richard Harrison) Subject: Re: Transmission Line Reflections Date: Wed, 4 Jan 2006 17:01:05 -0600 Message-ID: <3015-43BC53B1-299@storefull-3253.bay.webtv.net> References: W. Watson wrote: "It seems reasonable that if I have an open ended transmission line that the current would reflect back and change phase." That`s about what happens. In fact, the incident and reflected waves at an open circuit have voltages of the same phase and magnitudes. These correspond to a reflection coefficient of 1 on an angle of zero. The result is a doubling of the incident value of voltage at the open circuit. I recall this being called "the Ferranti effect". It stands to reason that energy is not created or destroyed but the ebergy associated with the H-field must go somewhere when the current stops. The only place it can go is into the E-field, so this accounts for the instantaneous voltage doubling at the open circuit. The current reverses direction and its incident and reflected values add to zero at the open end of the line. When either voltage or current has a phase reversal, but not both are reversed, a reversal of wave travel direction is indicated. The same thing happens at a short circuit but it is the voltages which add to zero, indicating its phase reversal at the short. When both current and voltage are reversed in phase, no change in travel direction is indicated as this happens regularly in the cycle of the wave. Best regards, Richard Harrison, KB5WZI Article: 220797 of rec.radio.amateur.antenna From: "Steve Nosko" Subject: Re: Shorting out a transmission line Date: Wed, 4 Jan 2006 16:57:42 -0600 Message-ID: References: <8jhrq1pjn7tanflcq4br47bnnq057ha8bi@4ax.com> <43aff794_5@newsfeed.slurp.net> "Paul Burridge" wrote in message news:g1tvq1h1gdc3mvi4jmqfkc4jm7hpqqrktl@4ax.com... > > > That just strikes me as plain stoopid. At MW, such filtering would be > far better achieved by lumped elements. A quarter wave stub at such > frequencies appears impractical, unwieldy and rather expensive! > -- Even at 50 KW? 73, Steve, K,9.D;C'I P.S. I suspect it is air line, no? Article: 220798 of rec.radio.amateur.antenna From: "Steve Nosko" Subject: Re: Shorting out a transmission line Date: Wed, 4 Jan 2006 17:05:01 -0600 Message-ID: References: <11qu3cv7eu6t505@corp.supernews.com> <11qu9fossjcp3a7@corp.supernews.com> I believe this is a good test and conclusion. I can only add two small things. 1- the impedance gets further from 50 ohms, the 269 MFJ ( Mine has this characteristic) shows more and more error. Try paralleling four 50 ohm loads (with your Tees) or measuring a good 200 ohm load. The 269 shows considerable imaginary at 4:1 real (:-( I think I have heard that the 259 is better. 2- The constant reference to the "pin" being much less than a 1/4 wave is not the correct focus. It is the impedance (primarily inductance in this case) which is the factor of interest relative to the frequency. What's that old rule of thumb? One nano Henry per inch?? One nano Henry per 1/10 inch... Been off that bench too long. 73, Steve, K9DCI "Dave Platt" wrote in message news:11qu9fossjcp3a7@corp.supernews.com... > >If I can find a scrap BNC male connector, and make a shorting-plug out > >of it, I'll run the coax-and-T experiment I suggested, and post some > >actual numbers for the systems's behavior at those frequencies I can > >coerce out of my MFJ-269. > > OK, I ran the test, and the results are pretty much as I had > anticipated. Although the test arrangement and gear isn't > lab-standard, I think it's good enough to confirm the basic principles. > > Test equipment: MFJ-259 antenna analyzer, with an N-to-BNC adapter. > > Transmission line and load: 12' length of RG-58 coax, with a 50-ohm > Ethernet terminator attached to the end. > > Shorting insertion: an additional 6' length of RG-58, with a couple of > BNC "T" adapters, which can be inserted between the analyzer and the > T-line-and-load. If the shorting plug is inserted it'll be 6' from > the analyzer and 12' from the load. > > Short circuit: a male BNC plug, with a short inserted between center > pin and shell as far down inside the shell as possible. > > First test: check quality of T-line and load, using only the 12' > section of RG-58 between analyzer and load. Note that the Imag(load) > numbers do not indicate the sign of the reactance... the MFJ won't do > that, alas. > > Frequency Real(load) Imag(load) Indicated SWR > 2.5 52 4 1.0 > 5 58 6 1.2 > 10 57 7 1.2 > 15 49 1 1.0 > 20 56 6 1.1 > 50 54 2 1.1 > 144 51 4 1.0 > 166 59 8 1.2 > 440 1.4 > > Impression: either the RG-58 or the Ethernet terminator isn't > exactly 50 ohms (not unexpected) or the MFJ's calibration isn't > perfect (likewise) but the figures are good enough to let us draw some > reasonable conclusions. > > Second test: insert the 6' RG-58 and its T connectors between the > analyzer and the 12' section. See how much this additional length of > line, and the parasitics of the T connectors, affect the load and SWR. > > Frequency Real(load) Imag(load) Indicated SWR > 2.5 54 4 1.1 > 5 59 5 1.2 > 10 50 10 1.2 > 15 49 1 1.0 > 20 51 8 1.1 > 50 48 5 1.1 > 144 50 4 1.0 > 166 40 2 1.2 > 440 1.1 > > Impression: the measured values change a bit, but the SWRs are close or > identical (save for the 440 measurement). The additional length of > line, and the parasitics from the T connectors, are shifting things > around a bit (especially at 440)... not unexpected. > > Third test: connect the shorting plug to one of the T connectors. See > what "pinning the line" does to the analyzer's view of the load. > > Frequency Real(load) Imag(load) Indicated SWR > 2.5 0 6 >31 > 5 0 12 >31 > 10 1 26 >31 > 15 1 43 >31 > 20 2 70 >31 > 50 0 44 28.7 > 144 7 33 15.4 > 166 166 353 13.0 > 440 >5 > > Impression: yeah, that looks like a short circuit, transformed via a > feedline. Nothing close to a 50-ohm-resistive load shows up at any of > the test frequencies. > > Fourth test: disconnect the 50-ohm load from the end of the 12' line, > creating an abrupt change in the load impedance. See what this does > to the figures from the third test - how much of the antenna load > change gets back "around" the short? > > Frequency Real(load) Imag(load) Indicated SWR > 2.5 0 6 >31 > 5 0 12 >31 > 10 1 25 >31 > 15 1 43 >31 > 20 2 70 >31 > 50 6 44 29.0 > 144 6 30 18.5 > 166 133 317 14.1 > 440 >5 > > Impression: changing the antenna load from 50-ohms-resistive to > near-infinite made a slight change in the impedance seen by the > analyzer, but not much at all at any frequency. The presence of the > short circuit 6 feet from the analuzer is still dominating the load > that the analyzer "sees". > > Special-distance test: with the short, and the 50-ohm load both in > place, sweep the analyzer frequency around the ranges at which the > analyzer-to-short distance is around 1/4 and 1/2 wavelength. See if > we can "see past" the short under these conditions. > > Measurements: with the short circuit in place, and a 50-ohm load at > the end of the 12' line, an impedance peak (Z>1500 ohms) is noted when > sweeping between 32.14 MHz and 32.94 MHz. An impedance minimum > (Real(load) of 2-3 ohms, Imag(load) of 0 ohms) is noted between 65.7 > MHz and 65.85 MHz. The indicated SWR remains high (22 or above) at > all frequencies between the impedance maximum and impedance minimum... > there's no point at which the load resembles anything like "50 ohms > resistive, little reactive component". > > Removing the 50-ohm load, and thus open-circuiting the antenna > feedline, has no significant effect on the impedance as seen at the > quarter-wavelength maximum, at the half-wavelength minimum, or at > points in between. > > Impression: we cannot "see past" the short circuit, no matter whether > it's a quarter-wavelength from the transmitter, a half-wavelength, or > some distance in between these two. The analyzer "sees" only what > would be expected for a short circuit, transformed by 6' of coax. > > Short-circuit quality test: measure impedance of the shorted BNC plug. > > At 16 MHz and below, the MFJ-269 shows it as 0+0j. Above 16 MHz, some > reactance shows up... 2 ohms at 28 MHz, 3 ohms at 42 MHz, 4 ohms and > 55 MHz, 8 ohms at 112 MHz, 10 ohms at 144 MHz, 12 ohms at 169 MHz. > The inductance of the shorted plug itself, and/or the length of the > N-to-BNC adapter on the analyzer, is having some effect. SWR remains > unreadably high: >31 up through VHF and >5 on 440. It's not the > highest-quality "short circuit" in the world, for certain, but at HF > and VHF it's close enough for our purposes here. > > So... what do I conclude from this? > > I conclude that at HF and VHF frequencies, if you accidentally short > your transmitter-to-antenna coaxial feedline (with a pin, nail, or a > loose strand of coax braid which "gets loose" inside a connector), > you're going to present your transmitter with an unrealistic load > (high, low, or nastily reactive) and that the power flow up the > feedline is going to stop at the short circuit. > > Since no "short circuit" in the real world is going to have 0+0j > impedance, this isn't *absolutely* true, but you can probably consider > it to be *practically* true and correct at these frequencies, with > this sort of shorting. > > I further conclude that with respect to the above, there's no 'magic' > about shorts which happen to occur at a quarter-wavelength distance > from the transmitter. In this situation, the transmitter will 'see' > something which behaves like a quarter-wavelength shorted stub... the > load further up the transmission line at the antenna remains > 'invisible' to the transmitter. > > At high-UHF and SHF/microwave frequencies, where a direct "short" is > likely to be a significant fraction of a wavelength, then the > additional reactance of the "short" will certainly affect how the > undesired connection affects what the transmitter "sees". It may > hurt, or help (helping to "tune out" reactance from the antenna > itself), or may be completely invisible. Allison is entirely correct > on this point, under these particular conditions. > > -- > 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: 220799 of rec.radio.amateur.antenna From: "Steve Nosko" Subject: Re: Crimp, Clamp or Solder? Date: Wed, 4 Jan 2006 17:16:33 -0600 Message-ID: References: <76fsq1hrdjvdt82p798efnk9iui6jv4vlo@4ax.com> <113sf.16964$wq.9439@bignews7.bellsouth.net> <0bj2r15i9iic4td11aejgpe330g8b07efe@4ax.com> "W8LNA" wrote in message news:udhsf.2134$OU3.370@news01.roc.ny... > kd5sak wrote: > > "Bill Turner" wrote in message > > news:0bj2r15i9iic4td11aejgpe330g8b07efe@4ax.com... > > > >>Nonsense. > >> > >>Properly crimped, the wire will break before the crimp "works loose". > >> > >>Your tire has multiple lug nuts to spread the stress, not because a > >>smaller number will "work loose". > >> > >>73, Bill W6WRT > > > > > > Guess that's right, let's see now. Formula ! car wheels just have one big > > lug nut, don't they? > > Yes, and six drive pegs > http://www.f1-country.com/f1-engineer/tyres/wheelrim.html > > so the nut only holds the wheel to the hub and doesn't take the stresses > of propelling the car. > W8LNA On street wheels the nuts do support torque, but not like a single central one would (like the formula 1 without the pegs). The holes in the wheel are tapered, the nut seats on the taper and the lug shaft (threaded lug) does not contact the wheel hole. The torque is transferred by radial forces on the nuts. (pardon any unintended pun) 73, Steve, K9DCI Article: 220800 of rec.radio.amateur.antenna From: "Steve Nosko" Subject: Re: Searching for circuit for active antenna Date: Wed, 4 Jan 2006 17:29:23 -0600 Message-ID: References: <41e8qhF1dpu51U1@individual.net> <3g14r1lbde70aqcvp1cq4qa8qo4of2q7vf@4ax.com> You'll get "about 155,000 results for "active antenna". in 0.04 seconds The first of which is a schematic. http://www.ee.washington.edu/circuit_archive/circuits/activeant.html 73, Steve, K,9'D;C.I "LarryLurker" wrote in message news:3g14r1lbde70aqcvp1cq4qa8qo4of2q7vf@4ax.com... > try "active antenna" in Google. > > > On Wed, 28 Dec 2005 02:43:56 +0100, Reinhard Zwirner > wrote: > > >Dear experts > > > >I'm searching for a simple but good-working and reliable circuit > >for a 10 kHz - 30 MHz active antenna. It would be very nice if > >someone showed me a link to such a circuit. > > > >TIA and a happy new year > > > >Reinhard Article: 220801 of rec.radio.amateur.antenna From: "Steve Nosko" Subject: Re: FM transmitter in a vehicle Date: Wed, 4 Jan 2006 18:25:24 -0600 Message-ID: References: <1135976653.858893.150990@g43g2000cwa.googlegroups.com> "Ron J" wrote in message news:1135976653.858893.150990@g43g2000cwa.googlegroups.com... > Happy New Year! > > If I have an FM transmitter in a vehicle, do I need to worry about the > vibration frequency? Is there such a thing as intermodulation from > vibrating objects attached to an FM transmitter? > > I'm curious. Short answers: Worry - Probably not Intermodulation - No. Really long answer... Not sure what you mean by "vibration frequency". Here's the logic for what is called "Environmental Desensitization", or "Environmental Desense" for short...sort of. The type of transmitter is not important for this discussion. The antenna produces an RF field around it and the vehicle (the desired effect since it extends out to infinity). Any conductor relatively near the vehicle or a conducting part of the vehicle (call it a parasitic conductor or "PC" for short) will have RF currents flowing in them as a result of the transmitter (this occurs whether it is near or not - actually the distance only affects the strength of the current, but for close spacing, the effect is easier to see & understand). More simply stated: "Everything in the world is a receiving antenna." The strength and relative phase of the current in the PC (compared to the transmitted signal) will depend on many things (distance to main antenna, shape, size, orientation, frequency, other objects and conductivity) These PC RF currents will also produce an RF field in the region (around the PC and vehicle). It is no different than the intentional transmitting antenna except it is not cut to a desired length and shape, but accidental. The PC RF field(s) will sum with the field from the transmitting antenna thus producing a slightly modified field - I'll call the "Sum-Field". The actual "Sum_Field" amplitude and phase depends on the relative strength and phase of the two fields at any point and is therefore complex. These fields sum in a vector addition manner. Sounds all pretty random up to here... However, we can say for sure that: If the current in the PC changes, the resulting "Sum-Field" will change. If the position of the PC changes, the current in the PC will change. If the size of the PC changes due to an intermittent connection with another near-by PC, the current in the PC will change. And we know that: If the PC current changes, the resulting PC field will change. And most certainly If the PC field changes, the "Sum-Field" will change. Keeping in mind that: A receiver near or far away will receive the "Sum-Field" at its location. This means that if we have a conductor near the transmitter that, due to any of the above changes, it can "modulate" the field in some way. The modulation must have some relation to the change causing it. It will indeed contain the same characteristic that causes the changing current / field. Therefore, the "modulation" will have the same characteristic as the original change, and it will most certainly contain that vibration frequency or the noise which is the intermittent contact. So, the bottom line is that the vibration (or noisy contact) will modulate the signal at the receiver. This modulation must most certainly be a combination of amplitude and phase modulation. This effect is there and usually small enough to be unnoticeable, therefore it is of little to no concern most of the time. It can be the cause of noise in a mobile instillation from things like tail pipe vibration, hood (bonnet) hinges and latch and the like. P.S. this same argument explains how directional antennas work, such as the common Yagi-Uda and all phased arrays whether parasitic or driven (phased). 73, Steve, K9DCI P.S. The Apollo recovery and communication ships had this problem due to the High power HF transmitters causing RF current in the Deck railing chains which caused noise sidebands which extended up into the microwave frequencies interfering with the radars...believe it or not - don't know if this is on the web, but I have the NASA papers somewhere. Article: 220802 of rec.radio.amateur.antenna From: Jim - NN7K Subject: Re: Scaling of Yagi design References: <9vLuf.169769$V7.114119@news-server.bigpond.net.au> Message-ID: Date: Thu, 05 Jan 2006 01:17:35 GMT And, consider: even then, It might not work as it does on another frequency. Have a friend (this years ago), who modeled the Komosko- Johnson yagi for 2 meters (a 13 el, antenna , that was emperically designed), long before modeling programs, and then antenna range measured. This was a staple of the old VHF handbooks, and the ARRL handbooks for years, and seemed to deliver exceptional results. He had pull at his local company (not to name them)! and had an EXACT copy made for 1296, and then entered it into a antenna contest- it failed misserably! (this not only was element length/Dia, spaceing, ,but BOOM diameter/length)!! It was (and is) a work of ART, but it wont make his retirement check (or Contest Score) any higher! For those that wish to try it- look for those names, or for W2NLY-W6QKI in the ARRL handbooks mentioned. But it must leave to the builder one of the following conclusions: 1) It was great on 144, but a dog on 1296, or: 2) It wasn't the greatest design , for even 144 (tho it compairs favorable with the range patterns that were shown in the VHF handbook, for 144)! As info, Jim NN7K David wrote: > Ian, > > Thanks for that. > > I did previously look at your site and bookmarked it. I am going to make > up the element cutting jig and bending jig (for when I want to > experiment with folded dipoles). > > Great site. > > Regards > > David > > Ian White GM3SEK wrote: > >> David wrote: >> >>> Hi, >>> >>> I have a design for a Yagi antenna at 436MHz and would like to scale >>> it to 921 MHz. The calculations I used from the understanding I have >>> obtained from reading various articles appears below. >>> >>> Would someone be kind enough to advise me if this procedure and >>> values look correct ? >> >> >> [...] >> >>> >>> Regards >>> >>> David Huisman >> >> >> >> >> The basic principle of scaling antennas according to wavelength is >> that you must make an *exact* scale model. That means scaling every >> dimension, and not adding any new or different 'features'. >> >> Often that isn't practical for mechanical engineering reasons, so then >> you need to apply corrections. However, you should still aim to keep >> those corrections as small as possible. For example, simple scaling is >> likely to produce odd, unavailable values for the element diameter, so >> it's OK to use corrections to change to the nearest commercially >> available diameter. But if you also decide to double the diameter, the >> correction is more risky - you're entering the territory of a >> completely new design. >> >> Sorry that I don't have time to check your particular dimensions in >> detail, David, but you can find resources for scaling and >> constructional techniques on my 'VHF/UHF Long Yagi Workshop' pages. >> There is a downloadable program which leads you through the relevant >> questions, and also a link to an online Javascript version. >> >> (From about 1200utc I will not have access to this newsgroup for the >> next few days, so I hope the above will keep you going.) >> >> Article: 220803 of rec.radio.amateur.antenna From: Jim - NN7K Subject: Re: FM transmitter in a vehicle References: <1135976653.858893.150990@g43g2000cwa.googlegroups.com> Message-ID: <6B_uf.8424$UF3.956@newssvr25.news.prodigy.net> Date: Thu, 05 Jan 2006 01:26:26 GMT Answer-- Don't worry about it! tho, during WWII, there was the use of a "WOBBULATOR" in some 450 MHz airborn , Friend or Foe radio sets, these were pre- crystal, P.L.L. type radios, Broad as a barn (kinda like tuneing a Grid Dip oscillator to a fm freq, and then YELLING at it-- it will fm it, but, it won't be reliable for communications)! But, with todays technology , you will get more phase flutter >from multipath than anything else! Jim NN7K Steve Nosko wrote: > "Ron J" wrote in message > news:1135976653.858893.150990@g43g2000cwa.googlegroups.com... > > >>Happy New Year! >> >>If I have an FM transmitter in a vehicle, do I need to worry about the >>vibration frequency? Is there such a thing as intermodulation from >>vibrating objects attached to an FM transmitter? >> >>I'm curious. > > > > > Short answers: > > Worry - Probably not > > Intermodulation - No. > > > > > > Really long answer... > > > > Not sure what you mean by "vibration frequency". > > > > Here's the logic for what is called "Environmental Desensitization", or > "Environmental Desense" for short...sort of. > > > > The type of transmitter is not important for this discussion. > > > > The antenna produces an RF field around it and the vehicle (the desired > effect since it extends out to infinity). > > > > Any conductor relatively near the vehicle or a conducting part of the > vehicle (call it a parasitic conductor or "PC" for short) will have RF > currents flowing in them as a result of the transmitter (this occurs whether > it is near or not - actually the distance only affects the strength of the > current, but for close spacing, the effect is easier to see & understand). > > More simply stated: "Everything in the world is a receiving antenna." > > > > The strength and relative phase of the current in the PC (compared to the > transmitted signal) will depend on many things (distance to main antenna, > shape, size, orientation, frequency, other objects and conductivity) > > > > These PC RF currents will also produce an RF field in the region (around the > PC and vehicle). It is no different than the intentional transmitting > antenna except it is not cut to a desired length and shape, but accidental. > > > > The PC RF field(s) will sum with the field from the transmitting antenna > thus producing a slightly modified field - I'll call the "Sum-Field". > > The actual "Sum_Field" amplitude and phase depends on the relative strength > and phase of the two fields at any point and is therefore complex. These > fields sum in a vector addition manner. Sounds all pretty random up to > here... > > > > However, we can say for sure that: > > > > If the current in the PC changes, the resulting "Sum-Field" will change. > > If the position of the PC changes, the current in the PC will change. > > If the size of the PC changes due to an intermittent connection with another > near-by PC, the current in the PC will change. > > > > And we know that: > > If the PC current changes, the resulting PC field will change. > > > > And most certainly > > If the PC field changes, the "Sum-Field" will change. > > > > Keeping in mind that: > > A receiver near or far away will receive the "Sum-Field" at its location. > > > > This means that if we have a conductor near the transmitter that, due to any > of the above changes, it can "modulate" the field in some way. The > modulation must have some relation to the change causing it. It will indeed > contain the same characteristic that causes the changing current / field. > Therefore, the "modulation" will have the same characteristic as the > original change, and it will most certainly contain that vibration > frequency or the noise which is the intermittent contact. > > > > So, the bottom line is that the vibration (or noisy contact) will modulate > the signal at the receiver. This modulation must most certainly be a > combination of amplitude and phase modulation. > > > > This effect is there and usually small enough to be unnoticeable, therefore > it is of little to no concern most of the time. It can be the cause of > noise in a mobile instillation from things like tail pipe vibration, hood > (bonnet) hinges and latch and the like. > > > > P.S. this same argument explains how directional antennas work, such as the > common Yagi-Uda and all phased arrays whether parasitic or driven (phased). > > > > 73, Steve, K9DCI > > > > P.S. The Apollo recovery and communication ships had this problem due to > the High power HF transmitters causing RF current in the Deck railing chains > which caused noise sidebands which extended up into the microwave > frequencies interfering with the radars...believe it or not - don't know if > this is on the web, but I have the NASA papers somewhere. > > Article: 220804 of rec.radio.amateur.antenna From: David Subject: Re: Scaling of Yagi design References: <9vLuf.169769$V7.114119@news-server.bigpond.net.au> Message-ID: <6R_uf.170236$V7.94549@news-server.bigpond.net.au> Date: Thu, 05 Jan 2006 01:43:30 GMT Jim, Thanks for your input of caution. I'm sure that along with all the horror stories there are a multitude of success stories. My belief is that antennas have been around for years and millions have been constructed on almost every frequency imaginable. In my case I am new to antenna design and green when it comes to determining the parameters that would best suit my applications. My requirements are not critical with regard to front/back ratio or the last drop of gain available for a specific design. I find there are always such a range of responses to a request. Some of these are the theorists that love to explain how black holes in the universe some 10 million light years away might effect free electrons floating on the end of a copper wire. Then we have the ones that are not particularly experienced but like to have a say on every topic. They would normally ask why you want it in the first place. "Oh, you want blue, why not have red". Between these extremes are a bunch of very kind people who have "played" with antennas and gained practical experience that they are prepared to pass on to others. Modeling programs have come a long way and my understanding is that as long as you model the unit correctly, your actual results should not be too far off. (I don't know how to model yet so hence the reason to ask for help). I imagine there are still some disasters when engineers build new cars but I believe this would mainly occur when something is overlooked or they are trying to achieve something new. I am not trying to break any new ground here, just looking for around 7 dBi gain from a Yagi at 921MHz. Regards David Huisman Jim - NN7K wrote: > And, consider: even then, It might not work as it does on another > frequency. Have a friend (this years ago), who modeled the Komosko- > Johnson yagi for 2 meters (a 13 el, antenna , that was emperically > designed), long before modeling programs, and then antenna range > measured. This was a staple of the old VHF handbooks, and the > ARRL handbooks for years, and seemed to deliver exceptional results. > He had pull at his local company (not to name them)! and had an > EXACT copy made for 1296, and then entered it into a antenna contest- > it failed misserably! (this not only was element length/Dia, spaceing, > ,but BOOM diameter/length)!! It was (and is) a work of ART, > but it wont make his retirement check (or Contest Score) > any higher! For those that > wish to try it- look for those names, or for W2NLY-W6QKI in the > ARRL handbooks mentioned. But it must leave to the builder one > of the following conclusions: 1) It was great on 144, but a dog > on 1296, or: 2) It wasn't the greatest design , for even 144 (tho > it compairs favorable with the range patterns that were shown > in the VHF handbook, for 144)! As info, Jim NN7K > > David wrote: > >> Ian, >> >> Thanks for that. >> >> I did previously look at your site and bookmarked it. I am going to >> make up the element cutting jig and bending jig (for when I want to >> experiment with folded dipoles). >> >> Great site. >> >> Regards >> >> David >> >> Ian White GM3SEK wrote: >> >>> David wrote: >>> >>>> Hi, >>>> >>>> I have a design for a Yagi antenna at 436MHz and would like to scale >>>> it to 921 MHz. The calculations I used from the understanding I have >>>> obtained from reading various articles appears below. >>>> >>>> Would someone be kind enough to advise me if this procedure and >>>> values look correct ? >>> >>> >>> >>> [...] >>> >>>> >>>> Regards >>>> >>>> David Huisman >>> >>> >>> >>> >>> >>> The basic principle of scaling antennas according to wavelength is >>> that you must make an *exact* scale model. That means scaling every >>> dimension, and not adding any new or different 'features'. >>> >>> Often that isn't practical for mechanical engineering reasons, so >>> then you need to apply corrections. However, you should still aim to >>> keep those corrections as small as possible. For example, simple >>> scaling is likely to produce odd, unavailable values for the element >>> diameter, so it's OK to use corrections to change to the nearest >>> commercially available diameter. But if you also decide to double the >>> diameter, the correction is more risky - you're entering the >>> territory of a completely new design. >>> >>> Sorry that I don't have time to check your particular dimensions in >>> detail, David, but you can find resources for scaling and >>> constructional techniques on my 'VHF/UHF Long Yagi Workshop' pages. >>> There is a downloadable program which leads you through the relevant >>> questions, and also a link to an online Javascript version. >>> >>> (From about 1200utc I will not have access to this newsgroup for the >>> next few days, so I hope the above will keep you going.) >>> >>> Article: 220805 of rec.radio.amateur.antenna Date: Wed, 04 Jan 2006 21:14:52 -0600 From: Tom Ring Subject: Re: Scaling of Yagi design References: <9vLuf.169769$V7.114119@news-server.bigpond.net.au> Message-ID: <43bc8f47$0$3754$39cecf19@news.twtelecom.net> Jim - NN7K wrote: > And, consider: even then, It might not work as it does on another > frequency. Have a friend (this years ago), who modeled the Komosko- > Johnson yagi for 2 meters (a 13 el, antenna , that was emperically > in the VHF handbook, for 144)! As info, Jim NN7K > When properly done, I have never had a scaled design fail to perform as expected. I have done several dozen. The designs were 144, 220, 222, and 432 as source and destination. I don't expect this one will surprise me as to how it performs, especially as it is insulated above the boom. tom K0TAR Article: 220806 of rec.radio.amateur.antenna From: David Subject: Re: Scaling of Yagi design References: <9vLuf.169769$V7.114119@news-server.bigpond.net.au> <43bc8f47$0$3754$39cecf19@news.twtelecom.net> Message-ID: Date: Thu, 05 Jan 2006 03:32:39 GMT That's what I expected from people who have practical experience and understand the principles (much better than I current do). I managed to track down thinner aluminum rod that is much closer to scaled values of elements in the original design. The values should be 3.78mm and I can get 3.175mm For the 4.73mm , I can get 4.763mm. This should now be close enough to only require small trim in length to compensate for small change in diameter. Tom Ring wrote: > Jim - NN7K wrote: > >> And, consider: even then, It might not work as it does on another >> frequency. Have a friend (this years ago), who modeled the Komosko- >> Johnson yagi for 2 meters (a 13 el, antenna , that was emperically > > > >> in the VHF handbook, for 144)! As info, Jim NN7K >> > > When properly done, I have never had a scaled design fail to perform as > expected. I have done several dozen. The designs were 144, 220, 222, > and 432 as source and destination. > > I don't expect this one will surprise me as to how it performs, > especially as it is insulated above the boom. > > tom > K0TAR > Article: 220807 of rec.radio.amateur.antenna Date: Wed, 04 Jan 2006 21:32:07 -0600 From: Tom Ring Subject: Re: Scaling of Yagi design References: <9vLuf.169769$V7.114119@news-server.bigpond.net.au> Message-ID: <43bc9351$0$3756$39cecf19@news.twtelecom.net> Jim - NN7K wrote: > wish to try it- look for those names, or for W2NLY-W6QKI in the > ARRL handbooks mentioned. But it must leave to the builder one > of the following conclusions: 1) It was great on 144, but a dog > on 1296, or: 2) It wasn't the greatest design , for even 144 (tho > it compairs favorable with the range patterns that were shown > in the VHF handbook, for 144)! As info, Jim NN7K And, except for the K1FO designs, the VHF handbook contains one of the worst collections of yagis ever assembled. They are at least as bad as the Cushcraft VHF/UHF yagis that had the dual reflectors. Article: 220808 of rec.radio.amateur.antenna Date: Wed, 04 Jan 2006 21:40:52 -0600 From: Tom Ring Subject: Re: Scaling of Yagi design References: <9vLuf.169769$V7.114119@news-server.bigpond.net.au> <43bc8f47$0$3754$39cecf19@news.twtelecom.net> Message-ID: <43bc955e$0$3764$39cecf19@news.twtelecom.net> David wrote: > That's what I expected from people who have practical experience and > understand the principles (much better than I current do). > > I managed to track down thinner aluminum rod that is much closer to > scaled values of elements in the original design. > > The values should be 3.78mm and I can get 3.175mm > For the 4.73mm , I can get 4.763mm. > > This should now be close enough to only require small trim in length > to compensate for small change in diameter. The diameter ratio would be fine given the first diameter you listed. The others would be fine also. Just specify what you want to use. tom K0TAR Article: 220809 of rec.radio.amateur.antenna From: David Subject: Re: Scaling of Yagi design References: <9vLuf.169769$V7.114119@news-server.bigpond.net.au> <43bc8f47$0$3754$39cecf19@news.twtelecom.net> <43bc955e$0$3764$39cecf19@news.twtelecom.net> Message-ID: Date: Thu, 05 Jan 2006 04:05:45 GMT Tom, I have heaps of 6mm in stock. The smaller diameter has to be ordered specially and is more expensive. So: Frequency 921 MHz. (20MHz BW or more would be good). Gain >= 7dBi F/B ratio not critical. 4 Element Yagi - input impedance of around 29 Ohms (can easily match with 2 par 75 Ohm 1/4 wave section). Unit to be operated vertically orientated at height greater than 2m. Element diameters 6mm Boom is 12mm square aluminium. Elements mounted 3-5mm above boom on nylon insulator block. Just need accurate lengths and spacing now. Tom Ring wrote: > David wrote: > >> That's what I expected from people who have practical experience and >> understand the principles (much better than I current do). >> >> I managed to track down thinner aluminum rod that is much closer to >> scaled values of elements in the original design. >> >> The values should be 3.78mm and I can get 3.175mm >> For the 4.73mm , I can get 4.763mm. >> >> This should now be close enough to only require small trim in length >> to compensate for small change in diameter. > > > The diameter ratio would be fine given the first diameter you listed. > The others would be fine also. Just specify what you want to use. > > tom > K0TAR > Article: 220810 of rec.radio.amateur.antenna Date: Wed, 04 Jan 2006 23:14:45 -0500 From: jawod Subject: Stupid question on twin feedline (air) Message-ID: <71286$43bc9d37$42a1bfc2$1899@FUSE.NET> I will assume that balanced (air) feedline is homebrew. What recommendations are there for spacing between the twin lines? Number of spacers per foot? If homebrew, how to keep spacers from migrating...will small wire "stays" modify feedline characteristics? This is all about feedline to simple dipole or inverted V. Thanks, a new (old) ham jawod aka john Article: 220811 of rec.radio.amateur.antenna From: richardharrison@webtv.net (Richard Harrison) Subject: Re: Transmission Line Reflections Date: Thu, 5 Jan 2006 00:23:40 -0600 Message-ID: <26048-43BCBB6C-1527@storefull-3251.bay.webtv.net> References: Wayne Watson wrote: "The voltage returns down the line, and the current does not." What happens on reflection is that either the phase of the current is reversed with an open circuit, or the phase of the voltage is reversed with a short circuit, in the event of a complete reflection from an open or a short. In either case, there is a reversal in phase of only one of the components of the electromagnetic wave, not both. However, the total wave is reflected. A transverse electromagnetic wave consists of two components, an electric field and a magnetic field. An incident wave has both parts in-phase until it is reflected. A reflected wave has its two parts 180-degrees out-of-phase upon its first reflection. This fact is how the directional coupler in the Bird Wattmeter distinguishes between the waves traveling in opposite directions through the wattmeter. Both voltage and current return upon reflection. The difference is zero phase difference in one direction, and 180-degrees difference in the opposite direction. Best regards, Richard Harrison, KB5WZI Article: 220812 of rec.radio.amateur.antenna From: richardharrison@webtv.net (Richard Harrison) Subject: Re: Stupid question on twin feedline (air) Date: Thu, 5 Jan 2006 01:01:26 -0600 Message-ID: <19245-43BCC446-1109@storefull-3252.bay.webtv.net> References: <71286$43bc9d37$42a1bfc2$1899@FUSE.NET> John wrote: "---how to keep spacers from migrating..." My 1970 edition of the ARRL Antenna Book shows how to construct open wire line. The insulating spacers have holes near their ends and their ends are also grooved for the line conductors. A small tiewire is run through the hole and its ends are tightly wrapped around the transmission line conductors to hold everything in place. Best regards, Richard Harrison, KB5WZI Article: 220813 of rec.radio.amateur.antenna From: Butch Magee Subject: Re: Stupid question on twin feedline (air) Date: Thu, 05 Jan 2006 02:11:23 -0600 Message-ID: <11rpl5b86d0r0ef@corp.supernews.com> References: <71286$43bc9d37$42a1bfc2$1899@FUSE.NET> <19245-43BCC446-1109@storefull-3252.bay.webtv.net> buy it already built. Why wear yourself out building stuff available on the shelf? Richard Harrison wrote: > John wrote: > "---how to keep spacers from migrating..." > > My 1970 edition of the ARRL Antenna Book shows how to construct open > wire line. The insulating spacers have holes near their ends and their > ends are also grooved for the line conductors. > > A small tiewire is run through the hole and its ends are tightly wrapped > around the transmission line conductors to hold everything in place. > > Best regards, Richard Harrison, KB5WZI > Article: 220814 of rec.radio.amateur.antenna Message-ID: <43bd1032$0$82676$ed2619ec@ptn-nntp-reader03.plus.net> From: Ted Subject: Query.. Date: Thu, 05 Jan 2006 12:25:23 +0000 I have about 40 feet of garden to erect an antenna....Could anyone tell me if I took 2 20 feet length of twin ladder and shorted the ends fed one side of the dipole with twin ladder and connected a 52 ohm resistor across the other side so the tx would see a match would be better than feeding a 40 foot endfed through an atu... My thinking is that most of the small antenna on the market are just dummy loads with a small amount of wire attached and appear to work so would my 40 feet work better.. ?? -- Regards Ted Wager Using Debian Linux Article: 220815 of rec.radio.amateur.antenna Message-ID: <43BD2F10.3672747B@UNCLE.org> From: Gabe Subject: FCC ULS Link Date: Thu, 05 Jan 2006 14:37:05 GMT hello, here is a link to the FCC ULS databasse, it has no ads to slow you down like other sites, http://gullfoss2.fcc.gov/cgi-bin/ws.exe/genmen/uls/call_res.hts?db_id=19&rows=&callsign= add it to your bookmarks, then after you go there just add the callsign you want to check to the end of the line and then hit enter again. Gabe Article: 220816 of rec.radio.amateur.antenna From: Bob Miller Subject: Re: Stupid question on twin feedline (air) Message-ID: References: <71286$43bc9d37$42a1bfc2$1899@FUSE.NET> Date: Thu, 05 Jan 2006 15:05:36 GMT On Wed, 04 Jan 2006 23:14:45 -0500, jawod wrote: >I will assume that balanced (air) feedline is homebrew. What >recommendations are there for spacing between the twin lines? Number of >spacers per foot? If homebrew, how to keep spacers from >migrating...will small wire "stays" modify feedline characteristics? > >This is all about feedline to simple dipole or inverted V. > >Thanks, > >a new (old) ham > >jawod aka john already-made 600 ohm line is available at www.w7fg.com bob k5qwg Article: 220817 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: Transmission Line Reflections References: Message-ID: Date: Thu, 05 Jan 2006 15:21:11 GMT W. Watson wrote: > It seems reasonable that if I have an open ended transmission line that > the current would reflect back and change phase. After all, the > electrons at the end have nowhere to go but back down the line. However, > the voltage is a different matter. There is no phase reversal (or > polarization change) There doesn't seem to be an intuitive reason for > this. However, if one examines the equations for current and capacitive > voltage, then it falls out of the math. Still, where is the non-math > that indicates this is true? The forward current hits an open-circuit. The net current is zero. Therefore, the reflected current must be equal in magnitude and opposite in phase to the forward current at the open-circuit. Since the net current goes to zero, i.e. the magnetic field goes to zero, all the energy existing at that point must migrate into the electric field thus increasing the voltage. And indeed, the voltage doubles at an open-circuit indicating that the reflected voltage is equal in magnitude and phase to the forward voltage. A simple RF voltage measurement at the open- circuit will prove that the above is true. > Now suppose instead the line is short circuited. The voltage returns > down the line, and the current does not. In this case, there doesn't > seem to be any non-math or intuitive feel for why the short should cause > this--either for voltage or current. Can one clue me in on what's really > happening above (voltage) and here (voltage and current)? Inquiring > minds want to know. It's (surprise) the reverse of an open-circuit. The net voltage goes to zero at the short indicating that the electric field is zero at that point. Therefore, all the energy existing at that point migrates into the magnetic field. The reflected voltage is therefore equal in magnitude and 180 degrees out of phase with the forward voltage. And, indeed, the current at the short is double the magnitude of the forward current indicating that the forward current and reflected current are equal in magnitude and phase at a short circuit. RF voltage and current measurements prove it to be true. -- 73, Cecil, http://www.qsl.net/w5dxp Article: 220818 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: Stupid question on twin feedline (air) References: <71286$43bc9d37$42a1bfc2$1899@FUSE.NET> Message-ID: Date: Thu, 05 Jan 2006 15:30:56 GMT jawod wrote: > I will assume that balanced (air) feedline is homebrew. What > recommendations are there for spacing between the twin lines? Number of > spacers per foot? If homebrew, how to keep spacers from > migrating...will small wire "stays" modify feedline characteristics? For all-HF-band operation with relatively high SWRs, the spacing doesn't much matter. 2"-6" is a practical range. Spacer spacing depends upon wind conditions. Two foot spacing seems reasonable at my QTH. Some spacers pinch the insulation on the feedline and thus stay in place. Very small tie wraps could also be used. -- 73, Cecil, http://www.qsl.net/w5dxp Article: 220819 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: Stupid question on twin feedline (air) References: <71286$43bc9d37$42a1bfc2$1899@FUSE.NET> <19245-43BCC446-1109@storefull-3252.bay.webtv.net> <11rpl5b86d0r0ef@corp.supernews.com> Message-ID: Date: Thu, 05 Jan 2006 15:32:58 GMT Butch Magee wrote: > buy it already built. Why wear yourself out building stuff available on > the shelf? Heaven forbid that hams build anything anymore. :-) -- 73, Cecil, http://www.qsl.net/w5dxp Article: 220820 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: Query.. References: <43bd1032$0$82676$ed2619ec@ptn-nntp-reader03.plus.net> Message-ID: Date: Thu, 05 Jan 2006 15:35:45 GMT Ted wrote: > I have about 40 feet of garden to erect an antenna....Could anyone tell > me if I took 2 20 feet length of twin ladder and shorted the ends > fed one side of the dipole with twin ladder and connected a 52 ohm > resistor across the other side ... Where is the ground for that 52 ohm resistor? -- 73, Cecil, http://www.qsl.net/w5dxp Article: 220821 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: WTB Outbacker Mobile HF Antenna References: Message-ID: Date: Thu, 05 Jan 2006 15:37:24 GMT Doug wrote: > Looking for an Outbacker mobile HF antenna. Since it is 9dB down from a screwdriver or bugcatcher, one wonders why. :-) -- 73, Cecil, http://www.qsl.net/w5dxp Article: 220822 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: Query.. Date: Thu, 5 Jan 2006 16:36:33 +0000 (UTC) Message-ID: References: <43bd1032$0$82676$ed2619ec@ptn-nntp-reader03.plus.net> > Where is the ground for that 52 ohm resistor? > -- > 73, Cecil ========================================= Really Cecil, you shouldn't ask awkward questions like that. You might gain the reputation of being a wicked troller. On the other hand, it cannot be denied, your question is apt and could be considered to be educational. Please continue! Due to a certain person who ought to know better, I suffer from the same misinterpretation of motives myself. ---- Reg. Article: 220823 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: WTB Outbacker Mobile HF Antenna Date: Thu, 5 Jan 2006 17:04:19 +0000 (UTC) Message-ID: References: "Cecil Moore" wrote - > Since it is 9dB down from a screwdriver or > bugcatcher, one wonders why. :-) ========================================== 9dB is only one and a half S-units. (Ignoring Roy's ancient S-meter). The Outbacker may still be well worth the money! But that's just the Capitalist System which places Religion above scientific facts. Sorry for becoming a little off topic. A drop of South African Western Cape helps to keep things in proportion. ----- ........................................................... Regards from Reg, G4FGQ For Free Radio Design Software go to http://www.btinternet.com/~g4fgq.regp ........................................................... Article: 220824 of rec.radio.amateur.antenna Message-ID: <43bd588b$0$63054$ed2e19e4@ptn-nntp-reader04.plus.net> From: Ted Subject: Re: Query.. Date: Thu, 05 Jan 2006 17:34:06 +0000 References: <43bd1032$0$82676$ed2619ec@ptn-nntp-reader03.plus.net> Cecil Moore wrote: > Ted wrote: >> I have about 40 feet of garden to erect an antenna....Could anyone tell >> me if I took 2 20 feet length of twin ladder and shorted the ends >> fed one side of the dipole with twin ladder and connected a 52 ohm >> resistor across the other side ... > > Where is the ground for that 52 ohm resistor? The feed goes to the centre..The ends are strapped together and the resistor connects between the free ends opposite the feed connection... -- Regards Ted Wager Using Debian Linux Article: 220825 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: Query.. References: <43bd1032$0$82676$ed2619ec@ptn-nntp-reader03.plus.net> <43bd588b$0$63054$ed2e19e4@ptn-nntp-reader04.plus.net> Message-ID: Date: Thu, 05 Jan 2006 18:19:16 GMT Ted wrote: > Cecil Moore wrote: > >>Ted wrote: >>>I have about 40 feet of garden to erect an antenna....Could anyone tell >>>me if I took 2 20 feet length of twin ladder and shorted the ends >>>fed one side of the dipole with twin ladder and connected a 52 ohm >>>resistor across the other side ... >> >>Where is the ground for that 52 ohm resistor? > > The feed goes to the centre..The ends are strapped together and the resistor > connects between the free ends opposite the feed connection... I'm afraid we need a schematic. Is this correct? 20ft 20ft +-------------------FP------------------+ | 52 ohm resistor +-------------------FP------------------+ -- 73, Cecil, http://www.qsl.net/w5dxp Article: 220826 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: friends,please help me!!!!!! References: <1136481553.458674.149950@g14g2000cwa.googlegroups.com> Message-ID: Date: Thu, 05 Jan 2006 18:21:37 GMT pcrkishan@gmail.com wrote: > I have two dish antennas at the roof of my apartment.They are lying > abandoned for many years. Are they for receiving geostationary satellites? -- 73, Cecil, http://www.qsl.net/w5dxp Article: 220827 of rec.radio.amateur.antenna Message-ID: <43bd6ee1$0$2691$ed2619ec@ptn-nntp-reader02.plus.net> From: Ted Subject: Re: Query.. Date: Thu, 05 Jan 2006 19:09:23 +0000 References: <43bd1032$0$82676$ed2619ec@ptn-nntp-reader03.plus.net> <43bd588b$0$63054$ed2e19e4@ptn-nntp-reader04.plus.net> Cecil Moore wrote: > Ted wrote: > >> Cecil Moore wrote: >> >>>Ted wrote: >>>>I have about 40 feet of garden to erect an antenna....Could anyone tell >>>>me if I took 2 20 feet length of twin ladder and shorted the ends >>>>fed one side of the dipole with twin ladder and connected a 52 ohm >>>>resistor across the other side ... >>> >>>Where is the ground for that 52 ohm resistor? >> >> The feed goes to the centre..The ends are strapped together and the >> resistor connects between the free ends opposite the feed connection... > > I'm afraid we need a schematic. Is this correct? > > 20ft 20ft > +-------------------resistor------------+ | connected connected > +-------------------FP------------------+ > Like so...Ends strapped and r at centre opposite feed... -- Regards Ted Wager Using Debian Linux Article: 220828 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: Query.. References: <43bd1032$0$82676$ed2619ec@ptn-nntp-reader03.plus.net> <43bd588b$0$63054$ed2e19e4@ptn-nntp-reader04.plus.net> <43bd6ee1$0$2691$ed2619ec@ptn-nntp-reader02.plus.net> Message-ID: Date: Thu, 05 Jan 2006 19:45:49 GMT Ted wrote: >>I'm afraid we need a schematic. Is this correct? >> >> 20ft 20ft >>+-------------------resistor------------+ | > > connected connected > >>+-------------------FP------------------+ OK, close to a T2FD. Here are the formulas for such an antenna. http://www.hard-core-dx.com/nordicdx/antenna/wire/t2design.html Looks like yours would be resonant around 8.2 MHz. -- 73, Cecil, http://www.qsl.net/w5dxp Article: 220829 of rec.radio.amateur.antenna Message-ID: <43bd7e27$0$63091$ed2e19e4@ptn-nntp-reader04.plus.net> From: Ted Subject: Re: Query.. Date: Thu, 05 Jan 2006 20:14:34 +0000 References: <43bd1032$0$82676$ed2619ec@ptn-nntp-reader03.plus.net> <43bd588b$0$63054$ed2e19e4@ptn-nntp-reader04.plus.net> <43bd6ee1$0$2691$ed2619ec@ptn-nntp-reader02.plus.net> Cecil Moore wrote: > Ted wrote: >>>I'm afraid we need a schematic. Is this correct? >>> >>> 20ft 20ft >>>+-------------------resistor------------+ | >> >> connected connected >> >>>+-------------------FP------------------+ > > OK, close to a T2FD. Here are the formulas for such an antenna. > > http://www.hard-core-dx.com/nordicdx/antenna/wire/t2design.html > > Looks like yours would be resonant around 8.2 MHz. Thanks very much for the info and the address.. -- Regards Ted Wager Using Debian Linux Article: 220830 of rec.radio.amateur.antenna From: Owen Duffy Subject: Re: Stupid question on twin feedline (air) Message-ID: <632rr1lc8kcupagcrp7tb5kg4cm3kvofvq@4ax.com> References: <71286$43bc9d37$42a1bfc2$1899@FUSE.NET> Date: Thu, 05 Jan 2006 20:59:34 GMT On Thu, 05 Jan 2006 15:30:56 GMT, Cecil Moore wrote: >jawod wrote: > >> I will assume that balanced (air) feedline is homebrew. What >> recommendations are there for spacing between the twin lines? Number of >> spacers per foot? If homebrew, how to keep spacers from >> migrating...will small wire "stays" modify feedline characteristics? > >For all-HF-band operation with relatively high SWRs, the >spacing doesn't much matter. 2"-6" is a practical range. >Spacer spacing depends upon wind conditions. Two foot >spacing seems reasonable at my QTH. Some spacers pinch Did you really mean two foot spacing. This imperial measurement system can be a bit tricky sometimes. >the insulation on the feedline and thus stay in place. >Very small tie wraps could also be used. -- Article: 220831 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: Stupid question on twin feedline (air) References: <71286$43bc9d37$42a1bfc2$1899@FUSE.NET> <632rr1lc8kcupagcrp7tb5kg4cm3kvofvq@4ax.com> Message-ID: Date: Thu, 05 Jan 2006 21:08:39 GMT Owen Duffy wrote: > Did you really mean two foot spacing? Two foot spacing between spacers, not between wires. I tried 4 foot spacing at first and it twisted in the wind so I installed twice as many spacers. -- 73, Cecil, http://www.qsl.net/w5dxp Article: 220832 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: WTB Outbacker Mobile HF Antenna Date: Thu, 05 Jan 2006 13:35:27 -0800 Message-ID: <11rr4922agp1acd@corp.supernews.com> References: Reg Edwards wrote: > > 9dB is only one and a half S-units. (Ignoring Roy's ancient S-meter). > > The Outbacker may still be well worth the money! > > But that's just the Capitalist System which places Religion above > scientific facts. Sorry for becoming a little off topic. > > A drop of South African Western Cape helps to keep things in > proportion. 9 dB is also the gain of a good long-boom 4 element Yagi over a dipole. You'd have to drink more than a spot of the wine to not see the difference. Roy Lewallen, W7EL Article: 220833 of rec.radio.amateur.antenna From: "Joe S." Subject: GeoTool antenna mounts for pickup truck stake holes Date: Thu, 5 Jan 2006 16:48:22 -0500 Message-ID: Anyone have experience with these mounts? http://www.geotool.com/antmount.htm As you see from their website, the mounts are mounted into the stake holes in the sides of a pickup bed. Anyone here used these mounts? What was your experience? What truck? How difficult/easy was the installation? Has the mount lasted? Thanks. Article: 220834 of rec.radio.amateur.antenna From: mcalhoun@ksu.edu Subject: Re: Stupid question on twin feedline (air) Date: 5 Jan 2006 16:53:06 -0600 Message-ID: References: <71286$43bc9d37$42a1bfc2$1899@FUSE.NET> >>I will assume that balanced (air) feedline is homebrew.... >If you can support the center of the dipole, weight is not >as much concern as if you cannot support it. With too heavy >a ladder line, your dipole may resemble a Y. If the center of the dipole is NOT supported, I've found the worst problem is the ladderline breaking -- from flexing caused by wind, etc. -- just below where it is connected to the antenna. My current dipole has a center support, but I've read that making the last section(s) of ladder-line out of stranded wire will reduce the flex-breaking problem. -- --Myron A. Calhoun. Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge PhD EE (retired). "Barbershop" tenor. CDL(PTXS). W0PBV. (785) 539-4448 NRA Life Member and Certified Instructor (Home Firearm Safety, Rifle, Pistol) Article: 220835 of rec.radio.amateur.antenna From: ehramm@dk3uz.ampr.org (Edmund H. Ramm) Subject: Re: Stupid question on twin feedline (air) References: <71286$43bc9d37$42a1bfc2$1899@FUSE.NET> Message-ID: Date: Thu, 5 Jan 2006 23:11:14 GMT In Cecil Moore writes: > For all-HF-band operation with relatively high SWRs, the > spacing doesn't much matter. 2"-6" is a practical range. > [...] IIRC the wires shouldn't be further apart than Lambda/100, otherwise the line will start to radiate even when balanced. (The fields wouldn't have enough time to cancel each other out.) Which would make 4" the maximum spacing if the line is to be used at 30Mhz. 73, Eddi ._._. -- e-mail: dk3uz AT darc DOT de | AMPRNET: dk3uz@db0hht.ampr.org If replying to a Usenet article, please use above e-mail address. Linux/m68k, the best U**x ever to hit an Atari! Article: 220836 of rec.radio.amateur.antenna From: "M.M." Subject: Re: GeoTool antenna mounts for pickup truck stake holes References: Message-ID: Date: Thu, 05 Jan 2006 16:29:27 -0700 Joe S. wrote: > Anyone have experience with these mounts? > > http://www.geotool.com/antmount.htm > > As you see from their website, the mounts are mounted into the stake holes > in the sides of a pickup bed. Anyone here used these mounts? What was your > experience? What truck? How difficult/easy was the installation? Has the > mount lasted? > I've had one on my Ford Ranger for several years with a 10M hamstick. It worked just fine. It was fairly easy to install...I had to remove the taillight assy to get access to the bottom of the pocket but that was not a big deal. I also had to drill a hole in the bottom of the pocket and needed a drill extension to reach but that wasn't too big a deal either. Altho the hamstick probably didn't tax it much, it seems to be a pretty rugged unit and seems to me to be a great idea. It's held up fine for quite a while (can't remember when I bought it) but I just removed it a few weeks ago when I gave the truck to my kid. It got a little rusty on top where the hamstick screws in but the rest of it is aluminum so won't rust. I'd certainly recommend it based on my experience with it. If the one I have will fit your truck, I'd make you a deal on it... 73... Mark AA7TA Article: 220837 of rec.radio.amateur.antenna From: Owen Duffy Subject: Re: Stupid question on twin feedline (air) Message-ID: References: <71286$43bc9d37$42a1bfc2$1899@FUSE.NET> <632rr1lc8kcupagcrp7tb5kg4cm3kvofvq@4ax.com> Date: Fri, 06 Jan 2006 01:05:35 GMT On Thu, 05 Jan 2006 19:48:55 -0500, Amos Keag wrote: >Owen Duffy wrote: >> On Thu, 05 Jan 2006 15:30:56 GMT, Cecil Moore wrote: >> >> >>>jawod wrote: >>> >>> >>>>I will assume that balanced (air) feedline is homebrew. What >>>>recommendations are there for spacing between the twin lines? Number of >>>>spacers per foot? If homebrew, how to keep spacers from >>>>migrating...will small wire "stays" modify feedline characteristics? >>> >>>For all-HF-band operation with relatively high SWRs, the >>>spacing doesn't much matter. 2"-6" is a practical range. >>>Spacer spacing depends upon wind conditions. Two foot >>>spacing seems reasonable at my QTH. Some spacers pinch >> >> >> Did you really mean two foot spacing. This imperial measurement system >> can be a bit tricky sometimes. > >50 cm, then Well Amos, I misunderstood the two foot spacing to be wire spacing rather than spacer spacing. Both spacings are discussed in the space of one paragraph, and it is a little open to misinterpretation. I thought he may have meant wire spacing and two inches rather than feet... hence the reference to the measurement system. Cecil did clear it up. BTW, two foot is closer to 60cm (60.96cm). Owen -- Article: 220838 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: WTB Outbacker Mobile HF Antenna Date: Fri, 6 Jan 2006 02:57:42 +0000 (UTC) Message-ID: References: <11rr4922agp1acd@corp.supernews.com> "Roy Lewallen" wrote - > Reg Edwards wrote: > > > > 9dB is only one and a half S-units. (Ignoring Roy's ancient S-meter). > > > > The Outbacker may still be well worth the money! > > > > But that's just the Capitalist System which places Religion above > > scientific facts. Sorry for becoming a little off topic. > > > > A drop of South African Western Cape helps to keep things in > > proportion. > > 9 dB is also the gain of a good long-boom 4 element Yagi over a dipole. > You'd have to drink more than a spot of the wine to not see the difference. > ========================================= Roy, you have the unfortunate habit of changing the subject in the middle of a discussion in the forlorn hope of it not being noticed. What have 4-element yagis to do with Outbackers? By switching to Chinese "Great Wall" white wine I can make my S-meter read whatever I fancy. You ought to try some! But perhaps you are a teetotaller who has never had the pleasure. If in fact you are indeed a teetotaller, then, I must admit, you deserve congratulations for having evaded the 'demon' drink. It's all in the genes, anyway! I acquired it from my Grandmother. ---- Reg. Article: 220839 of rec.radio.amateur.antenna From: "Joe S." Subject: Re: GeoTool antenna mounts for pickup truck stake holes Date: Thu, 5 Jan 2006 21:58:59 -0500 Message-ID: References: "M.M." wrote in message news:BYhvf.6952$JT.173@fed1read06... > Joe S. wrote: >> Anyone have experience with these mounts? >> >> http://www.geotool.com/antmount.htm >> >> As you see from their website, the mounts are mounted into the stake >> holes in the sides of a pickup bed. Anyone here used these mounts? What >> was your experience? What truck? How difficult/easy was the >> installation? Has the mount lasted? >> > > I've had one on my Ford Ranger for several years with a 10M hamstick. It > worked just fine. It was fairly easy to install...I had to remove the > taillight assy to get access to the bottom of the pocket but that was not > a big deal. I also had to drill a hole in the bottom of the pocket and > needed a drill extension to reach but that wasn't too big a deal either. > Altho the hamstick probably didn't tax it much, it seems to be a pretty > rugged unit and seems to me to be a great idea. It's held up fine for > quite a while (can't remember when I bought it) but I just removed it a > few weeks ago when I gave the truck to my kid. It got a little rusty on > top where the hamstick screws in but the rest of it is aluminum so won't > rust. I'd certainly recommend it based on my experience with it. If the > one I have will fit your truck, I'd make you a deal on it... > > 73... Mark AA7TA Thanks to all who answered -- I really appreciate your comments. Mark: Your experience is especially relevant as I have just purchased a used Mazda B4000 -- basically a Ranger with a Mazda nameplate. I lost my 16-year-old Nissan pickup along with an FT-857D in Hurricane Katrina ( go to www.schlatter.org to see some ugly photos ) and am replacing it with the Mazda. I rescued the ASAT-120 from the hurricane and bought a new FT-857 last week; I plan to install two antennas on the truck, dual-bander for 2 and 450 and the ATAS-120, will put them in the rear stake holes. Thanks again. 73, Joe Article: 220840 of rec.radio.amateur.antenna Subject: Re: Dipoles and the rig's RF ground... From: Dave Oldridge References: <1136148463.132269.164130@g49g2000cwa.googlegroups.com> <11rj9uu7bkogd37@corp.supernews.com> Message-ID: Date: Fri, 06 Jan 2006 04:03:18 GMT chuck wrote in news:Byxuf.2053$%W1.241@newsread2.news.atl.earthlink.net: > Is it not true that if the currents on the transmission line are > unbalanced (i.e., unequal on the two conductors) then the transmitter > must already be connected to ground? If not, what is the path of the > differential current? There's the rub, you see. It's RF and, on some frequencies, standing waves don't NEED to feed current to a ground for there to be common mode currents on the line. But yes, whatever current is required at the end of the transmission line will seek to ground itself through the radio. My amp had the output coil center-tapped to RF ground and the feedlines were tapped off it an equal amount on either side. -- Dave Oldridge+ ICQ 1800667 Article: 220841 of rec.radio.amateur.antenna Subject: Re: Dipoles and the rig's RF ground... From: Dave Oldridge References: <1136148463.132269.164130@g49g2000cwa.googlegroups.com> <11rj9uu7bkogd37@corp.supernews.com> <11rlqiv2po14n6d@corp.supernews.com> Message-ID: Date: Fri, 06 Jan 2006 04:08:43 GMT Roy Lewallen wrote in news:11rlqiv2po14n6d@corp.supernews.com: > Dave Oldridge wrote: >> >> Still, if the antenna is TRULY balanced (a situation that only rarely >> actually happens), you won't get common-mode currents. > > That's true only if by "balanced" you mean that the two feedline > conductors carry equal and opposite currents. In that case, common > mode current is zero by definition. But if you really mean > symmetrical, as most amateurs do when they say "balanced", you > certainly can have common mode current. No, I mean ELECTRICALLY balanced. And with the feedline at right angles to the antenna so that it doesn't pick up anything by induction. It's a tricky thing to do, yet back in the old days hams used to feed dipoles or extended double zepp antennas with open wire line and not get much RF in the shack. I know mine didn't. I was putting nearly 700 watts into the antenna and you could touch the amp chassis without any RF burns. Didn't have the fancy tools I have now for testing things, but still managed a good, clean and loud CW signal from an angled dipole. Worked a lot of DX on 75 with that antenna, including a nightly sked with Midway Is. for traffic (from Vancouver, BC.). -- Dave Oldridge+ ICQ 1800667 Article: 220842 of rec.radio.amateur.antenna Subject: Re: Antenna spacing From: Dave Oldridge References: Message-ID: Date: Fri, 06 Jan 2006 04:10:17 GMT "Ralph Mowery" wrote in news:jHEuf.1890$ZA2.483@newsread1.news.atl.earthlink.net: > > "Dave Oldridge" wrote in message > news:Xns973F42AD4851doldridgsprintca@64.59.135.159... >> Chris W <1qazse4@cox.net> wrote in >> news:IT3tf.45644$ih5.19066@dukeread11: >> >> > I want to put a short 2 meter yagi and a long 70cm yagi on the same >> > vertical mast. The 70cm will be a horizontally polarized, center >> > mounted 17' boom and the 2 meter will be a vertically polarized, >> > end mounted 6 foot boom. How far apart do they need to be? I will >> > only be transmitting with one at a time but one could be receiving >> > and the other transmitting, the 70cm will be for ATV receive only >> > for now. >> >> A good rule of thumb is to separate them by at least a half-wave at >> the lowest frequency. In this case that means about a meter (39") >> apart. >> >> > Sofar all the answers are assuming the question is will one antenna > affect the other antenna. One other thing to look at is will the > transmitter 'kill' the receiver of the other rig ? Indeed, though not too likely since the frequencies are a fair bit apart. -- Dave Oldridge+ ICQ 1800667 Article: 220843 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Matching network for end-fed half wave, Q calculations etc.? Date: Fri, 06 Jan 2006 11:16:30 -0800 Message-ID: <11rtggi4j9pusbb@corp.supernews.com> References: <1136517045.065705.123740@g44g2000cwa.googlegroups.com> An parallel LC network like you describe is usually made with L and C having reactances of roughly 200 ohms or so. That generally gives a loaded Q that results in good efficiency. As you suspect, the voltage will be high at the end of the antenna no matter how you feed it. Roy Lewallen, W7EL kiddi@marel.is wrote: > Hello: > > I am contemplating a half-wave wire antenna for the 160m band and would > end-feed it against my roof as a counterpoise. If the wire length is > carefully trimmed I should get a high feedpoint resistance with > negligible reactance. Then comes the question of how to match this to > a 50 Ohm system. > > The standard approach is using a parallel LC circuit and either make a > tap or a link for the 50 Ohm connection. In this case, how should I > select the L and C, as there are multiple choices leading to the same > resonance frequency but with different Q values. Any suggestions? > > Or, would another matching network be more desirable, for example in > terms of loss? An L-network might do the job, but it is not > immediately clear to me if it would have any advantages or > disadvantages over the parallel circuit. Any comments? > > I will be running substantial power into the antenna, so it is > important that the solution does not result in excessive losses (heat) > or voltages (although this will probably be inevitable at the > feedpoint). > > 73 - Kris, TF3KX > Article: 220844 of rec.radio.amateur.antenna From: "Steve Nosko" Subject: Re: Transmission Line Reflections Date: Fri, 6 Jan 2006 14:09:28 -0600 Message-ID: References: <11roggi5f4i1h3a@corp.supernews.com> Wayne, *** Imbedded comments: "W. Watson" wrote in message news:q5Yuf.3158$Hl6.836@newsread3.news.pas.earthlink.net... > Roy Lewallen wrote: > > > W. Watson wrote: > > > >> It seems reasonable that if I have an open ended transmission line > >> that the current would reflect back and change phase. After all, the > >> electrons at the end have nowhere to go but back down the line. > >> However, the voltage is a different matter. There is no phase reversal > >> (or polarization change) There doesn't seem to be an intuitive reason > >> for this. However, if one examines the equations for current and > >> capacitive voltage, then it falls out of the math. Still, where is the > >> non-math that indicates this is true? > >> > >> Now suppose instead the line is short circuited. The voltage returns > >> down the line, and the current does not. > > > > > > That's not true. Both are totally reflected. > Thanks for the response. Why is any wave reflected at all? In the open case, > I can easily visualize the electrons (drifting cloud) having nowhere to go > when they reach the end of the line, so the current literally has to go in > reverse. Perhaps the shorted line represents a reactive circuit to the > incident wave? Wayne, Welcome to the wide-world of the inquisitive. *** Please understand, I'm not trying to be, snooty, a wise-guy or know it-all. I'll say that I think you are trying to use an intuitive view when you don't have the proper background/experience to base the intuition on. I think that you are trying to use "standard" concepts when trying to understand waves. Intuition comes from some kind of experience that tells us how things work, but, in regular life, we only gain experience from mostly "normal" things. Waves are a bit different and it takes some new experiences to gain that intuition. That's why they teach those wave tanks in high school -- it give us some understanding of this wave phenomenon. I can liken it to trying to understand multiplication when all you know is addition and subtraction. Moving to multiplication or division isn't really hard, it just takes some new concepts we hadn't seen before,. However, once we understand it, it's "simple" and the concepts become second nature. We need to realize that some NEW concepts are needed to understand waves, in general. On to waves... Someone may be able to use pure math and "explain" waves, but there are more intuitive (gut feel) ways which help. Besides, I'd have to work really hard trying to reconstruct all that math from college. ( I couldn't solve a triple integral now to save my life) Waves can be hard to explain in terms of ONLY current and voltage - when we try to use our purely physical experience. I work hard to form mental models of how electronics works and found that there are some areas that are hard to understand with a simple Newtonian understanding (though I do my best to keep my "mental models", as I call my understanding, as simple as possible) - and it has served me well when trying to understand this stuff and explain it to others. The best analogy for waves is waves on water. Thought there is a major shortcoming in that electromagnetic waves in space don't need a medium to carry them, the rest works out pretty well. On a transmission line there are waves and they behave like water waves. Some important concepts to possibly help. Water has mass and it takes a force to move it. When a force ( a rock or wind) pushes on the water, it moves in a certain way - very analogous to electrical current. In short, a body of water has something analogous to a characteristic impedance. "Push" it with a voltage and it responds with an amount of current according to the analogous "ohm's law" of water. When the water in one place moves, it pushes on the next bit of water. That push causes a motion in a manner in a way only water can respond (with its "ohm's law"). This is what makes waves happen. There *IS* "something" moving along with that wave. Now put a wall in the water - the edge of the tank. The wave reflects--we CAN SEE it with our own eyes. While you can do some force, mass, acceleration and velocity math and make it all work out, I'll stop here. Going more general on you here... Some time go I realized that thinking about water pushing on water leads to something like a "characteristic impedance" of water. This concept allows the idea of the motion of the water being transferred to adjacent bits of water and this leads to a wave "propagating" / traveling` over the water. Now, with this in mind, whenever the stuff that is pushed on by the water does not respond just like water, something different happens. Since the two extremes are a short and open, it is reasonable to assume (and correct in a very general cense) that whatever does happen is somewhere between the "open" and "short" behavior. Unfortunately, with water, it is hard to come up with both a short and an open, so this model falls apart a bit. However, the Slinky toy, stretched out on the floor can be observed and have either a short or open placed at the end---as well as other various "loads". For the "short" hook it to a solid, stationary object (a wall). For the open, put a long string between the far (load) end and the wall. For the others, you can put dashpots and other springs (of different size and therefore "characteristic" impedance). I know this is a digression off your question, but I think you should study waves in other media which are more directly observable to feel better about transmission line waves. Hence your following comment and Lew's explanation is how we look at it. There is a summing of things going on at the "load". > > > >> In this case, there doesn't seem to be any non-math or intuitive feel > >> for why the short should cause this--either for voltage or current. > >> Can one clue me in on what's really happening above (voltage) and here > >> (voltage and current)? Inquiring minds want to know. > > > > > > The math is dictated by the boundary conditions, and those can be used > > to gain an intuitive feel for what's happening. When both forward and > > reflected waves are present, the voltage and current at any point on the > > line are the sum of the forward and reverse waves. When the line is open > > circuited, the current at the end of the line is of course zero. So the > > sum of the forward and reverse current wave is zero at the end, and the > > only way that can be is for the forward and reverse waves to be equal in > > magnitude and out of phase. *** Switching to voltage here, we realize that there is no such constraint on the voltage to be zero at the open, but what can it be? It's probably SOMETHING.. If we believe in waves and reflections, one possibility is that it is in phase, therefore the sum is double, but alas, I can't muster, at this time, an explanation of why in-phase. Perhaps someone has a better "mental model" that I. > > Likewise, when the line is shorted, the > > voltage is zero, and the only way that can happen is for the reverse > > voltage wave to be equal in magnitude and opposite in phase to the > > forward voltage wave. *** Switching to current at the short, leads to my reasoning just like the above and the same lack of an "Intuitive" explanation. Lew uses the characteristic impedance view below and that works for me, but then, I think I understand all this already! I think that if you 'believe', so to speak, in the Characteristic Impedance concept, this makes more "intuitive" sense. Good luck. Remainder un-edited for continuity. 73, Steve, K9DCI > Yes, this makes sense that one can deduce the result from the boundary > conditions. I'll stop here for the moment until I understand the answer to > the question above. > > Some confusion can result when discussing the reverse wave. The reverse > > current wave can be, and usually is, defined as positive in the same > > direction as the forward wave. If you use this definition, the current > > changes phase at a shorted end, since the sum of the two current waves > > has to equal zero when both are defined as being positive in the same > > direction. However, you can also say that the current simply reverses > > direction and remains the same in phase. Those two viewpoints are > > equivalent. I've been using, and will continue to use, the convention > > that the direction of positive current is toward the load for both > > waves, for this discussion. > > > > At an open end, the forward and reverse voltages are equal and in phase, > > and at a shorted end, the forward and reverse currents are equal and in > > phase. This can be seen by realizing that the voltage/current ratio of > > the forward wave is the same as for the reverse wave -- both equal the > > line Z0, but because of the current convention, the sign of the current > > reverses for the reflected wave. So we know that Vf/If = -Vr/Ir, where > > If and Ir are defined as positive when flowing toward the load. Now > > let's apply what we know about shorted ends to find what happens at an > > open end. At an open end, we know that If = -Ir. Since Vf/If = -Vr/Ir, > > it follows that Vr = Vf. Likewise, at an open end, we know that Vf = > > -Vr, so from the same equation If = Ir. > > > > Roy Lewallen, W7EL > > > > Wayne T. Watson (Watson Adventures, Prop., Nevada City, CA) > (121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time) > Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet > -- > "I often quote myself - it adds spice to > my conversation." - George Bernard Shaw > > Web Page: Article: 220845 of rec.radio.amateur.antenna From: Chris W <1qazse4@cox.net> Subject: Re: friends,please help me!!!!!! References: <1136481553.458674.149950@g14g2000cwa.googlegroups.com> <0_Sdndmk56UIDyDeRVn-gw@vnet-inc.com> Message-ID: Date: Fri, 06 Jan 2006 15:38:49 -0600 Topaz305RK wrote: > 1 2 3 4 5 6 7 8 9 10 > / > / > / > / > / > / > / > / >TROLL-O-METER > > If your going to do ascii art, might as well be a little more fancy :) 1 2 3 4 5 6 7 8 9 10 / / / / / / / / / / / ---TROLL-O-METER--- -- Chris W KE5GIX Gift Giving Made Easy Get the gifts you want & give the gifts they want One stop wish list for any gift, >from anywhere, for any occasion! http://thewishzone.com Article: 220846 of rec.radio.amateur.antenna From: Paul Burridge Subject: Need some pointers on building UHF/microwave 50 ohm termination/power splitter Date: Fri, 06 Jan 2006 22:58:52 +0100 Message-ID: Hi all, I need a couple of accessories to enable me to make some phase measurements with my HP network analyzer. I'd thought I could pick these up on ebay easily enough, but note the lack of availably with surprise and dismay. I need to therefore contrive two precision parts: Firstly, 50 ohm load that's essentially non-reactive up to 1.3Ghz. Power handling only need be a few tens of miliwatts. N-type connection. Secondly, a 50 ohm power splitter (one feed-in; three outputs) N-type connections, again flat up to 1.3Ghz. No switching needed, thankfully. If I can't source these parts elsewhere, how feasible is it to make them up and can anyone point me to any designs on the web that might fit the bill? I'm aware that the introduction of any stray reactances into the devices will render all subsequent measurements invalid so I need to get these parts right. At least 1.3Ghz capability should be achievable for a hobbyist with care. Thanks, P. -- "What is now proved was once only imagin'd" - William Blake Article: 220847 of rec.radio.amateur.antenna From: "John_H" References: Subject: Re: Need some pointers on building UHF/microwave 50 ohm termination/power splitter Message-ID: Date: Fri, 06 Jan 2006 23:16:01 GMT www.minicircuits.com can supply some of your needs as well. Article: 220848 of rec.radio.amateur.antenna From: Gary Cavie Subject: Re: Need some pointers on building UHF/microwave 50 ohm termination/power splitter Date: Fri, 6 Jan 2006 23:16:58 -0000 Message-ID: References: In article , pb@shove.your.spam.up.your.arse.atlanticstar.co.uk says... > Hi all, > > I need a couple of accessories to enable me to make some phase > measurements with my HP network analyzer. I'd thought I could pick > these up on ebay easily enough, but note the lack of availably with > surprise and dismay. > I need to therefore contrive two precision parts: > > Firstly, 50 ohm load that's essentially non-reactive up to 1.3Ghz. > Power handling only need be a few tens of miliwatts. N-type > connection. > > Secondly, a 50 ohm power splitter (one feed-in; three outputs) N-type > connections, again flat up to 1.3Ghz. No switching needed, thankfully. > > If I can't source these parts elsewhere, how feasible is it to make > them up and can anyone point me to any designs on the web that might > fit the bill? > > I'm aware that the introduction of any stray reactances into the > devices will render all subsequent measurements invalid so I need to > get these parts right. At least 1.3Ghz capability should be achievable > for a hobbyist with care. > > Thanks, > P. > Hi Paul, Take a look at Mini-circuits (www.mini-circuits.com). They seem to stock what you are after. Article: 220849 of rec.radio.amateur.antenna From: David Subject: Re: Need some pointers on building UHF/microwave 50 ohm termination/power References: Message-ID: Date: Fri, 06 Jan 2006 23:22:19 GMT http://www.minicircuits.com/ Have a range of splitters and loads. Paul Burridge wrote: > Hi all, > > I need a couple of accessories to enable me to make some phase > measurements with my HP network analyzer. I'd thought I could pick > these up on ebay easily enough, but note the lack of availably with > surprise and dismay. > I need to therefore contrive two precision parts: > > Firstly, 50 ohm load that's essentially non-reactive up to 1.3Ghz. > Power handling only need be a few tens of miliwatts. N-type > connection. > > Secondly, a 50 ohm power splitter (one feed-in; three outputs) N-type > connections, again flat up to 1.3Ghz. No switching needed, thankfully. > > If I can't source these parts elsewhere, how feasible is it to make > them up and can anyone point me to any designs on the web that might > fit the bill? > > I'm aware that the introduction of any stray reactances into the > devices will render all subsequent measurements invalid so I need to > get these parts right. At least 1.3Ghz capability should be achievable > for a hobbyist with care. > > Thanks, > P. -- Kind Regards David Huisman General Manager ----------------------------------------------------------------------- ORBIT COMMUNICATIONS Pty Ltd - Wireless Solutions that Work (Telemetry, Control, Monitoring, Security, HVAC ...) A.C.N. 107 441 869 Website : http://www.orbitcoms.com PO Box 4474 Lakehaven NSW 2263, AUSTRALIA Phone: 61-2-4393-3627 Fax : 61-2-4393-3685 Mobile: 61-413-715-986 Article: 220850 of rec.radio.amateur.antenna From: Chris Jones Subject: Re: Need some pointers on building UHF/microwave 50 ohm termination/power splitter Date: Fri, 06 Jan 2006 23:26:39 +0000 Message-ID: <11rtv0e2m530lfd@corp.supernews.com> References: Paul Burridge wrote: > Hi all, > > I need a couple of accessories to enable me to make some phase > measurements with my HP network analyzer. I'd thought I could pick > these up on ebay easily enough, but note the lack of availably with > surprise and dismay. > I need to therefore contrive two precision parts: > > Firstly, 50 ohm load that's essentially non-reactive up to 1.3Ghz. > Power handling only need be a few tens of miliwatts. N-type > connection. > > Secondly, a 50 ohm power splitter (one feed-in; three outputs) N-type > connections, again flat up to 1.3Ghz. No switching needed, thankfully. > > If I can't source these parts elsewhere, how feasible is it to make > them up and can anyone point me to any designs on the web that might > fit the bill? > > I'm aware that the introduction of any stray reactances into the > devices will render all subsequent measurements invalid so I need to > get these parts right. At least 1.3Ghz capability should be achievable > for a hobbyist with care. > > Thanks, > P. You can make a pretty good 50 Ohm termination with a PCB-mounting SMA connector. Cut off the centre pin of the PCB-end of the connector leaving 0.5mm or less protruding (careful of your eyes, the pin can go shooting off pretty fast, it's hard metal), and then solder two 0.1% 100 Ohm 0603 resistors between the centre pin and the outer (ground) part of the connector. The resistors should be diametrically opposite. I made one with 1% resistors and got the following: s11 < -30dB up to 6GHx and s11 < -47dB up to 500MHz It helps to tweak how flat you lie the resistors on the teflon at the back of the connector, but without a working VNA you just have to accept what you get. If you want a termination with a N connector, then you could use a really good adapter with the SMA termination I mentioned above, or work out something similar with a N connector however I have never tried that since I mostly use SMA anyway. I think a very accurate / flat power divider would be fairly hard to make well unless you can get boards made with microwave substrates. If you can work out your measurement setup such that the flatness etc of the divider is not so important, then that would help. There's a guy in the UK selling a one input two output type power divider with N connectors and a 50 Ohm N termination on e-bay at the moment if that helps you. Chris Article: 220851 of rec.radio.amateur.antenna From: Paul Burridge Subject: Re: Crimp, Clamp or Solder? Date: Sat, 07 Jan 2006 00:32:51 +0100 Message-ID: <5cvtr1dst3ojuoshd5afq4sbn525oqcmpa@4ax.com> References: On Fri, 23 Dec 2005 13:51:42 GMT, "Chuck S." wrote: >Clamp types have cause me problems over the years, stay away from them. >Crimp type work ok in the shack but not out side for a long time. Solder it >by far the best way to go. Another type that works good outside is >compression clamps. The ones meant to be used with hard line. They cost >more, but unless you like climbing up a 60 foot tower in a contest, they are >worth the cost! How about using clamp N-types *and* soldering them?? You'd have to drill a hole or two in the outer casing for the solder, but wouldn't it be the most secure solution? -- "What is now proved was once only imagin'd" - William Blake Article: 220852 of rec.radio.amateur.antenna From: Paul Burridge Subject: Re: Crimp, Clamp or Solder? Date: Sat, 07 Jan 2006 00:41:20 +0100 Message-ID: References: <76fsq1hrdjvdt82p798efnk9iui6jv4vlo@4ax.com> On Sat, 24 Dec 2005 22:37:07 -0800, Bill Turner wrote: >Don't forget to add Loctite, spot weld, drop forge, nuclear laser, >explosive forming, refractory conditioning, epoxy, RTV, sixteen >layers of Scotch #33 tape and the Pope's blessing. Naw.. Still doesn't meet Mil-Spec '88. :-) -- "What is now proved was once only imagin'd" - William Blake Article: 220853 of rec.radio.amateur.antenna From: Paul Burridge Subject: Re: Crimp, Clamp or Solder? Date: Sat, 07 Jan 2006 00:44:41 +0100 Message-ID: References: <76fsq1hrdjvdt82p798efnk9iui6jv4vlo@4ax.com> <113sf.16964$wq.9439@bignews7.bellsouth.net> <0bj2r15i9iic4td11aejgpe330g8b07efe@4ax.com> On Tue, 27 Dec 2005 19:00:57 GMT, "kd5sak" wrote: >Guess that's right, let's see now. Formula ! car wheels just have one big >lug nut, don't they? > Pit-stop time is critical. You want to race a car that takes 6 guys all fumbling in over- intimate proximity to change each wheel? -- "What is now proved was once only imagin'd" - William Blake