80 Metre Verticals
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Fred,
If your inverted 'L' was a bit less than a quarter wave long, it would have been capacitive and showing 57-j130 (not plus). In which case you needed a small inductor to match it to your 50 ohm coax, not a capacitor. 73, Tom G3OLB ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
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Concurring with Tom, assuming you have the polarity of the X correct, and
there's more. A short 1/4 wave-ish vertical that shows R=57 in the R+jX expression is a vertical/counterpoise or radial(s) combo that has far too much resistance and is a dead giveaway for a considerably inefficient antenna and may be wasting 3 dB somewhere. A full quarter wave vertical over 60 1/4 wave radials should be showing 32-35 ohms at resonance, e.g. 33+j0. A theoretical 1/4 wave L in free space with lossless conductors should be 12-15 ohms. In the real world over real dirt with an efficient counterpoise, and lacking various possible real-world inefficiencies an L should be something roughly 25 ohms. Mine is 28 ohms on a calm day over dried out dirt. Frankly, if it really is efficient, 57-j130 sounds like a fairly *longer* than 1/4 wave-ish L aerial wire over an FCP without using an isolation transformer. A bad idea for a stack of reasons. Otherwise, there is likely a lot of dielectric material inside the bend of the L adding loss in the R measurement in addition to 32-35 ohms. An efficient L should show lower R yet to be efficient. Mine is 28 ohms, measured with an AIM4170 with a calibrated feedline factored out by the software. An occasional measurement right at the feed is always very close. In your case R = 57 instead of R = 28 probably means that something like 29 ohms of that 57 is recoverable loss for some reason or other. 73, Guy K2AV On Tue, Feb 28, 2017 at 10:05 AM, Tom Boucher <[hidden email]> wrote: > Fred, > If your inverted 'L' was a bit less than a quarter wave long, it would have > been capacitive and showing 57-j130 (not plus). In which case you needed a > small inductor to match it to your 50 ohm coax, not a capacitor. > > 73, > Tom G3OLB > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to [hidden email] > Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
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So... if I am planning to move to the high desert of New Mexico in a few
years, what is the best low-band antenna option? I've used verticals over lots of radials in Massachusetts and Mississippi with good success, but if I'm up 6500 feet and the water table is WAY down there... what, a dipole? 73 de Chuck, WS1L On Tue, Feb 28, 2017 at 2:18 PM, Guy Olinger K2AV <[hidden email]> wrote: > Concurring with Tom, assuming you have the polarity of the X correct, and > there's more. > > A short 1/4 wave-ish vertical that shows R=57 in the R+jX expression is a > vertical/counterpoise or radial(s) combo that has far too much resistance > and is a dead giveaway for a considerably inefficient antenna and may be > wasting 3 dB somewhere. > > A full quarter wave vertical over 60 1/4 wave radials should be showing > 32-35 ohms at resonance, e.g. 33+j0. A theoretical 1/4 wave L in free space > with lossless conductors should be 12-15 ohms. In the real world over real > dirt with an efficient counterpoise, and lacking various possible > real-world inefficiencies an L should be something roughly 25 ohms. Mine is > 28 ohms on a calm day over dried out dirt. > > Frankly, if it really is efficient, 57-j130 sounds like a fairly *longer* > than 1/4 wave-ish L aerial wire over an FCP without using an isolation > transformer. A bad idea for a stack of reasons. > > Otherwise, there is likely a lot of dielectric material inside the bend of > the L adding loss in the R measurement in addition to 32-35 ohms. An > efficient L should show lower R yet to be efficient. Mine is 28 ohms, > measured with an AIM4170 with a calibrated feedline factored out by the > software. An occasional measurement right at the feed is always very close. > > In your case R = 57 instead of R = 28 probably means that something like 29 > ohms of that 57 is recoverable loss for some reason or other. > > 73, Guy K2AV > > > On Tue, Feb 28, 2017 at 10:05 AM, Tom Boucher <[hidden email]> wrote: > > > Fred, > > If your inverted 'L' was a bit less than a quarter wave long, it would > have > > been capacitive and showing 57-j130 (not plus). In which case you > needed a > > small inductor to match it to your 50 ohm coax, not a capacitor. > > > > 73, > > Tom G3OLB > > ______________________________________________________________ > > Elecraft mailing list > > Home: http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/mmfaq.htm > > Post: mailto:[hidden email] > > > > This list hosted by: http://www.qsl.net > > Please help support this email list: http://www.qsl.net/donate.html > > Message delivered to [hidden email] > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to [hidden email] > -- =================== Chuck Chandler [hidden email] =================== ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
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Hi Chuck,
In general, with lousy ground, horizontally polarized antennas RULE! The earth interacts with verticals in two ways. First, the soil under the vertical is a big resistor, burning TX power. Second, where the first reflection hits the earth (in the far field) reinforces the direct wave to form the vertical pattern. When ground conductivity is poor, that reflection is weak. By contrast, horizontally polarized antennas are only very slightly affected by ground losses, and then only almost straight up. i also have poor soil conductivity (Santa Cruz Mountains). I use verticals ONLY on 160M, where even a dipole at 140 ft in my redwoods is a low dipole electrically. When I first moved here, I had both. For a year or so, I made a lot of A/B comparisons between them, and the vertical nearly always won. About five years ago, the horizontal dipole came down in a storm, and I didn't even consider putting it back up. One of my 160 verticals is a Tee with a lot of radials. As an experiment, I hung a 67 ft vertical wire over the same radials for 80M. My high dipoles blew it away. In general, horizontal antennas on mountaintops don't need to be very high to work really well. I've done FD QRP several times from mountaintops using dipoles that were only 25-30 ft off the ground, and made QSOs to the midwest and east coast. 73, Jim K9YC 73, Jim K9YC On Tue,2/28/2017 12:51 PM, Chuck Chandler wrote: > So... if I am planning to move to the high desert of New Mexico in a few > years, what is the best low-band antenna option? I've used verticals over > lots of radials in Massachusetts and Mississippi with good success, but if > I'm up 6500 feet and the water table is WAY down there... what, a dipole? ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
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