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## Re: [TenTec] OT: Indoor Antenna

 To: Discussion of Ten-Tec Equipment Re: [TenTec] OT: Indoor Antenna Steve Hunt Discussion of Ten-Tec Equipment Fri, 03 Dec 2010 15:25:46 +0000 mailto:tentec@contesting.com>
 ```To illustrate Ken's point, here are some measurements I made on the feedpoint resistance of my 160m 40ft top-loaded vertical as I added radials. Rrad for this antenna should be about 5 Ohms. 6ft Ground rod only: 33 Ohms, Efficiency = 15%, VSWR = 1.5 Ground rod + 5 radials: 13 Ohms, Efficiency = 38.5%, VSWR = 3.8 Ground rod + 10 radials: 9 Ohms, Efficiency = 55.5%, VSWR = 5.5 Ground rod + 15 radials: 7 Ohms, Efficiency = 71.5%, VSWR = 7.1 I ended up with a 9:1 impedance transformer at the feedpoint to give me a reasonable match to 50 Ohms. With just the ground rod I would have had a reasonable match without any transformer, but the efficiency would have been 15% (-8.2dB). Estimated ground loss resistance for the 6ft Ground rod on its own was 28 Ohms. 73, Steve G3TXQ On 03/12/2010 07:01, Ken Brown wrote: > A quarter wavelength monopole with a really good counterpoise/ ground > radial system has a feed point radiation resistance of around 37 ohms > and very little loss resistance. That will give you an SWR of about > 1.4:1. If you use just a ground rod and have about 13 ohms of resistive > loss in the ground system, the series equivalent feed point impedance > will be about 50 ohms, and the SWR will be very near 1:1. Some people > think this is better. It does "tend to make the matching easier." > > I don't know what kind of ground you have, or whether your ground system > resistance would be 13 ohms with just a ground rod. The point I am > trying to make is that a really efficient vertical is likely to have a > higher SWR than a partially radiating dummy load. Many hams do choose a > lo > _______________________________________________ TenTec mailing list TenTec@contesting.com http://lists.contesting.com/mailman/listinfo/tentec ```
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