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Old June 7th 10, 07:46 PM posted to rec.radio.amateur.antenna
Cecil Moore Cecil Moore is offline
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First recorded activity by RadioBanter: Aug 2006
Posts: 572
Default Resonant condition

On Jun 7, 11:36*am, Jim Lux wrote:
* Have you a link to the data and test methodology?


I summarized the data from three CA 75m mobile shootouts at:

http://www.w5dxp.com/shootout.htm

I don't recall a test methodology being published. The test receiver
consisted of a ferrite loop antenna in the far field feeding a lab-
grade RF voltmeter. The power incident upon the 75m mobile antenna
system was assumed to be forward power minus reflected power on the
coax to the antenna system, measured using two Birds. The receive
results were normalized accordingly. I may have left out a detail or
two.

The SG-230 plus 11.5 whip at -12 dB was equal to a 75m hamstick. I
entered both the top-rated (0 dB reference) antenna and the (-12 dB)
autotuner+whip on the same vehicle. When I "superposed" all of the
three results, I assumed 0 dB for each top-rated antenna and let the
rest fall where they might. That may or may not have been a reasonable
assumption.

I suspect the SG-230 is designed to dissipate 100 watts (using large
#2 material powdered-iron toroids). During one shootout episode, I
forgot to attach the antenna to the mobile mount. The SG-230
faithfully tuned to close to a 1:1 match on the input - with a near-
infinite SWR on the output. It was a damp foggy day and the mobile
mount arced. That taught me not to mount the SG-230 unobserved in the
attic. :-)
--
73, Cecil, w5dxp.com