[TowerTalk] Force 12 WARC-7

[Paul Playford]

I see a few comments re Force 12's WARC-7 antenna so I thought I would add my experience.

Antenna is at 37' above clear desert.

I was grousing to W1XT re the antenna had unity Front to Back ratio on 30m and he suggested I find out where the F/B was by placing a signal source 50 feet or so away from the antenna and changing the signal source's frequency while listening on the WARC-7 until I did observe F/B.  I did as he suggested (why didn't I think of that?) and found it had about 20dB F/B at 9.75 MHz, a little low for 30m work.

I adjusted each reflector shorting bar outward from the boom by 8" (which subtracted 16" from each half reflector) and now I have 18 dB F/B at 10.125 MHz.

Then I observed the 30m resonant frequency was at 9.95 MHz so I moved each driven element shorting bar out by 1" (which subtracted 2" from each half driven element) and now the resonant frequency is at 10.125 MHz also.

As W1XT noted, adjusting for best F/B on a 2 element yagi is easy.  Adjusting for best F/B on a 3 element antenna gets complicated.

Now to play on 30m.

de Paul, W8AEF

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