--------------------------------------------------
From: "Gene Fuller" <w2lu@rochester.rr.com>
Sent: Tuesday, December 29, 2009 8:42 AM
To: "Jim Walker" <jim@walkersdomain.com>; "'Jim Thomson'"
<Jim.thom@telus.net>
Cc: <towertalk@contesting.com>
Subject: Re: [TowerTalk] Motor Driven vac used in 40M DE?
>
>
> I have the two-element version of the same Force 12, 40 meter antenna.
>
> I tuned mine in conjunction with the original instructions which provided
> for its best performance...both SWR and F/B. My lowest SWR is found at
> 7.050 and am able to work between 7.0 mhz to about 7.1 mhz without a
> tuner.
> Beyond 7.1, such as when working split DX SSB, I use my Palstar tuner.
>
> I still have directivity in the SSB portion of the band, but not as much
> as
> when I am the lower portion of the band.
>
> Conclusion: I agree with Rick. While you do eliminate the need for a
> tuner
> by using the Jennings cap, to retain full F/B performance, you need to
> adjust the dimensions of all three elements.
>
> Jim
> KBØX
### OK. The consensus is the F/B will degrade when trying to cover a
major portion of the band.
But what about the forward gain ?? Does it degrade greatly... or just
a little bit ?????
IOW.. I can live with greatly degraded FB... but if the forward gain
falls off over the cliff, that's unacceptable.
Does the F/S degrade as well ??? F/S at this location is MUCH more
important than F/B
F-12 claims if the REF is tuned for 6900 khz.... and the DE is tuned for
7070 khz... and the DIR is tuned for
7500 khz..... then the 2:1 swr points will be 7000 and 7280 It
also appears the swr rise's very slowly on the
high side of resonance. Your 2 -el is only 100 khz wide...swr
wise.... vs 280 khz for the 3-el version.
There is probably a hundred ways to kludge, and compromise the tuning. It
appears that if the DE is tweaked for
say 7150.... that the swr would rise very quickly < 7150..... and very
slowly >7150..... hence, F-12's original
DE setting of 7070.
Installing coils and vac relays on both the DIR and REF, plus control
cables is doable... but not my 1st choice.
Installing 2 x coils + 2 x vac relays on the DE is no big deal at all....
nor is one motor driven cap [ DE]
The DE is readily accessible at all times... in case something is amiss
[ditto with the balun + helical hairpin]
I have been off 40m for a long time. I understand the broadcast junk is off
of 7100-7200 ?
what about 7200-7300 ? Is is just as bad as b4... or did it get worse ?
IE: did they all just move up
a bit ?
Thanks for all the help here, much appreciated.
Jim VE7RF
>
>
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