[TowerTalk] Motor Driven vac used in 40M DE?

[Jim Thomson]

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From: "Gene Fuller" <w2lu at rochester.rr.com>
Sent: Tuesday, December 29, 2009 8:42 AM
To: "Jim Walker" <jim at walkersdomain.com>; "'Jim Thomson'" 
<Jim.thom at telus.net>
Cc: <towertalk at 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
>
>