In a message dated 98-06-01 09:56:08 EDT, DAVE.SHARRED@SAGEM.CO.UK writes:
> We have a club (Lichfield ARS) TH7DXX antenna, which is always used for
> our contest efforts. It always performs well, but we know the SWR is
> always bad on 15, (2:1); and 10m (3:1) in the desired part of a band for
> contesting.
>
> In Eu; I would summarise where you optimise antenna settings on a band
> in a contest as follows:
>
> CW SSB
> 20m 14.025 14.225
> 15m 21.025 21.300
> 10m 28.025 28.5 (you would obviously expect the antenna
> to be flatter on 10m)
>
> We have just spent some time trying to reslove these issues;and in
> particular on 10m. The data says that it is resonant (best SWR) at 29.6
> MHz ; and that data as published shows the SWR as being bad on, say
> 28.5MHz.
>
> We concur these figures, so the antenna works as designed. We tried
> lengthening the 10m sections on both the phased driven elements by 3.5"
> per side, which seemed to improve 10m (but not conclusive due to an
> intemittent that developed - will be fixed this week); and obviously
> lowered the resonant freq on 10/20 also. I feel that someone must have
> played with one of these and come up with some optimum settings to use.
>
> Does anyone know of a site or any other info with optimised data on
> TH7's ??
>
We found a similar problem with our TH7 during our tribander comparison
test. The interesting part was that the GAIN of the antenna on 15M was very
high so this ought to put to rest the necessity for having a 1:1 swr for
maximum performance.
I talked to Roger Cox at Hy-Gain and he said that users have had some
success by moving the feedpoint hardware around. Apparently the proximity of
the parts has something to do with it.
Nonetheless, the antenna still plays very well even with higher than
'normal' swr so put a transmatch in line (if you need it) and go nuts! No
penalty performance incurred.
Cheers, Steve K7LXC
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