Dennis and all,
I know Hy-Gain had AO modeling files for most of its antennas
when it was owned by Telex, but I don't think MFJ has all the data.
The first thing to check is whether you are using the "DX" setting
for the TH-7, which basically adds 2" to both driven elements,
between the boom and traps, so it affects all three bands.
Without examining a model, I would expect that the radiation
pattern is a decent compromise over the whole band, and that
lengthening the driven elements beyond the DX setting would
lower the frequency of the SWR curve without adversely affecting
the pattern or match. You can estimate what another 2" additional
length would accomplish by examining the VSWR curves in the
manual.
Some years ago, I successfully lowered the frequency of the VSWR
"sweet" spot of an Explorer14 using a similar empirical estimate.
73, Gary
K9AY
>
> Hello,
> I'd like to locate a YO or NEC-2 model for the th7dxx beam antenna.
> I'd
> like to lower the center frequency to cover the lower half of 10, 15, 20
> meters instead of the upper half. Any help would be greatly
> appreciated.
>
> Dennis Homerick, w8nw
>
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