I used eight elevated tuned radials. They angled about 45 deg from about 4' at
the feed to ~15' for their horizontal run. To initially tune, I used my MFJ-259
to feed a pair of radials (dipole), then cut the rest to match them. I set the
system resonance via the length of the vertical/horizontal "L".
Your point is a good one. It may be that all I was doing was tuning the entire
antenna system...radials and L portion...by adjusting the length of the L. I
never fussed with the length of the radials after build, nor did I check them
for tuned length.
I have other 80-90' trees available, but now am considering a top loaded wire
vert to see if it's more frequency stable as temps change.
73, Gary NL7Y
> Hi Gary,
>
> The frequency shift may have been partly due to the raised radials and
> relationship to the freezing earth.
>
> Frozen earth becomes an insulator so capacitive coupling between unfrozen
> earth and radials is getting less as temperatures drop. This can be overcome
> somewhat by also having on ground radials connected. This also helps the
> transmitted signal.
>
> Sorry you lost your tree.
>
> 73
> Bruce-K1FZ
>
>>
>> The following obs were an annual occurrence until my 85'+ support tree blew
>> down this year. The 160 antenna described below was supported by the tree,
>> and was no more than 4' from the trunk in the middle...the top an bottom
>> were closer, ~1'.
>>
>> A wire Inv-L (#12 stranded THHN) with tuned elevated radials for 160, pruned
>> in summer, dropped in resonance with each winter's freezing of the support,
>> surrounding trees of similar height, and the ground below. It took up to 3'
>> of vertical shortening (~2%) at the feed point to return it to 1.825, versus
>> the same resonant point in summer.
>> 73, Gary NL7Y
_______________________________________________
Stew Perry Topband Distance Challenge coming on December 29th.
|