Topband: Trees (not the N6TR kind)

[Gary and Kathleen Pearse]

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