[TowerTalk] Where to Tune Yagi??

[James R. Duffey]

Tom - In your post on rejuvenating the TH-3 you recommended:

"My old TH3 worked well in the segment it was tuned for
but was disappointing on the other end of the band.  For
both modes, best to tune for CW and use a tuner on SSB."

You are probably better off doing the opposite, tuning for the SSB part of
the band and using a tuner in the CW end of the band.

The frequency response of most Yagi antennas somewhat resemble a low pass
filter with gain usually rolling off much more sharply at the high frequency
end than the low frequency end. Therefore, cutting it for the CW end will
result in more deterioration in the SSB end then cutting it for the SSB end
will result in deterioration in the CW end.

This effect has been measured several times. It was clear in the plots of
frequency vs. gain that Wayne Overbeck, N6NB, did in his famous Yagi vs Quad
study in the May 79 (?) Ham Radio article, and is also particularly
noticable in most VHF designs up until computer optimization became popular.

I notice that some of the newer computer optimized Yagis do not exhibit this
property, so it is not intrinsic with the Yagi design as I once thought it
was.

I am pretty sure that the TH-3 is not computer optimized. :^)

Does anyone have a good solution to taking apart those Hy-Gain joints made
with the compression clamps that permanently dimple the tubing? I have
drilled out the dimple made in some and pulled apart the tubes, but in
others there seems to be no recourse other than cutting that portion of the
antenna out and using new tubing if the resultant tube is too short.

I have pieces of two old 14AVQs in the garage that I would like to make into
one good antenna. Taking apart the joints without cutting has proved to be
impossible. These antennas are over 30 years old by the way. Also, is the
parts department of MFJ stocking the Hy-Gain trap end caps?- Dr. Megacycle
KK6MC/5  

-- 
James R. Duffey KK6MC/5
30 Casa Loma Road
Cedar Crest, NM 87008


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