[TowerTalk] KT34 & Shunt Feeding

[Michael Tope]

From: "Phil - KB9CRY" <kb9cry at comcast.net>

> I've got to drop my KT34XA to upgrade the element to boom adapters (one
> of the original KLM version has become loose and will be upgraded with
> the DX Engr. type) and while it's down I want to perform other mods
> (it's already been upgraded with the M2 upgrades).  Anyway, this antenna
> is on top of a 72 ft. Trylon self supporting tower, which two years ago,
> I began shunt feeding on 160M.  That has worked like a champ but I'm
> concerned that the high voltages have been messing something up with the
> antenna.  Since the last year or so, I've noticed that the antenna seems
> dead on 10 & 15M.  I've verified it's an antenna problem by switching in
> the backup radio.  Front to back and SWRs on those bands are still OK
> but it just doesn't hear well; everything seems attentuated.  20M seems
> OK.  So, I have a few questions for the group


Phil,

Could it be that what you are observing is just the decline
in solar activity rather than a decline in your antenna sensitivity (10M is
definitely not what it was
2 years ago)?

With regard to the latter, you might try tuning at high
power for a long period on 160 meters, and then quickly
switch to the KT34XA to see if there is any noticeable
VSWR change caused by operation on 160 meters.
Assuming that you switch over to the KT34XA before
things have ample time to cool, this test would help you
to determine if 160 meter operation is causing the ferrite
material in the KLM balun to overheat beyond its Curie
temperature. Although a postive result from this test
wouldn't necessarily entail permanent degradation of
the balun, it would be useful in general to see if operation
on 160 meters was causing problems with the balun.

BTW, as someone suggested, you might want to
consider testing your coax just to make sure there
isn't any extra loss there. If there really is significant
loss in the system on 10 and 15 meters, it's probably
present on both transmit and receive. In that case,
then its probably not the balun since anything
that physically small with enough loss to show up on
receive (e.g. > 3dB) would go up in smoke really fast
on transmit (imagine that little KLM balun trying to
dissipate 750 watts). Extra loss in the feedline, on the
other hand, could easily be distributed over a large
area. Thus a lossy feedline would not necessarily fail
a smoke test as would a lossy balun.

Anyhow, those are the things I would try if it were
me. Good luck!

73 de Mike, W4EF....................