Before I climb the tower and start taking things apart, I would appreciate
any thoughts from those who have had prior experience with SWR changes on
the Telrex TB6EM. I have had this particular tribander installed at the
100' level for about 5 years now with no problems until this past week. We
have had a good bit of rain recently -- so weatherproofing of connections is
the first thing I may check.
15 meters seems to be somewhat OK, but the SWR on 10 and 20 meters seems to
be out of line. On the low end of 10 meters (CW portion 28.025) -- the SWR
is over 3:1 -- dropping to under 1.5:1 at around 28.600 mHz. The SWR on 20
Meters is about 3:1 at 14.000 mHz dropping only to 1.6:1 at 14.300 MHz. The
SWR is not lower than this on 10 and 20 -- 15 meters seems to be ok (1.1 :
1) on the low end -- rising to 2.8:1 at 21.200 mHz.
Unfortunately, I can't find the original SWR curves when the antenna was
installed -- and the auto-tuner may have been masking this issue for a while
now. However, it seems to me that I was experiencing less than 2:1 across
all the bands when the antenna was first up. I recall the antenna being
relatively broadbanded -- but used the auto-tuner in the 761 as a matter of
course.
Of course, this could be: a) normal for the TB6EM, b) a feedline problem, c)
a balun problem, d) a trap problem -- etc. But, before I start tinkering, I
thought I would get some advice from those out there that either have a TB6
or have worked on them in the past. Also -- those that have not had a TB6
but something similar -- maybe you can give me some troubleshooting
guidance.
Related to this -- I am wondering if the Balun that Telrex supplied with
this antenna is a 1:1 balun or not? I would like to replace it with another
one sometimes in the future as a matter of maintenance anyway, but I don't
know what characteristics the balun currently has.
Thanks in advance for any advice!
73,
Rush -- W4QA
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