Greetings,
I'm seeking input from TH7 users to help me sort out a problem.
Think it may have been addressed before, but I can't find the answers in
the archives.
Last summer, I put up a, supposed to be new, TH7 that had been pre
assembled at the element stage, by another. I finished the assembly and
we got the antenna up on an AB477 @ 45'.
It had a low broadband SWR curve on 10 meters that is quite acceptable,
but 15 & 20 meters both had very flat curves at 2:1.
I lived with the condition last season. A month ago, I brought the
thing to the ground for a complete meticulous rebuild. Every connection
was re-worked and each dimension was verified. I found several
dimensions on the driven elements that were wrong, due to the trap caps
having slid from their properly seated locations.
I thought these corrections ought to get it working correctly. But no
joy!
The antenna still works plenty of stuff, and has an excellent pattern.
Last week, I played with feedline lengths and found the feedline length
changed the swr, and was able to find a best case length that results in
fairly acceptable swr figures.
I suspect either the balun has a problem, indicated by the feedline
length change, or 15 meter traps in the driven elements are not right,
but
couldn't see any arcing or other evidence of failure.
I remember something in a past post about a trap upgrade initiated by
Hygain, or other such business, but can't find the details.
If it's traps, I'll plan on waiting till next year when parts are
available, to do something.
Additional information to eliminate interaction concerns:
The original installation had uninterupted guys on the AB477. The new
installation has insulators at 10' intervals for 30' from the top.
I have checked the problem with and without the 40/80 inverted vee below
it, at all azimuths. Nothing nothing external changes the problem, it is
in the TH7.
I'm planning on making a new balun and bringing it down again to replace
that.
I'm a one man antenna party, so the exercise is a bit of an ordeal,
specially with a breeze, which is about 330 days a year here!
Thought I'd check with reflectees first to get the most bang for my two
day exercise, or learn something that tells me to blow it off till next
year. Then I can just move on to the other projects (40 & 80 meter
antennas).
Any experience relating to these observations will be appreciated.
I'm still quite happy to work any of you, with the TH7, regardless of
the SWR.
We follow a steadfast policy here, to keep working people until nobody
calls, or it is time to go do something better!
--
73, Kurt, K7NV
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