Background:
For 160 meters, I shunt feed my tower. The tower totals 120? high with 20
ft. of Rohn 35 rotating above the 100 ft. level. I have philistrand guy
lines. All feedlines are grounded at the bottom of the tower and at the
antenna.
- 2 el. 40 Cushcraft 40-2CD @ 115?.
- TH6DXX @ 101 Ft.
- 16 element 2 meter antenna at 107 ft.
- sticking out of the top of the tower is a Stainless Steel tube
bolted tight to the top with a 16 Ele 2 meter antenna at 122? and a 432, 14
element at 128 ft.
- At ~75 ft. is a trapped WARC antenna and the elements are
isolated from the mast plate. The coax goes to a switchbox at the ground
level.
My problem is that the resonance on 160 meters changes about 50 kHz. This
usually seems to happen when using amplifier power. There is nothing I can
do around the bottom of the tower, or the feed point to create the resonance
change. However, I can at times move guy wires and see the resonance
change.
When I installed the tower 30 years ago, I painted the tower sections with
zinc tower paint, but did not paint the overlapping mating part of the
section where the bolts are.
I have bonded the mast pipe with a ¾? braided strap to the tower leg just
below the top tower bearing, I have grounded the antenna mast plates to the
tower legs thinking that the paint might be insulating the mast plate from
the tower.
This is quite a problem as the Alpha 87a will kick off line in the middle of
a QSO if the resonance changes.
You can see a video of the tower here.
I have removed the three 220 MHz yagi?s that used to be used in the old days
for Packet Cluster back bone links.
https://www.qrz.com/ <https://www.qrz.com/lookup>
Any suggestions as to what the problem is would be appreciated. I am
assuming that it is a long shot that the tower sections would be RF
intermittent.
Jim, KR9U
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