Installed a 50' Supertitan self support tower a couple years ago. It is
outfitted with Optibeam Yagis for HF and 6m along with a Foce12 2 element 40m
yagi. I also use quarter wave slopers for 80m and 160.
The tower foundation is connected to a UFER ground in the foundation as well as
each tower leg is connected to a ground rod and all 3 rods are connected by a
ground ring. There are than 3 long radials away from the tower as well as a
connection to a ring around the house.
The remote antenna switch has 6 positions and when not selected, all inputs are
grounded.
The problem is that 80m is very noisey and I have AM band intermodulation ever
10 kHz from 1.8 to almost 4 MHz. The AM intermod is caused by something in the
antenna/tower system and is not something happening in the receivers. I hear it
in the shack when the antennas are connected and can receive it on a portable
SW receiver when it is brought close to the tower.
With a portable SW receiver, I foud that the control lines used for the Rotor
and remote antenna switch seem to carry this AM intermod and also a lot of
noise in the lower HF band. Placed a couple chokes on the control line (5 turns
through five 2.5" ferrites) at the base of the tower and it reduced the AM
intermod detected around the base of the tower. The antennas on top still hear
it.
My question(s) - Amyone else experienced this problem? Is there a preferred
method to shield/choke/bypass the rotor and control lines? Should unused
antenna ports be left open or grounded? Is tehre a way to quiet down this stack
of metal?
Thanks for the help and bandwidth.
Ed VE4EAR
Feedlines are Andrew 7/8" Heliax ground to tower at top and bottom.
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