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
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