To those with shunt fed towers for Top Band,
I have had up a 100 foot 45G tower since 1993. It is festooned with
monobanders from 80 – 10 meters, and at the 30 foot level a larger bundle of
Heliax, RG-213/U, and multiple control cables leaves the tower. This bundle
runs about 50 feet in the air to my upper deck which is at the same height.
From here it goes up to the shack on the 2nd floor.
I recently installed a shunt feed system for 160 using three Jennings vacuum
variables in a plastic box I purchased from Mouser. Three variables were
necessary to resonate the #6 solid copper shunt wire that only goes up 30
feet. Of course I have begun to lay radials at the base, and I plan to lay a
lot more.
Typically it is prudent to have the wires come down to the ground level and
to ground all shields and run the bundle underground to the shack because of
RF issues. I did not want to put in new lines or to splice in more cabling.
Running 1500 watts was not initially possible due to RF getting into the
shack via the multiple lines. This would be expected!
I purchased a large number of the snap-on ferrite beads from DX Engineering
and placed them on every single line as they came up through the deck. I did
this after coming home last night and ran several tests running the legal
limit on 160. Now there is virtually no RF feedback in the shack. There was
a great deal before.
Their special Ferrite mix is ideal for use at HF and effectively decouples
unwanted RF from the lines. My next step is to order more and place them on
the lines as they exit the tower. Obviously these beads act as RF chokes
when placed around a current carrying conductor.
This may not be the ideal way to do it but it does work.
73,
John, W4NU
Atlanta
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