This weekend I installed a new Cushcraft 40-2CD (2el 40) at 70 feet at
the top of my Rohn 45G tower. I have a 20-4CD (4el 20) sidemounted at
60 feet. The antennas are independently rotateable. (Top guy point is
at 54 feet).
When I vary the directions of the two antennas, I see quite a lot of
interaction as evidenced by SWR changes. The greatest effect is on the
40 meter antenna, where the SWR can vary anywhere from flat to 2:1 at
what is supposed to be the resonant point.
I'm using an Ameritron RCS8 coax switch. It allows me to either float
or short unused antennas. It is set to float, as supplied by the
factory. The 40-2CD has an insulated driven element. All elements of
the 20-4CD are grounded to the boom.
I could set up the RCS8 to short the unused antenna, or I could just
drop the 20 meter antenna 5 feet further down the tower for additional
separation distance (about a 2 hour job).
I wonder if there is much to be gained in this situation by taking the
time to modify the coax switch vs just going for the additional
separation. Intuitively, it seems to me 5 extra feet would be more
effective.
Does anyone have experience with shorting vs floating with the RCS8?
Does anyone have experience with these two antennas on the same tower?
Any suggestions?
Tony KM0O
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