Topband: Vertical and horizontal polarised antennas in the same space (was Propagation improves from VK6 into Europe)
vk6vz at arach.net.au
Sat Nov 17 04:23:55 EST 2018
One way to get around the problem Frank W3LPL outlines below is to have one general/TX 160m antenna that you switch between vertical and horizontal polarisation.
If you can get up an inverted-V or flat-top dipole at 60 to 120 feet and feed it with open wire that runs away from the antenna feedpoint vertically, the feeders can be switched at ground level (using a double pole vacuum relay or similar) so they are shorted and fed against a counterpoise/ground system, with a separate coax feeder/matching unit.
For many years an east coast VK friend used this system, where he had a ‘shallow’ inverted vee 160m doublet about 90 feet high and took the open wire feed to ground. The inverted vee made a great capacity hat to the shorted open wire feeder/vertical radiator and I think he used to tune this against his ground system using an L-network or a series capacitor
I also recall KK4TR – and several others – successfully using similar antennas.
Corollary: You can't have too many antennas except when they
interfere with each other which they often do on Topband where
a wavelength is approximately 500 feet...
Even on 20 meters, the pattern of a Yagi is noticeably degraded
when it points through another 20 meter Yagi or tribander 500 feet
distant or more.
Fortunately most Topband receiving antennas don't interfere with
each other -- except at extremely close spacing -- because their
mutual impedance is negligible. But transmitting antennas and
other antenna-like radiators such as power lines -- even 1000 feet
away or more -- can significantly degrade the directivity of
Topband receiving antennas.
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