Back in the late 60's or early 70's we tried this on one of the stations
I was involved with. CP can work with separate antennas but only if the
vertical and horizontal elements are in the same vertical axis and fed in
quadrature or 90 degrees out of phase. And the SWR needed to be absolutely
flat, as in 0 reactance or the circular polarization and its benefits were
negated.. The results at the time showed some improvement in our mobile
coverage but there was a three db hit in general using the same transmitter
set up as before the CP experiment. The project was eventually abandoned.
Later the "roto-tillers", cycloid dipoles, and vees were developed where
the circularity was supposedly inherent to the antenna design. I personally
like the roto-tiller type as they seem to actually generate a circular
pattern with the vertical and horizontal radiation and circularity being
fairly predictable.
A lot of broadcasters consider circular polarization as a legal
back-door method of doubling your ERP. It's pretty much the standard for
most FM broadcasters anymore.
73,
Al, k9si, retired, mostly
> Years ago before CP antennas were commonly available, FM stations would
> feed two separate antennas on the tower. One >was H, the other V. Was
> that then 45 degree polarization??
