[TowerTalk] Re: Horizontal + Vertical Polarization Question

[Martin Ewing AA6E <aa6e@arrl.net>]

K9OM asks:

Has anyone experimented with feeding both a horizontally polarized and
vertically polarized antenna simultaneously on HF?  Such as, feeding a 
horizontally polarized yagi and a  vertical on 20, 15, or 10 meters?
------

Well, in my time, we called this circular polarization.  That's what you have if 
you feed H and V 90 degrees out of phase, anyway, and if the phase centers of 
the two antennas coincide.  If the antennas are not symmetric, you'll get 
elliptical polarization, i.e., circular plus linear.  If the antennas are 
physically offset, you'll get "interesting" interference fringes on top of the 
normal radiation pattern.

Circular polarized antennas are insensitive to the (linear) polarization angle 
of the incoming wave, so that eliminates one source of QSB.  (Propagation can 
twist the polarization angle, but typical HF propagation favors H polarization. 
 It's the same reason your Polaroid sunglasses work.) On the other hand, a 
right-hand circular antenna rejects left-hand circular waves, so if both sides 
are playing this game, you'd better agree which sense to use.  The optimum 
antenna (on receive, but same argument for transmit) for a linearly polarized 
wave is linearly polarized at the same orientation.  If you use circular receive 
for a linear transmit, you are going to be down 3 db against an optimum linear 
antenna.  So there's no free lunch.

73, Martin, AA6E


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