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[TowerTalk] Re: Horizontal + Vertical Polarization Question

To: towertalk@contesting.com
Subject: [TowerTalk] Re: Horizontal + Vertical Polarization Question
From: Martin Ewing AA6E <aa6e@arrl.net>
Date: Fri, 21 Nov 2003 09:39:14 -0500
List-post: <mailto:towertalk@contesting.com>
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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