A parabolic dish doesn't really have a polarity (at least none of the
ones I've seen).
The polarity comes with the feedhorn and waveguide. A rectangular
waveguide will be polarized, but a circular waveguide will essentially
accept all polarities.
If you're using an OMT (sometimes called an OMC), it will utilize a
circular waveguide to feed two opposite (or more correctly orthogonal)
waves into the dish.
The OMT is not making anything circularly polarized. It's just using the
circular waveguide (which accepts all polarities) to feed two separate
waves.
bp
<part15sbs{at}gmail{dot}com>
On 10/30/2015 9:06 AM, Craig Baird wrote:
We are getting ready to put up a licensed 11 GHz 2+0 link using
Cambium PTP820S radios. We have two 11 GHz frequencies that are
oppositely polarized for use on this path. I had assumed that we
would need to use dual polarity dishes in order to make this work, but
Cambium and our vendor are saying that we need to use single-pol
dishes. This completely baffles me. How can a single-pol antenna
transmit in two polarities? Cambium's answer is that it's because
we're using an OMT, and that device essentially makes the single-pol
antenna circularly polarized, so it will transmit both polarities. My
first thought is "what kind of voodoo is this?" Will this really
work??? I'd sure hate to start transmitting, only to find out from an
existing license holder that we're interfering with them because one
of our frequencies is coming out the antenna in the wrong polarity.
Can someone confirm for me that this will really fly?
Thanks!
Craig
