[amsat-bb] Loss Between Right and Left Circular

Glen Zook gzook at yahoo.com
Fri Oct 7 18:18:39 UTC 2016

Theoretically, going from right hand to left hand circular polarization results in an infinite loss.  However, in practice, the loss is generally around 20 dB although, in certain circumstances, it can be as high as 30 dB, or more.

It is the same going between vertical polarization and horizontal polarization.  Theoretically infinite but in practice more like 20 dB.

Going from linear polarization to either left hand or right hand circular polarization results in a 3 dB loss.
 Glen, K9STH 
Website: http://k9sth.net

      From: Greg D <ko6th.greg at gmail.com>
 To: Roger Cooper <rogern3rc at gmail.com> 
Cc: amsat-bb at amsat.org
 Sent: Friday, October 7, 2016 1:00 PM
 Subject: Re: [amsat-bb] Loss Between Right and Left Circular
Hi Roger,

Going from left to right, or right to left, with both sides being
circular is in that 30db loss realm.  I recall it being more like 20db,
but once you get in that range, a few db either way kind of doesn't
matter.  In practice it's not quite that bad, since in practice nothing
is perfectly circular, but, yeah, not a recipe for success.

Crossing circular (either handed) with linear is 3db, I believe.  Or was
it 6?  Anyway, not impossibly bad.  Hopefully you also have a preamp at
the antenna, which will offset a lot of this.  If not, I'd invest in
one, regardless of the polarization topic.

I have a pair of switchable beam antennas for satellite work.  My
observation is that most of the newer satellites these days appear to be
linear, and I've noticed that while there appears to be some difference
between right vs left on the ground, crossed with their linear signals,
most of the time it's not fatal.  Either can work for at least part of
the pass.

Bottom line is that you've got a workable antenna.  Try it and see what
you get.


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