[amsat-bb] Loss Between Right and Left Circular

Greg D ko6th.greg at gmail.com
Fri Oct 7 18:00:55 UTC 2016

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.

Greg  KO6TH

Roger Cooper wrote:
> About 10 years ago got interested in sat radio and bought a Left Circular
> Quadrifilar Helix Antenna which got good review in QST.  Didnt use it and
> now retired and trying to get on sat. Evidently most ham sats are right
> circular and depending on
> what I read. there is a 30db OR 3db loss going from one circular
> polarization to another. Which is it?
> Thanks  Roger N3RC
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