[amsat-bb] Left /Right Hand polarization ...

John Papay john at papays.com
Sat Jul 25 04:53:12 PDT 2009


AO51 435.300 is right hand circular polarization (RHCP).
AO51 435.150 is left hand (LHCP).  If you try to hear
a LHCP signal with a RHCP antenna that is really right
hand, you will have a drop in signal that can exceed
20db.  This will make the downlink unreadable at low
elevations.  You definitely want to have switchable
polarization on UHF if at all possible.

The reason that people have a hard time hearing SO50
when they are using RHCP is that although the antennas
are supposed to be linear polarized, they don't fare
well on RHCP throughout the pass.  I find that I have
to switch several times between right and left in order
to hear the bird throughout the pass. Before I had
switching, it was hit and miss with that bird.

The two meter side is not as important to switch unless
you plan to operate AO7 and VO52 which have downlinks on
2 meters.  If you do operate those birds, you'll be able
to do much better if you can switch.  Switching the uplink
on UHF on those birds sometimes makes a big difference too.

If you are serious about operating the birds, the investment
in polarity switching will be well worth it.

John K8YSE

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