RE: [amsat-bb] circular polarization sense

[Mark West <M.West@xxxxxxxxxxxxxx>]

>> Can someone help me understand this?
>> Ive been a bit confused about how much this affects signal strength if
you
>> get it 'wrong'.
>> My first problem is I dont know which Sats actually transmit in circular
>> pol.

>ALL of them.  The satellites are typically stabilized (from what I
>understand) by being spun.

The rotational velocity of a circular wave generated by an antenna like a
stationary cross yagi or quad helix is going to be equal to it's frequency.
I
think that is the type of antenna we are used to here. I suppose that you
could duplicate this with a linear antenna spinning very fast, but I doubt
we could physically accomplish the speeds required (c. 435 million RPM). ;^)

>>Theoretically, if you have the sense of the polarization wrong, you will
get
>>ZERO signal.  However, typically, due to distortions in the atmosphere and
>>what not, you will end up with an elliptical signal with an E-field vector
>>component greater in one direction than the other.

If you cross a linear with a circular you can expect a 3db loss (50%), if
you cross a right circular with a left circular you can expect a 6db loss
(75%).

>> Where can I find out what this info? does anyone already have a compiled
>> summary of these kind of specs? (Im also interested in SAT Antenna,
BeamW,
>> pol, power etc).

Get the satellite book from AMSAT

- Mark West

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