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Re: Up and dwnlink polarization of HAMSAT



----- Original Message -----
From: "Don, w7das" <w7das@cox.net>
To: <amsat-bb@AMSAT.ORG>
Sent: Friday, July 01, 2005 4:18 PM
Subject: Re: [amsat-bb] Up and dwnlink polarization of HAMSAT


> I may have read incorrectly, but I thought polarisation was determined by
> the rotation of the electric field about the axis as the wave moved AWAY
> from the source.  If this is true, wouldn't the polarisation be opposite
as
> it arrived on Earth?  i.e. transmitting with an LHCP antenna in space
would
> be best received with an RHCP antenna on Earth?
>
> 73,
> Don

Hi Don, W7DAS

In defining right-hand (RHCP) and left-hand (LHCP) circular polarization,it
is necessary to specify wheter the rotation is clockwise or counterclockwise
with respect to the transmitter or the receiver.
It would be possible to define an entirely consistent system from either
point of view but the Institute of Electrical and Electronic Engineers
(IEEE ) has standardized on the transmitting antenna as the reference point.
Thus, a right-hand (RHCP) circularly polarized wave is defined as one wich
rotates in a clockwise direction as seen propagating by the transmitter
side.
This same wave will appear to rotate counter-clockwise as seen by the
receiver, wich is why it is necessary to specify whether the transmitter or
the receiver is to be used as a reference for definition.
If the source is a satellite and the wave radiated by his antenna rotates in
a clockwise direction as seen moving away from the satellite than we
have a RHCP wave as per the IEEE definition.
The same RHCP wave will appear to rotate LHCP as seen standing behind the
reflector of the receiving antenna on Earth but in reality the wave rotates
in a clockwise direction while filling the capture area of the receiving
antenna and so it would best received with a RHCP antenna on Earth.

AMSAT adopted the IEEE definitions.

Best 73" de

i8CVS Domenico
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