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Re: 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


----- Original Message ----- 
From: "William Leijenaar" <pe1rah@yahoo.com>
To: <amsat-bb@amsat.org>
Sent: Friday, July 01, 2005 2:37 AM
Subject: [amsat-bb] Up and dwnlink polarization of HAMSAT


> Hi AMSATs,
>
> This morning I received the answer from ISRO about my
> question for the uplink polarization, and why they
> used LHCP on the downlink.
>
> The uplink of HAMSAT is in RHCP, opposite of the 2m
> downlink that is in LHCP.
>
> I was also supprized to hear that the downlink is in
> LHCP, as most amateur sats use RHCP.
> The reason that ISRO used RHCP and LHCP is to avoid
> interaction between the uplink and downlink signals.
>
> By using opposite polarizations the output of the
> satellite would less interact on its 70cm input.
> Personaly I think the antennas are at such close range
> that this will not really help...
> At least we know the right polarizations, and the
> reason why it is done.
>
> Myself I have fixed RHCP antennas, and actually have
> had never any problems with the HAMSAT.
>
> On the other hand the signals are that strong that it
> should be no problem, and most of the hams I hear on
> HAMSAT are in aligator mode and can use some
> polarization attenuation on the uplink :o)
>
> 73
> William
> PE1RAH
> ---
> ----
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----
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