[amsat-bb] Re: Polarity questions
angus at young5769.freeserve.co.uk
Fri Sep 19 13:19:19 PDT 2008
By having circular polarisation that matches the satellite (RHCP or LHCP but
the same polarity) you have very little QSB fading during the pass of the
satellite. Using my own system I normally start a pass on Horizontal as the
satellite is at AOS and then when it rises switch to the correct circular
polarity and as the satellite gets near to LOS I am back on horizontal
polarity with good quality signals through the entire pass.
try listening to a NOAA weather satellite on 137mhz on a fixed polarity
antenna i.e V or H and for some of the pass the signal is very good but as
the signal changes polarity the signal drops down into the noise and through
the satellite pass you will get these peaks and troughs of signals. This is
why if possible it is best to use circular or better still have the ability
to switch polarity during the pass.
----- Original Message -----
From: "pe0sat" <pe0sat at vgnet.nl>
To: <amsat-bb at amsat.org>
Sent: Friday, September 19, 2008 7:02 PM
Subject: [amsat-bb] Re: Polarity questions
> On Fri, September 19, 2008 16:58, Ryan Butler wrote:
>> Tim Tapio wrote:
> Hi Tim,
>>> How much signal reduction is there as the result of having the wrong
>>> circular polarization?
>> The difference between RHCP and LHCP is 20 dB
>> The difference between Horizontal and Vertical Linear is 20 dB
>> The difference between (RHCP or LHCP) and (Horizontal or Vertical) is 3
> If I understand right, you only get 3db extra when using CW/CCW but I have
> also read somewhere that you also lose 3db when running CW/CCW so why use
> Circulair polarisation and not just Horizontal or Vertical pol.
>> Ryan, NF0T
> 73's Jan / PE0SAT
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