R: [amsat-bb] continuing education

["i8cvs" <domenico.i8cvs@xxxxxx>]

Ed and Jerry

The sun as a black body generate and radiate a RF white noise wich is not
polarized.
If  i have a dish and i change the polarization of my feed  from vertical to
horizontal or from RHCP to LHCP i will always receive the same amount of
power from the sun or from the moon because of their  thermal radiation.
So,receiving the sun noise, i can compute my G/T constant without
tacking in to account the type of polarization used for my  feed.
A solar flux  unit  or  SFU=10E -22 W/m^2 and you can get this data for
9 frequency bands  as prepared from  7 different Observatory for the
U.S. Dept. of Commerce, NOAA, Space Environment Laboratory at

gopher://proton.sel.noaa.gov:70/11/lists/radio

73 de i8CVS Domenico


----- Original Message -----
From: Edward R. Cole <al7eb@ptialaska.net>
To: <amsat-bb@AMSAT.Org>
Sent: Wednesday, June 27, 2001 2:48 PM
Subject: Re: [amsat-bb] continuing education


> >From: Jerry Pixton <jpixton@shentel.net>
> >Hi all,
> >
> >thanks for the notes on metal in middle of helix. Think I will continue
> >along those lines. Makes the mechanical part easier.
> >
> >My question for todays "continuing education" session  ---
> >
> >When we compute the G/T performance metric, do we use the full gain of
the
> >antenna?  That is, we don't subtract 3 dB because of polarity mismatch
> >(circular to linear). Seems to me if we measure the G/T metric using the
> >sun then we are getting the whole gain.
> >
> >The 3 dB loss only comes in when we think about a particular signal we
want
> >to receive. Correct????? Or am I confused?
>
> Jerry,
>
> When you calculate G/T from sun measurements [vs cold sky] you input the
> solar flux, as precisely measured by an institutional radio observatory,
> into the calculations.  If they use linear polarization then your
> measurement will compare directly without a 3 dB correction factor.  If
> they made their observation using circular polarization then your
> mesurement will be -3 dB if you are linear.  Its safe to assume they use
> circular polarization since the sun radiates in many polarizations {and
> probably is randomly polarized}.  Also at VHF and UHF frequencies the
> ionosphere twists the signal via the Faraday Effect.  At 2.4G Faraday is
> negligible.  OK?
>
> Ed
>
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