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Re: Fw: SUISAT forensics...The reverse procedure


Unfortunately, the bulletin board cannot view the the sky noise chart that
you sent me.  Also, unfortunate that it is largely useless for frequencies
below 1GHz (obviously designed to show the celestial noise "window" between
1 and 10 GHz (roughly).  I would point you to fig. 8-4 and 8-6. Radio
Astronomy-2nd Ed., Kraus -1966.  In the first figure it shows many areas of
the sky at 200-MHz (close enough for use at 144-MHz) where sky temp<200K.
Even along the Galactic Plane.  The second figure is less detailed but
shows the spectrum of sky temp is approx = ambient temp of 290K away from
the Galactic center.

I could cite several Moon tracking programs that predict sky temperature
background.  They can show sky temps as low as 215K at 144-MHz.  I use this
antennas system to track the Moon for eme and am well award of sky
temperature.  I disagree that I have to assume that I was looking at the
Galactic center where Tsky=1200K or even 600K.  If Tsky were that high for
144-MHz, in general, then use of low noise preamps below 3 dB (290K) would
be unnecessary.  Think about it!

This does imply that the main-beam is clear of the horizon or other
terrestrial thermal radiators.  I allowed that my beam was close to the
horizon by using 275K and if you insist I will use 290K which will not
alter the results substantially.

Ed - KL7UW

At 09:42 AM 2/9/2006 +0000, John B. Stephensen wrote:
>Tsky is probably twice earth thermal noise levels at 144 MHz due to galactic
Ed - KL7UW  
http://www.qsl.net/al7eb - BP40iq 
144-EME: FT-847, mgf-1801/1402, 4xM2-xpol-20, 170w
432-EME: FT-847, mgf-1402, 1x21-ele (18.6 dBi), 60w
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