Interesting numbers, Dave.

W8PIL and I published a paper in QST in the 60s that dealt with the noise
into a receiver from extraterrestrial sources. For those numbers to be
limiting, one needs to be well away from people and one needs an antenna
that has a very large directivity. In the other hand, if your receiver is
in space, its antenna is not pointed at earth, and you have an antenna with
a moderate directivity, then the numbers we presented will limit SNR.

I was involved in the early measurements of the temperature of the moon with
a two-frequency feed using an 85 foot dish. Two-frequency = resonate at two
frequencies separated by 2 times the IF frequency so more "signal" could be
acquired. VT front end using every scheme in the book. Today, with almost
no design, an FET off-the-shelf would be much better.


What huge improvements I have seen in the NF of VHF and UHF amplifiers.
However, the techniques for achieving low NF have not changed from the ideas
contained in v18 of the MIT Radiation Lab series.

73, Mac N8TT
--
J. Mc Laughlin; Michigan U.S.A.
Home:
"Owen Duffy" wrote in message
...
Dave Oldridge wrote in
:

...
I used to have an FT-221 tricked out with a hot front end. Solar
noise would run the S meter up to well over the S9 mark and you could
even see the galactic plane passing through the antenna pattern.
Needless to say, it heard well on terrestrial 2m SSB.

That is no mean feat!

I think ambient noise temperature at 144MHz for an antenna pointed at
cold sky is somewhere around 200K to 250K, when you add a pretty good
receiver at say 30K, you are talking 230K to 280K total system noise, and
the sun is probably around 800K with a low end 4 bay EME antenna setup
(Gain~22dBi), for a noise rise of 10*log((800+255)/255) or 16dB.

A single yagi of gain around 15dBi is much poorer, not only is the sun
noise reduced proportionately to the gain reduction, but the ambient
noise increases with higher gain in the side and back area of the
antenna, but it still should be possible to reliably 'see' the sun with a
very good receiver.

Ambient noise temperature for a beam at zero elevation here in suburbia
varies from 1000K to 6000K depending on the day and time... so a very low
temperature receiver is wasted for terrestrial contacts.

Owen