There seems to be something that I'm missing in this preamp NF discussion.
When I studied preamps and NF ~30 years ago, I thought the NF of the system
of the first active device was the all-important thing. Whatever losses
were between the antenna feedpoint and the preamp input (coax, connectors,
relays) added to that.
Once that preamp brought up the S+N above a certain point, the NF of the
amplifiers downstream were not near as important.
Very low NFs, less than 0.5 dB, are easily obtainable with everything at
room temperature. (I used GaAs FETs at 144 MHz, but there are even better
devices today with lower NFs.)
A couple of papers I just downloaded and skimmed over seemed to reinforce
that.
Look at the last three slides with screen shots of AppCAD in NoiseCalc mode
at
http://ve2zaz.net/Presentations/Downloads/VE2ZAZ_EME_Presentation.pdf
and the paper at
http://dpmc.unige.ch/dubus/8804-2.pdf
There's much more to read on Google (I searched for *noise figure eme)* and
in my library, but I still have the flu and I'm done for now.
73, Mike
www.w0btu.com
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