"Jim-NN7K" . wrote in message
...


So-- Which is the most relevant noise measurement? Noise Figure-
or Noise Temperature? If one is better than another at a given
frequency, than another, and then the other is better at greater freqs,
WHY?

In my experience, the community seems to dictate the terminology. (If you
buy a big, long sandwich for lunch, is it a "hero," a "sub" or a "hoagie"?)

More to the point, when selecting an LNA for C-band satellite, you will
almost always see the noise temperature in the specs. However, for Ku-band,
the LNA noise figure is usually spec'ed.

As was pointed out, they are directly convertible. Go a little less than
halfway downpage at
http://www.microwaves101.com/encyclo...oisefigure.cfm
and see the graph of noise temperature versus noise figure. (This web page
also provides illustrations of what's already been presented here.)

The noise figure of the first stage strongly influences the total system
noise figure, hence the oft-seen placement of a low noise preamp close to
the antenna.