Xref: utzoo sci.electronics:4360 rec.ham-radio:7091
Path: utzoo!utgpu!watmath!clyde!att!rutgers!gatech!cwjcc!mailrus!nrl-cmf!ames!elroy!peregrine!ccicpg!cci632!dvh
From: dvh@cci632.UUCP (David Hallidy)
Newsgroups: sci.electronics,rec.ham-radio
Subject: Re: RF preamp techniques
Summary: whoops
Keywords: preamp, splitter, combiner, noise figure, gain
Message-ID: <23212@cci632.UUCP>
Date: 30 Nov 88 21:10:15 GMT
References: <2038@nunki.usc.edu> <23211@cci632.UUCP>
Organization: CCI, Communications Systems Division, Rochester, NY
Lines: 25



I forgot to add that the Avantek preamp circuit is specified
from 400-500 MHz. They also, in the same app. note, talk
about designs for the 900 MHz and 1300 MHz bands.

Also, the reason you don't want the preamp after the lossy
splitter (or cable) is because the system noise figure is
primarily determined by the gain and noise figure of the
first stage. In this case, the first stage has a 3dB NF, and
-3dB gain. Running the noise figure cascade on this system,
with a 0.4dB preamp after the splitter, will yield a noise
figure cascade somewhere in the 2dB range.

After the preamp, you can play a lot of games,for the same
reason- the first stage determines the overall noise figure-
assuming the preamp has enough stage gain to overcome the
loss and noise of the following stage(s). Therefore, if you
have a preamp with a 0.4dB NF and 20dB gain at the antenna,
you can overcome a lot of loss after the preamp and still
retain most of that excellent performance.

I think I got it all out this time.

73  Dave     KD5RO