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Old September 18th 06, 02:53 AM posted to rec.radio.amateur.antenna
Jim - NN7K Jim - NN7K is offline
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First recorded activity by RadioBanter: Aug 2006
Posts: 86
Default Receive Preamp question

Generally speaking, the BEST NOISE figure (factor,
ect. is what you want (best sensitivity),
however, the Gain would be a consideration, IF
you had excessive coax loss. (in this case, in
excess of 16 dB, which would be quite doubtful.
The gain of a vhf (or any amp, for that matter),
only needs to exceed your coax (and your front end
I.E. Reciever's Noise figure, so as to allow the
preamps noise figure to take precidence (establish
your floor sensitivity) I hope I stated that
correctly. And, even then, as long as THAT noise
figure is below the cold sky noise (from other
sources), then the cold sky noise (about 1.8 dB
on 2 meters) is the limiting factor on your
sensitivity, before figureing the SELECTIVITY of
your reciever (half the bandwidth, gain 6 dB,
half again, now gain another 6dB). Probably
as clear as mud, but the best I can describe it--
Jim -NN7K

Rod Maupin wrote:
I am wanting to buy some receive preamps and am wondering if I'm looking at
it the correct way. Here are two examples from two different manufacturers,
both for the same band.

#1) .55dB NF, 16dB gain
#2) .9dB NF, 20dB gain

So, do you go for more gain or less NF? Since this is for weak signal
VHF/UHF work, I would say go for less NF but you can tell me what you think.