It seems that I know the Friis equation.

I am asking because it seems difficult, and maybe impossible. I've
never heard of this high gain before, but I dont' know why I cann't
stack amplifiers and I am looking for somebody who can tell me what
exactly the problem is: you see the NF is nice, and I can get the SNR
if the band is narrow enough.

It also seems that I "don't know what I'm doing". So please explain a
little if you want me to understand. Thanks.

Harold E. Johnson wrote:
I asked what I don't know. I am expecting a helpful answer.

The frequency is 70MHz.


As Dale gave you an answer that is correct, you might reason with him, I
recognize that the last answer wasn't very helpful.

Basically, with 20 dB of gain, your noise figure will be well established
with the NF of that first stage. It will actually deteriorate a tenth of a
dB or so for the further stages down the line, but not very much.

If you need additional gain, it's best obtained after some selectivity. 140
plus dB of gain on a single frequency is going to be VERY difficult to tame
and keep from oscillation in it's own right.

W4ZCB