Andrea Baldoni wrote:



Hello.
I'm wondering about a thing...

When the AGC reduces the gain of an amplifier, composed by FETs (DG or SG)
or BJT, the SNR remains constant?

Or the performance of the amplifier may degrade/upgrade?

I'm researching about the matter and I just read that, in a BJT for
instance, emitter current is inversely proportional to the noise. So, if
AGC reduces the gain (so current), SNR degrade?

The question arises from a thing I just noted with a HF receiver...
disabling AGC reduces (slightly) the noise (at least in FM reception)...
Maybe just be a side effect, like noisy gain control signal...

Ciao,
AB

... Andrea Baldoni, 2002: messaggio non protetto da copyright.

You might also ask yourself whether it really matters or not. If your signal
is strong enough to begin driving the AGC to limit the system gain do you
really care what the noise level actually is? Once the AGC threshhold is
reached, if the signal strength goes up faster than the noise contribution
from the system goes up do you really care what the noise level actually
is?

tim ab0wr