[amsat-bb] Signal to Noise ratio

[Zach Metzinger]

On 2020-07-27 19:04, Albert Ozias via AMSAT-BB wrote:
> Do preamps improve the signal to noise ratio or simply amplify signal and noise?

Hello Albert,

No, a preamp cannot improve the SNR of the signal at its input terminal(s).

All amplifiers add noise to the signal that they are amplifying, and 
that added noise can't be removed.

That's the key point: An analog signal's SNR only goes down, never up.

The RF energy intercepted by your antenna is immediately combined with 
other sources of noise, mostly thermal noise, on the way to your radio 
for eventual demodulation.

A LNA (low-noise amplifier) does this while adding a minimum of noise to 
the signal. This prevents the SNR from degrading to a point where useful 
information can no longer be recovered from the demodulated signal, be 
it analog (voice) or digital (data).

Also note that your radio also adds its own measure of noise to the 
incoming signal, degrading the SNR. However, if the SNR has been 
preserved from the antenna through the LNA and coax, then the noise that 
the radio adds will not degrade the SNR appreciably.

This topic is involved and sometimes complex, but rewarding!

--- Zach
N0ZGO