[amsat-bb] Signal to Noise ratio

[W3AB/GEO]

To add to the excellent info Zach gave, the LNA should be mounted as close to the antenna as possible.

⁣___
Sent from my two way wrist watch
73 de W3AB/GEO​

On Jul 27, 2020, 17:39, at 17:39, Zach Metzinger via AMSAT-BB <amsat-bb at amsat.org> wrote:
>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
>
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