Do preamps improve the signal to noise ratio or simply amplify signal and noise?
"yes"
An amplifier can only amplify what it's fed, both signal and noise, and adds a little noise of its own. If it's positioned at the antenna it will work a lot better than if it's at the other end of the feed line at the radio. You want to amplify the signal before the noise induced by the coax can get in there.
Greg KO6TH
Albert Ozias via AMSAT-BB wrote:
Do preamps improve the signal to noise ratio or simply amplify signal and noise? _______________________________________________ Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: https://www.amsat.org/mailman/listinfo/amsat-bb
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
participants (3)
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Albert Ozias -
Greg D -
Zach Metzinger