Maurizio Panicara wrote:
>Is there a chance to read a signal that produces 0 (zero) dB S/N ?
Sure - in the absence of QRM, it's a workable CW signal.
You can easily set up a simulation with a signal generator and an RMS-
reading AC voltmeter.
0dB S/N is the same as (signal power) = (RX noise power), or
(S+N)/N = 2 = +3dB.
1. Switch in the 20dB attenuator ahead of the RX (makes the signal
generator easier to adjust).
2. Adjust the RX for a comfortable noise level, and a readable level on
the RMS meter (an audio step-up transformer may be useful here).
3. Tune the signal generator or the RX for your preferred CW note, and
then reduce the signal level until the meter reads 1.4x its previous
level - that is S/N = 0dB.
4. You will find you can hear the signal quite plainly - not loud, but
clear enough. Your S-meter won't have moved, but if it was Morse you'd
probably give the guy about 529.
5. Now play around with stronger and weaker signal levels, and different
bandwidths. You'll be surprised what you can detect, if you really get
your head down and listen.
6. Decide for yourself what 2dB is worth.
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
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