Brian Howie GM4DIJ
In message <hijh.1609755777674220352.sAJb@groups.io>, "Luc , on4aol" <firstname.lastname@example.org> writes
Goodmorning to all,Ok this might not be quite right.
In the absence of other noise, you hit the RF photon noise limit .ie you are limited by the noise on the signal. At 1296MHz the photon energy is 8.59×10^-25 joules. In a 10 Hz bandwidth, at an average of one photon per 1/B (or is it 1/2B) = 0.1 sec the power is 8.59x10^23 mW == -220dBm. 160dBm is about 10^6 RF photons in 0.1 sec
Of course you need more than one photon to make sense of the signal, so that sets the minimum SNR. Then there's local oscillator shot noise as you have to mix down to a frequency where you can get a 10Hz bandwidth.
At light frequencies single photon detection is possible ( it used to be part of my day job), but not at RF since you can't get the other noise sources low enough.
Anyway the answer to your question is that there is no threshold until you hit the quantum limit in the absence of all other noise.