Reply To: SDRUno 1.33 and RSP1; RF gain slider confusion

[blinkerParticipant]

Thanks for the app note info. I see the same results with AGC off. Here’s some data:

RSP 1 with SDRUno 1.33; AGC off; antenna input grounded (no signal)

4 (Highest)RF gain: noise floor at -125.6 dBm; S meter 0.5
3 RF gain: noise floor at -105.7 dBm; S meter 3.5
2 RF gain: noise floor at -115.9 dBm; S meter 2.0
1 (Lowest) RF gain: noise floor at -92.5 dBm; S meter 6.0

My current theory is that the RF gain positions represent the following:
4 LNA on; RF gain high
3 LNA off; RF gain high
2 LNA on; RF gain low
1 LNA off; RF gain low

Comparing 1 and 3, the noise floor is consistent with Andy2’s explanation of later stages adding noise to keep the ADC working efficiently. The S meter reading is correlated to noise level since there is no signal.