Effects of gain settings on internal noise path

1

I have modified the heimdall software as indicated for the krakensdr gnuradio Correlation Check (rtlsdr_set_bias_tee_gpio(rtl_rec->dev, 0, 1);) so that the noise source is always enabled.

Looking at the basic block diagram of the system, it looks like the noise source is switched in before the R820T2 tuner, so any mixing or gain settings should be applied to the noise signal path. However, when I adjust the gain settings via the gnuradio block or the radio direction finding web page and look at the spectrum, it doesn’t look like the noise power changes at all.

What am I missing?

2

It’s probably because the noise source is so powerful, that the tuner is always in saturation. This is fine for coherence calibration. But it does mean that when you change settings and the gain setting is on you wont see any changes in the spectrum.