Not sure if this really works, just a try. In newer version from gnuradio there’s the option for the built in agc in the UHD devices. For me, that doesn’t work. I played with this thing a while. Behind the 1. filter is a probe, that’s the value for the signal level (10.0*math.log(rf_pwr_lvl+1.0e-11)/math.log(10)). The variable „agc“ has the magic formula for the gain. I use with (10.0*math.log(rf_pwr_lvl+1.0e-11)/math.log(10))*-1)*0.5.