I use an SDR based panadapter (ROCKY) on the subrx. I've noticed the following on all bands 15-6 when switching in preamps. Noise floor no preamp = x Noise floor with preamp 1 = x to x+1 dB Noise floor with preamp 2 = X+10 to X+15 dB. Would have expected the noise floor with preamp 2 to be about x. What's going on? 73 de Brian/K3KO