gr-osmosdr disable RTL2832U AGC ?

another question: all my attempts at recording signals from satellites (NOAA POES weather satellites and ISS) have so far failed. For NOAA, I can sometimes get a faint signal, but nothing worth decoding to get a weather map (even with a 25 dB LNA preamp). Now, I have found one web page (cannot remember where) associating the poor receiver sensitivity to the RTL2832U DAGC. I remember seeing on this list that someone had managed to disable this DAGC, but is this functionality avaiable in the gnuradio gr-osmosdr block ? As an option provided to the gr-osmosdr block ? should the DAGC value be set to some specific value then ? Or kept at minimum value ? Thanks, JM