Series of measured T_rec (DSB) vs. mixer bias current I_bias curves at three different bias voltages for the 2.5 THz mixer used in the M-channel receiver during the 2011 operations. The mixer was measured in a laboratory test setup using a FIR gas laser at 2523 GHz. From top to bottom the traces are for bias voltages 0.65 mV, 0.5 mV and 0.4 mV. For these measurements the pump power of the FIR gas laser LO was varied by means of an attenuating wire grid.