Uncorrected T_rec (DSB) vs. intermediate frequency (IF) of the L2-channel at a LO frequency of 1821 GHz measured during GREAT system tests at the MPIfR lab: the blue, green and red lines are the measured T_rec (DSB) for the Martin-Puplett diplexer set at half path-length differences 45, 35 and 30 mm, respectively. The T_rec is dominated by the diplexer passband and a 3 dB noise roll-off of the HEB mixer  > 2.8 GHz is measured.