The heterodyne performance of Ge photoconductors doped with shallow impurities was investigated using optically pumped far infrared lasers. Two lasers operating on the 67‐μm NH3 Raman line generated difference frequencies from 0–100 MHz. An additional frequency point at 1.155 GHz was produced with two methanol‐isotope lasers at 118 μm. For three detectors with different doping levels IF bandwidths of 141, 63, and 8 MHz were measured using local oscillator powers of a few milliwatts. The detector gain and quantum efficiency were calculated from shot noise measurements. For impedance matched operation the calculated noise equivalent power (NEP) values are 2×10-18 W Hz-1 for the fastest detector and 6.5×10-19 W Hz-1 for the slowest detector.