The heterodyne performance of Ge photoconductors doped with shallow impurities was investigated using optically pumped far infrared lasers. Two lasers operating on the 67‐&mgr;m NH3Raman 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 &mgr;m. 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 2×10−18W Hz−1for the fastest detector and 6.5×10−19W Hz−1for the slowest detector.