Microwave Receiver Interference Characteristic Measurements

Interference measurements on a 6-Gc/s microwave receiver at RF frequencies for 600- and 960-channel loading are described. The receiver used a 70-Mc/s IF amplifier with a 25Mc/s bandwidth. The mechanism for creating interference at RF frequencies is presented and is verified by many figures that relate the interfering signal level at several baseband frequencies to the magnitude and relative frequency of the interfering carrier. The measurement technique, which is fully described, used a swept backward wave oscillator (BWO) as the interfering carrier, and a recorder tracked the BWO frequency and provided a continuous plot of interfering signal level from the output of a noise-loading test set receiver for combinations of noise modulation on both carriers. Use of the data is described, and a generalized chart is given for a constant -78 dBmO interfering signal level, with and without preselection for variations of interfering carrier magnitude and frequency under different modulation conditions.