A continuous monitor of microwave receiver noise-factor

A practical method is described for continuously monitoring the noise-factor of a microwave receiver without impairing its operational use. A very small modulated noise signal is introduced into the receiver, a sample of the i.f. output detected and the noise voltages in a narrow band about the modulation frequency selected and amplified. This composite signal is then applied to a coherent detector followed by a low-pass filter, whose output is shown on a meter calibrated to read the noise-factor of the receiving system. Details are given of a developed design intended for use with an S-band radar set, and capable of indicating a deterioration of 1·0 db in receiver noise-factor.