an automatic minimum discernible signal level analyzer for evaluating the low signal level detecting capabilities of a pulse - type receiver and including an rf frequency source phase - locked to the radar transmitter frequency and capable of being adjusted in power output by circuitry which automatically measures the statistical noise content of the receiver video and adjusts the power output of the rf source so that the video signal meets preset values of probability of false alarm and probability of detection , the absolute rf power being then a direct measure of the minimum discernible signal sensitivity of the receiver under test .