Abstract: A standard amplitude pulse is transmitted as a cyclically recurring pulse in a radar ranging system. At a receiver, identified by the pulse repetition rate of the recurring pulses, each pulse is analyzed for its deterioration from the standard in order to detect fading. An amplifier, having a controlled gain, is adjusted responsive to the analysis, and the uniformity is restored to the pulse despite variations in fading. In some cases, a threshold detection is used to prevent response to minor variations. A pulse repetition rate detector insures that the pulses are so controlled at only the identified station, and that the identified station responds only to pulses with the proper repetition rate.