Patent US 4,159,477

An arrangement for stabilizing the false alarm rate in a radar. The arrangement is provided with, in series, an amplifier with a variable and controllable gain, a demodulator and a comparator with a variable detection threshold. The signals after demodulation into video signals are chopped into range gates. A set of memories allows the mean values of the video signals to be stored. A control circuit allows the gain of the amplifier and the variable detection threshold of the comparator to be controlled after read out of the memories. The gain of the amplifier is varied in the opposite direction from the amplitude of the signals read out from the memories and the variable detection threshold of the comparator is varied in the same direction as the amplitude of the signal read out from the memories. A feed back amplifier is arranged between the memories and the gain control input of the amplifier.