Abstract: A method and apparatus for independently controlling a CWFM radio altimeter to reduce interference from another nearby altimeter employs a high-Q filter outside the bandpass of the signals which are developed and decoded for altitude indication to detect an approaching interference signal received from the other altimeter and produce an output to a threshold detector. When the output of the filter exceeds a predetermined level, the threshold detector causes the transmitted frequency of the altimeter to be stepped.In one embodiment, a digital counter is provided to cyclically count up and down at a desired sawtooth modulation frequency. The output of the counter is applied to a digital-to-analog converter to produce an output used to control the frequency of the transmitted signal. Additionally, the output of the counter is conducted to inputs of an adder having a preset add number therein.