Abstract: A pulse width discriminating circuit and technique is disclosed which enables the rejection of pulses having a width less than and greater than predetermined limits. A received pulse is provided as one input to a counting circuit which is driven by a clock to provide count outputs as long as an input pulse is present. The counter has an output selected to indicate when the width of the pulse has exceeded a minimum time, and an output selected to indicate when the width of the pulse has exceeded a maximum time. The minimum pulse width output signal controls the entry of a pulse in a shift register. The shift register is shifted by a divided clock signal from the same clock that drives the counter and provides an output to a decoding circuit after a predetermined time if the pulse width falls within the predetermined range. The maximum pulse width output signal is coupled to reset the shift register so that the pulse in the shift register is discarded if the input pulse exceeds a predetermined width.

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.