Interval modulation (IM) of a sinusoidal carrier.

Abstract

Interval Modulation (IM) of a sinusoidal carrier is a modulation technique unlike AM, FM, or PM. IM conveys the information of a message waveform by modulating an interval between bursts of a sinusoidal carrier. IM is accomplished by sampling the message waveform, producing a delay proportional to the amplitude of the sampled message waveform and, upon the completion of the delay, initiating a burst of a fixed number of full cycles of a sinusoidal carrier. With the completion of the burst, another sample of the message waveform is taken and the sequence of events repeats Because the length of a burst is fixed and because the delay between bursts is dependent upon the sampled value of the message waveform, the IM signal is non-periodic. An analysis is made of the IM signal modulated by a constant voltage modulating waveform and by general modulating waveforms. Descriptions are given for the circuits used in generation and detection of the IM signal. IM signal parameters are also considered for use with message waveforms in the audio frequency range.