1. Any device that effects modulation. In radio transmitters, for example, where the signal to be transmitted is usually modulated onto a carrier, one method of creating a modulator is to vary the reactance of the tuned circuit of an oscillator, such as by a varactor, thereby tuning the frequency. Where such an arrangement is used the modulator is referred to as a reactance modulator.

2. (master trigger) A device, usually a multivibrator, that is used in radar to generate a train of short pulses, each of which acts as a trigger for the oscillator.