Abstract: A device for controlling the conical scanning frequency of conical scanning radar systems. An antenna illuminator is caused to revolve by means of a three-phase asynchronous rotary field motor. The angular frequency of conical scanning is changed in a random or pseudo-random manner by means of a reference generator associated with the asynchronous motor, a random or pseudo-random signal generator, and a circuit comparing the signal of the reference generator and the signal of the signal generator. The comparison circuit provides "greater," "less" and "equal" outputs. A switching device driven by those outputs couples a braking magnetic-field or the three-phase supply to the motor, depending upon whether a "greater" or "less" output, respectively is the present comparison circuit. The "equal" output also controls the change of state for the random or pseudo-random signal generator.