THE BASIC idea of frequency memory is conveniently illustrated by Fig. 1 in which it is assumed that the antiresonant circuits are of comparable selectivity and impedance and are tuned to frequencies that are unrelated but of the same order of magnitude. Oscillation at either f1 or f2 can be initiated by supplying to the input a signal of suitable magnitude and the desired frequency. An input of short duration suffices, for once started the oscillation persists without change until the other frequency is injected or the power is turned off. That is, the circuit remembers the frequency of the last input. The output may be taken from other points, but the plate node is particularly convenient.