a digital memory system is provided wherein a received radio frequency signal is separated into a pair of quadrature signal channels , the signals in each one of the channel being sampled and stored in a digital memory at a rate substantially lower than the nyquist sampling rate . during recall the stored samples are sequentially read from the memories at the rate at which they were stored . the samples read from the memories in each of the channels are sampled at the relatively low sampling rate and are then combined into a single channel after shifting the phase of the signals in one of the channels 90 degrees , to form a composite signal having a plurality of radio frequency signal components , each one being separated in frequency from another one by an amount having a predetermined relationship to the pulse repetition frequency of the sampling pulses ; one of such radio frequency signal components having the frequency of the received signal . means , fed by the received radio frequency signal , are provided to selectively couple only the one of the produced plurality of radio frequency signal components of the composite signal having the frequency of the received radio frequency signal to an output for retransmission .