In a moving-target indicator in which the pulse-repetition period of an associated Doppler radar is subject to variation, incoming echo pulses appearing in the output of an i-f stage of the radar receiver are demodulated with the aid of two coherent reference signals in relative quadrature and the results are digitized for transmission over two parallel channels. In each channel, digitized signals corresponding to two consecutive echoes in a given range cell are subtracted from each other to provide a pair of difference signals which are passed through a weighting device for multiplication by factors which are trigonometric functions of a selected Doppler frequency and of the difference between the actual repetition period and a theoretical constant value of that period. The weighted signals are subjected to further filtering before being utilized for further processing or display.