Abstract: A digital automatic frequency control circuit for use with a scanning type superheterodyne receiver, such circuit having an input for receiving the output of a related discriminator, and an output for providing an incrementally variable tuning voltage to a related local oscillator. My novel circuit has a search mode and a lock mode, and during the search mode, when the receiver tuning is swept past a pulsed radio signal, the discriminator produces a sequence of voltage output pulses whose polarity for a desired signal will be different from that of the signal's image. My circuit recognizes the polarity relationships of such pulses, and makes use of such information in a highly advantageous manner in order to cause the receiver to enter the lock mode only when the received signal has the correct relationship with the local oscillator, with the image signal thus being ignored.