Abstract: An electronic trigger circuit for an RF source, which electronic trigger may be advantageously used in a radar apparatus, for instance. The trigger employs digital logic devices including a register or counter, a circuit for initiating counting in the register in response to a received pretrigger signal and a circuit responsive to the occurrence of selected count in the register for enabling the RF source. A timing signal is generated, based upon the pretrigger signal in timed relationship to the time at which the RF source should nominally generate its RF signal. Typically, the RF source generates its RF signal at sometime after being enabled. A comparator circuit is provided for comparing the phase relationship of the aforementioned timing signal and the occurrence of the RF signal and is in turn coupled to an arithmetic circuit effective for altering the number of states through which the register counts.