Abstract: In the generation of frequency-modulated interrogation frequencies for atomic frequency standards, the modulation characteristics can be tailored to the frequency discrimination characteristics of a physics package. The rate of phase change of a digital pulse train providing a frequency-modulated component of interrogation frequency for an atomic frequency standard can be varied, for example, by multiplexing a plurality of differently phased (delayed) pulse trains to vary the rate of phase change in a digital interrogation frequency component, or by effecting phase delays and phase advances through the addition and subtraction of pulses of a digital interrogation frequency component.

Abstract: A physics package interrogation signal can be digitally synthesized for use in an atomic frequency standard with one or more sets of integrally-related sub-multiples of a clock frequency in which one of the integrally-related sub-multiple frequencies is varied to provide frequency modulation between integrally-adjacent sub-multiple frequencies through the use of preloadable counters, the controlled delay and the synchronization of digital pulse trains and operation in plural modes. The method and apparatus can reduce false lock possibilities, optimize the ability of the physics package to remain locked, and reduce phase noise in the output of an atomic frequency standard.