This paper is a review of some of the basics of phase locked oscillators and the mechanics of “Cycle Slipping” in low carrier-to-noise environments.

We explore the concept of Allan deviation as a measure of phase error in situations where phase locking is not always guaranteed.

We also propose an improved version of the heterodyne method for measuring the Allan deviation of a phase-locked oscillator for use in characterizing the performance of a deep-space coherent transponder prototype.