AFC Tracking Algorithms

The automatic frequency control (AFC) loop is beginning to play an important role in digital data links. There is very little published literature which deals with AFC loop implementations and performance in noise (in contrast to the large body of literature dealing with phase-locked loops). This paper presents a brief discussion of eight different AFC loop implementations, including the block diagram, discriminator characteristic, and loop tracking error in the presence of gaussian noise. Tracking performance of the various loops is compared in the presence of noise for CW, DPSK, and MFSK signaling.