Jim said:
Although I hate feeding Jim's over-developed ego, I do have to endorse
one of his choices. I've got a copy of Floyd M. Gardner's "Phaselock
Techniques" ISBN 0-471-04294-3. My copy is around fifteen years old - a
copy of the second edition, first published in 1979, but since it is a
largely mathematical discussion of the subject, it has aged pretty
well. I've always found it very useful.
I've not used Phase-Locked Loops : Design, Simulation, and Applications
by Roland E. Best (ISBN: 0071412018) but the reviews do suggest that it
is less mathematical and more accessible.
Amazon offers 25 copies of Gardner and and only about a dozen of Best.