Abstract: The present invention relates to a time and frequency control unit which is apable of compensating for long-term crystal oscillator drift and other errors in a reference oscillator signal by both coarse and fine (vernier) controlling. The invention takes the reference oscillator frequency, f.sub.o, divides it by a controlled factor a and mixes f.sub.o with f.sub.o /a to produce an f.sub.o + f.sub.o /aSignal. The f.sub.o + f.sub.o /aSignal is then divided by a second controlled factor b and mixed again with f.sub.o to yield a signal of frequency f.sub.o .+-. (f.sub.o + f.sub.o /a) 1/b,Where f.sub.f, the final output frequency, is determined after a filter stage sets the operation sign of the above expression (to plus or minus). Where f.sub.f is intended to be constant with a changing f.sub.o, the values of a and b are changed. From the above expression, it is apparent that a change in a makes a fine correction whereas a change in b translates the frequency with a coarse adjustment.