Russ, I was trying to come up with a scenario that would cause this. If this were a digital loop (as in no sine waves), and you divided both the input and the output by two before applying them to the multiplier, they would wind up (I think) consistently either in phase or 180 degrees out of phase, depending on the sign of the VCO transfer function. Now, if you took either the input or the output and divided it by two outside the loop, you could get 180 degree ambiguity. Sorta far-fetched, but it's all I can come up with. And why you would do this, .. :?: