I was wondering whether it is possible to dither a FM signal at the output of a VCO?  If we assume the FM signal to be a pulse signal, how could one dither the positive going edges of the FM pulse? This brings me to the next question. Phase noise from the VCO will essentially dither the positive going edges of the generated FM signal. Thus, can phase noise be used to dither a FM signal? I guess the phase noise would have to be completely random which it might not be, depending on the source. I was just wondering whether phase noise and jitter are always unwanted.
What are your thoughts on this?

Cheers,
svensl

One way to dither the vco clock in a PLL is to modulate the feedback divider and increase its bandwidth to allow this "noise" to pass thru to the VCO.