[quote author="featherpillow"]I don't know if anyone on our lovely board here has experience in the digital realm...
I've always thought that a PLL clock is more stable than a crystal clock. Is this true, or am I mistaken?[/quote]
A PLL (phase locked loop) is something that has to have a variable frequency oscillator somewhere, the thing that the phase detector drives to synchronize with the incoming signal. This oscillator can be a VCXO (voltage-controlled crystal osc). Because of its need to be "pulled" up or down from its nominal center frequency it tends to be, all other things equal, less stable in the absolute sense than a non-tunable crystal osc. It will also usually have a lot more phase noise. And to the extent that it is working, its stability is just that of the source it's locking to. However (big however): it can have lower phase noise/jitter than the source, if the source is noisy/jittery, and if the loop filter is slow and makes the system have a big "flywheel" effect. This is why many pieces of equipment "re-clock" and get benefits.
For a system master clock you just want a really stable low phase noise crystal oscillator. There are some still better oscillators based on atomic transitions but good crystals, especially if oven-stabilized, are plenty good enough.
