On 8/3/2017 3:05 PM, Chris wrote:
On 08/03/17 17:27, rickman wrote:


Not sure if you are referring to the Shortt clock or the PLL. But the
statement applies equally to both. There is no magical stability in the
PLL. It is a control loop and as such the thing being controlled will
*never* remain in phase or at the same frequency as the reference.


I think the difference is that while a pll always has a phase offset
the reference and vco are in phase lockstep once the loop has aquired
lock. It's a closed loop system whereas the Shortt clock is an open
loop system, only getting a kick back into sync from time to time.

Like a hit and miss governor ?...

Chris




In this case I have to (surprise!) agree with Rickman. A phase locked
loop is never in lockstep with the reference - there is always a bit of
drift in the oscillator.

It's no different than driving down a highway. You can aim your car
straight down the road - but you need to continually make small
adjustments to account for things like the road and the wind.

The Shortt clock is not that much different, except that it purposely
runs at a slightly lower frequency than the reference, and the frequency
at which the comparison occurs is much lower.

But the result is the same - a signal that is accurate due to
compensation based on the instantaneous phase at specific times.

--
==================
Remove the "x" from my email address
Jerry Stuckle

==================