[time-nuts] Just any counter external reference and discipline mode.

[jimlux]

On 7/13/20 9:58 AM, Taka Kamiya via time-nuts wrote:
> I'm sorry to interject a newbie question....  I changed the title to distinguish from rest of the conversation.
> 
> I have heard this both ways about external references - whether it's used to phase lock internal source and used directly after some conditioning.  Both come from people on this list I trust.  Limiting discussion to HP counters from 70s to 90s, which is the truth?  Were there exceptions?  If so, why?  (I'm not interested in injection locking....)
> If some are phase locking, what does it phase lock?  Most counters have options on internal reference (ie. HP53132A has standard, mid performance, high performance, and ultra performance)  Does it phase lock the standard that's always there?  Or try to phase lock optional reference?  I really don't see the need for phase locking, as only critical element is rise time - so rather, signal conditioning makes sense.
> 
> At least for me, the general public, circuit diagram is not made available for later models.  I have no way to tell for sure what is being done inside.
> 
> ---------------------

There are also "frequency locked" devices that are not "phase locked" - 
they essentially discipline an internal oscillator by adjusting its 
frequency, but not with any sort of phase locked loop.

The 33600 series function generators from Agilent/Keysight are in this 
bucket. You can feed in a 10 MHz source and they'll (after a fairly 
short time, a few seconds) produce a 10 MHz output that is "right on 
frequency", but it won't have a predictable phase relationship with the 
external reference.