[time-nuts] Beginner's Atomic Clock

[Richard (Rick) Karlquist]

On 9/17/2019 12:33 AM, Dr. David Kirkby wrote:

> Is  there any advantage in using a GPS Rb disciplined oscillator vs a GPS
> disciplined high quality OCXO like the HP 10811A? I can’t understand why
> there should be, as a Rb source would use an OCCO in its output stage
> Therefore in each case
> 
> * Short term stability depends upon the quality of the OCXO
> * Long term stability depends upon GPS.
> 
> Perhaps there’s is period over which the the overall stability can be
> improved by adding a rubidium oscillator. I would be interested to know if
> that is the case or not.
> 
> Dave

What I was always told was that Rb has low enough noise coming off
the atoms such that it can use a relatively fast loop to lock
the OCXO and clean it up.  OTOH, the 5071 Cs has to use a very
long time constant loop to control the 10811, hence it doesn't
clean it up except very close to the carrier.  Even the high
performance version of the 5071 doesn't compare with Rb.

Rick N6RK