[time-nuts] GPS disciplined Rubidium

Brian Kirby kirbybq at bellsouth.net
Sat Jun 11 23:02:37 EDT 2005

Hello, Mike.

I tried to lock a FRS-C rubidium up to a Z3801A, in place of the HP10811 
oscillator.  I did not have much success, it ruined the short term and 
long term stability of the rubidium.  But, I'll say , I did not know 
what I was doing - or I know better now.

I believe that the Z3801A GPS controller/DAC outputs a new value every 
15 seconds - which may be too short of an update rate for a rubidium 

To use the Z3801A, you would need either an amplifier or attenuator 
network on the output of the DAC and it depends on the voltage 
sensitivity of your rubidium.  I can't find my notes, but I believe the 
10811 oscillator was 1x10-7 or 1x10-9 for a 1 volt change.   You will 
also need a low tempco summing amp and some type of precision voltage 
reference as you will need to "bias" your rubidium around the correct 

I have used Brook Shera's GPS controller to control the rubidium and it 
performs well.  It also needed an amp and precise reference.  Brooks had 
made several PICS (the present PIC uses a 60 second update rate) for my 
applications and the last set of data shows 100 sec variances at 
1x10-12, and 10,000 sec variances at 3x10-13.

Mike Feher wrote:

>OK, guess I am on a roll this AM. Whiling writing my lost post I was
>reconsidering one of my previous thoughts. What is the advantage of a GPS
>disciplined Rubidium. I sure do not see any. Yes, for those times when there
>is an outage of GPS, it may be handy, but the holdover time of a decent
>ovenized oscillator in the short term is actually better than that of a
>Rubidium, and if GPS is out for a long time, well, all bets are off anyway.
>Of course in that case a rubidium would be a better timekeeper. So, like
>everything else it seems to be a trade-off. I was thinking of taking one of
>my Z3801s and placing a Rubidium in it in place of the ovenized oscillator.
>The more I thought about it the more I decided it was not a worth while
>effort. Any comments? - Mike 
>Mike B. Feher, N4FS
>89 Arnold Blvd.
>Howell, NJ, 07731
>time-nuts mailing list
>time-nuts at febo.com

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