[time-nuts] Rubidium (Rb) or Caesium (Cs)

ws at Yahoo warrensjmail-one at yahoo.com
Mon Oct 3 23:58:16 UTC 2011

Doug wrote:
>If you are constantly jerking the control voltage back-and-forth ...

Interesting, I can certainly see how that could be the case if one tried to 
Track a GPS too fast,
Or used a noisy non Tbolt engine, Or a poor control loop.
But it is not in any way consistent with what I see happening.
Maybe it has something to do with the fact that my "constant Jerking" is 
only 2 e-15 per Dac step, which is far below any noise level,
and the daily change is under 1e-12 PP with a several hr time constant.
I wonder if that fits within their definition of only making small changes 
every 24 hrs?



I used to work at Efratom.  The rubidium engineers used to say that the LPRO
did not work well with constant frequency corrections such as with GPS.
They claimed that very slight corrections should only be made once every 24
hours.  And then, it may take up to a week or longer to pull the frequency
to the desired amount.  If you are constantly jerking the control voltage
back-and-forth, the LPRO will get to where it develops jitters!
Regards, Doug, K4CLE


-----Original message-----
From: WarrenS <warrensjmail-one at yahoo.com>
To: Discussion of precise time and frequency measurement
<time-nuts at febo.com>
Sent: Mon, Oct 3, 2011 16:59:19 GMT+00:00
Subject: [time-nuts] Rubidium (Rb) or Caesium (Cs)

Rubidium (Rb) or Caesium (Cs) standard reference oscillator?

What will give the more accurate absolute Frequency source over day to day
A primary Cs (the types available to time nuts) or a optimally disciplined
GPS Rb Osc?

By definition Cs is the primary time standard,
but there are several things that effect a time-nut's "Primary Cs
Standard's" absolute frequency including how it is built and maintained, if
it has the high stability option and Einstein.
What I'd like to find out is how accurate a GPS Disciplined_Rb_Osc can be
made compared to the typical Cs out there.

I'm experimenting to find out how accurate a freq standard can be made using
a LPRO Rb disciplined to a Tbolt.
Using a  temperature compensated and tweaked LPRO Rubidium (Rb) oscillator,
I'm getting low e-13 per deg F and day to day freq variations (compared to
GPS) even before being disciplined.
When the LPRO Rb is disciplined to GPS using a well setup Tbolt with an
extended time constant of a few hours,
their phase difference stays with-in a couple of ns RMS, and of course the
difference between them long term is zero.
What I would like to determine is how accurate that really is.



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