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

ws at Yahoo warrensjmail-one at yahoo.com
Mon Oct 3 20:45:48 EDT 2011


One problem is that I do not have anything that is known better or even near 
as good as the GPS to compare against when it comes to accuracy or stability 
at greater than one day.
(If I did I'd be working on making it better instead of improving a cheap 

As you point out, a HP5061A Cs does not start becoming more stable than a 
good Rb until after about a day, which by then the GPS is dominate in a good 
So my basic question:  Is the HP Cs is more stable than a good GPSDO setup 
at times greater than a day.

The Top hat test is a good Idea that I'll try and set something up,
but a couple of problems with it is that the 3 or 4 units under test should 
at least be close in noise and one needs more than one Cs to be sure of the 



> Dear Warren,
> On 03/10/11 18:58, WarrenS wrote:
>> Rubidium (Rb) or Caesium (Cs) standard reference oscillator?
>> What will give the more accurate absolute Frequency source over day to 
>> day averages?
>> 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.
> If you want "absolute frequency" then a GPSDO rules over any Cs a normal 
> time-nut can get.
> Looking only for stability, then a HP5065A will be more stable than a 
> HP5061A up to about 100 ks where the HP5061A becomes more stable according 
> to the ADEV charts that I have found after a quick look on the net (using 
> "HP5065A ADEV" and "HP5061A ADEV" as search terms).
>> 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.
> Best way is to measure against a cesium or free-running rubidiums. 
> Three-cornered hat will help.
> Cheers,
> Magnus

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