[time-nuts] Checking accuracy of Rubidium standards

Dan Rae danrae at verizon.net
Sat Nov 8 14:18:13 EST 2008


Randy wrote:
> I was wondering if it is worthwhile or even feasible to compare an LPRO
> Rubidium standard against a Z3801.  Since their frequencies are probably
> going to be extremely close anyway it would seem some special
> method/equipment would be required for high precision.  Suggestions?
>
>   
Randy, As I have just been doing this, I'll offer my 2 cent's worth.  
The problem I found is that the Rb standard, in my case an hp 5065A, has 
better short term stability than the gps unit.  So for getting down to 
the best accuracy that the Rb unit is capable of requires integration of 
some kind over a longish period.    I find using a pen recorder on the 
IF output of a mixer, with crude LP filtering on it will permit setting 
an Rb standard with confidence down to the 10 e -11 level. 

For approximate setting, triggering a double beam scope from your 
reference with the time base at it's fastest setting and the x 10 
magnifier in,  and the gain on the channel with the unit under test 
wound right up to give near vertical zero crossings, will enable you to 
see small phase shifts of the unit under test. With the 465B I was using 
for example that's 2 nanoseconds per major division  But it gets tiring 
watching it for a long time :^)

Fun though!

Dan





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