[time-nuts] Checking accuracy of Rubidium standards
danrae at verizon.net
Sat Nov 8 14:18:13 EST 2008
> 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 :^)
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