[time-nuts] Z3801A and FE-5680A Allen Variances

Bob Camp kb8tq at n1k.org
Sun Nov 1 21:26:30 EST 2015


Without being at NIST, there is no real way to report the ADEV on the 3801 past 100K seconds. They
change ADEV in the 1K to 20K region depending on the state of their internal filter. They should be below 1x10^-13
under most conditions once they get past 50K seconds. This all assumes the unit is working properly and 
has been on power for a good long time (many weeks). 

The 5680 ADEV past 1,000 seconds is highly dependent on the state of the temperature compensation 
process. Catch it at a dead zone and they will get into the low parts in 10^-13 from 5K to 20K seconds. Exactly
where they turn up depends on the temperature environment, aging (how long they have been on) and the 
approach you take to eliminating drift. (ADEV by definition is a “drift removed” calculation). ADEV under ideal 
conditions can be worked out as falling off by square root (tau) with the starting point being 1 to 2 x10^-11 at 1 second. 
At 100 seconds that’s 1 to 2 x10^-12 at 10,000 seconds it could be (but isn’t) 1 to 2 x10^-13. Since most of the long
term ADEV is a function of the temperature compensation dithering, there is a lot of variation unit to unit and even within 
the same unit under different conditions. 


> On Nov 1, 2015, at 6:47 PM, Larry McDavid <lmcdavid at lmceng.com> wrote:
> Would someone familiar with the facts please report the long-term Allen Variance of the HP Z3801A and the FE-5680A.
> -- 
> Best wishes,
> Larry McDavid W6FUB
> Anaheim, California  (SE of Los Angeles, near Disneyland)
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