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

Nick Sayer nsayer at kfu.com
Mon Nov 2 15:27:02 UTC 2015


I briefly considered designing a board that would GPS discipline the FE-5680A. It’d simply substitute an RS-232 level shifter for the DAC and would speak the protocol to trim the frequency. I haven’t done it, though, because the OH300’s performance specification at low tau is not that far removed from the FE-5680A’s, they’re far smaller and take a lot less power and their supply (at reasonable pricing) is far more certain.

> On Nov 1, 2015, at 6:26 PM, Bob Camp <kb8tq at n1k.org> wrote:
> 
> Hi
> 
> 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. 
> 
> Bob
> 
>> 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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