[time-nuts] Follow-up on Z3801A high EFC reading

[Graham / KE9H]

John:

If it was turned off for more than a year, in my experience, the HP10811 
(or similar)
oscillators at the heart of the Z3801A will take about three weeks to 
settle down,
and rejoin the previous mature aging curve.

I have built a few GPSDOs using HP10811 oscillators, that I bought off 
of eBay,
and they all took three weeks to settle down.

You can ask the experts on the list why.  Something about temperature 
related stress
relief and gas sublimation on the surface of the crystal.

--- Graham

==

On 7/16/2011 3:39 PM, John Ackermann N8UR wrote:
> Last week I posted about one of my Z3801As having a very high EFC 
> reading and an "EFC ERR" message in the health status when powered up 
> again after about 18 months of sleep and a 500 mile location change.
>
> Over the last week, the error message has continued, but the EFC has 
> consistently trended downward.  It started out at about 1015000 and is 
> now down to 1012070.  During the first day or so, the EFC count was 
> going down more than one unit per minute; in the last day or so, it's 
> more like 4 or 5 units per hour.  But since it's moving in the right 
> direction, I'm not going to try to rip open the outer oven at this point.
>
> This sort of aging effect is a bit odd given that this unit had been 
> running continuously for about 7 years before it was shut down for the 
> move; I might expect to see this is in a brand new unit but not in one 
> with so much running time.
>
> I've been comparing the 10 MHz output against a cesium during this 
> time, and an ADEV plot is attached.  It seems to indicate that the 
> performance is just fine -- the short term floor is probably limited 
> by the 5061B's noise, and we can see the 5061A long-term noise floor 
> starting to show up at 200K seconds, but there's certainly nothing 
> here to question the performance of the GPSDO.
>
> Now that I've captured this baseline data, I'm going to power cycle 
> the Z3801A to see if it lands in the same general vicinity.
>
> John
>
>
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