[time-nuts] Z380XA The saga of the aging 10811

Bob Benward rbenward at verizon.net
Sat Sep 5 14:19:17 EDT 2015


Hi All,

I would like to convey the saga of my Z3801A and my Z3805A.

 

I purchased a Z3801A a few years ago at the Dayton Hamfest.  I got it
running and a few months later the unit lost it's GPS lock.  I did some
trouble shooting and finally realized the unit ran out of EFC range.  I
opened the double oven 10811 and retuned the unit to the lower end.  The
unit ran for another year or so, and then the oscillator died.  The
frequency was close, but the amplitude dropped too low for the circuitry to
lock on to.  I put the Z3801A aside and purchased a Z3805A from China (I
think from Yixunhk).

 

I plugged in the Z3805A and it ran for a few years.  One day, a few days
after a relatively active thunderstorm, I notice the alert light was on and
I had lost GPS lock.  I thought a close strike wiped out the GPS receiver.
After a lot of screwing around, I figured out that the 10811 had also lost
EFC range.  The output voltage sat at the neg2.0V level and would not budge.
I opened up the 10811 and readjusted the tuning to put the EFC counts at
below 100K.  I never reassembled the oscillator, I just left it sprawled out
on the table.  Checking the EFC stats, it started with a relatively high
1E-8 per day of drift.  It has since calmed down to 5E-9, and you can see a
slight flattening of the curve in the plot.  I am also running about a
positive 5K counts/day.  The 5E-9 figure is still 10X higher than the basic
10811 spec, and with 5K counts/day, I have only 160 days left ( I am at
about 200K counts now, max=1000K).  It always seems the drift is up in EFC
counts, negative going voltage, and down in frequency.

 

An interesting observation, I would notice a periodic dip in the time
interval error.  I would come home from work, turn on the air conditioning,
and I after an hour or so, I would see the time interval error take a large
dip.  I didn't think the drift vs temperature was that sensitive.

 

I also wonder if the excessive heat of the double oven shortens the life or
accelerates the aging of a typical 10811.  The heat certainly dries out the
polyester tape and silicon rubber foam inside. Could it accelerate the aging
of the oscillator, shorting the life of the oscillator and the useful life
of the GPSDO?  It's no wonder the Morions on Ebay are sold by the
manufacturing date.  Once you run out of EFC, that's all she wrote..  It
makes me question the wisdom of buying a used 10811 double oven oscillator,
how much life is left?

 

So, does anyone have any comments on the excessive drift of the 10811?

 

On another tangent, I tried hooking up a Morion to the Z3805A.  I used an
inverting amplifier for the EFC since the coefficient is positive and on the
10811 is negative.  I never achieved good control before the Morion itself
died.  I will probably continue working on marrying a new OCXO to the Z380XA
control board.  I need an alternate source for the OCXO without depending on
used double oven 10811s.

 

 

Bob

AC2AZ

 

 



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