[time-nuts] Continously drifting HP 10811...

Mark Sims holrum at hotmail.com
Thu Nov 9 12:59:31 EST 2017

I put a UCT8663 DOCXO in my HP-53132A counter (using Gerry Sweeny's adapter board).   I bought a bunch of those DOCXOs around 10 years ago.  It was never powered up during that time.   Here are the notes that I made:

UTC 8663 mounted on Sweeny DOCXO card in a HP 53132A counter.  The 8663 had
not been powered up for over 10 years.  Below is the frequency drift per day
as the 8663 aged in.  THe 8663 is spec'd at 1E-10 (1 mHz) per day aging. From
past experience, they are capable of much better than that (1E-11 to 1E-12 per
day).  They seem to be limited in the HP-53132A application by the EFC DAC / VREF 

The 8663 was mounted on the Gerry Sweeny aftermarket OCXO board for the 531xx
counters.  For the first 30 days, the board was configured for the 0 .. 10V
EFC DAC range.  The Sweeny board powers the DAC with +/- 12V which is a bit 
out of the spec'd minimum +/- 13.5V required for optimum performance on 
the 0 .. 10V range.

The Sweeny OCXO board is based up on the HP design with a couple of nice mods.
First it has footprints for several common OCXO modules.  Second, it allows
the DAC range to be configured for 0 .. 5V,  0 .. 10V, and +/- 5V.  

The circuit feeds the OCXO output through a differential line driver.  The line
driver sends the OCXO to the HP counter mother board through a ribbon cable.
The motherboard makes the OCXO output available on a BNC on the counter
back panel.  Checking the ADEVs of the raw OCXO outout and the counter output
shows that the 53132A degrades the DOCXO output by around 1.5E-12 (raw DOCXO
value around 5.1E-12 at 200 seconds,  counter 10 MHz output BNC around

For the first 30 days the EFC DAC reading was recorded and the HP53132A was 
then auto-cal'd and the new EFC DAC output was recorded.  (The DAC readings
for the first 10 days were lost when a momentary power failue occured and the
system was not shut down cleanly).

The initial 30 day run was done with the Sweeny board DAC configured 
for the 0 .. 10V range.  Given the DOCXO EFC sensitivity (around 0.75 V / Hz)
and the 12-bit DAC, the minimum auto-cal resolution is 0.002 Hz.  Several
auto-cal cycles were performed each morning until one was within 0.001 Hz.

DAC readings were made by a Tektronix DMM914 4.5 digit DMM, not the best tool
for the task, but it was available.   The frequency reference for the tests was an
HP-5071A cesium beam unit. A TAPR TICC was used to measure the frequency of the

        drift (Hz/day)    DAC (after cal -> 24 hrs later)
day 1:    .298000 Hz       
day 2:    .057000 Hz       
day 3:    .033000 Hz       
day 4:    .022000 Hz       
day 5:    .017000 Hz       
day 6:    .011800 Hz       
day 7:    .009640 Hz      4.471V
day 8:    .008400 Hz      4.458V
day 9:    .006380 Hz      4.451V
day 10:   .003880 Hz      4.443V
day 11:   .002840 Hz      4.446V -> 4.438V  // power glitch caused reset
day 12:   .003470 Hz      4.437V -> 4.437V
day 13:   .002100 Hz      4.432V -> 4.433V
day 14:   .001590 Hz      4.430V -> 4.430V
day 15:   .001380 Hz      4.426V -> 4.428V
day 16:   .001660 Hz      4.424V -> 4.426V
day 17:   .000526 Hz      4.422V -> 4.423V
day 19:   .000284 Hz      4.421V -> 4.423V
day 20:   .000038 Hz      4.423V -> 4.424V
day 21:   .001019 Hz      4.420V -> 4.420V
day 22:   .001350 Hz      4.417V -> 4.418V
day 23:   .000402 Hz      4.417V -> 4.417V
day 24:   .000953 Hz      4.418V -> 4.419V
day 25:   .000304 Hz      4.417V -> 4.416V
day 26:  -.000441 Hz      4.417V -> 4.418V
day 27:   .000214 Hz      4.415V -> 4.415V
day 28:   .000517 Hz      4.415V -> 4.416V
day 29:  -.000998 Hz      4.415V -> 4.415V
day 30:   .001300 Hz      4.415V -> 4.414V
day 31:   .000423 Hz

Powered down, replaced 53132A fan, changed DAC range to 0 .. 5V, and 
the 53132A was put back into case (hence no more DAC readings).  The 0 .. 5V
DAC range reduced the auto-cal minimum step size to 0.001 Hz.   Hopefully 
it should also improve the DAC stability.

Warmup frequency error after power up:
   1 Hz     - 3m     
   0.1 Hz   - 3m 25s
   0.01 Hz  - 5m 45s
   0.001 Hz - 6m 15s

After 24 hours the unit was auto-cal'd once and left alone.
Doing an auto-cal swings the EFC voltage between min and max values.  This disturbance does
seem to affect the drift for a day or two.

The frequency error for the next week:

day 32:   .000152 Hz  (0.00009 Hz/day for last 18 hours)
day 33:  -.000825 Hz
day 34:  -.000730 Hz
day 35:  -.000287 Hz
day 36:  -.000144 Hz
day 37:  -.000086 Hz
day 38:  -.000083 Hz

More information about the time-nuts mailing list