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

Thu Nov 9 18:36:26 UTC 2017

Hi

One interesting thing to look at on modern OCXO’s:

Part of the factory alignment *probably* was intended to set the unit
at the center of the EFC range. Back in the days of people selecting caps 
or selecting resistors, that could be a pretty coarse kind of thing. At some 
point computers got into the act and OCXO’s got set very close to the 
center point. 

If you look at just about any of the OCXO’s that show up in GPSDO’s, they
are very close to mid range on the EFC. They may be ten or twenty years old.
They are mostly still on center. If you do the math on a 20 year old OCXO 
that is still < 0.1 ppm from center, that’s a crazy low drift rate.

No, not all OCXO’s are perfect after 20 years. There are a lot of examples that
have no output or have crushed cases. The stuff I’m talking about here are 
units that still are on the original card or something like that. Stuff that was
taken off a board with an axe …. not so much performance wise…..

Bob

> On Nov 9, 2017, at 12:59 PM, Mark Sims <holrum at hotmail.com> wrote:
> 
> 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 
> performance.
> 
> 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
> 6.5E-12)
> 
> 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
> DOCXO.
> 
> 
>        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
> 
> 
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