100 hours is not nearly enough time for the OCXO to stabilize... you need more like 1000+ hours. Here is results of measurements when I put an 8663 into an HP-53132A counter:
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 this 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. 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. 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 _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.