Hi Scott,
D'oh. Thanks for the correction! Like I said, I don't do these calculations
often.
If as Bob Camp implies, the aging isn't from the OXCO, then I'm a bit stumped.
I do have an op-amp in the EFC string with a voltage divider for gain. The
resistors are Panasonic ERA-6AEDxxxV resistors. Mouser says they're
temperature stable to 25PPM/C, but of course they don't mention an aging rate.
I don't really see anything else, other than the OCXO, that is likely to be
prone to a linear type of aging. The aging rate appears to be stable from unit
to unit, so naturally I considered the OCXO first.
There is one other bit in the EFC string that might be controversial, but I
don't see that it would be a candidate for the symptoms of aging.
Bob
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From: Scott Stobbe <[email protected]>
To: Bob Stewart <[email protected]>
Cc: Discussion of Precise Time and Frequency Measurement <[email protected]>
Sent: Saturday, November 5, 2016 9:19 PM
Subject: Re: [time-nuts] Thermal impact on OCXO
If your DAC spans the full EFC range than 1LSB is 1/2^20 ~ 1 PPM of the EFC
range, and the EFC tuning range is 8/10E6 ~ 1 PPM full scale, so 1 LSB is
~1PPT. So, if everything else is stable the DAC code reflects changes solely
due to the OCXO, which would be an aging of 24 PPT/day.
On Sat, Nov 5, 2016 at 9:57 PM, Bob Stewart <[email protected]> wrote:
Hi Scott,
The 20 bits span about 6 volts. The EFC range spans about 8Hz (+/-4Hz). I
don't do these calculations every day, but that's about 4.5PPT?
Bob ------------------------------ ------------------------------ -----
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From: Scott Stobbe <[email protected]>
To: Bob Stewart <[email protected]>; Discussion of precise time and frequency
measurement <[email protected]>
Sent: Saturday, November 5, 2016 8:38 PM
Subject: Re: [time-nuts] Thermal impact on OCXO
I think that's a nice plot, it looks like you have stepped 160 LSB over 7 days
or roughly 1 LSB per hour. With a 20bit dac you are trimming maybe 1 ppt/LSB to
4 ppt/LSB? In allan devation terms, the case of 1ppt/LSB, solely due to drift,
you're at 1E-12 at 3600*sqrt(2) = 5000 s, in the case of 4ppt/hour your at
1E-12 at 1280 s. Seems reasonable.
On Sat, Nov 5, 2016 at 2:47 PM, Bob Stewart <[email protected]> wrote:
Oh dear. I attached the wrong file. Here's the correct one.
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