[time-nuts] Beginner question - unexpected possible jitter in 1 PPS output of Motorola ONCORE UT+ module

[David Feldman]

Thank you, Tom - I appreciate the advice.

I am using a 74HC390 in the (divide-by-20, square wave output) divider chain, and sure enough, after looking more closely at the data sheet, it clocks on the FALLING edge (I thought otherwise - wrong)! I will stick an inverter in the path and that will probably fix it.

Will update again once that's taken care of.

Dave

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>Check rising/falling edge times, check trigger levels, check signal levels and load. Are you DC or AC coupled. How about power supply noise and grounding? Which edge are you actually triggering on? Is there crosstalk with the Tx line.
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>It is extremely unlikely that there's a problem with the UT+ itself -- this series of Motorola Oncore GPS boards has served the time & frequency community for two decades with no problems, or jitter, or off-by-100us errors.
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>It will be fun to meticulously track down the bug; don't just make it go away and move on. We will all learn from this interesting problem.
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>I'll trade you a perfect UT+ if you give up. At some point we time nuts stop getting excited about what works and delight in what doesn't, and why.
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