[time-nuts] Re: 10 MHz TCXO periodically jumping 20 mHz up and down

[Erik Kaashoek]

Mike, the counter resolution was 40ps with am RMS resolution of 120ps
Erik.

On 18-2-2022 11:36, Mike Ingle wrote:
> Hi Erik.
> What is your counter resolution/gate time?  At 1second, the interval
> difference from 10MHz + 5mHz is 500ps.  --mike
>
> On Fri, Feb 18, 2022 at 11:20 AM Erik Kaashoek <erik at kaashoek.com> wrote:
>
>> During long term testing of some 10 MHz TCXO  the output frequency seems
>> to jump within one second 20 mHz ( millihertz) up in frequency  every
>> 110 seconds up and after a 25 seconds, again within one second, the same
>> amount down. The noise in the frequency measurement was well below 5 mHz
>> In an ASCII drawing of frequency versus time this looked like:
>> ________|~~~~|___________|~~~~|________
>> Sometimes the high frequency period was very short (some seconds) or
>> absent but the overall period was within 5 seconds constant
>> This was tested with 4 different power supplies, although all where
>> mains connected, not yet tested with battery only, 2 different counters
>> and two different reference frequency standards.
>> The TCXO was thermally shielded and testing with some cold air showed a
>> different  behavior for external temperature changes (fast jump away and
>> slow return to stable frequency)
>> Also, with thermal shielding removed, touching the TCXO showed also a
>> fast jump away and slow returning to stable
>> Measuring the supply voltage did not show clear changes but the used
>> voltmeter only had 4 digits resolution.
>> The official spec of the TCXO is much worse so the device is well within
>> spec but I'm trying to understand why this could happen.
>> Does anyone know a possible cause for this behavior?
>> Could this be a small mains supply variation in a 110 seconds long cycle?
>> Or what else?
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