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

[Mike Ingle]

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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