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

[Magnus Danielson]

Hi Erik,

I think you have yourself a digital TCXO controller. Those use a 
tempsensor, use the reading to calculate the compensation and the use a 
normal varactor control to steer the frequency. Older TCXOs use a 
resistor/thermistor network to do the same work. You can probably read 
up on the vendors material to see that the keywords are there to support 
the suspicion.

So, what you see is really the resolution limit of reading/control. As 
long as it's within spec, and the transitions does not upset your system 
downstreams, I guess it's just fine. If you have issues with the steps, 
then another product is what you look for.

Cheers,
Magnus

On 2022-02-18 11:11, Erik Kaashoek wrote:
> During long term testing of some 10 MHz TCXOÂ  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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