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

[Erik Kaashoek]

Bill,
To test I removed the thermal insulation to increase the heat loss 
requiring more heat to be generated.
The jump pattern did not change!
Erik.

On 18-2-2022 11:26, bill wrote:
> Hello,
> My guess is that it is a quirk of the temperature compensation network 
> inside the TCXO.  I have seen similar behavior in commercial TCXOs as 
> temperature changes as a result of "break points" in the compensation 
> network.  It is difficult to know exactly unless it is possible to 
> understand what kind of temperature compensation is used inside the 
> oscillator.
> Cheers
> Bill
>
> On 18/02/22 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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