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 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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