[time-nuts] LTE-Lite module
kb8tq at n1k.org
Tue Oct 21 07:42:35 EDT 2014
The proper term for this is a frequency perturbation. It’s a low amplitude coupled resonance in the crystal. Essentially you are sweeping through another resonance as you tune the EFC. The result is a “blip” in the tuning curve. No they aren’t supposed to be there. Yes they do happen.
> On Oct 21, 2014, at 3:12 AM, Hal Murray <hmurray at megapathdsl.net> wrote:
> time-nuts at febo.com said:
>> The problem is that the ocxo maintains its frequency even though the EFC
>> control voltage is changing. Thus phase error is accruing making the efc
>> larger and larger due to the P term.
>> Then at some point the crystal 'snaps' and jumps in frequency, overshooting
>> the desired frequency and causing the P term to start pushing in the
>> opposite direction repeating the cycle.
> Does anybody understand the mechanism behind that behavior?
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