[ntp:questions] Making ntpd tweak a TCXO

MAYER Hans mayer at iiasa.ac.at
Sun Feb 7 11:03:42 UTC 2016

I cannot imagine what is your goal. I assume you want to adjust a very precise frequency 
with your TCXO. 
In any case you need a second time reference. 
This could be either a second local clock or over the network.
I have done this with a GPS reference and I adjusted a VCXO. 
( But beware, each XO has an ageing characteristic. ) 
If you are patient an offset of about 0.1 PPB is realistic. 
I used the peerstats file for calculation. 
As Mike wrote, the drift file is not a solution. 

Kind regards

From: questions [questions-bounces+mayer=iiasa.ac.at at lists.ntp.org] On Behalf Of Mike S [mikes at flatsurface.com]
Sent: Friday, February 05, 2016 4:36 PM
To: questions at lists.ntp.org
Subject: Re: [ntp:questions] Making ntpd tweak a TCXO

On 1/27/2016 11:55 AM, Mark Haun wrote:
> Does the NTP software provide any hooks that could be used to accomplish
> this?  I thought of a crude approach, simply writing a program to examine
> the drift file periodically, and using that information to adjust the TCXO.
> But that (a) fails to stop ntpd from adjusting the virtual clock frequency
> within the OS, and (b) isn't really a proper control loop.  I guess it would
> work, sort of, as a last resort.

Just a thought - monitor the ntpd loopstats log, and adjust your tcxo
based on the frequency offset. That's updated much more frequently than
the drift file, so would be more responsive than using the drift file.
You'd probably want something like a PID loop to filter jitter and avoid

It doesn't stop ntpd from adjusting the clock, but it would minimize the
size of the adjustment, which should long term average to 0.


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