[time-nuts] Thermal impact on OCXO

Bob Camp kb8tq at n1k.org
Sat Nov 5 12:54:04 EDT 2016


Hi

Remember - most holdover specs also include a delta temperature (like 40 to 70C) during the 
holdover period ….

Bob

> On Nov 5, 2016, at 12:15 PM, Bob Stewart <bob at evoria.net> wrote:
> 
> Hi Scott and Bob and others,
> I keep telling myself that I won't get involved with the temperature problem, and yet for some reason I keep going down that rabbit hole.  It seems to me that it's one thing to correct well enough to stay on frequency within some degree of accuracy, and yet another to try to also correct for phase.  The reality is that what I have is good enough for now.  At 12 hours of holdover, I'm usually a bit over 1uS out of phase.  Maybe I could better that, but I think I'll need a lot more understanding of the impact of aging vs temperature before I can get there.
> 
> Bob -----------------------------------------------------------------
> AE6RV.com
> 
> GFS GPSDO list:
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>      From: Scott Stobbe <scott.j.stobbe at gmail.com>
> To: Bob Stewart <bob at evoria.net>; Discussion of precise time and frequency measurement <time-nuts at febo.com> 
> Sent: Saturday, November 5, 2016 10:54 AM
> Subject: Re: [time-nuts] Thermal impact on OCXO
> 
> Sounds like you already realized this. Phase is the integral of frequency and the derivative of phase (phase rate) is frequency. So if you go from nominal frequency - slow - nominal or equivalently nominal frequency - fast - nominal the phase integrates up/down.
> It would be a little more complicated for an ocxo since it is servoing the xo temperature, you would need to know the disturbance rejection (gain, time constant for a simple Pi controller) to try and feedfoward correct the phase error.
> 
> On Friday, 4 November 2016, Bob Stewart <bob at evoria.net> wrote:
> 
> OK, never mind.  I see the obvious.  Phase changes faster at a higher frequency than it does at a lower frequency.
> 
> Bob
>  ----------------------------- ------------------------------ ------
> AE6RV.com
> 
> GFS GPSDO list:
> groups.yahoo.com/neo/groups/ GFS-GPSDOs/info
> 
>       From: Bob Stewart <bob at evoria.net>
>  To: Discussion of Precise Time and Frequency Measurement <time-nuts at febo.com>
>  Sent: Friday, November 4, 2016 8:56 PM
>  Subject: [time-nuts] Thermal impact on OCXO
> 
> In the general case, is the impact of changing the ambient temperature around an OCXO from, say, 40C to 41C the same as changing it from 41C to 40C all else being equal?  IOW, if I somehow have the same temperature ramp over the same time period in both directions, will I wind up with the same frequency and phase, or will the frequency revert but at some phase difference?
> 
> Bob - AE6RV
>  ----------------------------- ------------------------------ ------
> AE6RV.com
> 
> GFS GPSDO list:
> groups.yahoo.com/neo/groups/ GFS-GPSDOs/info
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