[time-nuts] Thunderbolt oven / non-stable operating temperature

[Tom Van Baak]

I think what I'll do is collect some data on a batch of TBolts that I have soaking here. It seems to me there's enough information that, over time, the tempco can be accurately determined. I mean, when you see LH plots with glaring diurnal patterns in both temp and DAC it's easy to roughly calculate the correlation by eye.

Alternately, when the TBolt is in disciplining-disabled mode, the tempco can be inferred from temp and quadratic PPS offset residuals (EFC gain is not a factor in this case). Or for greater precision, a simple match of variations in ambient temp and externally measured frequency would do the job.

I use different software to talk with my TBolts anyway, logging all communication in its native TSIP binary. I'll modify or write an automated tool to take the guesswork out of it.

/tvb

----- Original Message ----- 
From: "Charles P. Steinmetz" <charles_steinmetz at lavabit.com>
To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
Sent: Friday, December 14, 2012 2:36 AM
Subject: Re: [time-nuts] Thunderbolt oven / non-stable operating temperature


> tvb wrote:
> 
>>do either of you have actual tempco numbers?
> 
> I checked my notes and found that I did not record any free-running 
> tempco values.  My observations were based on the scale factors I had 
> to use to get the temperature and DAC graphs in Lady Heather to 
> overlay each other.  I initially noticed it because there was a very 
> pronounced tracking of the two graphs for one Tbolt and for the other 
> two there was not (the temperature-compensating component of the DAC 
> voltage is mostly lost in the noise).  I had checked the actual EFC 
> sensitivity of each oscillator in the vicinity of the operating 
> point, so all relevant variables were more or less controlled.
> 
> My impression is that the better ones are comparable to a single-oven 
> 10811, maybe even a bit better.  LH typically reports tempcos of 
> 1e-12/C to 1e-11/C.  My worse unit (and, from what I can infer from 
> LH plots posted to the list and on-line, it appears many others as 
> well) typically reports a tempco of 1e-10/C to 1e-9/C.  Of course, 
> the LH numbers are all to be taken with some caution since LH does 
> not have any a priori means to separate tempco and drift.
> 
> Best regards,
> 
> Charles