[time-nuts] Temperature stability for Thunderbolt: results

Bob Camp lists at rtty.us
Thu Jan 27 22:08:14 UTC 2011


The assumption is that other than OCXO short term and aging - all the bumps
and dips in the road have been eliminated. As I mentioned earlier that is
indeed an assumption that has a lot of sub assumptions that go into it. 

It also assumes that GPS is correct over the time period involved. 

To put some numbers on all this, here's some guesses. Accuracies of GPS on
the TBolt are an "eyeball" 2 ns or so. A thousand seconds is pretty long for
an OCXO short term floor. That would give you 2x10^-9 / 1000 = 2x10^-12 as a
limit on what's being done. At 10,000 seconds the OCXO would have to be
2x10^-13 - that's not happening. At 100 seconds it would need to be 2x10^-11
which is pretty high probability. 


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Tom Van Baak
Sent: Thursday, January 27, 2011 4:37 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Temperature stability for Thunderbolt: results

>>By this (quite possibly imperfect) measure: When the EFC goes down 
>>3:1, you have improved the thermals by 3X. If you started at 1 C 
>>swings, the OCXO is now seeing 1/3 C swings.
> Agreed (re: the EFC component that correlates to changes in Tbolt 
> ambient temperature).

A number of posts have mentioned LH measurements and
variations in DAC voltage or TI or OSC values. I'm curious
how close to the truth this is.

An analogy: suppose my goal is to drive 55 mph for a day
as smoothly as possible. There are two judges.

One judge is a passenger who at all times is looking at my
foot. Over the hours they see me push the accelerator at
varying depths; sometimes slacking off quite a bit and other
times pushing fairly hard. Occasionally they even see
me tap the brake.
They collect all this raw data and make graphs and conclude
that I am a mediocre driver since there was a lot of variation
in my performance and I could have done much better.

The other judge is a fully instrumented time nut in a vehicle
behind me; watching the position, velocity, and acceleration
of my car at all times to many decimal places. Moreover they
collect environmental and road condition data.
They see me keep really close to 55 mph regardless of the
straight roads, or all those up and down hills; around gradual
and tight curves, in daylight and at night, during the warmer
day and cooler night. They imagine I must be highly motivated
and alert, constantly and tirelessly adjusting acceleration to
meet the demands of the uneven road and driving conditions.
They conclude I'm an excellent driver.

Which judge is more correct? Which judge is LH?

If someone already has raw TBolt data (both internal and
external, simultaneously) with and without fine temperature
regulation let me know; we can see how well the judges


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