[time-nuts] Temperature stability for Thunderbolt: results
lists at rtty.us
Thu Jan 27 17:40:54 UTC 2011
With a "normal" TBolt running on the bench, it's very obvious that
temperature and EFC are directly related to each other. With a little
scaling (and possibly an inversion) the plot of one lays down on top of the
other. As long as you can eyeball that kind of relation, there's an issue.
Why watch EFC? My assumption is that the OCXO has been on for a good long
while and that it's settled down. In a Time Nut environment that's likely a
good assumption. I'm also assuming that the supply voltages are stable as is
the internal DAC. One is a pretty good bet for list members, the other is a
complete guess. Final assumption is that the short term on the OCXO is
significantly better than GPS over modest time ranges (very likely true). If
all that's true, what you are watching on the EFC is the TBolt correct out
the OCXO TC.
You could go crazy with auto correlation stuff, but I'm not sure your
measure of the outside temperature is going to be good enough to make more
than an eyeball approach useful.
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.
Ultimately what you would like is a setup that never needs to change the EFC
(much), so you could run a nice long loop and still have the PPS stay lined
up. That *should* give you a significant improvement in short term out of
the TBolt. Since it's done with the EFC plot and verified with a cheap
thermometer (rather than a bunch of crazy to find gear) it's a reasonable
basement Time Nut thing to do.
Certainly should add that without all the work done on Lady Heather, you
wouldn't have a chance of doing any of this. Can't eyeball a plot you don't
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Mark Sims
Sent: Thursday, January 27, 2011 7:05 AM
To: time-nuts at febo.com
Subject: [time-nuts] Temperature stability for Thunderbolt: results
With the temperature stabilized, compared to just 1 degree swings in
temperature I see a 10 times improvement in the 1PPS standard deviation,
and a 3 times improvement in the oscillator and dac control voltage.
Between that data and LH's EFC plot you should have some pretty good
information on just how much the temperature control is helping.
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