[time-nuts] Tbolt issues

Charles Steinmetz csteinmetz at yandex.com
Sat Sep 10 06:40:43 EDT 2016

Bert wrote:

>  would you please share your settings, this is exactly what we are  looking
>  for. We are doing it by trial and error but your expertise will help greatly.

Well, I spent the holiday weekend looking for the "safe place" where I 
recorded my final Tbolt tuning parameters -- without success.  After I 
tuned them and qualified them as fit for long-term duty, I disconnected 
the com ports and stashed them away in a very quiet and hard to access 
location with just the 10MHz coax connected, so I can't use the comms to 
extract the parameters without disturbing the Tbolts (which have now 
settled nicely, undisturbed for ~10 years).

But what I did wasn't rocket science -- I just read up on the tuning 
parameters, determined which ones would likely affect the stability of 
the 10MHz output, made some educated guesses about the likely best 
settings, and started playing.  It took me several weeks of 
experimentation (on and off), and the parameters I settled on were 
somewhat different between the two units I kept (primarily, the loop 
time constant and damping, which ideally should be set to complement the 
particular OCXO in each unit).

I recommend extreme caution when you hear suggestions to use low loop 
damping, or to monkey very much with the oscillator scale factor.  I 
found that high damping (far above the 1.2 default value) worked best 
for my units.  (Like you, I care most about the stability and accuracy 
of the 10MHz output.  I don't even have the PPS turned on.)

Before you do anything else, I strongly suggest a full factory reset to 
put everything into a known state, and work from there.

You have received some advice to use the "autotune" routine in Lady 
Heather.  I seem to recall several people reporting that it worked well 
for them, and there is nothing to lose by trying it.  However, in my 
case it screwed up the tuning of both units so badly that I had to do 
factory resets and then re-enter my custom parameters.  I might have 
been using a version of LH that didn't have the latest autotune code, or 
perhaps the autotune function needs to start from factory default 
settings, or maybe the phase of the moon was wrong -- but I was sure 
glad I had recorded the tuning parameters I worked out by experiment, so 
I didn't have to start over again!  Just be prepared to do another 
factory reset and start experimenting if autotune doesn't work to your 

So, I would suggest: (1) do a full factory reset, let it run for a few 
weeks, and take data; (2) use the autotune routine, let it run for a few 
weeks, and take data.  If you are not satisfied with the results at this 
point, (3) do another full factory reset and begin experimenting manually.

Best regards,


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