Re: [time-nuts] Lady Heather's Tbolt oscillator auto-tune function

[ws at Yahoo via time-nuts]

If you have a good antenna setup and a constant temperature environment:

The way to get the lowest noise over short time periods on a TBolt is to set
the TC setting as high as you can (typically 500 to 1000+), and set the
Damping factor as fast as you can (typically 0.7 to 1).

The reason is that the Tbolt has a simple basic PI phase lock loop
controller.
The Proportional gain is a function of 1/TC and the Integrator gain is a
function of the damping.
The Problem is that the GPS phase error signal is a noisy thing with short
and long term peak variations of about 10ns. 

Any GPS phase noise is directly fed thru to the Dac output scaled by the "P"
Gain.
With a 10 ns phase noise step and a 100sec TC, the "P" gain will change the
oscillator freq by 1e-10, on the very next one sec Dac update.
This is not done to keep the time correct; it is needed to correct the
Frequency in the desired time constant period.

This then causes the continuous up to 1e-10 freq steps, with the factory
default setting, the effect of which can be seen by plotting the DAC
voltage.
If the TC is made twice as long then the Dac noise step size is 1/2, etc.
If you have a good setup and a low ADEV osc at long time constants, then the
longer the TC, the better the short term Peak freq noise will be.
If you want the "Dac P-gain freq noise" peak to be under 1e-11 then the TC
must be set >1000sec. (which then needs to use the extended TC method)

Where as the Damping setting controls the integrator gain and its effect is
filtered and non linear. A change in damping from say 2.0 to 0.7 will
increase the Dac noise by up to only 25% but reduce the setting time by over
10 to one.


>Bert posted:
>For our work frequency has to be better than 1xE-11 one second.
>Unless someone can help us with settings we will not revisit Tbolt.

The attached shows that a modified Tbolt can do 1 sec freq error of about
1e-11 peak over most of this 2hr run. The 1 sec ADEV of this run was about
1e-12.
Sounds like best to go back to your previous system, because you are not
going to get there by randomly changing the settings.


ws



>> A damping setting in a Tbolt of greater than 2 is not a good idea.

>It is if one is only concerned about frequency stability and accuracy 
>and wants the best performance that can be obtained at tau < about 10 
>seconds.

>> And a TC setting of >1000 is not a good idea unless using the 'extended
>>TC' method.
>I did not suggest setting the TC >1000. 

>Best regards,
>Charles

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[time-nuts] Lady Heather's Tbolt oscillator auto-tune function

[Mark Sims]

I just ran a tbolt (which has been off for a couple of months) and logged the 
state for a couple of hours...  and then remembered something about the initial 
DAC value setting that I had figured out long ago... it has little to nothing 
to do with oscillator disciplining.The tbolt drives the GPS from the 10 MHz 
ocxo.  If the ocxo is too far off freq it can't track satellites.   The initial 
dac setting is used to speed up acquisition of satellites and not to speed up 
the OCXO disciplining loop lock.

As soon as a satellite is acquired (after a couple of minutes), the DAC voltage 
jumps and the disciplining starts.  A few seconds later when more sats are 
tracked, it gets underway in earnest (and by then the OCXO is warm enought to 
be within 0.1 Hz).  After 1 hour the box temperature has stabilized and the 
freq is within a couple of milli Hz.  After two hours the oscillator has 
settled down to the point where the DAC curve goes into "wandering around" 
instead of following  a smooth decay compensating for the oscillator warm-up.  
The attached image show the first hour of the process.
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Re: [time-nuts] Lady Heather's Tbolt oscillator auto-tune function

[Charles Steinmetz]

Warren wrote:


A damping setting in a Tbolt of greater than 2 is not a good idea.


It is if one is only concerned about frequency stability and accuracy 
and wants the best performance that can be obtained at tau < about 10 
seconds.



And a TC setting of >1000 is not a good idea unless using the 'extended TC'
mode.


I did not suggest setting the TC >1000.  My suggesetion was to set the 
"recovery" mode "max offset frequency" (the furthest the Tbolt will 
allow the oscillator to go off frequency in order to correct the PPS 
phase) in that range.  That only affects recovery (speeds it up), it 
doesn't do anything during normal operation.  It may not need to be 
>1000, 100 may be plenty.  I do not recall exactly where mine ended up.


Best regards,

Charles


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Re: [time-nuts] Tbolt issues

[ewkehren via time-nuts]

Know all that that is why we decided not to do it. Not knowing all the ins and 
outs and limits of the Tbolts that is why I asked the question to begin with
Bert Kehren




Sent from Samsung tabletCharles Steinmetz  wrote:Bert 
wrote:

> On our to do list was temperature control and clean up loop.  In order to do
> an analog clean up we need short interval changes and that is why  I went
> on the list since we have not been able to do it and looking at past  posting
> have not found data that will get us there.

To do any kind of "cleanup" at tau=1S, you need a source that is better 
at that tau than the one you are trying to clean up.  But if you have 
that, why use it to clean up something else?  Just use it as your 
standard.  (One might respond that the point would be to use the Tbolt 
to discipline the better oscillator at longer tau to correct drift, but 
you would need a very long time constant -- thousands of seconds -- 
which you cannot achieve with an analog loop.)  I do not think there is 
any realistic possibility of doing the kind of cleanup you propose in 
the analog domain.

Are you absolutely certain you tried the Tbolt with the damping set to 
10 seconds or more?  Did you let it settle for several weeks before 
deciding it wasn't doing what you need?

Perhaps you can try one last time:

1. Do a hard reset back to factory settings
2. Change TC to 500 seconds and damping to 10-12
3. Set recovery jam synch to "ON" with a threshold of 55-65 nS
4. Set recovery max offset frequency to >=1000 (this is in ppb)
5. Put it in an undisturbed location, inside a box of some kind
6. Let it sit for a month
7. Now, measure it

If this is better, but not quite good enough, try damping settings of 30 
and 100.

Alternatively, for a 10MHz reference you can just forget about and use, 
buy another PRS10 and discipline it with the PPS from the Tbolt.  I'd 
recommend buying a new one from SRS so you know that it has the PPS 
discipline feature and you could get help from SRS to optimize the 
discipline for your needs (the discipline is very adjustable and it is 
easy to get confused).

Best regards,

Charles


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Re: [time-nuts] Lady Heather's Tbolt oscillator auto-tune function

[Bob Camp]

Hi

> On Sep 11, 2016, at 11:04 AM, Charles Steinmetz  wrote:
> 
> I wrote:
> 
>>> Actually, for best results from a cold start, it is best to set  the 
>>> initial DAC voltage to whatever voltage produces 10.0 MHz *when the 
>>> oven is cold*.
> 
> Bob replied:
> 
>> …… errr … that’s pretty far off :) DAC at 10 or 20 minutes is probably the 
>> target.
> 
> No, DAC for 10.0 MHz with a stone cold oven is best for cold starts.  
> This setting is still best even if the oven is partly warm, because the loop 
> is moving the DAC in the same direction it needs to go -- it can "catch up" 
> gracefully without racing in the wrong direction in full saturation to meet 
> the crystal as it warms up, then banging back and forth from saturation in 
> one direction to saturation in the other direction before finally leveling 
> out.  It is the damped oscillatory approach to the capture zone, and 
> recovering from saturation (not just once, but multiple times), that slows 
> things down.
> 
> By starting the DAC to produce 10.0 MHz from the cold oven, all that 
> is avoided and the loop just tracks the warming crystal (or, if it can't 
> quite keep up, at least it is moving in the same direction and can catch up 
> gracefully without overshoot -- still much faster than starting from the DAC 
> voltage that produces 10.0 MHz with a fully warm oven).
> 
> Trust me, I tried all of this experimentally and know whereof I speak.
> 

To me, “stone cold oven” = OCXO has been off power for > 24 hours and the 
entire internal structure is at ambient. That might be 25C, it might be 
something else. You applied power about 2 seconds ago and you have an output. 
The oven is now beginning to warm up to some temperature in the 80C to 120C 
range. 

It’s an SC cut crystal. When the oven is at 25C (or worse, even colder) the 
frequency is off by > 30 ppm. The tuning range of the DAC is *maybe* a couple 
of ppm. Effectively, with an un-heated oven, there is no DAC setting. The DAC 
is railed and you still are not on 10 MHz exactly. As the oven warms up, the 
frequency is changing at ppm’s / minute sort of rates. You are not going to be 
able to follow that with the TBolt loop. As a practical matter, you have to let 
the oven warm up a bit before there even is a DAC voltage. You have to let it 
warm up a bit past the "EFC in range” point to be able to begin the lock 
process. That is likely to be some number of minutes (5, 10, 15) past the point 
that you apply power to a cold OCXO. 

My guess is that we have different interpretations of the term “stone cold 
oven”. 

Bob


> Best regards,
> 
> Charles
> 
> 
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[time-nuts] TM7000 Manual?

[Bruce Lane]

Fellow Clock-tickers,

Has anyone ever found a PDF of the manual for the Datum/Symmetricom
'TymMachine' TM7000? Googling has, so far, turned up nothing more than
the near-useless data sheet, and Microsemi's site doesn't seem to have
anything either (unless I missed it).

Thanks.

-- 
---
Bruce Lane, ARS KC7GR
http://www.bluefeathertech.com
kyrrin (at) bluefeathertech dot com
"Quando Omni Flunkus Moritati" (Red Green)
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Re: [time-nuts] Lady Heather's Tbolt oscillator auto-tune function

[Charles Steinmetz]

I wrote:


Actually, for best results from a cold start, it is best to set  the initial 
DAC voltage to whatever voltage produces 10.0 MHz *when the oven is 
cold*.


Bob replied:


…… errr … that’s pretty far off :) DAC at 10 or 20 minutes is probably the 
target.


No, DAC for 10.0 MHz with a stone cold oven is best for cold 
starts.  This setting is still best even if the oven is partly warm, 
because the loop is moving the DAC in the same direction it needs to go 
-- it can "catch up" gracefully without racing in the wrong direction in 
full saturation to meet the crystal as it warms up, then banging back 
and forth from saturation in one direction to saturation in the other 
direction before finally leveling out.  It is the damped oscillatory 
approach to the capture zone, and recovering from saturation (not just 
once, but multiple times), that slows things down.


By starting the DAC to produce 10.0 MHz from the cold oven, all 
that is avoided and the loop just tracks the warming crystal (or, if it 
can't quite keep up, at least it is moving in the same direction and can 
catch up gracefully without overshoot -- still much faster than starting 
from the DAC voltage that produces 10.0 MHz with a fully warm oven).


Trust me, I tried all of this experimentally and know whereof I speak.

Best regards,

Charles


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Re: [time-nuts] Tbolt issues

[Charles Steinmetz]

Bert wrote:


On our to do list was temperature control and clean up loop.  In order to do
an analog clean up we need short interval changes and that is why  I went
on the list since we have not been able to do it and looking at past  posting
have not found data that will get us there.


To do any kind of "cleanup" at tau=1S, you need a source that is better 
at that tau than the one you are trying to clean up.  But if you have 
that, why use it to clean up something else?  Just use it as your 
standard.  (One might respond that the point would be to use the Tbolt 
to discipline the better oscillator at longer tau to correct drift, but 
you would need a very long time constant -- thousands of seconds -- 
which you cannot achieve with an analog loop.)  I do not think there is 
any realistic possibility of doing the kind of cleanup you propose in 
the analog domain.


Are you absolutely certain you tried the Tbolt with the damping set to 
10 seconds or more?  Did you let it settle for several weeks before 
deciding it wasn't doing what you need?


Perhaps you can try one last time:

1. Do a hard reset back to factory settings
2. Change TC to 500 seconds and damping to 10-12
3. Set recovery jam synch to "ON" with a threshold of 55-65 nS
4. Set recovery max offset frequency to >=1000 (this is in ppb)
5. Put it in an undisturbed location, inside a box of some kind
6. Let it sit for a month
7. Now, measure it

If this is better, but not quite good enough, try damping settings of 30 
and 100.


Alternatively, for a 10MHz reference you can just forget about and use, 
buy another PRS10 and discipline it with the PPS from the Tbolt.  I'd 
recommend buying a new one from SRS so you know that it has the PPS 
discipline feature and you could get help from SRS to optimize the 
discipline for your needs (the discipline is very adjustable and it is 
easy to get confused).


Best regards,

Charles


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[time-nuts] Ovenaire OSC 49-56b OCXO

[Jeff AC0C]

Looking for data on this OCXO.  No other markings than “Precision Crystal 
Oscillator” and the serial.  If you have anything, appreciate it.  Thanks.

73/jeff/ac0c
www.ac0c.com
alpha-charlie-zero-charlie

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Re: [time-nuts] Lady Heather's Tbolt oscillator auto-tune function

[ws at Yahoo via time-nuts]

A cold oven freq is off by hundred's by Hz, Much much greater than the range
of the Dac
The TBolt does not start tuning until it's oven has warmed up.
Setting anything in the Tbolt biased on cold start turn-on is counter
productive. It takes days or weeks for it settle down.
At initial turn-on and when returning from a lost signal drop-out if the
phase is off, the Tbolts enters a fast Dac slue tune mode that sets the
phase and then the Freq to zero cross before entering its normal mode. 
Because of these, it does not mater in the least what the Dac is set to at a
cold start.
A damping setting in a Tbolt of greater than 2 is not a good idea.
And a TC setting of >1000 is not a good idea unless using the 'extended TC'
mode.
. . .



ws
 
*  

>> Actually, for best results from a cold start, it is best to set the
initial DAC voltage to whatever voltage produces 10.0 MHz *when the
oven is cold*.

Bob replied:

> .. errr . that's pretty far off :) DAC at 10 or 20 minutes is probably the
target.

No, DAC for 10.0 MHz with a stone cold oven is best for cold 
starts.  This setting is still best even if the oven is partly warm, 
because the loop is moving the DAC in the same direction it needs to go 
-- it can "catch up" gracefully without racing in the wrong direction in 
full saturation to meet the crystal as it warms up, then banging back 
and forth from saturation in one direction to saturation in the other 
direction before finally leveling out.  It is the damped oscillatory 
approach to the capture zone, and recovering from saturation (not just 
once, but multiple times), that slows things down.

By starting the DAC to produce 10.0 MHz from the cold oven, all 
that is avoided and the loop just tracks the warming crystal (or, if it 
can't quite keep up, at least it is moving in the same direction and can 
catch up gracefully without overshoot -- still much faster than starting 
from the DAC voltage that produces 10.0 MHz with a fully warm oven).

Trust me, I tried all of this experimentally and know whereof I speak.

Best regards,

Charles




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Re: [time-nuts] Lady Heather's Tbolt oscillator auto-tune function

[Bob Camp]

Hi

> On Sep 11, 2016, at 3:35 AM, Charles Steinmetz  wrote:
> 
> Mark wrote:
> 
>> Here's a little info on Lady Heather's oscillator autotune function for the 
>> Thunderbolt GPSDO
> 
> Thanks, Mark, that is very helpful.
> 
> Accordingly, for people interested in best frequency accuracy and stability, 
> I suggest (1) running autotune, then (2) manually setting damping to around 
> 10, and (3) setting the holdover recovery parameters manually as I described 
> in my last post (jam synch at 65-75nS and allow a large frequency error in 
> recovery mode).  The value autotune sets for loop time constant (500 seconds) 
> is a good starting point for Tbolts with the Trimble p/n 37265 OCXO.  A 
> particular Tbolt may respond to further optimization by tweaking the TC to 
> match the individual OCXO (by trial and error -- Plot ADEV, adjust TC, plot 
> ADEV, adjust TC, etc.), but the improvement will most likely be subtle.  You 
> should also review the elevation mask settings and adjust if necessary.
> 
>> Since the unit should be locked and stable, the current DAC setting is where 
>> the oscillator is at 10.000 MHz and will be set in EEPROM as the initial 
>> DAC setting. The tbolt uses this value to speed up locking the oscillator 
>> when powering up.
> 
> Actually, for best results from a cold start, it is best to set  the initial 
> DAC voltage to whatever voltage produces 10.0 MHz *when the oven is 
> cold*.

…… errr … that’s pretty far off :) DAC at 10 or 20 minutes is probably the 
target. 

>  Setting it to the voltage that produces 10.0 MHz when the oven is 
> warm guarantees that it is set wrong when the oven is cold, so on a cold 
> start the loop immediately goes into saturation to slew the DAC to the 
> voltage that does produce 10.0 MHz.  This slows down locking by quite 
> a bit.  Setting the initial DAC voltage so that the frequency is 10.0 
> MHz with a cold oven allows the loop to slowly adjust the DAC as the oven 
> warms up, rather than racing off at full speed to meet the warming crystal.  
> This speeds up locking from a cold start very substantially.
> 
> It is not clear to me how one could automate this process -- I found the 
> correct DAC settings by trial and error.  Ideally, this would be determined 
> every time the Tbolt does a cold start and the new value would take into 
> account any crystal drift since it was last set.  But LH has no way to tell 
> that any given start is a cold start (AFAIK), and it would want to determine 
> the correct cold-oven DAC voltage very quickly after power-up from a known 
> cold start (say, within 10 seconds).  It would be great if Tbolts had an oven 
> on/off command, but to my knowledge they don't.  LH could possibly give the 
> user instructions ("OK, now power down the Tbolt for at least 30 minutes.  
> When the Tbolt is fully cold, click the RESUME button below and then re-apply 
> power to the Tbolt...”).

…. It’s a little worse than that :)

Temperature does indeed get into the act, what was the temperature when the DAC 
setting was recorded, what is it now, what is the frequency vs temperature on 
that assembly? One could do a temperature run (or series of runs) and save the 
data. There are OCXO’s done that way. 

Exactly how long has the OCXO been off? There is a difference between 3 hours 
and 5 hours. Similarly there is a difference between one day and a week.

What temperature (and humidity and …) has the assembly been at while off? 
Temperature will impact the sealed OCXO. The parts on the board most certainly 
are sensitive to humidity. 

Did something weird happen? Was the unit rotated? (2g tip does matter). Was it 
dropped? Was it shaken around? There are a number of weird things that *could* 
happen. Some OCXO’s get acceleration compensated to take care of this. 

Is it the DAC at 5, 10, 15 or 60 minutes? The OCXO is moving pretty fast right 
after it turns on. For instance, the FE 405’s compensate for this in firmware. 

That’s a short list, one could easily double it in length. 

=

The *simple* answer is to use software. Rather than having the TBolt in one 
mode all the time, change it’s parameters when it first turns on. Give it a 
shorter TC and get it stabilized. Then feed it the “real” TC and let it go from 
there. I have absolutely no idea how a TBolt responds when you do this. I do 
have a lot of data on how other vendors parts respond when this takes place. In 
general it works pretty well.

Bob


> 
> Best regards,
> 
> Charles
> 
> 
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Re: [time-nuts] Tbolt issues

[Bert Kehren via time-nuts]

 
Yes Charles  
I was not part of or following the original Tbolt  discussions. My setup at 
the time was Loran C with Austron 2110, backed up with  Cs and 60 Khz using 
a Tracor 599H. My work was focused on FRK FRS Rb’s using  Shera with very 
good results. At the same time Juerg was using a PRS10  controlled by a Tbolt 
and feeding a OSA FO3/8600. With the demise of Loran C I  switched to Tbolt 
feeding the 2110 because I did see the frequency jumps.  Juerg’s PRS10 died 
a year ago and he replaced it with his Tbolt, expecting the  FO3 to clean 
up the Tbolt. After disappointing results on some of our work urged  him to 
do a cross matrix on all his sources and found out the FO3 did nothing to  
the Tbolt He bought his first one through Tarp. I bought 1 for him and 2 for 
me  all US sellers.  
Off list Tom has looked at Juergs data and we and he are  convinced that 
antenna and equipment is good. We have used auto tune and  variable settings. 
On our to do list was temperature control and clean up loop.  In order to do 
an analog clean up we need short interval changes and that is why  I went 
on the list since we have not been able to do it and looking at past  posting 
have not found data that will get us there. For our work frequency has  to 
be better than 1 E-11 one second, he had it with the PRS 10 setup. Unless  
some one can help us with settings that make analog loop clean up possible we 
 will not revisit Tbolt. Juerg will use it as an excellent 1pps source and 
I will  use it with the 2110 which is digital and has a 100 second  loop.We  
are already refocusing on work on a FRK/M100 GPSDO plan on having it up and 
 running with in a month, waiting for boards. Last two years distracted by 
clean  up of the Shera code before releasing it, controller for FE 5680 5650 
and FE  405.  
 
 
In a message dated 9/10/2016 5:48:49 P.M. Eastern Daylight Time,  
csteinm...@yandex.com writes:

Bert  wrote:

> Looks like we are not the only ones trying to improve  frequency
> performance and hopefully some one will share  settings.

You are coming very late to the Tbolt party.  There was  a veritable 
blizzard of posts about optimizing Tbolt performance, which  began maybe 
10 or 11 years ago (??) and lasted for several years, and a  steady 
trickle since then.  Everything that is possible to be said  was posted, 
often several times.  Go back in the list archives and  read this 
material -- it will answer all of your questions (and lots more  that you 
haven't asked yet).

Best  regards,

Charles


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Re: [time-nuts] ke5fx.com - something's up

[John Miles]

Yep.  It should be all good now (once the DNS records propagate.)

-- john, KE5FX

> Domain name expired on September 8th - needs renewing!
> 
> On 11/09/2016, at 10:48 AM, Nick Sayer via time-nuts wrote:
> 
> > I tried to look for Lady Heather docs today, but it appears like the ke5fx
> domain is… funky.
> >
> > The name servers are NS1.PENDINGRENEWALDELETION.COM and there are
> other indications that maybe the domain lapsed…?
> 

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Re: [time-nuts] Lady Heather's Tbolt oscillator auto-tune function

[Charles Steinmetz]

Mark wrote:


Here's a little info on Lady Heather's oscillator autotune function for the 
Thunderbolt GPSDO


Thanks, Mark, that is very helpful.

Accordingly, for people interested in best frequency accuracy and 
stability, I suggest (1) running autotune, then (2) manually setting 
damping to around 10, and (3) setting the holdover recovery parameters 
manually as I described in my last post (jam synch at 65-75nS and allow 
a large frequency error in recovery mode).  The value autotune sets for 
loop time constant (500 seconds) is a good starting point for Tbolts 
with the Trimble p/n 37265 OCXO.  A particular Tbolt may respond to 
further optimization by tweaking the TC to match the individual OCXO (by 
trial and error -- Plot ADEV, adjust TC, plot ADEV, adjust TC, etc.), 
but the improvement will most likely be subtle.  You should also review 
the elevation mask settings and adjust if necessary.



Since the unit should be locked and stable, the current DAC setting is where 
the oscillator is at 10.000 MHz and will be set in EEPROM as the initial 
DAC setting. The tbolt uses this value to speed up locking the oscillator when 
powering up.


Actually, for best results from a cold start, it is best to set  the 
initial DAC voltage to whatever voltage produces 10.0 MHz *when 
the oven is cold*.  Setting it to the voltage that produces 10.0 
MHz when the oven is warm guarantees that it is set wrong when the oven 
is cold, so on a cold start the loop immediately goes into saturation to 
slew the DAC to the voltage that does produce 10.0 MHz.  This 
slows down locking by quite a bit.  Setting the initial DAC voltage so 
that the frequency is 10.0 MHz with a cold oven allows the loop 
to slowly adjust the DAC as the oven warms up, rather than racing off at 
full speed to meet the warming crystal.  This speeds up locking from a 
cold start very substantially.


It is not clear to me how one could automate this process -- I found the 
correct DAC settings by trial and error.  Ideally, this would be 
determined every time the Tbolt does a cold start and the new value 
would take into account any crystal drift since it was last set.  But LH 
has no way to tell that any given start is a cold start (AFAIK), and it 
would want to determine the correct cold-oven DAC voltage very quickly 
after power-up from a known cold start (say, within 10 seconds).  It 
would be great if Tbolts had an oven on/off command, but to my knowledge 
they don't.  LH could possibly give the user instructions ("OK, now 
power down the Tbolt for at least 30 minutes.  When the Tbolt is fully 
cold, click the RESUME button below and then re-apply power to the 
Tbolt...").


Best regards,

Charles


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Re: [time-nuts] ke5fx.com - something's up

[Andy ZL3AG]

Domain name expired on September 8th - needs renewing!

On 11/09/2016, at 10:48 AM, Nick Sayer via time-nuts wrote:

> I tried to look for Lady Heather docs today, but it appears like the ke5fx 
> domain is… funky.
> 
> The name servers are NS1.PENDINGRENEWALDELETION.COM and there are other 
> indications that maybe the domain lapsed…?

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