Re: [time-nuts] Heathkit clock available

[Brian Lloyd]

I have a couple of Nixie clock kits I got from pvelectronics.co.uk. They
have a plug in GPS module. No doubt it does not meet time-nuts standards
but to my eye and ear, the tick is spot-on with WWV, which makes it
suitable for setting my watch and knowing when to walk the dogs. With the
Pound Sterling doing so poorly against the dollar, these actually seem like
a pretty reasonable deal.

http://pvelectronics.co.uk

Besides, Nixies are cool.

-- 



Brian Lloyd
706 Flightline
Spring Branch, TX 78070
br...@lloyd.aero
+1.210.802-8FLY (1.210.802-8359)
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Re: [time-nuts] Noisy Sulzer 2.5 - Suggestions?

[Chuck Harris]

My old 2.5A was acting up in strange drifty ways.  I opened the oven, and found
that all of the white cube shaped ceramic capacitors in the oscillator were 
covered
with fuzz on the electrode ends.  I am guessing that they were growing a great
tin whisker beard.  I cleaned it all off, and performance improved greatly.

-Chuck Harris

Ed Palmer wrote:
> I picked up a Sulzer 2.5 (not 2.5A or 2.5B or 2.5C) oscillator and 5P power 
> supply. 
> It's working, but the AlDev at low tau is poor. After a few days of operation 
> the
> AlDev @ 1sec. is only 1e-10.  It's not the power supply.  I'm running under 
> 'AC fail'
> conditions with a lab power supply standing in for the batteries.  This 
> bypasses
> almost everything in the power supply.  Eventually, I plan to replace the 
> batteries
> with lead-acid and replace the circuit board with an improved circuit.
> 
> So, I'll be opening up the oscillator to see what's what.  My first 'usual 
> suspect'
> will be the Ta capacitors, but I'm wondering about all those carbon 
> composition
> resistors.  Should I be looking at a wholesale replacement with metal film?  
> Maybe
> just in the oscillator and AVC areas?  Are there any other known trouble 
> spots with
> these oscillators?
> 
> I haven't been able to find any info on the 2.5.  The manuals and schematics 
> for the
> 5A and the 2.5B/C are some help, but the 2.5 is very different from the 
> 2.5B/C.  Any
> info would be greatly appreciated.
> 
> Thanks,
> 
> Ed
> 
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Re: [time-nuts] Noisy Sulzer 2.5 - Suggestions?

[Ed Palmer]

I was expecting, and I'm seeing, improvements at high values of tau 
(i.e. aging) as time passes, but I've never noticed an improvement at 
low tau on any of my oscillators.  Probably because my measuring 
equipment isn't good enough to see it!  I'll watch for that in the future.


Ed

On 2016-08-17 7:03 PM, Bob Camp  wrote:

Hi

Let it run for a month before you worry much about measuring what it is doing ….
Some (but not all) of those old crystals took a while to settle in.

Bob



>On Aug 17, 2016, at 4:25 PM, Ed Palmer  wrote:
>
>I picked up a Sulzer 2.5 (not 2.5A or 2.5B or 2.5C) oscillator and 5P power 
supply.  It's working, but the AlDev at low tau is poor. After a few days of 
operation the AlDev @ 1sec. is only 1e-10.  It's not the power supply.  I'm 
running under 'AC fail' conditions with a lab power supply standing in for the 
batteries.  This bypasses almost everything in the power supply.  Eventually, I 
plan to replace the batteries with lead-acid and replace the circuit board with an 
improved circuit.
>
>So, I'll be opening up the oscillator to see what's what.  My first 'usual 
suspect' will be the Ta capacitors, but I'm wondering about all those carbon 
composition resistors.  Should I be looking at a wholesale replacement with metal 
film?  Maybe just in the oscillator and AVC areas?  Are there any other known 
trouble spots with these oscillators?
>
>I haven't been able to find any info on the 2.5.  The manuals and schematics 
for the 5A and the 2.5B/C are some help, but the 2.5 is very different from the 
2.5B/C.  Any info would be greatly appreciated.
>
>Thanks,
>
>Ed


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Re: [time-nuts] Noisy Sulzer 2.5 - Suggestions?

[paul swed]

Ed,
Thats quite the challenge and yes the carbon resistors must be about 50
years old now. So questioning them is reasonable. I have a c so take my
next comment with caution.
The oscillator is a small circuit and then it runs to buffers and
multipliers and stuff.
Lots of parts of every type. Maybe it makes sense to isolate and measure
just the oscillator circuit to see how it behaves without all of the other
stuff. Also there were various regulators in that can. Lots of
possibilities for trouble. But also worth the effort to figure it out.
Great old oscillators.
Regards
Paul
WB8TSL


On Wed, Aug 17, 2016 at 4:25 PM, Ed Palmer  wrote:

> I picked up a Sulzer 2.5 (not 2.5A or 2.5B or 2.5C) oscillator and 5P
> power supply.  It's working, but the AlDev at low tau is poor. After a few
> days of operation the AlDev @ 1sec. is only 1e-10.  It's not the power
> supply.  I'm running under 'AC fail' conditions with a lab power supply
> standing in for the batteries.  This bypasses almost everything in the
> power supply.  Eventually, I plan to replace the batteries with lead-acid
> and replace the circuit board with an improved circuit.
>
> So, I'll be opening up the oscillator to see what's what.  My first 'usual
> suspect' will be the Ta capacitors, but I'm wondering about all those
> carbon composition resistors.  Should I be looking at a wholesale
> replacement with metal film?  Maybe just in the oscillator and AVC areas?
> Are there any other known trouble spots with these oscillators?
>
> I haven't been able to find any info on the 2.5.  The manuals and
> schematics for the 5A and the 2.5B/C are some help, but the 2.5 is very
> different from the 2.5B/C.  Any info would be greatly appreciated.
>
> Thanks,
>
> Ed
>
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[time-nuts] Lady Heather Data Explained?

[Mark Sims]

Well,  what now gets shown / plotted depends upon the receiver type.

For Thunderbolts the standard plots are the DAC (EFC) volatge,  temperature 
sensor reading,  and the PPS and OSC offset values from the primary timing 
message (the OSC plot defaults to OFF since it generally looks like a lot of 
annoying noise).  If you cozy up with a copy of the Thunderbolt manual, you 
should be able to figure out that the various values shown mean.

Lady Heather calculates and displays plots of the ADEV values of the PPS and 
OSC readings.  These don't have a whole lot of correlation to true ADEV values 
since they are not referenced to an independent reference (the idea for 
including the ADEV stuff was to eventually interface to an external time 
interval counter).  Despite that,  the ADEV values can give you and idea of how 
well the unit is working (particularly when the unit is configured with 
disciplining turned off).   
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Re: [time-nuts] GPSDO - probably a stupid question.

[Bob Camp]

Hi

A mixer style phase detector running a GHz range oscillator is one example of a 
system that technically updated the EFC several billion times a second. There 
does not have to be a DAC involved. 

The point is still looking at the noise characteristics of the oscillator and 
the reference. 
It is best done in the frequency domain as phase noise. We substitute ADEV, but 
that
is not an ideal proxy. Either way you want the loop to cross over from one to 
the other 
somewhere in the vicinity of the “equal noise” point if it exists. If there is 
no equal noise
point, that makes you wonder a bit about why you are locking one to the other 
:) 

Taking ADEV, since that’s what we have the data on:

GPS starts out somewhere in the 20 ns to 0.2 ns range at 1 second depending on 
what 
you are looking at, which module you are using, and who you trust for your 
data. That 
compares to a good OCXO that should be in the 0.001 ns range at 1 second. There 
is a 
long way to go (larger time span) before the OCXO and GPS are anywhere near 
the same noise level. You will need to get to 200 seconds with the best GPS 
numbers above.
You will need to get to 100X that with the worst ones. Yes, there is a bit of 
hand waving
in all of that. 

Bob

> On Aug 17, 2016, at 6:14 PM, Nick Sayer via time-nuts  
> wrote:
> 
> Well, on a practical level, if you update the EFC that frequently then the 
> DAC change glitches will dominate the actual output even if you’re not 
> actually moving the needle much. 
> 
> 
>> On Aug 17, 2016, at 2:53 PM, Bob kb8tq  wrote:
>> 
>> Hi
>> 
>> You can update the EFC a billion times a second.  Update rate and bandwidth 
>> are not the same thing. If you want good ADEV, the loop better not have a 
>> bandwidth greater than 0.01 Hz. GPS ADEV is pretty awful at 1 and 10 
>> seconds. It is starts to be good past a few thousand seconds. Yes, older 
>> modules are a bit worse than newer ones. Also sawtooth correction can make 
>> things a bit better.
>> 
>> Bob
>> 
>> Sent from my iPad
>> 
>>> On Aug 17, 2016, at 2:51 PM, Nick Sayer via time-nuts  
>>> wrote:
>>> 
>>> Updating the EFC more quickly reduces the ADEV, though. I find that the 
>>> fiddly part of tuning a GPSDO design is balancing the ADEV against phase 
>>> control. If you want keep an iron fist on the phase, you can only do so by 
>>> constantly swatting around the frequency.
>>> 
>>> I won't say that getting more frequent phase feedback is a bad thing, but 
>>> if you're trying to get the PLL time constant to be longer rather than 
>>> shorter that it won't help a lot. 
>>> 
>>> Sent from my iPhone
>>> 
 On Aug 17, 2016, at 9:57 AM, Peter Reilley  
 wrote:
 
 You can get crystal oscillators that have a frequency control signal and 
 are more
 stable than the run of the mill oscillators.   Changing the GPS oscillator 
 would
 require modifying a very tightly populated circuit board.   Perhaps not 
 possible.
 
 What about some of the SDR (software defined radio) projects that aim to
 implement GPS functionality?   If you used the GPS chipping rate (1.023 
 MHz)
 to dicipline the 10 MHz oscillator then you are less sensitive to crystal 
 instabilities.
 You are updating the crystal one million times a second rather than once 
 per second.
 This is assuming that the chipping rate of the transmitter is just as good 
 as the
 1 PPS signal.   This info from here;
 https://www.e-education.psu.edu/geog862/node/1753
 and here;
 https://en.wikipedia.org/wiki/GPS_signals
 
 Even using the 50 bits/sec data rate of the GPS signal would allow 
 updating the
 GPSDO faster than the 1 PPS signal.
 
 Pete.
 ___
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 To unsubscribe, go to 
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>>> 
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Re: [time-nuts] Lady Heather Data Explained?

[Jeff AC0C]

I appreciate Richard's query also.  Not sure what I'm looking at on my 
screen either.  Fantastic eye candy!   I assume that seeing "discipline OK" 
and "phase locked" is likely a very good thing and in the first order 
approximation, that means things are as they should be.


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

-Original Message- 
From: William H. Fite

Sent: Wednesday, August 17, 2016 2:20 PM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] Lady Heather Data Explained?

The phrase, "ill documented' comes to mind. It is a wonderful piece of
software but opaque and intimidating to the newbie.


On Wednesday, August 17, 2016, Richard Mogford > wrote:


Does anyone have a description of the various types of data on the Lady
Heather user interface?

I can figure out some of it, but still have some questions.

For example, what are the data being graphed on the moving time chart?

Richard
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--
If you gaze long enough into the abyss, your coffee will get cold.
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Re: [time-nuts] GPSDO - probably a stupid question.

[KA2WEU--- via time-nuts]

There are no (rarely maybe ) stupid questions, mostly silly answers 
 
 
In a message dated 8/17/2016 5:03:07 P.M. Eastern Daylight Time,  
elfchief-timen...@lupine.org writes:

Wouldn't  you also not be able to actually sync to the individual chips, 
since you  can't really see the start of any given chip so much as you 
just see the  correlation over larger sections of the stream? Plus you'd 
have to track  only one SV at a time (right? Since I doubt the edges of 
every chip are  perfectly aligned across all SVs even under the best 
conditions), so  things like brief multipath excursions or even 
atmospheric/ionospheric  fluctuations would push you off by a bit as well...

(which is why, of  course, you have the long control loop that GPSDOs  use)

-j


On 2016-08-17 11:41 , Didier Juges wrote:
> In  fact, you do not want to "update the crystal one million  
times/second".
> The whole point of a GPSDO is to combine the excellent  short term 
stability
> of the crystal with the excellent long term  stability of the GPS signal. 
If
> you update the crystal in real time  from the GPS data, you do not need 
the
> crystal...
> The control  loop of GPSDOs usually have an effective bandwidth measured 
in
> minutes  or even hours in the case of rubidium oscillators.
>
>
> On  Wed, Aug 17, 2016 at 11:57 AM, Peter Reilley  

> wrote:
>
>> You can  get crystal oscillators that have a frequency control signal and
>>  are more
>> stable than the run of the mill oscillators.Changing the GPS 
oscillator
>> would
>> require modifying a  very tightly populated circuit board.   Perhaps not
>>  possible.
>>
>> What about some of the SDR (software defined  radio) projects that aim to
>> implement GPS  functionality?   If you used the GPS chipping rate  (1.023
>> MHz)
>> to dicipline the 10 MHz oscillator then  you are less sensitive to 
crystal
>> instabilities.
>> You  are updating the crystal one million times a second rather than  
once
>> per second.
>> This is assuming that the chipping  rate of the transmitter is just as 
good
>> as the
>> 1 PPS  signal.   This info from here;
>>  https://www.e-education.psu.edu/geog862/node/1753
>> and  here;
>>  https://en.wikipedia.org/wiki/GPS_signals
>>
>> Even using  the 50 bits/sec data rate of the GPS signal would allow
>> updating  the
>> GPSDO faster than the 1 PPS signal.
>>
>>  Pete.
>>
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Re: [time-nuts] GPSDO - probably a stupid question.

[Magnus Danielson]

Hi,

I agree.

There is however a subtle detail, how they leak out over time.

At one time we had to lock an 155,52 MHz oscillator up to 8 kHz, this 
for a 2,48832 Gb/s link, which needs to pass the SDH STM-16 jitter and 
wander specifications. The first attempt at that PLL was using a 4046, 
and the charge-pump was being used. The charge-pump has dead-time, and 
well, they thought it was good to only push the EFC here and there. What 
this meant was that they created a triangle-waved frequency modulation 
of low rate, which then created phase modulations as it went through the 
integration of the oscillator. The scale-up factor made this quite 
noticeable at the actual bit-rate. It made the point that you need to 
update often to keep deviations limited, and when doing it at a higher 
frequency, they are easier to filter out.


In essence, you need to think what each comparison or update creates as 
a step response and how it is averaged out over time.


In this regard a PWM is a really bad signal, as it can push the 
strongest amplitude at the lowest frequency, which becomes hardest to 
filter. For one design I needed to increase the resolution, so I made an 
interpolation but with inversed spectral density to that of PWM, to push 
the highest amplitude to the highest frequency so that filtering becomes 
easier. Turned out to be quite easy and work well.


High update rates can be very useful even if the bandwidth of the loop 
is low. The bandwidth only limits how low the updaterate can be, but the 
phase-noise purity makes update rates and smoothing mechanisms interesting.


Cheers,
Magnus

On 08/17/2016 11:53 PM, Bob kb8tq wrote:

Hi

You can update the EFC a billion times a second.  Update rate and bandwidth are 
not the same thing. If you want good ADEV, the loop better not have a bandwidth 
greater than 0.01 Hz. GPS ADEV is pretty awful at 1 and 10 seconds. It is 
starts to be good past a few thousand seconds. Yes, older modules are a bit 
worse than newer ones. Also sawtooth correction can make things a bit better.

Bob

Sent from my iPad


On Aug 17, 2016, at 2:51 PM, Nick Sayer via time-nuts  
wrote:

Updating the EFC more quickly reduces the ADEV, though. I find that the fiddly 
part of tuning a GPSDO design is balancing the ADEV against phase control. If 
you want keep an iron fist on the phase, you can only do so by constantly 
swatting around the frequency.

I won't say that getting more frequent phase feedback is a bad thing, but if 
you're trying to get the PLL time constant to be longer rather than shorter 
that it won't help a lot.

Sent from my iPhone


On Aug 17, 2016, at 9:57 AM, Peter Reilley  wrote:

You can get crystal oscillators that have a frequency control signal and are 
more
stable than the run of the mill oscillators.   Changing the GPS oscillator would
require modifying a very tightly populated circuit board.   Perhaps not 
possible.

What about some of the SDR (software defined radio) projects that aim to
implement GPS functionality?   If you used the GPS chipping rate (1.023 MHz)
to dicipline the 10 MHz oscillator then you are less sensitive to crystal 
instabilities.
You are updating the crystal one million times a second rather than once per 
second.
This is assuming that the chipping rate of the transmitter is just as good as 
the
1 PPS signal.   This info from here;
https://www.e-education.psu.edu/geog862/node/1753
and here;
https://en.wikipedia.org/wiki/GPS_signals

Even using the 50 bits/sec data rate of the GPS signal would allow updating the
GPSDO faster than the 1 PPS signal.

Pete.
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Re: [time-nuts] Noisy Sulzer 2.5 - Suggestions?

[Bob Camp]

Hi

Let it run for a month before you worry much about measuring what it is doing ….
Some (but not all) of those old crystals took a while to settle in. 

Bob


> On Aug 17, 2016, at 4:25 PM, Ed Palmer  wrote:
> 
> I picked up a Sulzer 2.5 (not 2.5A or 2.5B or 2.5C) oscillator and 5P power 
> supply.  It's working, but the AlDev at low tau is poor. After a few days of 
> operation the AlDev @ 1sec. is only 1e-10.  It's not the power supply.  I'm 
> running under 'AC fail' conditions with a lab power supply standing in for 
> the batteries.  This bypasses almost everything in the power supply.  
> Eventually, I plan to replace the batteries with lead-acid and replace the 
> circuit board with an improved circuit.
> 
> So, I'll be opening up the oscillator to see what's what.  My first 'usual 
> suspect' will be the Ta capacitors, but I'm wondering about all those carbon 
> composition resistors.  Should I be looking at a wholesale replacement with 
> metal film?  Maybe just in the oscillator and AVC areas?  Are there any other 
> known trouble spots with these oscillators?
> 
> I haven't been able to find any info on the 2.5.  The manuals and schematics 
> for the 5A and the 2.5B/C are some help, but the 2.5 is very different from 
> the 2.5B/C.  Any info would be greatly appreciated.
> 
> Thanks,
> 
> Ed
> 
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Re: [time-nuts] GPSDO - probably a stupid question.

[Clint Jay]

Interested to know if anyone has done this with a ublox receiver,  I
spotted the option in some of the technical documents and went as far as
finding a stockist for the external DAC I think it'd need.

On 17 Aug 2016 22:02, "Mark Sims"  wrote:

> The Ublox modules (at least some of them) can support an external
> oscillator and have  messages for controlling oscillator parameters and
> disciplining.
>
> 
>
> > This is actually done.  But you need to design the GPS receiver from the
> ground up to use a very high quality oscillator.   The Thunderbolt is an
> example of this.  It has a 10MHz OCXO used as the internal clock.
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Re: [time-nuts] GPSDO - probably a stupid question.

[Nick Sayer via time-nuts]

Well, on a practical level, if you update the EFC that frequently then the DAC 
change glitches will dominate the actual output even if you’re not actually 
moving the needle much. 


> On Aug 17, 2016, at 2:53 PM, Bob kb8tq  wrote:
> 
> Hi
> 
> You can update the EFC a billion times a second.  Update rate and bandwidth 
> are not the same thing. If you want good ADEV, the loop better not have a 
> bandwidth greater than 0.01 Hz. GPS ADEV is pretty awful at 1 and 10 seconds. 
> It is starts to be good past a few thousand seconds. Yes, older modules are a 
> bit worse than newer ones. Also sawtooth correction can make things a bit 
> better.
> 
> Bob
> 
> Sent from my iPad
> 
>> On Aug 17, 2016, at 2:51 PM, Nick Sayer via time-nuts  
>> wrote:
>> 
>> Updating the EFC more quickly reduces the ADEV, though. I find that the 
>> fiddly part of tuning a GPSDO design is balancing the ADEV against phase 
>> control. If you want keep an iron fist on the phase, you can only do so by 
>> constantly swatting around the frequency.
>> 
>> I won't say that getting more frequent phase feedback is a bad thing, but if 
>> you're trying to get the PLL time constant to be longer rather than shorter 
>> that it won't help a lot. 
>> 
>> Sent from my iPhone
>> 
>>> On Aug 17, 2016, at 9:57 AM, Peter Reilley  wrote:
>>> 
>>> You can get crystal oscillators that have a frequency control signal and 
>>> are more
>>> stable than the run of the mill oscillators.   Changing the GPS oscillator 
>>> would
>>> require modifying a very tightly populated circuit board.   Perhaps not 
>>> possible.
>>> 
>>> What about some of the SDR (software defined radio) projects that aim to
>>> implement GPS functionality?   If you used the GPS chipping rate (1.023 MHz)
>>> to dicipline the 10 MHz oscillator then you are less sensitive to crystal 
>>> instabilities.
>>> You are updating the crystal one million times a second rather than once 
>>> per second.
>>> This is assuming that the chipping rate of the transmitter is just as good 
>>> as the
>>> 1 PPS signal.   This info from here;
>>> https://www.e-education.psu.edu/geog862/node/1753
>>> and here;
>>> https://en.wikipedia.org/wiki/GPS_signals
>>> 
>>> Even using the 50 bits/sec data rate of the GPS signal would allow updating 
>>> the
>>> GPSDO faster than the 1 PPS signal.
>>> 
>>> Pete.
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>> 
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Re: [time-nuts] GPSDO - probably a stupid question.

[Bob kb8tq]

Hi

You can update the EFC a billion times a second.  Update rate and bandwidth are 
not the same thing. If you want good ADEV, the loop better not have a bandwidth 
greater than 0.01 Hz. GPS ADEV is pretty awful at 1 and 10 seconds. It is 
starts to be good past a few thousand seconds. Yes, older modules are a bit 
worse than newer ones. Also sawtooth correction can make things a bit better.

Bob

Sent from my iPad

> On Aug 17, 2016, at 2:51 PM, Nick Sayer via time-nuts  
> wrote:
> 
> Updating the EFC more quickly reduces the ADEV, though. I find that the 
> fiddly part of tuning a GPSDO design is balancing the ADEV against phase 
> control. If you want keep an iron fist on the phase, you can only do so by 
> constantly swatting around the frequency.
> 
> I won't say that getting more frequent phase feedback is a bad thing, but if 
> you're trying to get the PLL time constant to be longer rather than shorter 
> that it won't help a lot. 
> 
> Sent from my iPhone
> 
>> On Aug 17, 2016, at 9:57 AM, Peter Reilley  wrote:
>> 
>> You can get crystal oscillators that have a frequency control signal and are 
>> more
>> stable than the run of the mill oscillators.   Changing the GPS oscillator 
>> would
>> require modifying a very tightly populated circuit board.   Perhaps not 
>> possible.
>> 
>> What about some of the SDR (software defined radio) projects that aim to
>> implement GPS functionality?   If you used the GPS chipping rate (1.023 MHz)
>> to dicipline the 10 MHz oscillator then you are less sensitive to crystal 
>> instabilities.
>> You are updating the crystal one million times a second rather than once per 
>> second.
>> This is assuming that the chipping rate of the transmitter is just as good 
>> as the
>> 1 PPS signal.   This info from here;
>> https://www.e-education.psu.edu/geog862/node/1753
>> and here;
>> https://en.wikipedia.org/wiki/GPS_signals
>> 
>> Even using the 50 bits/sec data rate of the GPS signal would allow updating 
>> the
>> GPSDO faster than the 1 PPS signal.
>> 
>> Pete.
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Re: [time-nuts] Speaking clock

[Didier Juges]

I would like to find an emulator of the old voice synthesizer used in the
Atlanta airport subway. "The next stop is concourse A. The color coded maps
in this vehicle match the station colors." "This vehicle is leaving the
station, please hold on."
They replaced it in 1996 for the Olympics but I remember it as if it was
yesterday...
(I used to travel a lot)

Didier KO4BB


On Mon, Aug 8, 2016 at 6:28 AM, Morris Odell 
wrote:

> Hi all,
>
> There was a thread about this a few weeks ago and I mentioned that I was
> working on one with a "Stephen Hawking" voice - well here's a video:
>
> https://youtu.be/lmg0YsHlB3g
>
> So far it's not GPS controlled but that will come one day.
>
> Cheers,
>
> Morris
>
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[time-nuts] Lady Heather Data Explained?

[William H. Fite]

The phrase, "ill documented' comes to mind. It is a wonderful piece of
software but opaque and intimidating to the newbie.


On Wednesday, August 17, 2016, Richard Mogford > wrote:

> Does anyone have a description of the various types of data on the Lady
> Heather user interface?
>
> I can figure out some of it, but still have some questions.
>
> For example, what are the data being graphed on the moving time chart?
>
> Richard
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>


-- 
If you gaze long enough into the abyss, your coffee will get cold.
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[time-nuts] GPSDO - probably a stupid question.

[Mark Sims]

The Ublox modules (at least some of them) can support an external oscillator 
and have  messages for controlling oscillator parameters and disciplining.



> This is actually done.  But you need to design the GPS receiver from the
ground up to use a very high quality oscillator.   The Thunderbolt is an
example of this.  It has a 10MHz OCXO used as the internal clock.
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Re: [time-nuts] Holdover

[Magnus Danielson]

Hi,

You do the jamming when you have a reference again.

You have three possibilities when the reference/GPS comes back:

1) Re-acquire frequency and phase lock directly

The time error between the generated PPS and the reference PPS is 
directly applied to the control loop which then will start to track in.


This works, but if you have been in hold-over for a long time, the 
trace-in might take quite some time.


To overcome this, heuristics can be used to increase the loop bandwidth, 
as the trace-in time depends heavily on it. Then the heuristics also 
needs to adjust the bandwidth back to narrow-band.
Shifting of bandwidth needs to be done with care, and there is an art to 
design the loop for it and the heuristics to work well. A Kalman filter 
could be used, but just tossing your trust to the Kalman as if it is a 
silver bullet is quite foolish, the Kalman needs it's heuristics and 
design to do well, so well, I'm not sure the difference is very large in 
the end.


2) Jam phase into about right phase and then re-acquire frequency and 
phase from there.


Here you start with detecting that the phase is way out there, so throw 
a wrench into the machinery to re-set the counters and thus push the 
generated PPS into about the same phase. For a 10 MHz clock you select 
the 100 ns cycle that fits and you can with easy methods be within +/- 
100 ns and with a little bit care be within +/- 50 ns by such a jamming 
action.


The effect of the jamming is that you have the phase about where you 
want it, but a phase error will remain. Just close the loop with the 
remaining phase error and any frequency error will also be need to be 
captured.


The benefit is that you don't need to back out as much in bandwidth and 
the process goes quicker.


3) Jam phase and frequency and then re-acquire frequency and phase.

Just as you jam the phase, you then measure the frequency error and 
re-set the frequency state. You then measure the frequency during some 
time, set it and then close the loop.


Again you have the benefit of the phase-jam, but the frequency 
measurement time is similar to the closing of the loop and well, your 
milage vary depending how well you do the heuristics.


A re-occuring theme is that there is heuristics controlling the process, 
and that can be both a help and a threat to system properties.

Let's just say that one needs to work on it and many details.

Cheers,
Magnus


On 08/17/2016 10:06 AM, Azelio Boriani wrote:

...the Z3801A requires the device to be in holdover... with the GPS
PPS already acquired: I think that the "jam sync" must be done against
some reference...

On Wed, Aug 17, 2016 at 4:49 AM, Mark Sims  wrote:

The Trimble GPSDOs and most of the SCPI ones (like the Z3801A) have "jam sync" 
commands that force the receiver to do an immediate time sync (the Z3801A requires the 
device to be in holdover before it will accept a jam sync).  Some also have commands 
where you an also specify thresholds where the receiver alarms and/or does an automatic 
jam sync and thresholds for loss-of-signal time before the device goes into holdover mode.

---

I have selected a somewhat more intricate setup in which you can set a
re-assignment limit, so when the phase error is outside of that limit,
you turn the output off, jumps the phase difference, and then starts to
track in from there. The reason being that at some time deviation, the
time it takes to track in the phase error is too large to be practical
so turning of and jump has less impact.
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Re: [time-nuts] GPSDO - probably a stupid question.

[Didier Juges]

In fact, you do not want to "update the crystal one million times/second".
The whole point of a GPSDO is to combine the excellent short term stability
of the crystal with the excellent long term stability of the GPS signal. If
you update the crystal in real time from the GPS data, you do not need the
crystal...
The control loop of GPSDOs usually have an effective bandwidth measured in
minutes or even hours in the case of rubidium oscillators.


On Wed, Aug 17, 2016 at 11:57 AM, Peter Reilley 
wrote:

> You can get crystal oscillators that have a frequency control signal and
> are more
> stable than the run of the mill oscillators.   Changing the GPS oscillator
> would
> require modifying a very tightly populated circuit board.   Perhaps not
> possible.
>
> What about some of the SDR (software defined radio) projects that aim to
> implement GPS functionality?   If you used the GPS chipping rate (1.023
> MHz)
> to dicipline the 10 MHz oscillator then you are less sensitive to crystal
> instabilities.
> You are updating the crystal one million times a second rather than once
> per second.
> This is assuming that the chipping rate of the transmitter is just as good
> as the
> 1 PPS signal.   This info from here;
> https://www.e-education.psu.edu/geog862/node/1753
> and here;
> https://en.wikipedia.org/wiki/GPS_signals
>
> Even using the 50 bits/sec data rate of the GPS signal would allow
> updating the
> GPSDO faster than the 1 PPS signal.
>
> Pete.
>
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[time-nuts] Lady Heather Data Explained?

[Richard Mogford]

Does anyone have a description of the various types of data on the Lady Heather 
user interface?

I can figure out some of it, but still have some questions.

For example, what are the data being graphed on the moving time chart?

Richard
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Re: [time-nuts] GPSDO - probably a stupid question.

[Peter Reilley]

You can get crystal oscillators that have a frequency control signal and 
are more
stable than the run of the mill oscillators.   Changing the GPS 
oscillator would
require modifying a very tightly populated circuit board.   Perhaps not 
possible.


What about some of the SDR (software defined radio) projects that aim to
implement GPS functionality?   If you used the GPS chipping rate (1.023 MHz)
to dicipline the 10 MHz oscillator then you are less sensitive to 
crystal instabilities.
You are updating the crystal one million times a second rather than once 
per second.
This is assuming that the chipping rate of the transmitter is just as 
good as the

1 PPS signal.   This info from here;
https://www.e-education.psu.edu/geog862/node/1753
and here;
https://en.wikipedia.org/wiki/GPS_signals

Even using the 50 bits/sec data rate of the GPS signal would allow 
updating the

GPSDO faster than the 1 PPS signal.

Pete.
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Re: [time-nuts] GPSDO - probably a stupid question.

[Chris Albertson]

On Tue, Aug 16, 2016 at 6:02 PM, Peter Reilley 
wrote:

> As a neophyte, I was wondering: rather that trying to discipline an
> external
> oscillator to create a GPSDO and produce a precise 10 MHz why not
> discipline the oscillator
> of the GPS receiver itself?
>
>
This is actually done.  But you need to design the GPS receiver from the
ground up to use a very high quality oscillator.   The Thunderbolt is an
example of this.  It has a 10MHz OCXO used as the internal clock.

I've seen the same thing done with NTP servers.  Rather then adjust the
system time using software, why not discipline the mother board's XO?   Yes
but it is a large amount of work to modify an existing product.



-- 

Chris Albertson
Redondo Beach, California
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Re: [time-nuts] Trimble Troubles

[Vlad]

In my project box with TB, I noticed higher than usual temperature as we 
had weather heat waves. It was around 50 Celsius. The only remedy for 
that was to implement simple fan at rear of the box. And it helps to get 
back to usual numbers (around 40 degree C). However even at 50 C, my TB 
didn't shows me complains regarding major HW alarms.




On 2016-08-15 16:01, Colin Haig wrote:

Hi all,
Recently I've added a KO4BB TBolt Monitor to my Trimble Thunderbolt.
Nice accessory.
A few weeks before it arrived, I started getting the occasional VCC at
Rail / Bad OSC problem.
Any suggestions on how I might resolve?
We've also been experiencing much higher than normal temperatures for
the last 2 months (e.g. 36C vs 25C) so the air conditioner is hard at
work.
I've added vent holes to the box its all packed into, but not sure
what exactly is going on.
Thanks in advance,
Colin VE3MSC


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--
WBW,

V.P.
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Re: [time-nuts] GPSDO - probably a stupid question.

[Björn Gabrielsson]

Some (all?) Novatel receivers have an option to sync their internal TCXO
or let it freewheel.

--

 Björn

> The stability of the typical GPS receiver oscillator is usually inadequate
> to be useful as a GPSDO. An OCXO (as in the Trimble Thunderbolt for
> example) or equivalent is usually required. One can't usually just add a
> varicap to adjust the frequency of a packaged oscillator. If an external
> crystal is used the varicap should be placed in series with the crystal.
> However to do this reliably one needs to know the crystal parameters and
> those of the oscillator circuit. If you need to adjust the frequency both
> up and down (due to crystal parmeter tolerances) then an inductor in
> series with the crystal and varicap will also be required.
> Bruce
>
>
> On Wednesday, 17 August 2016 7:05 PM, Peter Reilley
>  wrote:
>
>
>  As a neophyte, I was wondering: rather that trying to discipline an
> external
> oscillator to create a GPSDO and produce a precise 10 MHz why not
> discipline the oscillator
> of the GPS receiver itself?  This could be done with a varactor diode
> across crystal of the
> receiver's oscillator.  Of course there are the same problems with
> trying to servo this
> oscillator as there are trying to servo an external oscillator but there
> are fewer parts.
>
> Being a beginner I assume that I am missing something, but what?
>
> Thanks,
> Pete.
>
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>
>
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Re: [time-nuts] Subject: Re: Working with SMT parts

[Bob Albert via time-nuts]

Well I got my adapter boards from China and managed to build my first SMT 
project, a square wave generator for TDR use.  And it works!  The IC seems to 
run hot so I used my IR temperature measurement device and it checks out at 
about 37C, acceptable.  I can now drive a square wave at about 3 kHz into 50 
Ohms.  The rise time isn't very short but I must have not used the best part 
for the generator.  Still, I can do some TDR experimenting as long as the line 
isn't too short.
Thanks to all for the ideas and encouragement.  I didn't use a microscope, 
mostly just a magnifier.  My tiniest soldering iron is a bit large but it did 
the job.
Bob
 

On Saturday, August 13, 2016 4:06 PM, Michael Seibel  
wrote:
 

 SMD  manual assembly / re-rework is easily accomplished wearing surgeons
glasses. Mine are KEELER with prescription lens and fold up 4 diopter
telescopes - for me perfect.

 

Also have a Nikon w/10 Mp digital camera; used only to document my findings
and eliminate any "arguments".  Seldom used.

Mike Seibel

m.sei...@verizon.net

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Re: [time-nuts] Holdover

[Azelio Boriani]

...the Z3801A requires the device to be in holdover... with the GPS
PPS already acquired: I think that the "jam sync" must be done against
some reference...

On Wed, Aug 17, 2016 at 4:49 AM, Mark Sims  wrote:
> The Trimble GPSDOs and most of the SCPI ones (like the Z3801A) have "jam 
> sync" commands that force the receiver to do an immediate time sync (the 
> Z3801A requires the device to be in holdover before it will accept a jam 
> sync).  Some also have commands where you an also specify thresholds where 
> the receiver alarms and/or does an automatic jam sync and thresholds for 
> loss-of-signal time before the device goes into holdover mode.
>
> ---
>
> I have selected a somewhat more intricate setup in which you can set a
> re-assignment limit, so when the phase error is outside of that limit,
> you turn the output off, jumps the phase difference, and then starts to
> track in from there. The reason being that at some time deviation, the
> time it takes to track in the phase error is too large to be practical
> so turning of and jump has less impact.
> ___
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[time-nuts] Lady Heather

[Mark Sims]

It gets there by downing a fifth of bourbon and staggering around endlessly...  
Or you should be able to do a /gq on the command line.

The next version of Lady Heather I am working on makes getting to the sat 
signal quality display easier... G Q from the keyboard will toggle it (in 
addition to the current S A S command).   G Q attempts to remember the previous 
screen config and restore it when you toggle the signal level display on/off... 
sometimes it even works.

Also the "Z" zoom screen keyboard command that shows the various clocks and 
signal displays in full screen has been improved.  You will  now be able to 
select which feature gets zoomed.   Z Q will zoom the signal quality display to 
full screen,  ZW does the watch, ZC does the clock, ZM does the satellite 
position map, ZB does the combined watch/map,  ZF does the lat/lon scattergram.

And yes,  the command line handler in Lady Heather does not support spaces or 
quoted strings in arguments...  and why anybody would need more than 8.3 file 
names or more than 640kB of memory is beyond me (/s)  ...  Frankly, spaces in 
file names are seldom a good idea.  Too much hacky software out there chokes on 
them.   That's why Sir Ascii invented the '_'.

Anybody that attempts to figure out Lady Heather's command line and keyboard 
handlers should first have a large quantity of serious painkillers and eye/mind 
bleach at hand.

-

> I see the line that turns it on "plot_signals = 4", but I'll be darned if I 
> can see how the code gets there.  Mark?
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Re: [time-nuts] GPSDO - probably a stupid question.

[Bruce Griffiths]

The stability of the typical GPS receiver oscillator is usually inadequate to 
be useful as a GPSDO. An OCXO (as in the Trimble Thunderbolt for example) or 
equivalent is usually required. One can't usually just add a varicap to adjust 
the frequency of a packaged oscillator. If an external crystal is used the 
varicap should be placed in series with the crystal. However to do this 
reliably one needs to know the crystal parameters and those of the oscillator 
circuit. If you need to adjust the frequency both up and down (due to crystal 
parmeter tolerances) then an inductor in series with the crystal and varicap 
will also be required.
Bruce
 

On Wednesday, 17 August 2016 7:05 PM, Peter Reilley 
 wrote:
 

 As a neophyte, I was wondering: rather that trying to discipline an external
oscillator to create a GPSDO and produce a precise 10 MHz why not 
discipline the oscillator
of the GPS receiver itself?  This could be done with a varactor diode 
across crystal of the
receiver's oscillator.  Of course there are the same problems with 
trying to servo this
oscillator as there are trying to servo an external oscillator but there 
are fewer parts.

Being a beginner I assume that I am missing something, but what?

Thanks,
Pete.

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Re: [time-nuts] GPSDO - probably a stupid question.

[Pete Stephenson]

On Aug 17, 2016 09:04, "Peter Reilley"  wrote:
>
> As a neophyte, I was wondering: rather that trying to discipline an
external
> oscillator to create a GPSDO and produce a precise 10 MHz why not
discipline the oscillator
> of the GPS receiver itself?   This could be done with a varactor diode
across crystal of the
> receiver's oscillator.   Of course there are the same problems with
trying to servo this
> oscillator as there are trying to servo an external oscillator but there
are fewer parts.

It's a very good idea, and is precisely what the Trimble Thunderbolt does
with its 10MHz OCXO that it uses both as a system clock and a 10MHz output.

Cheers!
-Pete
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Re: [time-nuts] Holdover

[Bob Stewart]

Hi Magnus,
I don't remember seeing such a report.  Could you tell me where to find a copy? 
 I've got a lot of code-space left on this PIC, so assuming I can get the 
hardware to cooperate, much is possible.

Bob -
AE6RV.com

GFS GPSDO list:
groups.yahoo.com/neo/groups/GFS-GPSDOs/info

  From: Magnus Danielson 
 To: Bob Stewart ; Discussion of precise time and frequency 
measurement  
Cc: mag...@rubidium.se
 Sent: Wednesday, August 17, 2016 1:05 AM
 Subject: Re: [time-nuts] Holdover
   
Bob,

That is what seem to work well in commercial products, including my designs.
Have you seen the RAI report on GPSDOs? I think we discussed it before, 
that will be a relevant reading.

Not all system implements 3), and it is a bit complex, so consider it an 
option to add, but not necessarily always used. Sometimes you don't want 
to do that.

Cheers,
Magnus

On 08/17/2016 02:08 AM, Bob Stewart wrote:
> Thanks Magnus!
>
> These look like good guidelines.  I'll see what I can come up with.
>
> Bob
>
> -
> AE6RV.com
>
> GFS GPSDO list:
> groups.yahoo.com/neo/groups/GFS-GPSDOs/info
>
>
> 
> *From:* Magnus Danielson 
> *To:* time-nuts@febo.com
> *Cc:* mag...@rubidium.se
> *Sent:* Tuesday, August 16, 2016 6:49 PM
> *Subject:* Re: [time-nuts] Holdover
>
> Bob,
>
> On 08/16/2016 11:31 PM, Bob Stewart wrote:
>> Hi Attila,
>> In my unit, which is a frequency standard, I chose to tell the
> receiver to stop sending 1PPS pulses when it loses sync to the sats.
> And since the 1PPS is no longer coming, the PLL does nothing and the DAC
> doesn't change.  (Let's avoid the question of aging correction for
> now.)  So, I'm wondering where to go and what to do if I want to get
> time from my unit.  Clearly I could just tell the receiver to continue
> to send 1PPS pulses and sync to those - marking the time as unreliable.
> When the receiver synced back up, then it would warp the time output,
> the 1PPS would warp in phase, and the PLL would correct the phase error.
>>
>> So, that's one way, but probably not a desirable way.  My interest was
> in the option of using the OCXO to create the time, which clearly gives
> a better option when the receiver syncs back up to the sats.  Is there a
> published standard for this, or is this something that everyone (except
> the newbie) knows so well that it's not worth discussing?
>
> There is no standard, but a few basic ways to go about which seems
> reasonable and used by most is:
>
> 1) As you go into hold-over, keep producing PPS etc
> 2) As you leave hold-over, attempt to adjust the phase back.
> 3) If your system been in hold-over for a longer time, say that it
> reasonably deviates outside of +/- 10 us (or some other limit), alarm
> and turn output off
>
> I have selected a somewhat more intricate setup in which you can set a
> re-assignment limit, so when the phase error is outside of that limit,
> you turn the output off, jumps the phase difference, and then starts to
> track in from there. The reason being that at some time deviation, the
> time it takes to track in the phase error is too large to be practical
> so turning of and jump has less impact.
>
> Cheers,
> Magnus
>
>> Bob
>>  -
>> AE6RV.com
>>
>> GFS GPSDO list:
>> groups.yahoo.com/neo/groups/GFS-GPSDOs/info
>>
>>      From: Attila Kinali >
>>  To: Bob Stewart >; Discussion
> of precise time and frequency measurement  >
>>  Sent: Tuesday, August 16, 2016 3:46 PM
>>  Subject: Re: [time-nuts] Holdover
>>
>> On Tue, 16 Aug 2016 04:35:40 + (UTC)
>> Bob Stewart > wrote:
>>
>>> It's been pointed out to me that I didn't understand the function of
>>> the 1PPS of a time standard.  I confess that somehow I had confused the
>>> term to be timing standard; which would be an entirely different thing.
>>> But, this is time-nuts, so I should have realized...
>>> Anyway, is there a standard, or at least an accepted practice, for how
>>> holdover is handled in a time standard?
>>
>> There are many ways how to do that and which one you choose depends
>> on the application and its requirements. You can find everything between
>> "jump imediatly" and "just keep the frequency stable and don't care about
>> alignment".
>>
>>                Attila Kinali
>>
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>
>


  

Re: [time-nuts] Holdover

[Bob Stewart]

Thanks Chris.  Those are more considerations that I hadn't thought of.  I begin 
to see why there's no "standard".

Bob
 -
AE6RV.com

GFS GPSDO list:
groups.yahoo.com/neo/groups/GFS-GPSDOs/info

  From: Chris Albertson 
 To: Bob Stewart ; Discussion of precise time and frequency 
measurement  
 Sent: Tuesday, August 16, 2016 7:59 PM
 Subject: Re: [time-nuts] Holdover
   


What to do during and right after holdover depends on the reason you have a 
time standard.  If it is for maintaining a lab standard, then just shut down as 
you can't perform your primary function.  It you have this standard because you 
are required to time stamp financial transactions then you have to keep going 
until you estimate some error threshold then stop.  If you are using it to aim 
a telescope then again, stop using it the estimated error is enough that you'd 
miss your targets.    It depends on the use case.
I remember aiming a telescope when our best source of time was NTP over a 
dial-up phone modem in the days before always-on Internet  This was in the 
1980's and it worked well enough.  The normal case was "outage" as the modem 
connection was short and only a few times per day.  But was good enough to 
re-calibrate a local  clock Chris Albertson
Redondo Beach, California

  
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Re: [time-nuts] Holdover

[Magnus Danielson]

Bob,

That is what seem to work well in commercial products, including my designs.
Have you seen the RAI report on GPSDOs? I think we discussed it before, 
that will be a relevant reading.


Not all system implements 3), and it is a bit complex, so consider it an 
option to add, but not necessarily always used. Sometimes you don't want 
to do that.


Cheers,
Magnus

On 08/17/2016 02:08 AM, Bob Stewart wrote:

Thanks Magnus!

These look like good guidelines.  I'll see what I can come up with.

Bob

-
AE6RV.com

GFS GPSDO list:
groups.yahoo.com/neo/groups/GFS-GPSDOs/info



*From:* Magnus Danielson 
*To:* time-nuts@febo.com
*Cc:* mag...@rubidium.se
*Sent:* Tuesday, August 16, 2016 6:49 PM
*Subject:* Re: [time-nuts] Holdover

Bob,

On 08/16/2016 11:31 PM, Bob Stewart wrote:

Hi Attila,
In my unit, which is a frequency standard, I chose to tell the

receiver to stop sending 1PPS pulses when it loses sync to the sats.
And since the 1PPS is no longer coming, the PLL does nothing and the DAC
doesn't change.  (Let's avoid the question of aging correction for
now.)  So, I'm wondering where to go and what to do if I want to get
time from my unit.  Clearly I could just tell the receiver to continue
to send 1PPS pulses and sync to those - marking the time as unreliable.
When the receiver synced back up, then it would warp the time output,
the 1PPS would warp in phase, and the PLL would correct the phase error.


So, that's one way, but probably not a desirable way.  My interest was

in the option of using the OCXO to create the time, which clearly gives
a better option when the receiver syncs back up to the sats.  Is there a
published standard for this, or is this something that everyone (except
the newbie) knows so well that it's not worth discussing?

There is no standard, but a few basic ways to go about which seems
reasonable and used by most is:

1) As you go into hold-over, keep producing PPS etc
2) As you leave hold-over, attempt to adjust the phase back.
3) If your system been in hold-over for a longer time, say that it
reasonably deviates outside of +/- 10 us (or some other limit), alarm
and turn output off

I have selected a somewhat more intricate setup in which you can set a
re-assignment limit, so when the phase error is outside of that limit,
you turn the output off, jumps the phase difference, and then starts to
track in from there. The reason being that at some time deviation, the
time it takes to track in the phase error is too large to be practical
so turning of and jump has less impact.

Cheers,
Magnus


Bob
 -
AE6RV.com

GFS GPSDO list:
groups.yahoo.com/neo/groups/GFS-GPSDOs/info

 From: Attila Kinali >
 To: Bob Stewart >; Discussion

of precise time and frequency measurement >

 Sent: Tuesday, August 16, 2016 3:46 PM
 Subject: Re: [time-nuts] Holdover

On Tue, 16 Aug 2016 04:35:40 + (UTC)
Bob Stewart > wrote:


It's been pointed out to me that I didn't understand the function of
the 1PPS of a time standard.  I confess that somehow I had confused the
term to be timing standard; which would be an entirely different thing.
But, this is time-nuts, so I should have realized...
Anyway, is there a standard, or at least an accepted practice, for how
holdover is handled in a time standard?


There are many ways how to do that and which one you choose depends
on the application and its requirements. You can find everything between
"jump imediatly" and "just keep the frequency stable and don't care about
alignment".

   Attila Kinali


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[time-nuts] GPSDO - probably a stupid question.

[Peter Reilley]

As a neophyte, I was wondering: rather that trying to discipline an external
oscillator to create a GPSDO and produce a precise 10 MHz why not 
discipline the oscillator
of the GPS receiver itself?   This could be done with a varactor diode 
across crystal of the
receiver's oscillator.   Of course there are the same problems with 
trying to servo this
oscillator as there are trying to servo an external oscillator but there 
are fewer parts.


Being a beginner I assume that I am missing something, but what?

Thanks,
Pete.

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Re: [time-nuts] Holdover

[Bob Stewart]

Thanks Magnus!

These look like good guidelines.  I'll see what I can come up with.
Bob
 -
AE6RV.com

GFS GPSDO list:
groups.yahoo.com/neo/groups/GFS-GPSDOs/info

  From: Magnus Danielson 
 To: time-nuts@febo.com 
Cc: mag...@rubidium.se
 Sent: Tuesday, August 16, 2016 6:49 PM
 Subject: Re: [time-nuts] Holdover
   
Bob,

On 08/16/2016 11:31 PM, Bob Stewart wrote:
> Hi Attila,
> In my unit, which is a frequency standard, I chose to tell the receiver to 
> stop sending 1PPS pulses when it loses sync to the sats.  And since the 1PPS 
> is no longer coming, the PLL does nothing and the DAC doesn't change.  (Let's 
> avoid the question of aging correction for now.)  So, I'm wondering where to 
> go and what to do if I want to get time from my unit.  Clearly I could just 
> tell the receiver to continue to send 1PPS pulses and sync to those - marking 
> the time as unreliable.  When the receiver synced back up, then it would warp 
> the time output, the 1PPS would warp in phase, and the PLL would correct the 
> phase error.
>
> So, that's one way, but probably not a desirable way.  My interest was in the 
> option of using the OCXO to create the time, which clearly gives a better 
> option when the receiver syncs back up to the sats.  Is there a published 
> standard for this, or is this something that everyone (except the newbie) 
> knows so well that it's not worth discussing?

There is no standard, but a few basic ways to go about which seems 
reasonable and used by most is:

1) As you go into hold-over, keep producing PPS etc
2) As you leave hold-over, attempt to adjust the phase back.
3) If your system been in hold-over for a longer time, say that it 
reasonably deviates outside of +/- 10 us (or some other limit), alarm 
and turn output off

I have selected a somewhat more intricate setup in which you can set a 
re-assignment limit, so when the phase error is outside of that limit, 
you turn the output off, jumps the phase difference, and then starts to 
track in from there. The reason being that at some time deviation, the 
time it takes to track in the phase error is too large to be practical 
so turning of and jump has less impact.

Cheers,
Magnus

> Bob
>  -
> AE6RV.com
>
> GFS GPSDO list:
> groups.yahoo.com/neo/groups/GFS-GPSDOs/info
>
>      From: Attila Kinali 
>  To: Bob Stewart ; Discussion of precise time and frequency 
>measurement 
>  Sent: Tuesday, August 16, 2016 3:46 PM
>  Subject: Re: [time-nuts] Holdover
>
> On Tue, 16 Aug 2016 04:35:40 + (UTC)
> Bob Stewart  wrote:
>
>> It's been pointed out to me that I didn't understand the function of
>> the 1PPS of a time standard.  I confess that somehow I had confused the
>> term to be timing standard; which would be an entirely different thing.
>> But, this is time-nuts, so I should have realized...
>> Anyway, is there a standard, or at least an accepted practice, for how
>> holdover is handled in a time standard?
>
> There are many ways how to do that and which one you choose depends
> on the application and its requirements. You can find everything between
> "jump imediatly" and "just keep the frequency stable and don't care about
> alignment".
>
>                Attila Kinali
>
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Re: [time-nuts] Holdover

[Chris Albertson]

What to do during and right after holdover depends on the reason you have a
time standard.  If it is for maintaining a lab standard, then just shut
down as you can't perform your primary function.  It you have this standard
because you are required to time stamp financial transactions then you have
to keep going until you estimate some error threshold then stop.  If you
are using it to aim a telescope then again, stop using it the estimated
error is enough that you'd miss your targets.It depends on the use case.

I remember aiming a telescope when our best source of time was NTP over a
dial-up phone modem in the days before always-on Internet  This was in the
1980's and it worked well enough.  The normal case was "outage" as the
modem connection was short and only a few times per day.  But was good
enough to re-calibrate a local  clock

Chris Albertson
Redondo Beach, California
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[time-nuts] Holdover

[Mark Sims]

The Trimble GPSDOs and most of the SCPI ones (like the Z3801A) have "jam sync" 
commands that force the receiver to do an immediate time sync (the Z3801A 
requires the device to be in holdover before it will accept a jam sync).  Some 
also have commands where you an also specify thresholds where the receiver 
alarms and/or does an automatic jam sync and thresholds for loss-of-signal time 
before the device goes into holdover mode.

---

I have selected a somewhat more intricate setup in which you can set a 
re-assignment limit, so when the phase error is outside of that limit, 
you turn the output off, jumps the phase difference, and then starts to 
track in from there. The reason being that at some time deviation, the 
time it takes to track in the phase error is too large to be practical 
so turning of and jump has less impact.
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