Re: [time-nuts] High rate, high precision/accuracy time interval counter methods

[Bruce Griffiths]

On Tuesday, May 03, 2016 02:31:17 PM Attila Kinali wrote:
> Hi,
> 
> We had here a discussion about measuring events (ie time stamping
> them precisely) with high rates. As some of you know, Javier and
> his group, Bruce and me are working on a system that should give
> us something better than 10ps (my guess is that we should get close
> to 1ps) at a rate of (guestimated) 1MHz per channel. (Based on the
> excitation of a LC tank and measuring the ring-down/phase with an ADC).
> 
> As it is with researches, we want the moon, and prossible even more.
> So we were talking about getting the measurement rate up even higher,
> to 10MHz and if possible 50MHz with the same precision. The above
> approche will not work above 1MHz. Using different filters it might
> be possible to get it up to maybe 10MHz, but it would be an awkward
> design at best.
> 
> The only methods I am aware of (and could find) that achieve such high
> rates are those, based on (vernier) delay lines (and their equivalent
> ring oscillator ones) in ASICs. But this means that a costly ASIC needs
> to be produced.
> 
> Does someone know of other methods that could achieve high measurements
> rates with better than 10ps precision/accuracy? (This question is mostly
> a hypothetical question out of interest, I don't plan to build one...yet :-)
> 
>   Attila Kinali
Massive parallelism of a simple NUTT style interpolator (charge capacitor with 
say 10mA, rundown with say 1uA, use 100MHz clock or faster clock ).
With a custom IC for the analog part, a resolution of 1ps should be feasible.
An FPGA can do all the non critical stuff like the rundown counting.
The problem is to ensure that the front end logic that selects the next non- 
busy interpolator doesn't accumulate excessive jitter from cascaded gates.
The same issue of accumulated jitter produced by cascaded gates/inverters can 
limit the performance of vernier delay line style interpolators. Minimising 
the number of series inverters by using a higher frequency clock (100MHZ, 
1GHz??) should help somewhat.

Bruce
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Re: [time-nuts] High rate, high precision/accuracy time interval counter methods

[Magnus Danielson]

I sine sampling works, but a continuous sampling allows for N samples 
to reduce the noise by sqrt(N) rather than 2 samples. The white-noise 
will be the limiting factor for the higher rates.


Least-square estimation provides a 2.5 dB improvement over straight 
sample average.


Cheers,
Magnus

On 05/03/2016 10:33 PM, David wrote:

Wouldn't this be a natural application of a centroid or transition
midpoint timing TDC implemented with a pulse shaper, fast ADC, and
FPGA?

What about sampling inphase and quadrature sine waves?  This should be
more amendable to a microcontroller only solution and if I had to
start working on something immediately, this is what I would try
first.

I assume in the earlier discussion Bruce mentioned these methods since
they are included on his page of the various ways to implement TDCs:

http://www.ko4bb.com/~bruce/TDC.html

On Tue, 3 May 2016 08:40:53 -0700, you wrote:


HP/Agilent/Keysight laser interferometers
measure at the kind of rates you are talking
about and (last time I heard) could divide
an interference fringe down to 1/512 of a
wavelength.  As you say, they definitely use
an ASIC with a ring oscillator.  Perhaps
there is some way you could repurpose the
interferometer electronics to make your
measurement.

You also might consider that over 25 years
ago, HP developed the 5313X counters with
interpolators implemented in FPGA's.  The
FPGA's available now are vastly more
sophisticated and much faster.  Perhaps there
is a way you do your ASIC in an FPGA.

If you really do need an ASIC, the best way
to get that done is to partner with a university
and have some PhD student design it.  Universities
often have arrangements to do this.

Rick

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Re: [time-nuts] High rate, high precision/accuracy time interval counter methods

[David]

Wouldn't this be a natural application of a centroid or transition
midpoint timing TDC implemented with a pulse shaper, fast ADC, and
FPGA?

What about sampling inphase and quadrature sine waves?  This should be
more amendable to a microcontroller only solution and if I had to
start working on something immediately, this is what I would try
first.

I assume in the earlier discussion Bruce mentioned these methods since
they are included on his page of the various ways to implement TDCs:

http://www.ko4bb.com/~bruce/TDC.html

On Tue, 3 May 2016 08:40:53 -0700, you wrote:

>HP/Agilent/Keysight laser interferometers
>measure at the kind of rates you are talking
>about and (last time I heard) could divide
>an interference fringe down to 1/512 of a
>wavelength.  As you say, they definitely use
>an ASIC with a ring oscillator.  Perhaps
>there is some way you could repurpose the
>interferometer electronics to make your
>measurement.
>
>You also might consider that over 25 years
>ago, HP developed the 5313X counters with
>interpolators implemented in FPGA's.  The
>FPGA's available now are vastly more
>sophisticated and much faster.  Perhaps there
>is a way you do your ASIC in an FPGA.
>
>If you really do need an ASIC, the best way
>to get that done is to partner with a university
>and have some PhD student design it.  Universities
>often have arrangements to do this.
>
>Rick
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Re: [time-nuts] High rate, high precision/accuracy time interval counter methods

[Magnus Danielson]

Rick,

Unless you uses the high-speed SERDES blocks, the jitter and systematic 
noises inside FGPAs can be pretty prohibitive.


Enrico Rubiola and his team have made some of the best characterizations 
of FPGAs I've seen, but I know from several other experinces that timing 
can uhm shift around.


I proposed some 10 years ago to use the 10 Gb/s SERDES for 100 ps 
resolution counter, the chip that could support it then could do 8 
channels. It had some fancy tweaking so you could fine-tune the sampling 
point to align channels up. Would still be a fun project to do.


The normal logic path isn't "as fun".

I'd say that the precision timing stuff should be done in a separate 
front-end, but the sea of logic to handle all the dataflows can be done 
in a FPGA.


Cheers,
Magnus

On 05/03/2016 05:40 PM, Richard (Rick) Karlquist wrote:

HP/Agilent/Keysight laser interferometers
measure at the kind of rates you are talking
about and (last time I heard) could divide
an interference fringe down to 1/512 of a
wavelength.  As you say, they definitely use
an ASIC with a ring oscillator.  Perhaps
there is some way you could repurpose the
interferometer electronics to make your
measurement.

You also might consider that over 25 years
ago, HP developed the 5313X counters with
interpolators implemented in FPGA's.  The
FPGA's available now are vastly more
sophisticated and much faster.  Perhaps there
is a way you do your ASIC in an FPGA.

If you really do need an ASIC, the best way
to get that done is to partner with a university
and have some PhD student design it.  Universities
often have arrangements to do this.

Rick

On 5/3/2016 5:31 AM, Attila Kinali wrote:

Hi,

We had here a discussion about measuring events (ie time stamping
them precisely) with high rates. As some of you know, Javier and
his group, Bruce and me are working on a system that should give
us something better than 10ps (my guess is that we should get close
to 1ps) at a rate of (guestimated) 1MHz per channel. (Based on the
excitation of a LC tank and measuring the ring-down/phase with an ADC).

As it is with researches, we want the moon, and prossible even more.
So we were talking about getting the measurement rate up even higher,
to 10MHz and if possible 50MHz with the same precision. The above
approche will not work above 1MHz. Using different filters it might
be possible to get it up to maybe 10MHz, but it would be an awkward
design at best.

The only methods I am aware of (and could find) that achieve such high
rates are those, based on (vernier) delay lines (and their equivalent
ring oscillator ones) in ASICs. But this means that a costly ASIC needs
to be produced.

Does someone know of other methods that could achieve high measurements
rates with better than 10ps precision/accuracy? (This question is mostly
a hypothetical question out of interest, I don't plan to build
one...yet :-)

Attila Kinali


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Re: [time-nuts] High rate, high precision/accuracy time interval counter methods

[Magnus Danielson]

Hi Attila,

On 05/03/2016 02:31 PM, Attila Kinali wrote:

Hi,

We had here a discussion about measuring events (ie time stamping
them precisely) with high rates. As some of you know, Javier and
his group, Bruce and me are working on a system that should give
us something better than 10ps (my guess is that we should get close
to 1ps) at a rate of (guestimated) 1MHz per channel. (Based on the
excitation of a LC tank and measuring the ring-down/phase with an ADC).

As it is with researches, we want the moon, and prossible even more.
So we were talking about getting the measurement rate up even higher,
to 10MHz and if possible 50MHz with the same precision. The above
approche will not work above 1MHz. Using different filters it might
be possible to get it up to maybe 10MHz, but it would be an awkward
design at best.


Getting to those rates will be challenging, especially with the LC tank.

For the higher rates a more traditional interpolator needs to be used, 
charge a cap with the error pulse and sample that.



The only methods I am aware of (and could find) that achieve such high
rates are those, based on (vernier) delay lines (and their equivalent
ring oscillator ones) in ASICs. But this means that a costly ASIC needs
to be produced.


13.3 MHz (or every 75 ns) is achievable with the HP5372A, but it had 
relatively meager single-shot resolution, 200 ps, compared to its 
predecessor. It uses the delay vernier approach rather than the 
triggered oscillator vernier (HP5370A/B) just because of sample-rate.
The HP5371A/5372A is made to analyze jitter rather than high resolution 
long term stuff. Even as the limit shifts over time, high speed will end 
up having somewhat lower resolution than a lower rate could offer.


However, with higher rate, you can use the least-square methods of mine 
to get results and fight the white noise that way.



Does someone know of other methods that could achieve high measurements
rates with better than 10ps precision/accuracy? (This question is mostly
a hypothetical question out of interest, I don't plan to build one...yet :-)


Well, if you sample at sufficiently high rate, you can estimate the 
rising/falling edge using least-square methods and then interpolate the 
position. There is only a relatively small burst of samples needed, and 
the least-square processing can be done using high-speed FPGA methods 
similar to what is found in the article I sent you.


An alternative to the edge estimator method is to continuously sample, 
mix with a reference frequency, decimate and then do arc-tangent of the 
I/Q samples. This is what is used for phase-noise measurement such as 
the Symmetricom/Microsemi test-kits, TimePod, and also the new R 
phase-noise system. The phase values can be produced at very high rates 
there and the noise of such setups can be maintained relatively low 
compared to the comparator systems. For such systems the noise per 
phase-sample is maybe even better understood as the averaging time over 
the phase vs. noise is relatively simple process to understand.

Pipeline CORDIC can be used for arctan processing.

Cheers,
Magnus
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[time-nuts] DHS S Demonstrates Precision Timing Technology at the New York Stock Exchange

[Brooke Clarke]

Hi:

A couple of weeks ago the DHS was looking into eLORAN-C for reliable timing:
https://www.dhs.gov/science-and-technology/news/2016/04/20/st-demonstrates-precision-timing-technology-ny-stock-exchange

--
Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
The lesser of evils is still evil.

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Re: [time-nuts] MSF 60KHz Problems?

[Poul-Henning Kamp]

In message <66e02a.1a25af43.445a4...@aol.com>, GandalfG8--- via time-nuts write
s:

>With this bypassed and a stronger signal I've also identified some varying  
>levels of close in interference around 60KHz, so it looks to be time for a 
>more  detailed look at the antenna system overall.

60 kHz is often polluted by switch-mode power supplies.

Check your surroundings for new consumer electronics.

Also:  Lawnmover robots.


-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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Re: [time-nuts] help

[Adrian Godwin]

Since you have an impulse clock system, you could use that to fire the bell
- you could modify a slave clock or use one of these :

http://www.ebay.co.uk/itm/111982558390

or possibly this one :

http://www.ebay.co.uk/itm/291730808914

The first seems rather expensive to me, I've more commonly seen them at
more like the second price. You can probably find one nearer to you.

You still then have the problem that you want to drive the impulse from an
accurate time source. There are impulse drivers that operate from a cheap
crystal available on ebay. I don't think we want to talk about those here.

A nicer solution would be to transform the 1pps signal from a gps receiver
into a suitable pulse : again, this is easy to do with a microcontroller
and a small amount of electronics, but it seems like a useful idea. Perhaps
worth working out properly and publishing.

I have in the past run a slave clock from an RS232 port : it needs a small
circuit to generate the current pulse (powered by the RS232 port itself)
and operated by a small script program on a computer, so locked to NTP.
However, it needs a computer (preferably Unix) running 24/7.




On Mon, May 2, 2016 at 7:11 PM, Mark Sims  wrote:

> If you want to get fancy you could modify Lady Heather to do the deed.
> Heather has a "singing clock" mode and a cuckoo/chime clock mode for
> playing sound files at various times.  It also has routines for controlling
> the serial port DTR and RTS lines (currently used for PWMing a fan if
> temperature control mode is enabled).   You could add some code to the
> program to pulse the DTR or RTS line... these can easily drive a solid
> state relay.
>
>
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Re: [time-nuts] MSF 60KHz Problems?

[GandalfG8--- via time-nuts]

Thanks to all who've commented on this.
 
All the reports I've received have suggested that MSF is behaving  normally 
and I've taken a closer look at my antenna system, where I've  found more 
loss at 60KHz than expected in the multicoupler I've been  using.
 
With this bypassed and a stronger signal I've also identified some varying  
levels of close in interference around 60KHz, so it looks to be time for a 
more  detailed look at the antenna system overall.
 
Regards
 
Nigel
GM8PZR 
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Re: [time-nuts] help

[Tom Van Baak]

It turns out OP (Bill Baker) is using a very nice GMR1000 GPS time standard:

http://www.masterclock.com/products/master-clocks/gmr1000/

So that's why he was asking about an off-the-shelf device to turn SMPTE into an 
hourly switch for his fog bell.

Since the GMR1000 also has a network connection, the proposed Raspberry Pi 
solutions will work. In addition, the GMR1000 has a serial port that will 
output NMEA (GPZDA), so even a simple PIC or Arduino solution is possible.

Given a choice between RS232 + Arduino on the one hand and LAN + Raspberry Pi + 
Linux + NTP on the other, I'd pick Arduino. But I know people that would throw 
Linux at this; everyone has their favorite hammer. In fact, I bet Walter 
Shawlee could design a simple TTL shift-register circuit that would parse the 
RS232 GPZDA bitstream and drive the fog bell on the hour. And a hundred years 
from now his TTL board and the bell would be the only parts still working.

/tvb

For more information read GMR1000.pdf and GMR+Series+User+Manual.pdf from the 
site above.


> - Original Message - 
> From: "Bill Baker via time-nuts" 
> Sent: Sunday, May 01, 2016 12:26 PM
> Subject: [time-nuts] help
>
> My problem:  I'd like some kind of off-the-shelf device that can take the 
> time code
> and switch on or impulse another circuit-- specifically  I'd like to trigger 
> a 180 year-old
> fog bell (I'm a lighthouse nut as well, www.henryisland.com) on the hour and 
> maybe
> be able to impulse my minute school clocks.  I'm not at this group's 
> technical level,
> so it's got to be pretty easy to program. So I need a box that I can program 
> with
> SMPTE time in and a timed switch impulse out.  Any ideas?
>Many thanks,
>W1BKR

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Re: [time-nuts] help

[albertson . chris]

You don't care about the lag in cron. You care about the variation of the lag.  
 

Then again. The main cause of lag in a fog horn is the speed of sound  

You set cron to fire at T minus the average lag time. 

> On May 2, 2016, at 2:36 PM, Nick Sayer via time-nuts  
> wrote:
> 
> 
>> On May 2, 2016, at 9:51 AM, jimlux  wrote:
>> 
>> 
>> The real question is whether "cron" is timely enough.  No matter, just write 
>> a script (or python) that reads time in a loop (and you can put a sleep in 
>> there) and pulses the GPIO when needed.
> 
> A Raspberry Pi with nothing else on its plate will have a cron-to-shell 
> script latency easily under 100 ms, possibly under 10.
> 
> If it were me and I were triggering a relay for some sort of external 
> circuit, I’d probably be happy it was on the right side of 500 ms. If I cared 
> more than that, then step 1 would be to do as others have suggested and come 
> up with a microcontroller + GPS solution instead of NTP + cron. Ironically, 
> that’d be around the same price (albeit more engineering work).
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Re: [time-nuts] MSF 60KHz Problems?

[Alan Melia]

Hi Nigel its been running about 17msecs fast for that last couple of months 
but it seemed to be corrected last week, maybe the exciter failed completely 
:-))  Gotta be all this snow you have been getting !!


Best Wishes
Alan
G3NYK


- Original Message - 
From: "GandalfG8--- via time-nuts" 

To: 
Sent: Tuesday, May 03, 2016 3:15 PM
Subject: [time-nuts] MSF 60KHz Problems?



Is anyone else seeing anthing unusual with the MSF 60KHz signal from
Anthorn?

For the past 24 hours or so, at least, all I've been monitoring here,
approx 100 miles from Anthorn, is what seems to be a much weaker than 
usual
carrier that's pulsing at significantly faster than once per second. It's 
weak

enough that I wondered at first if it  possibly wasn't even MSF but
something else on the same  frequency.

There's no scheduled maintenance in my diary and I haven't been able to
find reference online to any problems, my first concern was that it  might 
be

an antenna problem but the Anthorn eLoran signals on 100KHz seem to  be
coming in fine on the same antenna.

What's really odd though is that several minutes ago I powered up  an EES
MSF clock from that same antenna feed and this has now  synchronised and 
is

displaying the correct time.

Regards

Nigel
GM8PZR
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Re: [time-nuts] help

[Martin Burnicki]

Am 3. Mai 2016 18:06:49 MESZ, schrieb Hendrik Dietrich :
>
>Picking up the time from a DAYTIME Server is easier to implement than 
>NTP, these respond just with a string containing date and time.

If you don't want to run NTP then eventually you sould use the "time" protocol 
rather than daytime . 

"time" returns UTC,  but IIRC then daytime can even return some local time,  
and the string format may depend on / vary wit the server you are contacting. 
It's more for human interaction. 

Martin 

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[time-nuts] help

[Hendrik Dietrich]

Hi,

about getting time from the Internet to a clockwork:
Have a look at the ESP8266, which you can get from china for as low as 
4€ in the embodiment of a AMICA board:


Its a controller with some GPIOs and WLAN enabled, freely programmable 
(Either with the ARDUINO IDE, or with a LUA or BASIC Firmware.)
Picking up the time from a DAYTIME Server is easier to implement than 
NTP, these respond just with a string containing date and time.
At ~100 mA fully on its a good competitor to the Raspies regarding 
current consumption.


BR
Hendrik

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Re: [time-nuts] MSF 60KHz Problems?

[David J Taylor]

Is anyone else seeing anthing unusual with the MSF 60KHz signal from
Anthorn?

For the past 24 hours or so, at least, all I've been monitoring here,
approx 100 miles from Anthorn, is what seems to be a much weaker than usual
carrier that's pulsing at significantly faster than once per second. It's 
weak

enough that I wondered at first if it  possibly wasn't even MSF but
something else on the same  frequency.

There's no scheduled maintenance in my diary and I haven't been able to
find reference online to any problems, my first concern was that it  might 
be

an antenna problem but the Anthorn eLoran signals on 100KHz seem to  be
coming in fine on the same antenna.

What's really odd though is that several minutes ago I powered up  an EES
MSF clock from that same antenna feed and this has now  synchronised and is
displaying the correct time.

Regards

Nigel
GM8PZR
___

Just checked at 15:53 UTC and the signal doesn't sound double-speed.  It's 
many years since I've listened to MSF as a background (!) but it doesn't 
sound wrong, and the strength doesn't seem way down.  All but one of the MSF 
clocks here are OK, and I recall that one clock having a completely wrong 
display recently but I didn't note down just when.  I've reset the battery 
in that clock and am waiting for it to display something valid!


73,
David GM8ARV
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-tay...@blueyonder.co.uk
Twitter: @gm8arv 


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Re: [time-nuts] High rate, high precision/accuracy time interval counter methods

[Richard (Rick) Karlquist]

HP/Agilent/Keysight laser interferometers
measure at the kind of rates you are talking
about and (last time I heard) could divide
an interference fringe down to 1/512 of a
wavelength.  As you say, they definitely use
an ASIC with a ring oscillator.  Perhaps
there is some way you could repurpose the
interferometer electronics to make your
measurement.

You also might consider that over 25 years
ago, HP developed the 5313X counters with
interpolators implemented in FPGA's.  The
FPGA's available now are vastly more
sophisticated and much faster.  Perhaps there
is a way you do your ASIC in an FPGA.

If you really do need an ASIC, the best way
to get that done is to partner with a university
and have some PhD student design it.  Universities
often have arrangements to do this.

Rick

On 5/3/2016 5:31 AM, Attila Kinali wrote:

Hi,

We had here a discussion about measuring events (ie time stamping
them precisely) with high rates. As some of you know, Javier and
his group, Bruce and me are working on a system that should give
us something better than 10ps (my guess is that we should get close
to 1ps) at a rate of (guestimated) 1MHz per channel. (Based on the
excitation of a LC tank and measuring the ring-down/phase with an ADC).

As it is with researches, we want the moon, and prossible even more.
So we were talking about getting the measurement rate up even higher,
to 10MHz and if possible 50MHz with the same precision. The above
approche will not work above 1MHz. Using different filters it might
be possible to get it up to maybe 10MHz, but it would be an awkward
design at best.

The only methods I am aware of (and could find) that achieve such high
rates are those, based on (vernier) delay lines (and their equivalent
ring oscillator ones) in ASICs. But this means that a costly ASIC needs
to be produced.

Does someone know of other methods that could achieve high measurements
rates with better than 10ps precision/accuracy? (This question is mostly
a hypothetical question out of interest, I don't plan to build one...yet :-)

Attila Kinali


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Re: [time-nuts] MSF 60KHz Problems?

[Iain Young]

Hi Nigel

On 03/05/16 15:15, GandalfG8--- via time-nuts wrote:


Is anyone else seeing anthing unusual with the MSF 60KHz signal from
Anthorn?



Can't check from here at the moment, but sounds normal from the WebSDR 
at UTwente...



Iain
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[time-nuts] High rate, high precision/accuracy time interval counter methods

[Attila Kinali]

Hi,

We had here a discussion about measuring events (ie time stamping
them precisely) with high rates. As some of you know, Javier and
his group, Bruce and me are working on a system that should give
us something better than 10ps (my guess is that we should get close
to 1ps) at a rate of (guestimated) 1MHz per channel. (Based on the
excitation of a LC tank and measuring the ring-down/phase with an ADC).

As it is with researches, we want the moon, and prossible even more.
So we were talking about getting the measurement rate up even higher,
to 10MHz and if possible 50MHz with the same precision. The above
approche will not work above 1MHz. Using different filters it might
be possible to get it up to maybe 10MHz, but it would be an awkward
design at best.

The only methods I am aware of (and could find) that achieve such high
rates are those, based on (vernier) delay lines (and their equivalent
ring oscillator ones) in ASICs. But this means that a costly ASIC needs
to be produced.

Does someone know of other methods that could achieve high measurements
rates with better than 10ps precision/accuracy? (This question is mostly
a hypothetical question out of interest, I don't plan to build one...yet :-)

Attila Kinali

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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[time-nuts] MSF 60KHz Problems?

[GandalfG8--- via time-nuts]

Is anyone else seeing anthing unusual with the MSF 60KHz signal from  
Anthorn?
 
For the past 24 hours or so, at least, all I've been monitoring here,  
approx 100 miles from Anthorn, is what seems to be a much weaker than usual  
carrier that's pulsing at significantly faster than once per second. It's  weak 
enough that I wondered at first if it  possibly wasn't even MSF but 
something else on the same  frequency.
 
There's no scheduled maintenance in my diary and I haven't been able to  
find reference online to any problems, my first concern was that it  might be 
an antenna problem but the Anthorn eLoran signals on 100KHz seem to  be 
coming in fine on the same antenna.
 
What's really odd though is that several minutes ago I powered up  an EES 
MSF clock from that same antenna feed and this has now  synchronised and is 
displaying the correct time.
 
Regards
 
Nigel
GM8PZR
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Re: [time-nuts] synchronization for telescopes

[Attila Kinali]

Hoi Michael,

On Mon, 2 May 2016 07:52:09 +1000
Michael Wouters  wrote:


> I don't think a cheap receiver like a LEAxxx will quite get you there.

I have some numbers of an project of the ETH that did use standard
LEA-6T recording the phase data and got in the post processing
to an uncertainty of <4mm averaging over several hours. Translating
that to timing resolution would mean an uncertainty of less than 13ps.
Of course, this number is completely theoretical, but it shows that
it should be possible to go below 1ns in time resolution, if the
phase data could be related to a stable reference oscillator in
post-processing and if the offsets between the different receiver
and antenna combinations are calibrated out.

> The number I quoted is for high quality geodetic receivers. There are
> crucial differences between these and the cheap receivers in regard to
> time-transfer. The first is how you relate your external clock's 1 pps
> to GPS time.

That's why I'm proposing timing receivers. They are the ones that have
the additional software and hardware bits which allow to relate an
external oscillator to the satellite phases.

> The other important difference is the resolution of the receiver's
> measurements. A cheap receiver reports the code measurements at
> relatively coarse resolution, sometimes a few ns, whereas a geodetic
> receiver reports at much higher resolution. If you had a cheap
> receiver, the code measurement resolution is seldom specified so you
> would have to test candidate receivers.

I don't know what resolution the LEA family offers there, but the
spec of the protocol defines a 1ps resolution in the data. So I would
guess that the phase data resolution is probably in the order of 10-100ps.

> I have many years of raw code measurement data from many identical
> receivers operating on baselines of a few km up to 20 km. I will try
> to have a look later this week to confirm/deny/make ambiguous what I
> said above.

If you have time to dig that data out, that would be very nice.

Attila Kinali

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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[time-nuts] help

[Mark Sims]

If you want to get fancy you could modify Lady Heather to do the deed.  Heather 
has a "singing clock" mode and a cuckoo/chime clock mode for playing sound 
files at various times.  It also has routines for controlling the serial port 
DTR and RTS lines (currently used for PWMing a fan if temperature control mode 
is enabled).   You could add some code to the program to pulse the DTR or RTS 
line... these can easily drive a solid state relay.

  
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