PTTI 2012
I just returned from PTTI (Precise Time and Time Interval), the annual conference hosted by USNO, NASA, JPL, etc. Those of you unfamiliar with PTTI can read more (http://pttimeeting.org/). Many of you know this site by the fantastic collection of 40 years of archived (and free) technical papers (http://pttimeeting.org/archivemeetings/).
There are other annual professional conferences related to time & frequency: FCS (IEEE International Frequency Control Symposium), EFTF (European Frequency and Time Forum), and ION GNSS (Institute of Navigation). There is also the excellent NIST Time and Frequency Metrology Seminar in Boulder. I've heard of but have not attended: Asia-Pacific Workshop on Time and Frequency, and Inter-American Metrology System (SIM) conference. There may be more.
You are fortunate if your employer sends you to one of these conferences. Depending on your location, time, budget, and level of interest, I believe most of these are open to individuals in case you are drawn more by hobby and passion than by profession. Or simply read the conference technical papers which are usually available on the web.
About 50 papers were presented over 3 days at PTTI this year (pttimeeting.org/ptti_advanceprogram.pdf). The papers appear in the PTTI archives in a few months. Given that this is a professional conference and most of the attendees are affiliated with national metrology laboratories, it's not surprising that about half the papers cover state-of-the-art (i.e., not yet on eBay) subjects like optical clocks and national or international time transfer over satellite or fiber. Still, there are always a number of talks of more general interest to us time nuts. In the next few postings I'll give more details on a couple of topics:
- Neutrino time-of-flight update
- UTCr/Rapid UTC
- USNO rubidium fountains
- WWVB/Xtendwave
- Loran/UrsaNav
- Vendor presentations/Symmetricom/Miles
- M12/uBlox GPS board
- Quartz in space
- ION/PTTI 2013 in Bellevue, WA (!)
- The state of Time-Nuts
/tvb
Continuing from previous posting...
Still, there are always a number of talks of more general interest to us time nuts.
In the next few postings I'll give more details on a couple of topics:
- Neutrino time-of-flight update
Last years' faster-than-light neutrino fiasco is now old news, but I think many of us were curious how other neutrino experiments around the world would react. Not surprisingly, they all got very serious about precision timing! As one presenter mentioned, purchase orders for high-end timing gear were suddenly approved with remarkable ease.
There were a total of 6 talks by people working with neutrino experiments. From what I could tell (having done similar work at home) they totally have their act together now. NIST and USNO were involved with MINOS, the local US effort (neutrinos from FermiLab to the Soudan mine in Minnesota), both in providing gear (high-end dual-frequency or post-processed GPS receivers and local cesium clocks) to absolute calibration using TWSTFT (two way satellite time & frequency transfer).
One talk covered the challenge of measuring distance (presumably there are survey-nuts as well as time-nuts). You think measuring nanoseconds is hard until you hear what it takes to measure distance, including down an opaque slanted mineshaft, and get a final number like 734,286.554 meters!
While PTTI normally concerns itself with national timing laboratories, it was nice to see a whole new community (neutrino physics) get involved in the practical world of nanosecond timing.
- UTCr/Rapid UTC
Some of you know that TAI/UTC is computed from a monthly average of hundreds of atomic clocks around the world. Given the recent improvement in clock performance, intercontinental comparison techniques, and automated communications (internet), BIPM started a pilot program this year to generate a more responsive and fully automated "UTC". One problem with UTC is that physical measurements of, and virtual corrections to, contributing clocks occurs only once a month. This means that your national lab might drift a few ns before being told it is drifting.
Those of you who have built your own GPSDO or explored time constants can relate. So UTCr is an experiment where labs report daily and results are computed weekly based on a monthly moving average, or something like that. I had not heard about this before, but if you google for words like "Rapid UTC" UTCr BIPM you can learn more. The whole subject of time scales is deep and interesting.
- USNO rubidium fountains
While many national labs have developed cesium fountains (for accuracy), USNO has been gradually building rubidium fountain clocks (for stability) and 4 of them are now fully operational. The ADEV of these clocks gets well under 1e-16. The paper will have all the details but the note I made was that with 20 months of data, the stability was near 5e-17 at tau 4 months. That's 100x better than a commercial cesium standard; better than all of USNO's other 70 cesium clocks and 15 H-masers combined. Yes, I've added "rubidium fountain" to my automated eBay searches.
Like always, each of the Rb clocks is a little different. You measure this not by using an external reference (since no better clock is available) but by using the 3-cornered hat technique where you compare clock i against the mean of N clocks.
- WWVB/Xtendwave
This presentation was similar to the one made last year. From the talk, and discussions afterwards, it's clear good progress is being made. As of October 29, 2012 the extended WWVB format is now default, but reception tests are continuing, and the format perhaps slightly tweaked. A prototype receiver was shown in a shoebox. I did not get to see inside.
My guess is that by next year we'll see real hardware and a final spec. I suggested the time-nuts community might be willing to test the new receivers when they are available. Contact me off-list if you want to help. I can't promise anything, but I know that NIST/Xtendwave have embarked on a project that will greatly improve reception quality and totally solve the DST announcement problems. I also believe that a passion-driven, no-cost, geographically-diverse set of time nuts can help make this a well-tuned success.
They also mentioned another cool feature being developed -- a high-rate modulation where, reception permitting, the entire 60 bit message is encoded into a single 1-second frame.
- Loran/UrsaNav
Not sure what to say about this presentation. Apparently this company got the rights to the US Loran transmitters(?) and plans to use them to provide an alternative source of precise time, for example, to the telecom community. CW instead of very low duty cycle Loran pulses would improve S/N and timing accuracy. You can probably read more about it on their web site. Any additional source of precise time is probably a good thing -- when NTP, WWVB, GPS, and your local atomic clock fails. But the presentation raised more questions than answers. I look forward to reading the paper.
I'll finish up in the next posting.
/tvb
In message AB5B0278225B4BD483382A39E6834203@pc52, "Tom Van Baak" writes:
- USNO rubidium fountains
While many national labs have developed cesium fountains (for
accuracy), USNO has been gradually building rubidium fountain clocks
(for stability) and 4 of them are now fully operational. The ADEV
of these clocks gets well under 1e-16. The paper will have all the
details but the note I made was that with 20 months of data, the
stability was near 5e-17 at tau 4 months. That's 100x better than
a commercial cesium standard; better than all of USNO's other 70
cesium clocks and 15 H-masers combined. Yes, I've added "rubidium
fountain" to my automated eBay searches.
I happened to miss a turn (or something...) and stumbled into the
building where they keep those fountains when I visited USNO some
months ago. WhatI found most remarkable about them were how compact
they were, I still expected fountains to be room size, but these
were rack-sized.
I asked what the material cost would be and if a competent amateur
would be able to do something like that, and the clear message was
that the single biggest problem was the vacuum for a vessel that
size (when you can't use ferromagmnetic materials) and getting
the optical bench calibrated. "Apart from that it's just some
plumbing"
- Loran/UrsaNav
CW instead of very low duty cycle Loran pulses would improve S/N [...]
Actually, it probably will not.
The one smart thing about the LORAN signal is S/N, which means that
LORAN for timing purposes is incredible insensitive to noise and
at the same time, incredible transmitter power economy.
The one caveat is that the GRI has to be a good number, preferably
a four (or more!) digit prime number.
(You need to grok moduls-arithmetic to really appreciate this, but
its the magnitude of the prime factors of the product of the GRI
and the disturbing CW which counts: The smaller the are, the harder
it is to filter the CW-RFI out.)
This is why Europe switched to 4-digit GRIs and almost totally solved
CW-RFI by doing so, and why the Russian Chayka at GRI 8000 is totally
useless near anything resembling a transmitter.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@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.
Hi
I went through a similar process quite a while ago. The dimensions of the actual fountain can be quite small. One could make one the size of a shoe box and still have it perform quite well.
Bob
On Dec 3, 2012, at 2:07 PM, Poul-Henning Kamp phk@phk.freebsd.dk wrote:
In message AB5B0278225B4BD483382A39E6834203@pc52, "Tom Van Baak" writes:
- USNO rubidium fountains
While many national labs have developed cesium fountains (for
accuracy), USNO has been gradually building rubidium fountain clocks
(for stability) and 4 of them are now fully operational. The ADEV
of these clocks gets well under 1e-16. The paper will have all the
details but the note I made was that with 20 months of data, the
stability was near 5e-17 at tau 4 months. That's 100x better than
a commercial cesium standard; better than all of USNO's other 70
cesium clocks and 15 H-masers combined. Yes, I've added "rubidium
fountain" to my automated eBay searches.
I happened to miss a turn (or something...) and stumbled into the
building where they keep those fountains when I visited USNO some
months ago. WhatI found most remarkable about them were how compact
they were, I still expected fountains to be room size, but these
were rack-sized.
I asked what the material cost would be and if a competent amateur
would be able to do something like that, and the clear message was
that the single biggest problem was the vacuum for a vessel that
size (when you can't use ferromagmnetic materials) and getting
the optical bench calibrated. "Apart from that it's just some
plumbing"
- Loran/UrsaNav
CW instead of very low duty cycle Loran pulses would improve S/N [...]
Actually, it probably will not.
The one smart thing about the LORAN signal is S/N, which means that
LORAN for timing purposes is incredible insensitive to noise and
at the same time, incredible transmitter power economy.
The one caveat is that the GRI has to be a good number, preferably
a four (or more!) digit prime number.
(You need to grok moduls-arithmetic to really appreciate this, but
its the magnitude of the prime factors of the product of the GRI
and the disturbing CW which counts: The smaller the are, the harder
it is to filter the CW-RFI out.)
This is why Europe switched to 4-digit GRIs and almost totally solved
CW-RFI by doing so, and why the Russian Chayka at GRI 8000 is totally
useless near anything resembling a transmitter.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@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.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
OK now that I am setting out to build one. Would the challenge for a
amateur be that the components you build with are basically dirty. Some how
on the copper pipe it would need to be clean and then brazed I might guess.
All of that makes for a dirty element.
To the vacuum. I used to make vaccuum pumps out of old refrigerator motors.
That would be the first stage of pump down. But how do you take it down
below that? Then I speculate you use a ion pump to get rid of the stuff
that remains.
Regards
Paul.
On Tue, Dec 4, 2012 at 7:37 AM, Bob Camp lists@rtty.us wrote:
Hi
I went through a similar process quite a while ago. The dimensions of the
actual fountain can be quite small. One could make one the size of a shoe
box and still have it perform quite well.
Bob
On Dec 3, 2012, at 2:07 PM, Poul-Henning Kamp phk@phk.freebsd.dk wrote:
writes:
- USNO rubidium fountains
While many national labs have developed cesium fountains (for
accuracy), USNO has been gradually building rubidium fountain clocks
(for stability) and 4 of them are now fully operational. The ADEV
of these clocks gets well under 1e-16. The paper will have all the
details but the note I made was that with 20 months of data, the
stability was near 5e-17 at tau 4 months. That's 100x better than
a commercial cesium standard; better than all of USNO's other 70
cesium clocks and 15 H-masers combined. Yes, I've added "rubidium
fountain" to my automated eBay searches.
I happened to miss a turn (or something...) and stumbled into the
building where they keep those fountains when I visited USNO some
months ago. WhatI found most remarkable about them were how compact
they were, I still expected fountains to be room size, but these
were rack-sized.
I asked what the material cost would be and if a competent amateur
would be able to do something like that, and the clear message was
that the single biggest problem was the vacuum for a vessel that
size (when you can't use ferromagmnetic materials) and getting
the optical bench calibrated. "Apart from that it's just some
plumbing"
- Loran/UrsaNav
CW instead of very low duty cycle Loran pulses would improve S/N [...]
Actually, it probably will not.
The one smart thing about the LORAN signal is S/N, which means that
LORAN for timing purposes is incredible insensitive to noise and
at the same time, incredible transmitter power economy.
The one caveat is that the GRI has to be a good number, preferably
a four (or more!) digit prime number.
(You need to grok moduls-arithmetic to really appreciate this, but
its the magnitude of the prime factors of the product of the GRI
and the disturbing CW which counts: The smaller the are, the harder
it is to filter the CW-RFI out.)
This is why Europe switched to 4-digit GRIs and almost totally solved
CW-RFI by doing so, and why the Russian Chayka at GRI 8000 is totally
useless near anything resembling a transmitter.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@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.
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
I used to work on oxygen clean systems... that cleaning is done primarily
with liquid freon (R-113 and ultrasound - may be hard to get now). The
Vacuum stuff is expensive but off the shelf. The complicated part to me is
the lasers and microwave... in addition to the super-stable oscillator you
need to take maximum advantage of this stuff. Seems like a lot more than
plumbing to me. If you look at the papers on portable rubidium fountains
they are significantly bigger than a shoebox (65 cm).
Doc
KX0O
On Tue, Dec 4, 2012 at 8:06 AM, paul swed paulswedb@gmail.com wrote:
OK now that I am setting out to build one. Would the challenge for a
amateur be that the components you build with are basically dirty. Some how
on the copper pipe it would need to be clean and then brazed I might guess.
All of that makes for a dirty element.
To the vacuum. I used to make vaccuum pumps out of old refrigerator motors.
That would be the first stage of pump down. But how do you take it down
below that? Then I speculate you use a ion pump to get rid of the stuff
that remains.
Regards
Paul.
On Tue, Dec 4, 2012 at 7:37 AM, Bob Camp lists@rtty.us wrote:
Hi
I went through a similar process quite a while ago. The dimensions of the
actual fountain can be quite small. One could make one the size of a shoe
box and still have it perform quite well.
Bob
On Dec 3, 2012, at 2:07 PM, Poul-Henning Kamp phk@phk.freebsd.dk
wrote:
writes:
- USNO rubidium fountains
While many national labs have developed cesium fountains (for
accuracy), USNO has been gradually building rubidium fountain clocks
(for stability) and 4 of them are now fully operational. The ADEV
of these clocks gets well under 1e-16. The paper will have all the
details but the note I made was that with 20 months of data, the
stability was near 5e-17 at tau 4 months. That's 100x better than
a commercial cesium standard; better than all of USNO's other 70
cesium clocks and 15 H-masers combined. Yes, I've added "rubidium
fountain" to my automated eBay searches.
I happened to miss a turn (or something...) and stumbled into the
building where they keep those fountains when I visited USNO some
months ago. WhatI found most remarkable about them were how compact
they were, I still expected fountains to be room size, but these
were rack-sized.
I asked what the material cost would be and if a competent amateur
would be able to do something like that, and the clear message was
that the single biggest problem was the vacuum for a vessel that
size (when you can't use ferromagmnetic materials) and getting
the optical bench calibrated. "Apart from that it's just some
plumbing"
- Loran/UrsaNav
CW instead of very low duty cycle Loran pulses would improve S/N [...]
Actually, it probably will not.
The one smart thing about the LORAN signal is S/N, which means that
LORAN for timing purposes is incredible insensitive to noise and
at the same time, incredible transmitter power economy.
The one caveat is that the GRI has to be a good number, preferably
a four (or more!) digit prime number.
(You need to grok moduls-arithmetic to really appreciate this, but
its the magnitude of the prime factors of the product of the GRI
and the disturbing CW which counts: The smaller the are, the harder
it is to filter the CW-RFI out.)
This is why Europe switched to 4-digit GRIs and almost totally solved
CW-RFI by doing so, and why the Russian Chayka at GRI 8000 is totally
useless near anything resembling a transmitter.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@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.
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
--
Doc
Bill Dailey
KXØO
In message CAMPhiorJihW9z6-q0+Qfd+GPLjs6e8_ovWrDxQoxV=92Hgjo8A@mail.gmail.com
, Bill Dailey writes:
If you look at the papers on portable rubidium fountains
they are significantly bigger than a shoebox (65 cm).
Diameter is controlled by dispersion of the launched atoms (=recovery rate)
and the layers of shielding.
65cm looked like close to a minimum for USNO grade, amateurs could probably
make do with less shielding.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@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.
Hi
Indeed, you likely won't get USNO grade with a shoe box sized part. You can
get one to work and do quite good ADEV. No, I haven't done it, I'm just
going on what I've been told. The main point being that for a basement
project - smaller is probably lower cost.
Bob
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Poul-Henning Kamp
Sent: Tuesday, December 04, 2012 9:19 AM
To: Discussion of precise time and frequency measurement; Bill Dailey
Subject: Re: [time-nuts] PTTI 2012, part 2
In message
CAMPhiorJihW9z6-q0+Qfd+GPLjs6e8_ovWrDxQoxV=92Hgjo8A@mail.gmail.com
, Bill Dailey writes:
If you look at the papers on portable rubidium fountains
they are significantly bigger than a shoebox (65 cm).
Diameter is controlled by dispersion of the launched atoms (=recovery rate)
and the layers of shielding.
65cm looked like close to a minimum for USNO grade, amateurs could probably
make do with less shielding.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@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.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Agreed and they probably wouldn't use a cryogenic sapphire oscillator.
Sent from mobile
On Dec 4, 2012, at 8:34 AM, "Bob Camp" lists@rtty.us wrote:
Hi
Indeed, you likely won't get USNO grade with a shoe box sized part. You can
get one to work and do quite good ADEV. No, I haven't done it, I'm just
going on what I've been told. The main point being that for a basement
project - smaller is probably lower cost.
Bob
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Poul-Henning Kamp
Sent: Tuesday, December 04, 2012 9:19 AM
To: Discussion of precise time and frequency measurement; Bill Dailey
Subject: Re: [time-nuts] PTTI 2012, part 2
In message
CAMPhiorJihW9z6-q0+Qfd+GPLjs6e8_ovWrDxQoxV=92Hgjo8A@mail.gmail.com
, Bill Dailey writes:
If you look at the papers on portable rubidium fountains
they are significantly bigger than a shoebox (65 cm).
Diameter is controlled by dispersion of the launched atoms (=recovery rate)
and the layers of shielding.
65cm looked like close to a minimum for USNO grade, amateurs could probably
make do with less shielding.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@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.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Basements the key. So for me bigger is better. Heck if its a rack thats ok.
It gets interesting in what types of components you can use if you are
willing to go larger.
Great point on the laser and optics. Funny thing is for small change you
can actually get used optics bench components at least at the last MIT flea
I ran across the items. They were snapped up by the way.
From what I have seen of time-nuttery and Hydrogen masers I am actually not
all that sure its beyond this group.
Regards
Paul
On Tue, Dec 4, 2012 at 9:34 AM, Bob Camp lists@rtty.us wrote:
Hi
Indeed, you likely won't get USNO grade with a shoe box sized part. You can
get one to work and do quite good ADEV. No, I haven't done it, I'm just
going on what I've been told. The main point being that for a basement
project - smaller is probably lower cost.
Bob
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Poul-Henning Kamp
Sent: Tuesday, December 04, 2012 9:19 AM
To: Discussion of precise time and frequency measurement; Bill Dailey
Subject: Re: [time-nuts] PTTI 2012, part 2
In message
CAMPhiorJihW9z6-q0+Qfd+GPLjs6e8_ovWrDxQoxV=92Hgjo8A@mail.gmail.com
, Bill Dailey writes:
If you look at the papers on portable rubidium fountains
they are significantly bigger than a shoebox (65 cm).
Diameter is controlled by dispersion of the launched atoms (=recovery rate)
and the layers of shielding.
65cm looked like close to a minimum for USNO grade, amateurs could probably
make do with less shielding.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@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.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.