Loran-C sync
Hi,
in https://en.wikipedia.org/wiki/Loran-C I read that a Loran station
made use of up to three atomic clocks.
They were "synchronized to within 100 ns ofCoordinated Universal Time
https://en.wikipedia.org/wiki/Coordinated_Universal_Time(UTC), the
actual accuracy achieved as of 1994 was within 500 ns.^"
https://en.wikipedia.org/wiki/Loran-C#cite_note-LORANC2-6-43
^Now I wonder: They only had their 9192631770ticks/sec, how did they
know about UTC ?
https://en.wikipedia.org/wiki/Loran-C#cite_note-LORANC2-6-43
^THX
^Cheers
^Detlef
^https://en.wikipedia.org/wiki/Loran-C#cite_note-LORANC2-6-43
--
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Detlef,
Now I wonder: They only had their 9192631770 ticks/sec, how did they
know about UTC?
UTC officially began in 1972 but even before that point there was close
coordination of clocks around the world. You are correct that powering
up a cesium clock gives you how long a second is, but not what precise
time it is. The time synchronization of clocks was done by various
means, such as radio, TV, satellite, and especially, portable quartz or
atomic clocks.
You can guess that radio would have some limitations due to atmosphere,
but for millisecond work it was fine. And you can guess that using
satellites was still kind of new and expensive in the 50's and 60's. So
for highest precision they simply carried portable clocks around to
synchronize the clocks at each Loran site, or each NASA site, or
military site, etc. Sometimes by car, sometimes by plane. This was
standard practice for decades. I've talked to a number of old timers who
were part of that "flying clock" era. Now with GPS, all the fun is over.
Example of portable quartz clock for microsecond synchronization:
http://leapsecond.com/museum/au1210/
Example of portable cesium clock for very sub-microsecond synchronization:
http://leapsecond.com/museum/fts4010/
A wonderful site with lots of info the flying clock era:
https://www.hpmemoryproject.org/news/flying_clock/celebration_01.htm
And my favorite "flying clock" experiment:
http://leapsecond.com/museum/HK50/
/tvb
And to add eLORAN has been on te air in the west for at least a year and a
half.
Rodger and I on a daily basis are tracking the eloran signal at 2000 and
2400 miles using Austron 2100Fs.
Its interesting to watch the variations in propagation delay.
Paul
WB8TSL
On Thu, Dec 5, 2024 at 12:54 PM Tom Van Baak via time-nuts <
time-nuts@lists.febo.com> wrote:
Detlef,
Now I wonder: They only had their 9192631770 ticks/sec, how did they
know about UTC?
UTC officially began in 1972 but even before that point there was close
coordination of clocks around the world. You are correct that powering
up a cesium clock gives you how long a second is, but not what precise
time it is. The time synchronization of clocks was done by various
means, such as radio, TV, satellite, and especially, portable quartz or
atomic clocks.
You can guess that radio would have some limitations due to atmosphere,
but for millisecond work it was fine. And you can guess that using
satellites was still kind of new and expensive in the 50's and 60's. So
for highest precision they simply carried portable clocks around to
synchronize the clocks at each Loran site, or each NASA site, or
military site, etc. Sometimes by car, sometimes by plane. This was
standard practice for decades. I've talked to a number of old timers who
were part of that "flying clock" era. Now with GPS, all the fun is over.
Example of portable quartz clock for microsecond synchronization:
http://leapsecond.com/museum/au1210/
Example of portable cesium clock for very sub-microsecond synchronization:
http://leapsecond.com/museum/fts4010/
A wonderful site with lots of info the flying clock era:
https://www.hpmemoryproject.org/news/flying_clock/celebration_01.htm
And my favorite "flying clock" experiment:
http://leapsecond.com/museum/HK50/
/tvb
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Hi Tom:
The military uses "Have Quick" as a microsecond hardware time synchronization protocol.
For sure the PLGR and DAGR GPS receivers support it and I think some of the the Trimpack GPS receivers support it.
Do you know if there's a Time Nuts "Have Quick" way to set clocks?
https://prc68.com/I/DAGR.shtml#HQ1PPS
https://prc68.com/I/PLGR.shtml#HQTOD
https://prc68.com/I/O1814.shtml#TOD
https://prc68.com/I/Trimpack.shtml#PSN-10
--
Have Fun,
Brooke Clarke
https://www.PRC68.com
axioms:
- The extent to which you can fix or improve something will be limited by how well you understand how it works.
- Everybody, with no exceptions, holds false beliefs.
-------- Original Message --------
Detlef,
Now I wonder: They only had their 9192631770 ticks/sec, how did they know about UTC?
UTC officially began in 1972 but even before that point there was close coordination of clocks around the world. You
are correct that powering up a cesium clock gives you how long a second is, but not what precise time it is. The time
synchronization of clocks was done by various means, such as radio, TV, satellite, and especially, portable quartz or
atomic clocks.
You can guess that radio would have some limitations due to atmosphere, but for millisecond work it was fine. And you
can guess that using satellites was still kind of new and expensive in the 50's and 60's. So for highest precision
they simply carried portable clocks around to synchronize the clocks at each Loran site, or each NASA site, or
military site, etc. Sometimes by car, sometimes by plane. This was standard practice for decades. I've talked to a
number of old timers who were part of that "flying clock" era. Now with GPS, all the fun is over.
Example of portable quartz clock for microsecond synchronization:
http://leapsecond.com/museum/au1210/
Example of portable cesium clock for very sub-microsecond synchronization:
http://leapsecond.com/museum/fts4010/
A wonderful site with lots of info the flying clock era:
https://www.hpmemoryproject.org/news/flying_clock/celebration_01.htm
And my favorite "flying clock" experiment:
http://leapsecond.com/museum/HK50/
/tvb
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Hi
Back in the day, USNO monitored all of the US Loran chains. They published a monthly ( … might have been weekly …) circular that showed the offset of each chain to USNO’s master clock setup. Since USNO is a “primary time source” for the US, that pretty much makes them correct against whatever the master time standard was.
If you happened to be sitting out in the middle of nowhere and wanted to trace time via Loran-C, you had them mail you (yes mail from the post office :) :) ) the circular. When it got to you, the data there could be compared to your past measurements to validate them.
Bob
On Dec 5, 2024, at 11:35 AM, dschuecker via time-nuts time-nuts@lists.febo.com wrote:
Hi,
in https://en.wikipedia.org/wiki/Loran-C I read that a Loran station made use of up to three atomic clocks.
They were "synchronized to within 100 ns ofCoordinated Universal Time https://en.wikipedia.org/wiki/Coordinated_Universal_Time(UTC), the actual accuracy achieved as of 1994 was within 500 ns.^" https://en.wikipedia.org/wiki/Loran-C#cite_note-LORANC2-6-43
^Now I wonder: They only had their 9192631770ticks/sec, how did they know about UTC ?
https://en.wikipedia.org/wiki/Loran-C#cite_note-LORANC2-6-43
^THX
^Cheers
^Detlef
^https://en.wikipedia.org/wiki/Loran-C#cite_note-LORANC2-6-43
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The group might be interested in one of my old pubs, enclosed.
Don
----- Original Message -----
From: "paul swed via time-nuts" time-nuts@lists.febo.com
To: "Discussion of precise time and frequency measurement" time-nuts@lists.febo.com
Cc: "paul swed" paulswedb@gmail.com
Sent: Thursday, December 5, 2024 12:56:45 PM
Subject: [time-nuts] Re: Loran-C sync
And to add eLORAN has been on te air in the west for at least a year and a
half.
Rodger and I on a daily basis are tracking the eloran signal at 2000 and
2400 miles using Austron 2100Fs.
Its interesting to watch the variations in propagation delay.
Paul
WB8TSL
On Thu, Dec 5, 2024 at 12:54 PM Tom Van Baak via time-nuts <
time-nuts@lists.febo.com> wrote:
Detlef,
Now I wonder: They only had their 9192631770 ticks/sec, how did they
know about UTC?
UTC officially began in 1972 but even before that point there was close
coordination of clocks around the world. You are correct that powering
up a cesium clock gives you how long a second is, but not what precise
time it is. The time synchronization of clocks was done by various
means, such as radio, TV, satellite, and especially, portable quartz or
atomic clocks.
You can guess that radio would have some limitations due to atmosphere,
but for millisecond work it was fine. And you can guess that using
satellites was still kind of new and expensive in the 50's and 60's. So
for highest precision they simply carried portable clocks around to
synchronize the clocks at each Loran site, or each NASA site, or
military site, etc. Sometimes by car, sometimes by plane. This was
standard practice for decades. I've talked to a number of old timers who
were part of that "flying clock" era. Now with GPS, all the fun is over.
Example of portable quartz clock for microsecond synchronization:
http://leapsecond.com/museum/au1210/
Example of portable cesium clock for very sub-microsecond synchronization:
http://leapsecond.com/museum/fts4010/
A wonderful site with lots of info the flying clock era:
https://www.hpmemoryproject.org/news/flying_clock/celebration_01.htm
And my favorite "flying clock" experiment:
http://leapsecond.com/museum/HK50/
/tvb
time-nuts mailing list -- time-nuts@lists.febo.com
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Don Latham
PO Box 404,
Frenchtown, MT, 59846
406-626-4304
dschuecker via time-nuts writes:
Now I wonder: They only had their 9192631770ticks/sec, how did they
know about UTC ?
Dave Mills told me a lot about this:
Via feedback from monitoring receivers and stations.
It's actually pretty interesting how they had to calibrate things.
If you look in old Loran-C tables, you will see things like:
# GRI and Chain Name
# Station
# Latitude / Longitude
# Emission / Coding Delay
# Power in Kilowatts
5543 CALCUTTA
Master / Balasore
021° 29' 08.000" N 086° 55' 18.000" E
0
43
Whiskey / Diamond Harbor
022° 10' 18.000" N 088° 12' 25.000" E
18,510.68 18,000.00
11
Xray / Patpur
020° 26' 48.000" N 085° 49' 47.000" E
36,542.75 36,000.00
11
The master signal being the reference /as transmitted in air/ has
no assigned delays.
The "coding delay" was what the slave stations steeed to, they would
receive the master signal and aim their antenna current, which they
could measure, at the "coding delay".
However, the antennas introduce a delay, which depends on not only
the antenna physics, but also the geology it stands on and the
salinity of the first many nautical miles of sea water.
So they measured the actual delays at some distance, and blessed
those numbers as "emission delays" for the receivers to use.
Dave Mills told me that the emission delays were classified at first
but that stopped when he pointed out that anybody could trivially
measure them, by doing so.
The emission delays varied, not only with weather, ice is
dielectric, but also seasonally due due to changes in sea salinity
and soil moisture.
This was a problem, because the emission delays were also built
into navigational charts and smart receivers, so as things got more
advanced, magnetic field monitoring antennas, located kilometers
away, far enough to measure the actually emitted signal, replaced
the the antenna current as steering target.
I took a picture of one of the monitoring antennas at L9007M:
https://phk.freebsd.dk/L9007M
Eventually the slaves stopped following the masters, and steed to
GPS instead, and since that took one long-ish trip through the
atmosphere out of the equations, it almost doubled the navigational
precision.
If you do the math, you will find that there is not
an integral number of 55.43 millisecond periods in any year,
Loran-C time therefore started at 1958-01-01 00:00Z, and master
stations counted from that.
This meant that if you could receive two or three chains, you could
work backwards and figure out what time it was, because the modulus
arithmetic of the GRI values gave good long periods.
Tables with "Time of coincidence" were published, which listed when
the signal from each loran station & chain would coincide with the
UTC second, which happened on a daily-ish basis.
Some of the Austron receivers have hardware where you pushed
a button after the previous UTC second, and would take special
notice of the next Loran-C pulse.
When the European host states took over the stations on their soil
and created the "NELS", somebody decided to renumber their chains
to four digits, because that made the modulus arithmetic come out
unique for three chains and gave you very long period for two
chains.
It also meant that not a single Loran-C receiver in existence could
receive their signals and since GPS was a thing, they only got very
few users in "specialized military applications".
The M stations were monitored from various military laboratories,
notably USNO, and corrections sent to them as required, but Dave
just knew the telegrams arrived, and this part of the system is
barely mentioned in the open sources.
As far as I can tell, NIST's measurements were at best used as a
sanity-check on USNO's own measurements.
Maybe Demetrios can tell us how that part of it worked ?
Poul-Henning
--
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.
Rodger and I are both using Loop antennas. Rodgers is a original Austron
Loop antenna. I have been experimenting with square loops.
Fron4' X4' to 10' X 10'. The 4' has always been problematic and am bringing
it in this weekend.I am also using homebrew fet preamps.
Stations are hard to say. But it appears to be Fallon Nv. and thats 2400
miles for me George in Washington is not on the air currently.
Cooling issues. There is a third station in Montana thats questionable for
me at least.
None of teh stations ever emit a master. They all behave as secondaries.
It also seems that the Austron 2100F tracks more quickly then the 2100T.
Its interesting to look at the logs and see the frequency offset shift
around.
Paul
WB8TSL
On Fri, Dec 6, 2024 at 4:56 AM Poul-Henning Kamp via time-nuts <
time-nuts@lists.febo.com> wrote:
dschuecker via time-nuts writes:
Now I wonder: They only had their 9192631770ticks/sec, how did they
know about UTC ?
Dave Mills told me a lot about this:
Via feedback from monitoring receivers and stations.
It's actually pretty interesting how they had to calibrate things.
If you look in old Loran-C tables, you will see things like:
# GRI and Chain Name
# Station
# Latitude / Longitude
# Emission / Coding Delay
# Power in Kilowatts
5543 CALCUTTA
Master / Balasore
021° 29' 08.000" N 086° 55' 18.000" E
0
43
Whiskey / Diamond Harbor
022° 10' 18.000" N 088° 12' 25.000" E
18,510.68 18,000.00
11
Xray / Patpur
020° 26' 48.000" N 085° 49' 47.000" E
36,542.75 36,000.00
11
The master signal being the reference /as transmitted in air/ has
no assigned delays.
The "coding delay" was what the slave stations steeed to, they would
receive the master signal and aim their antenna current, which they
could measure, at the "coding delay".
However, the antennas introduce a delay, which depends on not only
the antenna physics, but also the geology it stands on and the
salinity of the first many nautical miles of sea water.
So they measured the actual delays at some distance, and blessed
those numbers as "emission delays" for the receivers to use.
Dave Mills told me that the emission delays were classified at first
but that stopped when he pointed out that anybody could trivially
measure them, by doing so.
The emission delays varied, not only with weather, ice is
dielectric, but also seasonally due due to changes in sea salinity
and soil moisture.
This was a problem, because the emission delays were also built
into navigational charts and smart receivers, so as things got more
advanced, magnetic field monitoring antennas, located kilometers
away, far enough to measure the actually emitted signal, replaced
the the antenna current as steering target.
I took a picture of one of the monitoring antennas at L9007M:
https://phk.freebsd.dk/L9007M
Eventually the slaves stopped following the masters, and steed to
GPS instead, and since that took one long-ish trip through the
atmosphere out of the equations, it almost doubled the navigational
precision.
If you do the math, you will find that there is not
an integral number of 55.43 millisecond periods in any year,
Loran-C time therefore started at 1958-01-01 00:00Z, and master
stations counted from that.
This meant that if you could receive two or three chains, you could
work backwards and figure out what time it was, because the modulus
arithmetic of the GRI values gave good long periods.
Tables with "Time of coincidence" were published, which listed when
the signal from each loran station & chain would coincide with the
UTC second, which happened on a daily-ish basis.
Some of the Austron receivers have hardware where you pushed
a button after the previous UTC second, and would take special
notice of the next Loran-C pulse.
When the European host states took over the stations on their soil
and created the "NELS", somebody decided to renumber their chains
to four digits, because that made the modulus arithmetic come out
unique for three chains and gave you very long period for two
chains.
It also meant that not a single Loran-C receiver in existence could
receive their signals and since GPS was a thing, they only got very
few users in "specialized military applications".
The M stations were monitored from various military laboratories,
notably USNO, and corrections sent to them as required, but Dave
just knew the telegrams arrived, and this part of the system is
barely mentioned in the open sources.
As far as I can tell, NIST's measurements were at best used as a
sanity-check on USNO's own measurements.
Maybe Demetrios can tell us how that part of it worked ?
Poul-Henning
--
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.
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