On Sun, 20 Jan 2008 15:19:06 +0000 (UTC), (Geoffrey
S. Mendelson) wrote:

John Kasupski wrote:
Note that we're probably talking errors in the amount of nanoseconds
(per second) here, certainly not errors that are going to cause
somebody to be ten minutes late for work, but for commercial or
scientific applications requiring a time reference that is related
directly to a national or international reference, GPS may not
necessarily cut the mustard.

Yes, but don't loose sight of the fact that this discussion is really
about consumer items. One person metioned in a previous post that his
clock syncs three times a week, other than that, it "runs free".

Well, my comments about GPS stemmed from David's comments that "Any
commercial entity who really needs accurate time switched over to GPS
a decade ago." But you're right, this has drifted off the topic of the
original post to the thread, which was related to consumer devices -
and David's comment downthread is also correct in pointing out that
there are GPS receivers (such as those made by ESE) that are properly
designed and can, in fact, provide a GPS time and frequency standard
that is traceable to a national or international time standard.

So IMHO if you build a consumer device that syncs every 5 minutes to
a GPS or GPS based standard, it will be a lot more accurate than
the average one that syncs every 2-3 days to a radio signal.

Yes, assuming it can get a signal...which problem exists with the
WWVB-based devices as well (and which was the whole point of the
article cited by the OP).

If it were to sync every minute to a time signal inserted in a cellular
control channel, it be even more accurate. Last I checked, the AT&T
Wireless 850mHz GSM (whatever name it is called now) network covers 98%
of the surface area of the U.S.

Since it is a receiver it can be broadbanded and if it were to cover
the GSM 850/900 mHz and 1800/1900 mHz bands it would work everywhere
there is GSM coverage. Except for Estonina and Brazil, an 850/900 mHz
receiver would be enough.

This does leave out parts of the Pacific Rim (Japan and Korea) and
some parts of Oz, but on the whole it cover almost the entire
populated earth.

FWIW, this Wikipedia article states that around 80% of the world's
population enjoys mobile phone coverage as of 2006 and that this is
expected to increase to 90% by the year 2010:

http://en.wikipedia.org/wiki/Mobile_phone

Despite that claim, even here in the United States there is still a
significant amount of territory away from major cities and interstate
highways where no wireless phone will work at all - but radios will
work, and consumers have other sources for getting the correct time
provided that they aren't too lazy to do it themselves rather than
expecting every device they own to do it for them.

IOW, self-setting clocks as consumer items are a convenience, not a
necessity. I'd be more concerned about wireless phones not working due
to the fact that this renders them useless for placing emergency
calls, rather than because it prevents these devices from updating
their time displays.

73 DE John, KC2HMZ

On Sun, 20 Jan 2008 06:40:03 -0800, David wrote:

Did you visit the ESE web site? They make the master clocks used in
broadcasting (and a lot of public service and labs) and they have very
well thought-out innards.

Yes, and yes. I never meant to insinuate that it was impossible to
obtain an accurate time standard using GPS. I did mean to point out
that to do so requires a properly designed receiver, which goes way
beyond the type of consumer-grade device the original poster had in
mind when telling us about NIST's plans to possibly add an east coast
equivalent to WWVB.

Is GPS like NTP in as they just give a raw number of seconds since a
certain date and that the receiver computes the real time from that,
based on its firmware?

Well...I'd have to say yes, since they are both based on the same
standard, which is TAI.

As I understand things, NTP actually references the UTC time scale
with a refined version of Marzullo's Algorithm called the intersection
algorithm. Like the original Marzullo's algorithm, the intersection
algorithm is used to select from among several sources for estimating
accurate time. It supports leap seconds, and the sources it uses can
include atomic clocks, GPS clocks or other radio clocks, computers
that are directly connected to such devices, and/or computers that are
able to use the Internet to poll computers that are directly connected
to such devices.

UTC (again as I understand things) is defined by a large collection
(about 300) of atomic clocks in over 50 national laboratories
worldwide, using the atomic time scale TAI (Temps Atomique
International, or International Atomic Time). TAI is sort of based on
counting seconds, in that it counts something called SI seconds, which
are defined in relationship to the radiation state of the Cesium-133
atom by international agreement. UTC is then derived from TAI, and is
periodically updated with leap seconds in order to more closely track
time standards based on the Earth's rotation.

I think I pretty much explained how GPS receivers estimate the time in
my previous reply upthread to a post by Geoffrey, so I won't repeat
all that again here, but when all is said and done, a fixed 19 second
offset from TAI gives GPS time. UTC and TAI were synchronized to an
exact fixed offset of 33 seconds at the end of 1971.

So the answer to your question. I would conclude that GPS and NTP are
alike in that both are synchronized to the same international
standard, based on cesium atomic clocks.

JK

John Kasupski wrote:
Yes, assuming it can get a signal...which problem exists with the
WWVB-based devices as well (and which was the whole point of the
article cited by the OP).

That is a problem of any radio based device, whether it uses GPS,
60kHz (or the European equivalent) signals, cell phone, etc.

I understand that analog TV signals in the U.S. also had time
coding in them to eliminate the flashing "12:00" problem.
Of course that's about to go away, and I have no idea if U.S.
HDTV signals include time coding or not.

When someone asked on another list about this several months ago,
so that he could get an heirloom digital clock to receive the 60kHz
signals in a place that was too well shielded and electricaly noisy,
I looked into generating the time signals with a PC. :-)

Programing wise it was simple, one could take the system clock
and build the data stream. If it was kept in sync with NTP, it
would be close enough for those clocks that only display to
minute or second resolution.

The problem for me was building a transmitter, because such parts
are almost impossible to get locally, and I had no clock to test
it and not much chance of getting one.

At some point I would like to build and market a WiFi NTP clock,
but that has to wait.


IOW, self-setting clocks as consumer items are a convenience, not a
necessity. I'd be more concerned about wireless phones not working due
to the fact that this renders them useless for placing emergency
calls, rather than because it prevents these devices from updating
their time displays.

Good point.

Geoff.


--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM
IL Voice: (07)-7424-1667 U.S. Voice: 1-215-821-1838
Visit my 'blog at http://geoffstechno.livejournal.com/

Geoffrey S. Mendelson wrote:
John Kasupski wrote:
Note that we're probably talking errors in the amount of nanoseconds
(per second) here, certainly not errors that are going to cause
somebody to be ten minutes late for work, but for commercial or
scientific applications requiring a time reference that is related
directly to a national or international reference, GPS may not
necessarily cut the mustard.

Yes, but don't loose sight of the fact that this discussion is really
about consumer items. One person metioned in a previous post that his
clock syncs three times a week, other than that, it "runs free".

So IMHO if you build a consumer device that syncs every 5 minutes to
a GPS or GPS based standard, it will be a lot more accurate than
the average one that syncs every 2-3 days to a radio signal.

If it were to sync every minute to a time signal inserted in a cellular
control channel, it be even more accurate. Last I checked, the AT&T
Wireless 850mHz GSM (whatever name it is called now) network covers 98%
of the surface area of the U.S.

Since it is a receiver it can be broadbanded and if it were to cover
the GSM 850/900 mHz and 1800/1900 mHz bands it would work everywhere
there is GSM coverage. Except for Estonina and Brazil, an 850/900 mHz
receiver would be enough.

This does leave out parts of the Pacific Rim (Japan and Korea) and
some parts of Oz, but on the whole it cover almost the entire
populated earth.

Geoff.



Much of the western USA has no cellular service period.

John Kasupski wrote:


IOW, self-setting clocks as consumer items are a convenience, not a
necessity. I'd be more concerned about wireless phones not working due
to the fact that this renders them useless for placing emergency
calls, rather than because it prevents these devices from updating
their time displays.

73 DE John, KC2HMZ


I like my atomic clocks and my atomic watches because they are always
correct, without having to use the internet. I have always insisted on
having the correct time (see Ken Nordine). The example of the clock
that only set itself 3 times a week was to show that they can work
inside a commercial building, albeit not terribly well.

If you're between Tucson and El Paso, or between El Paso and Laredo,
etc., you'd best be carrying a 4 Watt CB radio for emergencies. That
fancy telephone is very hit and miss.

On Jan 20, 7:19*am, (Geoffrey S. Mendelson) wrote:
John Kasupski wrote:
Note that we're probably talking errors in the amount of nanoseconds
(per second) here, certainly not errors that are going to cause
somebody to be ten minutes late for work, but for commercial or
scientific applications requiring a time reference that is related
directly to a national or international reference, GPS may not
necessarily cut the mustard.

Yes, but don't loose sight of the fact that this discussion is really
about consumer items. One person metioned in a previous post that his
clock syncs three times a week, other than that, it "runs free".

So IMHO if you build a consumer device that syncs every 5 minutes to
a GPS or GPS based standard, it will be a lot more accurate than
the average one that syncs every 2-3 days to a radio signal.

If it were to sync every minute to a time signal inserted in a cellular
control channel, it be even more accurate. Last I checked, the AT&T
Wireless 850mHz GSM (whatever name it is called now) network covers 98%
of the surface area of the U.S.

Since it is a receiver it can be broadbanded and if it were to cover
the GSM 850/900 mHz and 1800/1900 mHz bands it would work everywhere
there is GSM coverage. Except for Estonina and Brazil, an 850/900 mHz
receiver would be enough.

This does leave out parts of the Pacific Rim (Japan and Korea) and
some parts of Oz, but on the whole it cover almost the entire
populated earth.

Geoff.

--
Geoffrey S. Mendelson, Jerusalem, Israel *N3OWJ/4X1GM
IL Voice: (07)-7424-1667 U.S. Voice: 1-215-821-1838
Visit my 'blog athttp://geoffstechno.livejournal.com/

JK & GSM,

Where Do You Find The Time "Tick-Tock" - To Argue . . .
The Finer Points of Time Down To The Nearest Second ? )

And the Reality -is- for most Non-Techincal Consumers of Time :
Time that 'is' "Accurate to the Nearest Minute" is Good Enough.

=SO= For Them - Any Time In-Accuracy Less-Than 31 Seconds :
Is To The Nearest Minute. -and- That Is Good Enough For Me ~ RHF

David is Right : An Atomic Clock that resets itself a few times a
Week and uses a single set of Batterys {runs independently} that
Lasts for a Year of more : Meets the Needs of Non-Techincal
Consumers of Time.

-But- Then Again - Any common Consumer Product that has
a Time Display and is "Accurate to the Nearest Minute" also
Meets the Needs of Non-Techincal Consumers of Time.

RHF wrote:

On Jan 20, 7:19 am, (Geoffrey S. Mendelson) wrote:
John Kasupski wrote:
Note that we're probably talking errors in the amount of nanoseconds
(per second) here, certainly not errors that are going to cause
somebody to be ten minutes late for work, but for commercial or
scientific applications requiring a time reference that is related
directly to a national or international reference, GPS may not
necessarily cut the mustard.

Yes, but don't loose sight of the fact that this discussion is really
about consumer items. One person metioned in a previous post that his
clock syncs three times a week, other than that, it "runs free".

So IMHO if you build a consumer device that syncs every 5 minutes to
a GPS or GPS based standard, it will be a lot more accurate than
the average one that syncs every 2-3 days to a radio signal.

If it were to sync every minute to a time signal inserted in a cellular
control channel, it be even more accurate. Last I checked, the AT&T
Wireless 850mHz GSM (whatever name it is called now) network covers 98%
of the surface area of the U.S.

Since it is a receiver it can be broadbanded and if it were to cover
the GSM 850/900 mHz and 1800/1900 mHz bands it would work everywhere
there is GSM coverage. Except for Estonina and Brazil, an 850/900 mHz
receiver would be enough.

This does leave out parts of the Pacific Rim (Japan and Korea) and
some parts of Oz, but on the whole it cover almost the entire
populated earth.

Geoff.

--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM
IL Voice: (07)-7424-1667 U.S. Voice: 1-215-821-1838
Visit my 'blog athttp://geoffstechno.livejournal.com/

JK & GSM,

Where Do You Find The Time "Tick-Tock" - To Argue . . .
The Finer Points of Time Down To The Nearest Second ? )

And the Reality -is- for most Non-Techincal Consumers of Time :
Time that 'is' "Accurate to the Nearest Minute" is Good Enough.

=SO= For Them - Any Time In-Accuracy Less-Than 31 Seconds :
Is To The Nearest Minute. -and- That Is Good Enough For Me ~ RHF

David is Right : An Atomic Clock that resets itself a few times a
Week and uses a single set of Batterys {runs independently} that
Lasts for a Year of more : Meets the Needs of Non-Techincal
Consumers of Time.

-But- Then Again - Any common Consumer Product that has
a Time Display and is "Accurate to the Nearest Minute" also
Meets the Needs of Non-Techincal Consumers of Time.

Heck, I remember when folks were making fun of my big GMT clock here in the
shack, but it keeps on a rockin' and a tick-tock'in, and has been for almost 25
years now. Put in a new battery once a year, set it to WWV every few weeks and
that's good enough for me!

dxAce
Michigan
USA

On Jan 20, 11:49*am, (Geoffrey S. Mendelson) wrote:
John Kasupski wrote:
Yes, assuming it can get a signal...which problem exists with the
WWVB-based devices as well (and which was the whole point of the
article cited by the OP).

That is a problem of any radio based device, whether it uses GPS,
60kHz (or the European equivalent) signals, cell phone, etc.

I understand that analog TV signals in the U.S. also had time
coding in them to eliminate the flashing "12:00" problem.
Of course that's about to go away, and I have no idea if U.S.
HDTV signals include time coding or not.

When someone asked on another list about this several months ago,
so that he could get an heirloom digital clock to receive the 60kHz
signals in a place that was too well shielded and electricaly noisy,
I looked into generating the time signals with a PC. :-)

Programing wise it was simple, one could take the system clock
and build the data stream. If it was kept in sync with NTP,

- it would be close enough for those clocks that only display
- to minute or second resolution.

Yes there is the practical consideration that most common
Consumer Products that have a Time Display "Only" display
the Time-to-the-Minute {No Seconds} and therefore Time that
is "Accurate to the Nearest Minute" meets the Needs of these
Non-Techincal Consumers of Time.

In article , David
wrote:

Geoffrey S. Mendelson wrote:
John Kasupski wrote:
Note that we're probably talking errors in the amount of nanoseconds
(per second) here, certainly not errors that are going to cause
somebody to be ten minutes late for work, but for commercial or
scientific applications requiring a time reference that is related
directly to a national or international reference, GPS may not
necessarily cut the mustard.

Yes, but don't loose sight of the fact that this discussion is really
about consumer items. One person metioned in a previous post that his
clock syncs three times a week, other than that, it "runs free".

So IMHO if you build a consumer device that syncs every 5 minutes to
a GPS or GPS based standard, it will be a lot more accurate than
the average one that syncs every 2-3 days to a radio signal.

If it were to sync every minute to a time signal inserted in a cellular
control channel, it be even more accurate. Last I checked, the AT&T
Wireless 850mHz GSM (whatever name it is called now) network covers 98%
of the surface area of the U.S.

Since it is a receiver it can be broadbanded and if it were to cover
the GSM 850/900 mHz and 1800/1900 mHz bands it would work everywhere
there is GSM coverage. Except for Estonina and Brazil, an 850/900 mHz
receiver would be enough.

This does leave out parts of the Pacific Rim (Japan and Korea) and
some parts of Oz, but on the whole it cover almost the entire
populated earth.

Geoff.



Much of the western USA has no cellular service period.

Most of the population is on the coast and has cell service.

--
Telamon
Ventura, California

"Telamon" wrote in message
...
Much of the western USA has no cellular service period.

Most of the population is on the coast and has cell service.


Until they travel away from the populated areas. Big stretches of Death
Valley with no service. May have changed since I was last there in 2000,
but there were even quite a few dead spots on the highway between Stockton
and Fairfield. By contrast, here in the ROK, we have nearly 100% cell
penetration (can't say absolutely 100%, since there is the occasional dead
spot inside a building or a tunnel, but even most tunnels have service...
they make sure there is a cell tower posted at at least one end of every
tunnel).

Of course, the states is a much bigger place, so much more difficult to get
100% penetration of service.