Position error with Loran-C is about a half foot per nanosecond, as moving a half foot from station A to station B causes a half nanosecond delay from station A and a half nanosecond advance from station B. At 100kHz, the propagation is by surface wave so changes in the ionosphere do not have a major affect on the signals.
My learning about Loran-C for timing was to come up with a frequency reference for a proposed Josephson junction voltage standard.
Erik_MagThe digital modulation schemes used by cell phones require very tight synchronization between the towers. Each one has a GPS receiver to provide a very stable time and frequency reference. In addition, the phones themselves have to be synchronized to the towers, so part of the handshaking between the tower and phone would be time information.
Thirty years ago, the best way of getting accurate time and frequency references was via Loran-C, where the receivers would use the phase of the 100kHz signal to extract sub-microsecond timing information.
Remember to put this in perspective that the speed of light is essentially a foot per nanosecond.
The digital modulation schemes used by cell phones require very tight synchronization between the towers. Each one has a GPS receiver to provide a very stable time and frequency reference. In addition, the phones themselves have to be synchronized to the towers, so part of the handshaking between the tower and phone would be time information.
Thirty years ago, the best way of getting accurate time and frequency references was via Loran-C, where the receivers would use the phase of the 100kHz signal to extract sub microsecond timing information.
BaltACDMy Android phone gets its time automatically - I don't know its source, however, it seems to be on the same program as my W10 computer.
Not exactly sure how cell phones work it but office phones and the like get their time display from the phone PBX which should be synchronized to the local Central Office Switch which the PBX is a child of. Phone switches are basically Unix or Linux server boxes.
rdamon I used to listen to WWV as a kid. :)
I used to listen to WWV as a kid. :)
Must have been boring after a couple of hours.
But seriously, in my teens I used to like working on clocks, and I used to use WWV to set and adjust them.
_____________
"A stranger's just a friend you ain't met yet." --- Dave Gardner
OvermodAs will all manner of "atomic" clocks and watches ... although it may take them a while to actually synchronize.
Indeed, I have one hanging over my ham shack (bench). Still, for those who may want to try "old school," the option is there.
Larry Resident Microferroequinologist (at least at my house) Everyone goes home; Safety begins with you My Opinion. Standard Disclaimers Apply. No Expiration Date Come ride the rails with me! There's one thing about humility - the moment you think you've got it, you've lost it...
tree68A relatively inexpensive shortwave receiver, and decent band conditions, will bring WWV (and WWVH) right into your home.
The German service is nominally more precise in the same way PAL has 'higher resolution' than NTSC: it broadcasts at over 70kHz.
Note that the atomic watches killed, almost at a stroke, the market for actual true-high-precision watches outside the snob markets ... or railroading. Just as even the cheap quartz commodity movements can be regulated to COSC 'chronometer' rating, resetting them regularly every so often by radio makes them accurate over long spans of time even if they are not truly precise.
The railroad service, however, can't assume reception of the correct signal, and so more precise running is needed. Of course the standard is still... within 30 seconds a week, and you get your 'updates' not electrically from a standard clock but by someone responsible time-hacking.
A relatively inexpensive shortwave receiver, and decent band conditions, will bring WWV (and WWVH) right into your home. In addition to time hacks, the stations also broadcast standard audio tones, including the A above middle C (440 Hz) so you can tune your instrument, too...
WWV broadcasts on 2.5, 5, 10, 15 and 20 MHz from a location near Fort Collins, Colorado. WWVH broadcasts on 2.5, 5, 10 and 15 MHz from Kauai, Hawaii.
A quick search on-line gave me shortwave radios from $25 to $250.
BaltACDI seem to recall that one could call a number (maybe the Operator) that was specifically dedicated to communicating 'the correct time';
https://onmilwaukee.com/articles/calling-time-weather
Those who know the musician Vangelis (remember Chariots of Fire or Argentine coverage of the Falklands/Malvinas war?) may remember his fascination with the Post Office Speaking Clock, which you can still access in Blighty by dialing 123. And then there is Naval Observatory dial-up, although in this age of long-distance too cheap to meter they cut you off after a couple of minutes.
For those of you who wonder how anyone could be so patient and so accurate all that time, here is how the trick was done back in the day: time drums on Audiochrons.
https://m.youtube.com/watch?feature=youtu.be&t=84&v=n52MMiH0dS8
Western Union ran a service from the '30s all the way into the '60s that used a midget version of railroad master-clock synchronization to provide 'correct time for 5 cents a day' -- as with the phones of that era, you didn't own the clock, you leased it.
(Incidentally, there were Synchronomes and 'other variants' that had no time display; they were used to indicate the duration of long-distance calls -- surprisingly NOT in sixth-of-a-second increments although that would have been technically easy.)
I'll have to think of something time-related to replace this double post.
Here's the skinny on the broadcast time service circa early 2005 (in PDF format):
https://tf.nist.gov/general/pdf/1969.pdf
For those of you concerned with 100Hz time signal accuracy over 60kHz radio, consider 2nd Space Ops, which keeps the clocks in GPS synchronized to each other to within a few nanoseconds.
If you thought it was cool to have clocks more accurate than earth's rotation, you'll just love how Coordinated Universal Time is figured... but you will NOT love some of the things Earth does while you're watching it accurately enough!
The NIST broadcasts time over shortwave frequencies 24 hours a day. I used to havea shortwave radio and would get my time from one of their broadcasts.
They also have telephone access (303) 499-7111 (Ft. Collins CO site. there is another numbr for an Hawaii broadcasting site.) which connects the caller for two minutes. It automatically disconnects after two minutes because it's not a toll-free number. It is our time standard and I have this number on my cell phone.
Back in the standard code of operating rules era, Rule no. 1 until late in that area was about obtaining the proper time and transmitting it to all points every day at a specific time.
Jeff
wjstix BaltACD On the B&O a 'time signal' was sent over the telegraph and telephone wires at Noon. In the late 1930's my dad worked as a telegrapher for Postal Telegraph in Galesburg IL, and Postal did the same thing - my dad would set his pocket watch based on the hourly update. Because of that it wasn't unusual for the telegraph office to get calls asking for the exact time, even from one of the railroads in town if they missed their own hourly update for some reason. One day, the Santa Fe and the CB&Q both called for the correct time, along with city hall and a local bank. Each time, dad took out his watch and gave them the time. One of his co-workers finally shook his head and said "Bob, you realize about half of northern Illinois is keeping time right now based on your pocket watch!"
BaltACD On the B&O a 'time signal' was sent over the telegraph and telephone wires at Noon.
In the late 1930's my dad worked as a telegrapher for Postal Telegraph in Galesburg IL, and Postal did the same thing - my dad would set his pocket watch based on the hourly update. Because of that it wasn't unusual for the telegraph office to get calls asking for the exact time, even from one of the railroads in town if they missed their own hourly update for some reason. One day, the Santa Fe and the CB&Q both called for the correct time, along with city hall and a local bank. Each time, dad took out his watch and gave them the time. One of his co-workers finally shook his head and said "Bob, you realize about half of northern Illinois is keeping time right now based on your pocket watch!"
I seem to recall that one could call a number (maybe the Operator) that was specifically dedicated to communicating 'the correct time'; one could also call 'Information' to get the number of someone who did not have a unlisted number (we also used to get Telephone Books of the name, address and telephone number of everyone that did not have a unlisted number in the local area).
Never too old to have a happy childhood!
A watchmaker had a small shop on the main road through town. He noted that every morning a man would stop at the shop window to set his pocket watch by the time on the clock in the window. This went on for years.
One day the man came in the shop and said he was retiring from his job at the courthouse. He said he appreciated having been able to stop at the window every morning to set his watch, so that when he rang the bell in the courthouse belfry at noon, he would be accurate for everyone in the town and surrounding farms to know it was noon.
The watchmaker said, "That is interesting; I set that clock every day by when the noon bell rings at the courthouse."
Semper Vaporo
Pkgs.
"A man with one watch knows what time it is. A man with two is never sure". --- Ben Franklin
BaltACDOn the B&O a 'time signal' was sent over the telegraph and telephone wires at Noon.
The one I use on my laptop is at http://www.thinkman.com/dimension4/
TBS (then WTBS) would start at the :05 and :35 to hope that you would stay tuned as the other shows had already started.
NTP (Network Time Protocol) is used to sync time on a computer or other device.
I use the ones at https://tf.nist.gov/tf-cgi/servers.cgi
Leo_Ames I deliberately pad my DVR recordings by a minute both ways just to accomodate that poor time keeping. Back when I can remember watching Little House on the Prairie on weekday mornings during things like snowdays in the early to mid 1990's, TBS always started at 3 minutes after the hour and advertised it as such. As a child, I didn't think too much of it. As an adult looking back on the practice, I imagine it was a deliberate attempt to time it in order to catch channel surfers that didn't find anything else that caught their eye. As they're browsing through a few dozen channels, they'd stumble across a rerun of a favorite show just starting (They'd also always air Matlock and The Love Boat in the morning, but I'd only watch Little House). With seemingly 1,000 channels these days, that strategy is probably defunct for the most part now. If cable subscribers are doing any browsing these days, it's likely through their on-screen program guide or just browsing through a small group of favorite channels. For me personally, my cable box mostly just stays on Turner Classic Movies these days.
I deliberately pad my DVR recordings by a minute both ways just to accomodate that poor time keeping.
Back when I can remember watching Little House on the Prairie on weekday mornings during things like snowdays in the early to mid 1990's, TBS always started at 3 minutes after the hour and advertised it as such.
As a child, I didn't think too much of it. As an adult looking back on the practice, I imagine it was a deliberate attempt to time it in order to catch channel surfers that didn't find anything else that caught their eye. As they're browsing through a few dozen channels, they'd stumble across a rerun of a favorite show just starting (They'd also always air Matlock and The Love Boat in the morning, but I'd only watch Little House).
With seemingly 1,000 channels these days, that strategy is probably defunct for the most part now. If cable subscribers are doing any browsing these days, it's likely through their on-screen program guide or just browsing through a small group of favorite channels.
For me personally, my cable box mostly just stays on Turner Classic Movies these days.
The few minutes off the hour or half hour is deliberate. Part of the reason I once read was to hold viewers to a specific channel. And some cable channels will do it, at least part of the time. Especially when they're running a block of episodes for one show over a few hours.
When I worked at a radio station (WFMS) in a previous era, I had to play the station break within the hour and 1 minute after the hour. I was told it was an FCC requirement and I and the station were both in trouble if I failed. We had a clock on the control room wall that was set by the chief engineer (the owner of the station) by the National Bureau of Standards WWV radio signal.
Time used to be very important, but these days, with all the greator accuracy available, it seems nobody really cares much anymore.
I'd actually like it if classic tv channels like MeTV would cease trying to fit into a rigid 30/60 minute format.
I hate watching cliff notes versions of classic tv shows, so mostly ignore that channel these days since they'll lop off 3 or 4 minutes of a classic 25-26 minute long tv show to accomodate commercials.
I have a specific program on my laptop that I use for ham radio digital programs. Those technologies are dependent on everyone using the same time - a few seconds late or early will foul up the coordination between users. The program reaches out to one of several time sources when I boot up and adjusts the computer time accordingly.
When I installed a trunked radio system some years ago, it included a GPS based time source.
OTOH, I spent some time shipboard in the 1970's, and we had a cesium standard onboard.
I find the premium cable channels don't really care about time. Many times they will try to start a program on the hour, but if the previous program ends way off the hour, they'll just start the next one after a few commercials/promos.
My experience in the broadcast industry, though, usually had programs starting on time. In radio, sometimes it seems like a DJ will play a song that can be cut off when approaching a time sensitive slot, like the news.
Back when I can remember watching Little House on the Prairie on weekday mornings during things like snowdays in the early to mid 1990's, TBS always started at 5 minutes after the hour and advertised it as such.
Semper VaporoYep, GPS has improved time keeping greatly... but how come my two cell phones have different times on them, my 2 computers have different times and all eight TV stations cannot get programs to start on-the hour or half hour... they are all "close" to the same time, but the widest variation is about 60 seconds (the ABC network station is about 1 minute ahead of all the others), though most are within 5 to 10 seconds of each other. If they are all syncd to the same time source, they really ought to be at least within 1 second of each other.
Computers get their time from a internet source - with my Dell with Windows 10 that source is time.nist.gov Your time source may vary.
My Android phone gets its time automatically - I don't know its source, however, it seems to be on the same program as my W10 computer.
What I have noticed on TV Scheduling - some programs are scheduled to minutes after what one considers 'proper time'. Some show may be schedule from 8:30 to 9:03 and its following show from 9:03 to 10:05. Not everything is scheduled on the hour and half hour.
Yep, GPS has improved time keeping greatly... but how come my two cell phones have different times on them, my 2 computers have different times and all eight TV stations cannot get programs to start on-the hour or half hour... they are all "close" to the same time, but the widest variation is about 60 seconds (the ABC network station is about 1 minute ahead of all the others), though most are within 5 to 10 seconds of each other. If they are all syncd to the same time source, they really ought to be at least within 1 second of each other.
BaltACD On the B&O a 'time signal' was sent over the telegraph and telephone wires at Noon. Those charged with maintaining the clock at the TT designated Standard Clock loctions had the responsibility set and/or regulate their clock to Standard Time as transmitted. For the B&O the time signal was said to originate from the Naval Observatory. Time keeping for the Navy was critical to navigation; for the railroads it was critical to Timetable operations.
On the B&O a 'time signal' was sent over the telegraph and telephone wires at Noon. Those charged with maintaining the clock at the TT designated Standard Clock loctions had the responsibility set and/or regulate their clock to Standard Time as transmitted. For the B&O the time signal was said to originate from the Naval Observatory. Time keeping for the Navy was critical to navigation; for the railroads it was critical to Timetable operations.
Do a search for "Electric Time Service" - this was an article written ca 1880 about how clocks were synchronized in the northeast US. At that time, the master clock was at Allegheny Observatory which had a transit telescope set up to track time by when selected stars reached their zenith. The earth's rotation is very steady with respect to the stars, it was only ca 1930 that clocks became good enough to track variations in the earth's rotation.
The article stated that a time signal was carried over a dedicated wire and that several cities had a "time ball" that would be dropped at noon.
Noawadays, GPS is capable of synchronizing clocks to better than 100 nano seconds for a run of the mill receiver.
BaltACDDon't know about the railroad at Milford, MI.
Well, you made me go back and look...
Turns out it wasn't the depot clock, but the local telephone switchboard clock. Each day the operator would blow a whistle at noon - then one day it was ten minutes early, thanks to some pranksters, and stayed that way for several days before the error was discovered and rectified. In that time, people had reset their clocks. Trains arrived "early" and people arrived at out of town appointments "early" as well.
The railroad through Milford was at first the Flint and Pere Marquette, then the Pere Marquette, then C&O, and the rest we know. Recently Lake States took over operation from CSX, although as far as the station goes, the matter is moot - the station was razed several years ago for condominiums.
BaltACDOn the B&O a 'time signal' was sent over the telegraph and telephone wires at Noon. Those charged with maintaining the clock at the TT designated Standard Clock loctions had the responsibility set and/or regulate their clock to Standard Time as transmitted. For the B&O the time signal was said to originate from the Naval Observatory. Time keeping for the Navy was critical to navigation; for the railroads it was critical to Timetable operations.
I read from local to Wisconsin historians that the Milwaukee had their Telegraph along the Chicago to Twin Cities line, in-tact until 1985 when they started to dismantle it. I heard they did similar with their timekeeping using a signal via telegraph line at a specific time. The clock in the coupula on the top of the Brookfield Depot way back in the day was set this way. The whole Town of Brookfield depended on the clock, allegedly they had a ladder up into the Coupula of the station from the Telegraphers office. They choose Brookfields Depot for a clock specifically as it was then known as Brookfield Jct and was an interchange point with at least one other railroad.
Interestingly enough, railroad Standard Time did not begin in 1883 or concern time zones. The railroad had a standard regulator which kept 'official time' -- this is what initially got adjusted by Naval Observatory or similar time adjustment when telegraphs came in. Other key clocks were designated as 'standard clocks' and kept adjusted relative' to the master standard -- ATSF for example, taking a leaf from ship chronometers, used a set of little cards showing how many seconds the standard clock was from the master, until there was enough deviation to physically open and reset it.
Meanwhile employees with accurate enough watches would synchronize with standard time on starting, then report correct time to each station as they progressed; the local clerk would set, and presumably as necessary regulate, his clocks accordingly. Where remote 'standard clocks' existed, crews could then reset their watches to them. This gave accurate 'enough' time everywhere in an age before high speed but very much dependent on timetable.
The later improvement on this came when each station agent listened for a time synchronization signal on the telegraph every night and could either set or post deviation. Even later, clocks were built that could synchronize themselves to a time signal (this initially from a company that made electrically self-winding clocks).
To this day, the master regulators remain some of the most interesting and valuable collector's timepieces-- imagine a grandfather clock so accurate that it has bearing jewels on the pulleys of its weights!
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