Time signal

Source: Wikipedia, the free encyclopedia.

For broader coverage of this topic, see Time standard.
These automatic signal clocks were synchronized by telegraphy in 1905 before the widespread use of radio

A time signal is a visible, audible, mechanical, or electronic

time of day
.

Railways
were among the first customers for time signals, which allowed synchronization of their operations over wide geographic areas. Dedicated radio time signal stations transmit a signal that allows automatic synchronization of clocks, and commercial broadcasters still include time signals in their programming.

Today, global navigation satellite systems (

GNSS) radio signals are used to precisely distribute time signals over much of the world. There are many commercially available radio controlled clocks available to accurately indicate the local time, both for business and residential use. Computers often set their time from an Internet atomic clock source
. Where this is not available, a locally connected GNSS receiver can precisely set the time using one of several software applications.

Audible and visible time signals

One sort of public time signal is a

Big Ben
was the only time standard the general public needed.

Accurate knowledge of time of day is essential for

seaport
cities to enable navigators to set their chronometers.

Signal guns

In

fishermen of the 6:00 pm Sunday closing of fishing.) The 9:00 pm firing was later established as a time signal for the general population. Until a time gun was installed, the nearby Brockton Point lighthouse keeper detonated a stick of dynamite. Elsewhere in Canada, a "Noon Gun" is fired daily from the citadels in Halifax and Quebec City and from Signal Hill in St. John's, Newfoundland and Labrador.[1]

In the same manner, a Noon Gun has been fired in Cape Town, since 1806.[2] The gun is fired daily from the Lion Battery at Signal Hill.

The Noonday Gun serves a similar purpose in Hong Kong. The tradition, which started in the 1860s under British colonial rule, has become a tourist attraction in recent times.

A cannon was fired at one o'clock every weekday at

Santiago
, is shot every noon.

In

WWII
for about twenty years until 21 April 1959, the 2712th anniversary of Rome's founding, and has been in use since then.

For many years an old cannon was fired "about noon" from a mountain near Kabul.[3][4]

Sirens, whistles, and other audible signals

In many Midwestern US cities where tornadoes are a common hazard, the

emergency sirens are tested regularly at a specified time (say, noon each Saturday); while not primarily intended to mark the time, local people often check their watches when they hear this signal. In many non-seafaring communities, loud factory whistles served as public time signals before radio made them obsolete. Sometimes, the tradition of a factory whistle becomes so deeply entrenched in a community that the whistle is maintained long after its original function as a time keeper became obsolete.[5] For example, the University of Iowa's power plant whistle has been reinstated several times by popular demand after numerous attempts to silence it.[6]

Visual signals

Greenwich Observatory
, London

In 1861 and 1862, the Edinburgh Post Office Directory published time gun

Royal Observatory in Greenwich, London, and the time ball has dropped at 1:00 pm every day since then.[8] The first American time ball went into service in 1845.[7] In New York City, the ceremonial Times Square Ball drop on New Year's Eve in Times Square
is a vestige of a visual time signal.

Electrical time signals

United Kingdom

The first telegraph distribution of time signal in the United Kingdom, indeed, in the world, was initiated in 1852 by the

Greenwich Observatory. This included a system for synchronising the drop of the time ball at Greenwich with other time balls around the country, one of which was atop the Electric's offices in the Strand.[9]

Other synchronised time balls were atop the

Admiralty.[9]

United States

Telegraph signals were used regularly for time coordination by the United States Naval Observatory starting in 1865.[10] By the late 1800s, many U.S. observatories were selling accurate time by offering a regional time signal service.[11]

Sandford Fleming proposed a single 24-hour clock for the entire world. At a meeting of the Royal Canadian Institute on 8 February 1879 he linked it to the anti-meridian of Greenwich (now 180°). He suggested that standard time zones could be used locally, but they were subordinate to his single world time.

Advertisement for a telegraph time signal service (1900)

Standard time came into existence in the United States on 18 November 1883. Earlier, on 11 October 1883, the General Time Convention, forerunner to the American Railway Association, approved a plan that divided the United States into several time zones. On that November day, the US Naval Observatory telegraphed a signal that coordinated noon at Eastern standard time with 11 am Central, 10 am Mountain, and 9 am Pacific standard time.

A March 1905 issue of The Technical World describes the role of the United States Naval Observatory as a source of time signals:

One of the most important functions of the Naval Observatory is found in the daily distribution of the correct time to every portion of the United States. This is effected by means of telegraphic signals, which are sent out from Washington at noon daily, except Sundays. The original object of this time service was to furnish mariners in the seaboard cities with the means of regulating their chronometers; but, like many another governmental activity, its scope has gradually broadened until it has become of general usefulness. The electrical impulse which goes forth from the Observatory at noon each day, now sets or regulates automatically more than 70,000 clocks located in all parts of the United States, and also serves, in each of the larger cities of the country, to release a time-ball located on some lofty building of central location. The dropping of the time-ball – accompanied, at some points, with the simultaneous firing of a cannon – is the signal for the regulation by hand of hundreds of other clocks and watches in the vicinity.

Radio time sources

See also: Radio clock § List of radio time signal stations
A modern LF Radio clock

Dedicated time signal broadcasts

The telegraphic distribution of time signals was made obsolete by the use of AM, FM,

satellite navigation systems. Time signals have been transmitted by radio since 1905.[12] There are dedicated radio time signal stations
around the world.

Time stations operating in the

shortwave band can cover wider areas with relatively low-power transmitters, but the varying distance that the signal travels increases the uncertainty of the time signal on a scale of milliseconds.[13]

Radio time signal stations broadcast the time in both audible and machine-readable

time code form that can be used as references for radio clocks and radio-controlled watches. Typically, they use a national or regional longwave digital signal; for example, station WWVB in the U.S. .[13]

The audio portions of the shortwave

mobile phones
are used, the delays are often more than 100 ms, due to the multiple access methods used to share cell channels. In rare instances when the telephone connection is made by satellite, the time is delayed by 250–500 ms.

The audio from the broadcasts is available by telephone by dialling U.S. numbers (303) 499-7111 for WWV (Colorado), and (808) 335-4363 for WWVH (Hawaii). Calls (which are not toll-free) are disconnected after 2 minutes.

A low cost LF radio clock receiver, antenna left, receiver right.

Loran-C time signals formerly were also used for radio clock synchronization, by augmenting their highly accurate frequency transmissions with external measurements of the offsets of LORAN navigation signals against time standards.

General broadcasters

As radio receivers became more widely available, broadcasters included time information in the form of voice announcements or automated tones to accurately indicate the hour. The BBC has included time "pips" in its broadcasts from 1922.[12]

In the United States many information-based radio stations (full-service, all-news and news/talk) also broadcast time signals at the beginning of the hour. In New York,

Beethoven's 5th Symphony
at the beginning of the hour continuously, since 1943.

Broadcast stations using iBiquity Digital's "HD Radio" system are contractually required[14] to delay their analog broadcast by about eight seconds, so it remains in sync with the digital stream. Thus, network-generated time signals and service cues will also be delayed by about eight seconds. (Because of the delay, when WBEN-AM in Buffalo, New York was broadcasting time markers, and was simulcast on an FM station that broadcast in HD; the FM signal did not carry the time signal. WBEN does not broadcast in HD.) Local signals may also be delayed.

The

KYW-AM in Philadelphia broadcasts a time signal at the top of the hour along with its jingle
.

KSL
(AM-FM) in Salt Lake City uses a "clang" that originates from the Nauvoo Bell on Temple Square, in Salt Lake City, which has been a staple on the station since the early 1960s.

In Canada, the national English-language non-commercial

Radio-Canada, broadcasts a similar signal at noon. Vancouver radio station CKNW also broadcasts time signals, using a chime every half-hour. Time signals on CBC broadcasts may be delayed up to 3 seconds due to network processing delays between the local radio transmitter and the time signal origin in Ottawa. The CBC's predecessor, the Canadian National Railways Radio network, broadcast the time signal over its Ottawa station, CNRO (originally CKCH), at 9 pm daily and also on its Moncton station, CNRA, beginning in 1923. CNRA closed in 1931 but the broadcasts continued on CNRO when the station was acquired by the Canadian Radio Broadcasting Commission in 1933 and by the CBC in 1936 before going national in 1939.[17]

In Australia, many information-based radio stations broadcast time signals at the beginning of the hour, and a speaking clock service was also available until October 2019. However, the VNG dedicated time signal service has been discontinued.[18]

In Cuba, Radio Reloj is a radio station which has a time signal over news. Radio Reloj translates to Clock Radio.

Digital delay

Program material, including time signals, that is transmitted digitally (e.g.

DAB, Internet radio
) can be delayed by tens of seconds due to buffering and error correction, making time signals received on a digital radio unreliable when accuracy is needed.

See also

References

  1. ^ Parks Canada Agency, Government of Canada (10 April 2019). "Noon Day Gun - Signal Hill National Historic Site". www.pc.gc.ca.
  2. ^ "Noon Gun -". bokaap.co.za. Retrieved 8 April 2018.
  3. ^ "The noon gun". Christian Science Monitor. 22 April 1982. Retrieved 8 April 2018.
  4. ^ "The Old Noon Day Gun of Kabul - Afghanistan". digitalsilver.co.uk. Archived from the original on 28 August 2017. Retrieved 8 April 2018.
  5. ^ Ross, Jenna (9 April 2015). "Midwestern towns with sirens weigh nostalgia against nuisance". Minneapolis Star Tribune. Retrieved 21 June 2018.
  6. ^ Snee, Tom (18 April 2011). "The enduring exhalations of The Whistle". Iowa Now. Archived from the original on 22 June 2018. Retrieved 21 June 2018.
  7. ^ a b Aubin, David The Heavens on Earth: Observatories and Astronomy in Nineteenth-Century Science and Culture p.164. Duke University Press, 2010
  8. ^ "Greenwich Time Ball". greenwichmeantime.co.uk. Archived from the original on 23 October 2010. Retrieved 8 April 2018.
  9. ^
    OCLC 655205099
    .
  10. ^ "Timekeeping at the U.S. Naval Observatory". Archived from the original on 19 December 2017. Retrieved 10 April 2018.
  11. ISBN 9780804738743
    . Retrieved 29 March 2019.
  12. ^
    ISBN 0863413277
    .
  13. ^
    ISBN 978-3-527-40780-4
    .
  14. ^ Licensing fact sheet 2009 (PDF) (Report). iBiquity Digital Corporation. Archived from the original (PDF) on 13 July 2011 – via ibiquity.com.
  15. ^ Bartlett, Geoff (5 November 2014). "'The beginning of the long dash' indicates 75 years of official time on CBC". CBC News (cbc.ca). Retrieved 8 April 2018.
  16. ^ Taekema, Dan (10 October 2023). "The end of the long dash: CBC stops broadcasting official 1 P.M. time signal". CBC News (cbc.ca). Retrieved 2 December 2023.
  17. ^ "The beginning of the long dash". CBC News (cbc.ca). CBC Archives. 1939. Archived from the original on 8 June 2016. Retrieved 8 April 2018.
  18. ^ Kruijshoop, Alfred; Walker, Marjorie. "Introduction". Time NZ & A (Report). Retrieved 23 November 2013 – via tufi.alphalink.com.au.[permanent dead link]

Further reading

  • Downing, Michael (2005). Spring Forward: The annual madness of Daylight Saving Time. Shoemaker and Hoard.
    ISBN 1-59376-053-1
    .

External links
Magazine was published from 1904–1905 by the
Armour Institute of Technology
.
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