CHU is the

call sign In broadcasting and radio communications, a call sign (also known as a call name or call letters—and historically as a call signal—or abbreviated as a call) is a unique identifier for a transmitter station. A call sign can be formally as ...

of a

shortwave Shortwave radio is radio transmission using radio frequencies in the shortwave bands (SW). There is no official definition of the band range, but it always includes all of the high frequency band (HF), which extends from 3 to 30 MHz (app ...

time signal A time signal is a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day. Church bells or voices announcing hours of prayer gave way to automatically operated chimes on public clocks; however, au ...

radio station Radio broadcasting is the broadcasting of audio (sound), sometimes with related metadata, by radio waves to radio receivers belonging to a public audience. In terrestrial radio broadcasting the radio waves are broadcast by a land-based rad ...

operated by the Institute for National Measurement Standards of the National Research Council. CHU's signal is used for continuous dissemination of official Canadian government

s, derived from

atomic clock An atomic clock is a clock that measures time by monitoring the resonant frequency of atoms. It is based on atoms having different energy levels. Electron states in an atom are associated with different energy levels, and in transitions betwee ...

History

Radio time signals allowed accurate and rapid distribution of time signals beyond the range of the telegraph or visual signals. This was of particular value in surveying remote areas, where time signals allowed accurate determination of longitude. In the summer of 1914, a survey party at Quinze Dam in the

Ottawa River The Ottawa River (, ) is a river in the Canadian provinces of Ontario and Quebec. It is named after the Algonquin word "to trade", as it was the major trade route of Eastern Canada at the time. For most of its length, it defines the border betw ...

watershed attempted to receive time signals transmitted from Kingston; however, signals were not resolvable and the time signal from NAA in

Arlington, Virginia Arlington County, or simply Arlington, is a County (United States), county in the U.S. state of Virginia. The county is located in Northern Virginia on the southwestern bank of the Potomac River directly across from Washington, D.C., the nati ...

was used instead.Malcolm M. Thomson, ''The Beginning of the Long Dash: A History of Timekeeping in Canada'', University of Toronto Press, 1978, ,1 Chapter 6 The station was started in 1923 by the Dominion Observatory in

Ottawa Ottawa is the capital city of Canada. It is located in the southern Ontario, southern portion of the province of Ontario, at the confluence of the Ottawa River and the Rideau River. Ottawa borders Gatineau, Gatineau, Quebec, and forms the cor ...

Ontario Ontario is the southernmost Provinces and territories of Canada, province of Canada. Located in Central Canada, Ontario is the Population of Canada by province and territory, country's most populous province. As of the 2021 Canadian census, it ...

, Canada, with a

of 9CC on an experimental basis until 1928. Regular daytime transmission began under the callsign of VE9OB in January 1929 on a wavelength of 40.8 metres (about 7.353 MHz). Continuous transmission at 90 metres began at the end of 1929, with other wavelengths being used experimentally. Time signals were generated from the observatory's own pendulum clocks. The transmitter oscillators were condenser-tuned and so frequency stability was not high until quartz crystal control was implemented in 1933. In 1938, the call was changed to CHU, operating on frequencies of 3.33, 7.335 and 14.67 MHz, at a transmitter power of only 10 W. The 1,000 Hz tone imposed on the carrier was derived from the quartz oscillator that determined transmit frequency, but the seconds pulses were still derived from the observatory pendulum clocks. The station automatically sent its call sign in Morse code once per hour, and pulses were coded to identify the time of day. Since the CHU power was not high enough to cover much of Canada, including survey parties working in the North, observatory time signals were also transmitted by a Department of Transport station with 2 kW power. In 1947, three new transmitters with 300 W power were installed for the three frequencies, relocated to the station's present rural location. In 1951, a Collins transmitter rated for 3 kW was put in service on 7.335 MHz. The purpose of the station was to provide accurate time-keeping information, especially to rural and remote areas that didn't have local access to accurate time. The station also pioneered the use of

microwave Microwave is a form of electromagnetic radiation with wavelengths shorter than other radio waves but longer than infrared waves. Its wavelength ranges from about one meter to one millimeter, corresponding to frequency, frequencies between 300&n ...

and

satellite A satellite or an artificial satellite is an object, typically a spacecraft, placed into orbit around a celestial body. They have a variety of uses, including communication relay, weather forecasting, navigation ( GPS), broadcasting, scient ...

communication to transmit its signal to remote areas. Initially, the signal consisted of a constant frequency interrupted by patterns of

Morse Code Morse code is a telecommunications method which Character encoding, encodes Written language, text characters as standardized sequences of two different signal durations, called ''dots'' and ''dashes'', or ''dits'' and ''dahs''. Morse code i ...

pulses to indicate the time. In the 1930s, station identification via Morse Code was added to the transmission. Since deciphering even a simple time code "by ear" was occasionally difficult under field conditions, voice announcements of time and station identification were added to CHU in 1952, using a speaking clock made by Ateliers Brillié Frères of France. Fredrick Martin Meach of the Canadian embassy in Paris recorded the time announcements in English, which were stored on strips of photographic film and played back under control of the observatory clocks. In 1960, the speaking clock was replaced with one manufactured by Audichron corporation and rented by the Dominion Observatory; this unit had more intelligible voice quality and lower maintenance. New English voice announcements were recorded by Harry Mannis of the

Canadian Broadcasting Corporation The Canadian Broadcasting Corporation (), branded as CBC/Radio-Canada, is the Canadian Public broadcasting, public broadcaster for both radio and television. It is a Crown corporation that serves as the national public broadcaster, with its E ...

. Bilingual announcements started in 1964, with French speech provided by Miville Couture of CBC Montreal. The station switched to digital audio in the 1990s. Until 1959, the carrier frequency, tone frequency and second pulses were derived from independent sources, and the carrier stability as that of any commercial short wave transmitter. A divider chain was put into service so that all of the CHU signals were derived from Western Electric standard crystal oscillators with pulses for seconds monitored by continuous comparison with the observatory clocks. By 1978 all parts of the CHU transmitted signal were derived from an NRC-designed cesium beam frequency standard. Also in 1959, the 14.67 MHz transmitter was replaced with a new 20 kW unit. All site antennas were replaced with vertical antennas by 1971. The station continued to be operated by the Observatory until 1970, when its operation was transferred to the Institute for National Measurement Standards at the National Research Council. Effective January 1, 2009, the 7.335 MHz frequency was changed to 7.85 MHz. The change was necessary due to an ITU HF global reallocation at the 2003 World Radio Conference (WRC-03), where the 7.3 MHz range was reallocated to broadcasting. The power output was later reduced from 10 kW to 5 kW due to complaints from

New Zealand New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...

that the signal was causing interference on its new frequency.

Transmission system

The station is unmanned and equipped with modified 1960s-era 10 kW transmitters and is controlled remotely from the National Research Council's headquarters on Montreal Road. CHU transmits 3 kW signals on 3.33 and 14.67

MHz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), often described as being equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose formal expression in terms of SI base u ...

, and a 5 kW signal on 7.85 MHz. These nonstandard time signal frequencies were chosen to avoid interference from WWV and WWVH. The signal is amplitude modulated, with the lower

sideband In radio communications, a sideband is a band of frequencies higher than or lower than the carrier frequency, that are the result of the modulation process. The sidebands carry the information transmitted by the radio signal. The sidebands c ...

suppressed ( emission type H3E). The same information is carried on all three frequencies simultaneously including announcements every minute, alternating between English and French. The CHU transmitter is located near Barrhaven, Ontario, 15 km (10 miles) southwest of Ottawa's central business district. The systems feeding the transmitters are duplicated for reliability, and have both battery and generator protection. The generator can also supply the transmitters. The announcements are made using digitally recorded voices. Individual vertical

dipole antenna In radio and telecommunications a dipole antenna or doublet is one of the two simplest and most widely used antenna types, types of antenna; the other is the monopole antenna, monopole. The dipole is any one of a class of antennas producin ...

s are used for each frequency. CHU has long been licensed as a "fixed service" within the band allocations of the

International Telecommunication Union The International Telecommunication Union (ITU)In the other common languages of the ITU: * * is a list of specialized agencies of the United Nations, specialized agency of the United Nations responsible for many matters related to information ...

. , CHU has three

s at the station, contained in a special enclosure to eliminate possible electromagnetic interference and compared with the atomic clocks at NRC's headquarters. CHU mails QSL cards to acknowledge listeners' reception reports.

Time signal format

The primary time signal is a series of 300 ms-long 1,000 Hz tones, transmitted once per second, on the second. The following exceptions to the pattern provide additional information: * The top of the minute is marked by a half-second-long beep. * The top of the hour is marked with a one-second-long beep, followed by nine seconds of silence. * The 29th second of a minute is always omitted (no beep). * Between one and sixteen seconds past the minute (except at the top of the hour), CHU transmits the difference between UT1 and

Coordinated Universal Time Coordinated Universal Time (UTC) is the primary time standard globally used to regulate clocks and time. It establishes a reference for the current time, forming the basis for civil time and time zones. UTC facilitates international communicat ...

(UTC) by using split tones. For positive DUT1 values from +0.1 to +0.8 s, seconds 1 through 8 are split. For negative DUT1 values from −0.1 to −0.8 s, seconds 9 through 16 are split. * Between 31 and 39 seconds past the minute inclusive, the once-per-second tones are reduced to 10-millisecond "ticks" while a digital time code is transmitted. The digital time code is formatted so that a Bell 103-compatible 300-baud modem can decode it, and CHU is the only time signal station that uses this format for its time code transmissions. * For the last 9 seconds of each minute (seconds 51 to 59), the once-per-second tones are again cut to 10 milliseconds each, while CHU transmits a brief voice station identification, followed by voice announcements of the next minute in UTC, alternating between French and English. French announcements, using the voice of

Radio-Canada Radio-Canada may refer to: * CBC/Radio-Canada, the Canadian Broadcasting Corporation *Ici Radio-Canada Télé, the CBC's main French-language television network *Ici Radio-Canada Première Ici Radio-Canada Première (formerly Première Chaîne) i ...

news anchor Simon Durivage, are transmitted first on the odd minutes, while English announcements, voiced by late

CBC Radio CBC Radio is the English-language radio operations of the Canadian Broadcasting Corporation. The CBC operates a number of radio networks serving different audiences and programming niches, all of which (regardless of language) are outlined below ...

announcer Harry Mannis, come first on the even minutes. The digital time code sends 10 characters at 300 bits per second using 8N2

asynchronous serial communication Asynchronous serial communication is a form of serial communication in which the communicating endpoints' interfaces are not continuously synchronized by a common clock signal. Synchronization ( clock recovery) is done by data-embedded signal ...

. This follows the Bell 103 standard, a 2,225 Hz tone to represent a mark (1 bit) and 2,025 Hz tone for a space (0 bit). Immediately after the 10 ms tick, a mark tone is sent until 133.3 ms, then 110 data bits, ending at precisely 500 ms. The final stop bit is extended by 10 ms of mark tone to ensure it is detected reliably, and the final 490 ms of the second are silent. The time of day (day of year through second) is transmitted twice during each second from 32 to 39. During second 31, additional information (year, DUT1, daylight saving time, and leap second warning bits) is transmitted. A similar '' National Research Council Time Signal'' was broadcast by the

(CBC) radio services daily at noon ET on Radio-Canada's '' Première Chaîne'', and 1 p.m. ET on ''

CBC Radio One CBC Radio One is the English-language news and information radio network of the publicly owned Canadian Broadcasting Corporation. It is commercial-free and offers local and national programming. It is available on AM and FM to 98 percent o ...

''. Its last broadcast was on October 9, 2023.

Western Canada signal coverage

CHU often cannot be received in

Western Canada Western Canada, also referred to as the Western provinces, Canadian West, or Western provinces of Canada, and commonly known within Canada as the West, is a list of regions of Canada, Canadian region that includes the four western provinces and t ...

on any of its broadcast frequencies. Propagation conditions, low transmitter power coupled with the typical two ionospheric hops distances from Ottawa result in relatively weak time signals for Western Canada. Electromagnetic interference can further aggravate reception difficulty in urban areas in the West. CHU can be practically unusable in most of Western Canada,

Nunavut Nunavut is the largest and northernmost Provinces and territories of Canada#Territories, territory of Canada. It was separated officially from the Northwest Territories on April 1, 1999, via the ''Nunavut Act'' and the Nunavut Land Claims Agr ...

, and the

Northwest Territories The Northwest Territories is a federal Provinces and territories of Canada, territory of Canada. At a land area of approximately and a 2021 census population of 41,070, it is the second-largest and the most populous of Provinces and territorie ...

, for significant stretches of time. U.S. stations WWV and

WWVH WWVH is the callsign of the U.S. National Institute of Standards and Technology's shortwave radio time signal station located at the Pacific Missile Range Facility, Pacific Missile Range Facility Barking Sands, in Kekaha, Hawaii, Kekaha, on the ...

are the fallback in Western Canada. In the high Arctic, however, both the U.S. shortwave time stations and CHU become essentially unusable or unreliable. Canada has no

longwave In radio, longwave (also spelled long wave or long-wave and commonly abbreviated LW) is the part of the radio spectrum with wavelengths longer than what was originally called the medium-wave (MW) broadcasting band. The term is historic, dati ...

time signal transmitters. The American station

WWVB WWVB is a longwave time signal radio station near Fort Collins, Colorado, and is operated by the National Institute of Standards and Technology (NIST). Most radio clock, radio-controlled clocks in North America use WWVB's transmissions to set th ...

is the only option for reliable time signals during

geomagnetic storm A geomagnetic storm, also known as a magnetic storm, is a temporary disturbance of the Earth's magnetosphere that is driven by interactions between the magnetosphere and large-scale transient Plasma (physics), plasma and magnetic field structur ...

s in the Western Arctic, based on WWVB's published pattern maps. If WWVB is not available, those who need precision time transfer may be able to use GPS time transfer instead.

References

External links