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CHU (radio station)
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CHU (radio station)
CHU was the call sign of a shortwave time signal radio station that was operated by the Institute for National Measurement Standards of the National Research Council. CHU's signal was used for continuous dissemination of official Canadian government time signals, derived from atomic clocks.
The National Research Council announced that the station would close June 22, 2026, after more than a century of operation. NRC continues to provide telephone talking clock, web clock, and Network Time Protocol services. CHU's final time announcement was transmitted at 10:10 am Eastern Daylight Time (14:10 Coordinated Universal Time), on June 22, 2026.
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 watershed attempted to receive time signals transmitted from Kingston; however, signals were not resolvable and the time signal from NAA in Arlington, Virginia was used instead.
The station was started in 1923 by the Dominion Observatory in Ottawa, Ontario, Canada, with a call sign of 9CC on an experimental basis until 1928. Regular daytime transmission began under the callsign of VE9OB in January 1929 on a wavelength of about 40.8 metres (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.[citation needed] 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 and satellite communication to transmit its signal to remote areas.
Initially, the signal consisted of a constant frequency interrupted by patterns of Morse Code 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. 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 was 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.
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CHU (radio station)
CHU was the call sign of a shortwave time signal radio station that was operated by the Institute for National Measurement Standards of the National Research Council. CHU's signal was used for continuous dissemination of official Canadian government time signals, derived from atomic clocks.
The National Research Council announced that the station would close June 22, 2026, after more than a century of operation. NRC continues to provide telephone talking clock, web clock, and Network Time Protocol services. CHU's final time announcement was transmitted at 10:10 am Eastern Daylight Time (14:10 Coordinated Universal Time), on June 22, 2026.
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 watershed attempted to receive time signals transmitted from Kingston; however, signals were not resolvable and the time signal from NAA in Arlington, Virginia was used instead.
The station was started in 1923 by the Dominion Observatory in Ottawa, Ontario, Canada, with a call sign of 9CC on an experimental basis until 1928. Regular daytime transmission began under the callsign of VE9OB in January 1929 on a wavelength of about 40.8 metres (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.[citation needed] 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 and satellite communication to transmit its signal to remote areas.
Initially, the signal consisted of a constant frequency interrupted by patterns of Morse Code 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. 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 was 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.