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CHU (radio station): Wikis


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City of license Ottawa, Ontario, Canada
Broadcast area North America
Frequency 3330 kHz, 7850 kHz, 14670 kHz
First air date 1929
Format Time
Power 3 kW (3330, 14670 kHz), 10 kW (7850 kHz)
Transmitter coordinates 45°17′47″N 75°45′22″W / 45.29639°N 75.75611°W / 45.29639; -75.75611
Former callsigns VE9OB (1929-1938)
Owner National Research Council of Canada

CHU is the call sign of a shortwave time signal radio station operated by the Institute for National Measurement Standards of the National Research Council of Canada.



The station was started in 1929 by the Dominion Observatory in Ottawa, Ontario, Canada. It was operated by the Observatory until 1970. The call letters CHU were assigned in 1938. Until then, the call was VE9OB.

Broadcast format

CHU's signal is used for continuous dissemination of official Canadian government time signals. Unlike other time stations, time signals are the only type of information broadcast from this station.

The CHU time signal and radio frequencies are derived from atomic clocks.

CHU will acknowledge listeners' reception reports.

A similar time signal from the National Research Council is used by CBC radio services daily at noon ET on Radio-Canada's Première Chaîne, and 1pm ET on CBC Radio One.

Transmission system

CHU transmits 3 kW signals on 3330 and 14670 kHz, and a 10 kW signal on 7850 kHz. The signal is amplitude modulated, with the lower sideband 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 at 45º 17' 47" N, 75º 45' 22" W near Barrhaven, Ontario, 15 km 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 antennas are used for each frequency.

CHU has long been licensed as "fixed service" within the band allocations of the International Telecommunications Union.

CHU's 10 kW signal has been transmitted on 7850 kHz since January 1, 2009. Before then, the signal was transmitted on 7335 kHz.

Time signal format

The actual time signal is a series of 300 ms-long 1000 Hz tones, transmitted once per second, on the second. The top of the minute is marked by a half-second-long beep, and the top of the hour is marked with a one second-long beep, followed by nine seconds of silence. Thereafter, every second except for the 29th second past the minute, CHU transmits a 300-millisecond tone. Between one and sixteen seconds past the minute, CHU transmits the difference between UT1 and Coordinated Universal Time (UTC) by using split tones.

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 modem can decode it,[1] and CHU is the only time signal station that uses this format for its time code transmissions.

At ten seconds before each minute, the once-per-second tones are again cut to 10 milliseconds each, this time 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 are transmitted first on the odd minutes, while English announcements come first on the even minutes.

Western Canada signal coverage

Proposed CHU transmitter for Western Canada

CHU quite often cannot be received in Western Canada on any of its broadcast frequencies. Propagation conditions and the distance from Ottawa result in relatively weak signals. Electrical interference can further aggravate reception difficulty. CHU is practically unusable in most of Western Canada, as well as Nunavut and the Northwest Territories.

Subject to limitations of their own, WWV and WWVH are the fallback in Western Canada as far as getting time signals via shortwave is concerned. In the High Arctic, however, both the US time stations and CHU become essentially unreliable or unusable.

A proposal has been published to create a companion time signal station for Western Canada.[2] Proposed coverage is shown in the graphic.


  1. ^ "CHU Broadcast Codes". National Research Council of Canada, Institute for National Measurement Standards. 2009-08-28. Retrieved 2010-03-14. 
  2. ^ "CHU Time Station Western Canada Coverage Gap Elimination Proposal". 2007-02-05. Retrieved 2007-11-24. 

External links



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