CHU (callsign)
| City | Ottawa, Ontario, Canada |
|---|---|
| Broadcast area | North America |
| Frequency | 3330 kHz, 7850 kHz, 14670 kHz |
| First air date | 1923 |
| Format | Time |
| Language(s) | English, French |
| 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 |
| Former callsigns | 9CC (1923-1928), VE9CC (after 1928) VE9OB (until 1938) |
| Owner | National Research Council of Canada |
| Website | http://www.nrc-cnrc.gc.ca/eng/services/time/short_wave.html |
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.
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 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 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 14.670 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. In 1951, a Collins transmitter rated for 3 kW was put in service on 7.335 MHz.
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