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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. == 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 watershed attempted to receive time signals transmitted from Kingston; however, signals were not resolvable and the time signal from Arlington, Virginia was used instead.〔Malcolm M. Thomson, ''The Beginning of the Long Dash: A History of Timekeeping in Canada'', University of Toronto Press, 1978, ISBN 0-8020-5383-1,1 Chapter 6〕 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 7353 kHz). 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 3330, 7335 and 14670 kHz, at a transmitter power of only 10 W. The 1000 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 7335 kHz.〔 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 Atlier Brillie Freres 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.〔 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 the seconds pulses divided down and 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 14670 kHz 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, CHU's 7 MHz frequency was changed to 7850 kHz, due to an allocations change and interference on 7335 kHz. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「CHU (radio station)」の詳細全文を読む スポンサード リンク
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