Radio Station CHU is operated by the Institute for
National Measurement Standards
of the National Research Council of Canada.

The call letters CHU were first used for Canadian time transmission in 1938, on the modern frequencies, 3330 KHz, 7335 KHz and 14670 KHz. Before that the call letters of essentially the same transmissions were VE9OB. The carrier frequency has been the specified standard since 1934; before that the quartz oscillators had been tuned to standard wavelengths. Continuous transmissions at a wavelength of 20.4 m had started in 1933, joining the 40.8 m and 90 m transmissions, which began in 1929 (daytime only). Daily transmission on a wavelength of 52.5 m had begun in 1928 under the call letters 9CC (later VE9CC), but ceased with the startup of 40.8 m operation. 9CC had started experimental time transmission in 1923 on 275 m, and license 3AF had operated in 1922. Thus there is quite a range of possible dates to assign to the establishment of CHU; we lean towards 1929 as being the start of daily time transmissions at essentially the modern frequencies. Of course there has been quite a change in equipment and accuracy over the years, but the largest improvement was with the change to cesium atomic clocks in 1967. In 1970 the responsibility of operating CHU was transferred from the astronomers at the Dominion Observatory, to the physicists at the National Research Council.

Since 1970, the National Research Council has been charged with maintaining official time for Canada. The short wave radio station CHU is one, but only one of the ways that official time is disseminated across Canada. Visit our web site http://inms-ienm.nrc-cnrc.gc/time_services/shortwave_broadcasts_e.html for more details.

Following international accepted recommendations, Canada and other countries have official time scales in agreement within 10mS. Since CHU’s transmissions are well within 100mS of official Canadian time, for all distant users of CHU, the dominant source of time error comes from the radio wave path reflecting off the ionosphere as the radio signal travels from the transmitter (in Ottawa, Ontario, Canada) to the user. The time delay is 3.3mS per km of path, and generally varies b less than 1mS, due to uncertainties in path including the uncertainty in the number of skips made by the radio wave (reflections down from the ionosphere and back up from the surface of the Earth). For a fixed receiver when the number of skips does not change, the variation in the path delay will usually be less than 100mS. A small additional delay comes from the radio receiver, and may be significant.

Before April 1, 1990, CHU’s time announcements were given as Eastern Standard Time. Since that time CHU’s time announcements have been given as Coordinated Universal Time (UTC). The change from EST to UTC was done to remain in the spirit of the recommendations of the International Consultative Committee on Radio: ‘that the standard time broadcasts on standard frequencies be given in UTC’. In a narrow sense, since CHU does not broadcast on the frequencies allocated for frequency standards, one might argue that these recommendations do not necessarily apply to CHU. However, since CHU is received across Canada’s 6 time zones and around the world, we made the change when it became possible technically to change from EST to UTC without difficulty.

The warble tone at seconds 31 to 39 allow any computer with a Bell 103 compatible 300 bps modem to receive and decode an accurate source of time. The details on the CHU broadcast code can be found on the following web site http://inms-ienm.nrc-cnrc.gc.ca/time_services/chu.html .Reception reports from around the world, are gladly accepted from listeners. We will respond with a QSL card. Please send reception reports to:

Radio Station CHU
National Research Council of Canada
1500 Montreal Road, Bldg M-36
Ottawa, Ontario, Canada
K1A 0R6
Or by e-mail to radio.chu@nrc.ca

Editor- We wish to thank Mr. Raymond Pelletier- Engineer at CHU, Dr. Rob Douglas and the fine folks at the National Research Council of Canada in providing this information for use on our website.

UPDATE: We have received a rather disturbing note regarding the operations of CHU/Canada. Every minute, alternating with French and English, the following announcement is being broadcast.

"On April 1, 2007, CHU needs to stop operating, change frequencies, or relicence.
Contact radio.chu@nrc.gc.ca or mail CHU Canada K1A 0R6."

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