[ntp:questions] CHU Public Notice : http://inms-ienm.nrc-cnrc.gc.ca/time_services/shortwave_broadcasts_e.html

hjsjms at cs.com hjsjms at cs.com
Wed Dec 13 14:09:00 UTC 2006

Does anyone know how the definitions of a broadcast and fixed signal
differ?  It sounds like ITU is expanding the number and kind of
stations that can use that frequency.  Implicit within that decision is
that the time signals from WWV on 5 and 10 mhz could fill the void
which may not be the case.

I wonder what the process of re-doing the CHU license for the 7335
frequency involves and whether they may find themselves competing with
other signals.  Best solution might be to shift to a nearby frequency.

> Max Power wrote:
> NRC Short Wave Station Broadcasts (CHU)
> http://inms-ienm.nrc-cnrc.gc.ca/time_services/shortwave_broadcasts_e.html
> About the New Messages on CHU - October, 2006
> The added messages on CHU are:
> "On April 1, 2007, CHU needs to stop operating, change frequencies, or
> re-licence. Contact radio.chu at nrc.gc.ca or mail CHU Canada K1A 0R6," and
> « En avril 2007, CHU doit soit cesser ses opérations, soit changer de
> fréquence, soit renouveler sa licence. Contactez radio.chu at cnrc.gc.ca ou
> écrivez à CHU Canada, Conseil national de recherches, K1A 0R6. »
> This outreach is to collect information from users of CHU to help shape
> recommendations concerning what should be done concerning changes to CHU
> that will have to be in place by April 2007.
> In April 2007 the licence on 7.335 MHz will have to be modified to reflect
> changes on the status of the band allocation by the International
> Telecommunications Union. This frequency has been changed from "fixed
> service" to "broadcast". (The ITU decision does not affect the frequencies
> 3.33 MHz and 14.67 MHz.)
> Some alternatives are:
> Re-licencing just might be possible, calling the 7.335 MHz a "broadcast".
> It is also possible to stop using that frequency (the most useful of the
> three we use). Stopping one signal is the easiest solution but could create
> problems for some clients who are counting on this particular signal.
> Change the frequency from 7.335 MHz to a nearby fixed-service frequency. It
> would need some investment from our part in new hardware and in manpower. It
> could also create problems for clients, and likely not all radios will be
> able to tune to the new frequency.
> Closure of the entire CHU operation, as discussed below.
> To be seriously considered, any of the above alternatives will need to have
> a zero-based budgeting justification prepared, comparing it against the
> least expensive alternative of closing CHU entirely. CHU is entering a phase
> where major investment in new transmitters will be required if it is to be
> kept operating. In the absence of input from the CHU user community,
> concerning the importance of CHU's contribution in the modern world, this
> last option is an inescapable recommendation.
> The CHU code is also used as a radio clock, which can be used as a reference
> clock for an NTP time server. Software drivers have been written that can
> obtain the date and time from the code and that tune a digitally tuned radio
> to one of our 3 frequencies, to get the best signal. Users of this service
> generally don't listen to the audio broadcast. So we cannot gauge the usage
> by sending this announcement.
> Please, if you know of anyone using CHU but not aware of the possible
> changes to its frequency usage, let them know and ask them to contact us
> about any essential uses. Also if you have an important use for CHU signals,
> please tell us how you use our signals.
> We are preparing the case to keep CHU in operation.
> CHU Time Service
> Time accuracy superior to telephone time accuracy is available throughout
> Canada and in many other parts of the world by means of NRC's radio time
> signals broadcast continuously from short wave radio station CHU. If
> corrections are made for the propagation delay from CHU to the user, and for
> delays in the user's receiver, an accuracy of better than 1 ms can be
> obtained. Signal availability at a user's location depends on ionospheric
> conditions. CHU also broadcasts a time code which can be decoded with common
> computers and modems.
> Three frequencies are used: 3330, 7335, and 14 670 kHz. The transmission
> mode, upper single sideband with carrier re-inserted, provides time signal
> service without requiring a special SSB radio, and also provides three
> standard frequencies. The frequencies are derived from one of a trio of
> closely synchronized atomic clocks located at the transmitter site. Three
> clocks are employed to permit majority logic checking. CHU time signals are
> also derived from these clocks. The clocks at the CHU transmitter site,
> about 20 km from NRC's time laboratory, are compared daily with the NRC
> primary cesium clocks.
> Normally CHU's emission times are accurate to 10-4 s, with carrier frequency
> accuracy of 5x10-12, compared to NRC's primary clocks, which are usually
> within 10 microseconds and 1x10-13 compared to UTC. UTC is the international
> official time reference. It is constructed by the Bureau International des
> Poids et Mesures (BIPM), based on the average of laboratory and commercial
> atomic clocks located in laboratories around the world. It is steered in
> frequency using the primary cesium standards (such as those at NRC) located
> at some of the major time laboratories. UTC loosely follows the
> irregularities of the astronomical time scale UT1, which is needed in
> astronomical observations and in celestial navigation. Since 1972, leap
> seconds have been used to keep UTC within 0.9 s of UT1. The difference [UT1-
> UTC] is called DUT1, and this fraction of a second [-0.8 s to +0.8 s] is
> broadcast by means of an internationally accepted code. To decode the size
> of DUT1, in tenths of a second, a user counts the number of emphasized
> seconds markers in one minute. For CHU, the emphasized seconds pulses are
> split, so that a double tone is heard. When the emphasis is on seconds 1
> through 8, DUT1 is positive; and when DUT1 is negative, seconds 9 through 16
> are used.
> The first minute of each hour commences with a full 1 s pulse of 1000 Hz
> tone, followed by 9 s of silence, and then the normal pattern of 0.3 s
> pulses of 1000 Hz at one-second intervals. The normal pattern for each of
> the next 59 minutes starts with a 0.5 s 1000 Hz pulse, followed by the DUT1
> code employing split 0.3 s pulses where required, and normal 0.3 s pulses up
> to and including that at 28 seconds. The pulse at 29 seconds is omitted.
> Following the normal pulse at 30 seconds, for a 9 s period, 1000 Hz pulses
> of 0.01 s occur, each followed by the CHU FSK digital time code described in
> CHU Broadcast Codes. The pulses between 40 and 50 seconds are of normal
> length. In the final 10 s period of each minute a bilingual station
> identification and time announcement is made, with the 1000 Hz seconds
> pulses shortened to "ticks". Each minute's announced time refers to the
> beginning of the pulse which follows. Since April 1, 1990, the announced
> time is always UTC.
> The CHU station is located 15 km southwest of Ottawa at 45º 17' 47" N, 75º
> 45' 22" W. Main transmitter powers are 3 kW at 3330 and 14 670 kHz, and 10
> kW at 7335 kHz. Individual vertical antennas are used for each frequency.
> The electronics 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 by a talking
> clock using digitally recorded voices.
> Historical Information
> Radio station CHU is operated by the Institute for National Measurement
> Standards at 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.
> Following internationally accepted recommendations, Canada and other
> countries have official time scales in agreement within 10µs. Since CHU's
> transmissions are well within 100µs 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
> 3.3µs per km of path, and generally varies by 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 100µs.
> 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 six 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 here.
> 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
> 1200 Montreal Road, Bldg M-36
> Ottawa, Ontario, Canada K1A 0R6
> Or by e-mail to radio.chu at nrc-cnrc.gc.ca

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