Radio Station CHU
Time accuracy superior to telephone time accuracy is available
throughout Canada and in many other parts of the world by means of the
NRC's radio time signals broadcast continuously from shortwave 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, 7850, 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 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 the NRC's time laboratory, are
compared daily with the NRC's primary cesium clocks.
Normally the time broadcast by CHU is accurate to 10-4 s and any offsets of the carrier frequency from UTC(NRC) are less than 5x10-12.
UTC(NRC) is the version of Coordinated Universal Time (UTC) that is
realized at the NRC. It is maintained to within 100 ns of UTC and has a
frequency offset of less than 1x10-13.
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 primary
cesium clocks located at some of the major time laboratories.
UTC was defined to coordinate atomic clocks so that they could all
agree and still loosely follow 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 45° 17' 47"
N, 75° 45' 22" W. Main transmitter powers are 3 kW at 3330 and
14 670 kHz, and 5 kW at 7850 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. The digital voice announcements entered into service in 1990.
The voice in English is that of Harry Mannis (a former CBC announcer)
and the voice in French is that of Simon Durivage (of Radio-Canada).
Historical information
Radio station CHU is operated by the NRC. The call letters CHU were
first used for Canadian time transmission in 1938, on the frequencies,
3330 kHz, 7335 (7850 since 2009) kHz and 14670 kHz. The 2009 change in
frequency was to avoid new interference permitted since 2007, when the
International Telecommunications Union reallocated the 7300-7350 kHz
band, changing it from fixed service to general broadcast use. After
this change, our 7335 kHz transmissions began to be obscured by numerous
broadcasters from around the world who started to use that frequency.
Before 1938 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 shortwave 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, these recommendations do not strictly 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 codes can be found here.
nrc.canada.ca/shortwave
Il 24 febbraio 2023 dalle 11.45 alle 11.50 UTC sulla frequenza 14670 kHz in modalità USB, SINPO 4 4 3 4 3.
Ho ricevuto dal sito trasmittente di Ottawa, ON – Canada, la stazione “14,67 MHz NRC shortwave station broadcasts (CHU)”, il segnale era buono, anche se c'era molto rumore di fondo.
La stazione radio CHU Ottawa è a circa 6268 km dal mio QTH
Per l'ascolto ho utilizzato il ricevitore SDRplay RSPdx abbinato ad un personal computer con CPU Intel Core i7-4771 3.5 Ghz e software SDRuno, mentre l'antenna è una Loop 1,1 m con preamplificatore da 20 dB (tutto autocostruito).
Rapporto d'ascolto inviato all'indirizzo email: radio.chu@nrc-cnrc.gc.ca, conferma con lettera contenente QSL dopo 11 gg.
AUDIO MP3
