Radio clock
A radio clock or radio-controlled clock (RCC), and often colloquially (and incorrectly
One common style of radio-controlled clock uses time signals transmitted by dedicated terrestrial longwave radio transmitters, which emit a time code that can be demodulated and displayed by the radio controlled clock. The radio controlled clock will contain an accurate time base oscillator to maintain timekeeping if the radio signal is momentarily unavailable. Other radio controlled clocks use the time signals transmitted by dedicated transmitters in the shortwave bands. Systems using dedicated time signal stations can achieve accuracy of a few tens of milliseconds.
GPS satellite receivers also internally generate accurate time information from the satellite signals. Dedicated GPS timing receivers are accurate to better than 1 microsecond; however, general-purpose or consumer grade GPS may have an offset of up to one second between the internally calculated time, which is much more accurate than 1 second, and the time displayed on the screen.
Other broadcast services may include timekeeping information of varying accuracy within their signals.
Single transmitter
Radio clocks synchronized to a terrestrial time signal can usually achieve an accuracy within a hundredth of a second relative to the time standard,[1] generally limited by uncertainties and variability in radio propagation. Some timekeepers, particularly watches such as some Casio Wave Ceptors which are more likely than desk clocks to be used when travelling, can synchronise to any one of several different time signals transmitted in different regions.
Longwave and shortwave transmissions
Radio clocks depend on coded time signals from radio stations. The stations vary in broadcast frequency, in geographic location, and in how the signal is modulated to identify the current time. In general, each station has its own format for the time code.
List of radio time signal stations
Frequency | Callsign | Country Authority | Location | Aerial type | Power | Remarks |
---|---|---|---|---|---|---|
25 kHz | RJH69 |
VNIIFTRI |
Triple umbrella antenna[a] | 300 kW | This is Beta time signal.[2] The signal is transmitted in non-overlapping time: 02:00–02:20 UTC RAB99 04:00–04:25 UTC RJH86 06:00–06:20 UTC RAB99 07:00–07:25 UTC RJH69 08:00–08:25 UTC RJH90 09:00–09:25 UTC RJH77 10:00–10:25 UTC RJH86 11:00–11:20 UTC RJH63 | |
RJH77 | VNIIFTRI |
Arkhangelsk 64°21′29″N 41°33′58″E / 64.35806°N 41.56611°E |
Triple umbrella antenna[b] | 300 kW | ||
RJH63 | VNIIFTRI |
Krasnodar 44°46′25″N 39°32′50″E / 44.77361°N 39.54722°E |
Umbrella antenna[c] | 300 kW | ||
RJH90 | VNIIFTRI |
Nizhny Novgorod 56°10′20″N 43°55′38″E / 56.17222°N 43.92722°E |
Triple umbrella antenna[d] | 300 kW | ||
RJH86[2][e] | VNIIFTRI |
Bishkek 43°02′29″N 73°37′09″E / 43.04139°N 73.61917°E |
Triple umbrella antenna[f] | 300 kW | ||
RAB99 | VNIIFTRI |
Khabarovsk 48°29′29″N 134°48′59″E / 48.49139°N 134.81639°E |
Umbrella antenna[g] | 300 kW | ||
40 kHz | JJY | Japan NICT |
Mount Otakadoya, Fukushima 37°22′21″N 140°50′56″E / 37.37250°N 140.84889°E |
Capacitance hat , height 250 metres (820') |
50 kW | Located near Fukushima[3]
|
50 kHz | RTZ | VNIIFTRI |
Irkutsk 52°25′41″N 103°41′12″E / 52.42806°N 103.68667°E |
Umbrella antenna | 10 kW | PM time code |
60 kHz | JJY | Japan NICT |
Mount Hagane, Kyushu 33°27′54″N 130°10′32″E / 33.46500°N 130.17556°E |
Capacitance hat, height 200 metres (656') | 50 kW | Located on Kyūshū Island[3]
|
MSF |
United Kingdom NPL |
Anthorn, Cumbria 54°54′27″N 03°16′24″W / 54.90750°N 3.27333°W[h] |
Triple T-antenna[i] | 17 kW | Range up to 1,500 km (1000 miles) | |
WWVB | United States NIST |
Near Fort Collins, Colorado[4] 40°40′41″N 105°02′48″W / 40.67806°N 105.04667°W |
Two capacitance hats, height 122 metres (400') | 70 kW | Received through most of mainland U.S.[3] | |
66.66 kHz | RBU | VNIIFTRI |
Taldom, Moscow 56°43′59″N 37°39′47″E / 56.73306°N 37.66306°E[j] |
Umbrella antenna[k] | 50 kW | PM time code |
68.5 kHz | BPC | China NTSC |
Shangqiu, Henan 34°27′25″N 115°50′13″E / 34.45694°N 115.83694°E |
4 guyed masts, arranged in a square | 90 kW | 21 hours per day, with a 3 hour break from 05:00–08:00 ( China Standard Time) daily (21:00–24:00 UTC)[5]
|
|
HBG |
METAS |
Discontinued as of 1 January 2012 | |||
77.5 kHz | DCF77 | Germany PTB |
Vertical omni-directional antennas with top-loading capacity, height 150 metres (492')[6] | 50 kW | Located southeast of Frankfurt am Main with a range of up to 2,000 km (1250 miles)[3][7] | |
BSF | Taiwan | Zhongli 25°00′19″N 121°21′55″E / 25.00528°N 121.36528°E |
T-antenna[m] | [8] | ||
100 kHz[n] | BPL | China NTSC |
Pucheng, Shaanxi 34°56′56″N 109°32′35″E / 34.94889°N 109.54306°E |
Single guyed lattice steel mast | 800 kW | Loran-C compatible format signal on air from 05:30 to 13:30 UTC,[9] with a reception radius up to 3,000 km (2000 miles)[10] |
RNS-E | VNIIFTRI |
Bryansk 53°08′00″N 34°55′00″E / 53.13333°N 34.91667°E |
5 guyed masts | 800 kW | CHAYKA compatible format signal[2] 04:00–10:00 UTC and 14:00–18:00 UTC | |
RNS-V | VNIIFTRI |
Alexandrovsk-Sakhalinsky 51°05′00″N 142°43′00″E / 51.08333°N 142.71667°E |
Single guyed mast | 400 kW | CHAYKA compatible format signal[2] 23:00–05:00 UTC and 11:00–17:00 UTC | |
129.1 kHz[o] | DCF49 | Germany PTB |
Mainflingen 50°00′58″N 09°00′29″E / 50.01611°N 9.00806°E |
T-antenna | 100 kW | EFR radio teleswitch[11] time signal only (no reference frequency) FSK ± 170 Hz 200 baud |
135.6 kHz[o] | HGA22 | Hungary PTB |
Single guyed mast | 100 kW | ||
139 kHz[o] | DCF39 | Germany PTB |
Burg bei Magdeburg 52°17′13″N 11°53′49″E / 52.28694°N 11.89694°E |
Single guyed mast | 50 kW | |
162 kHz[p] | ALS162 | France ANFR |
Allouis 47°10′10″N 02°12′16″E / 47.16944°N 2.20444°E |
Two guyed steel lattice masts, height 350 metres (1150'), fed on the top | 800 kW | AM-broadcasting transmitter, located 150 km (100 miles) south of Paris with a range of up to 3,500 km (2200 miles), using PM with encoding similar to DCF77[q] |
198 kHz[p][r] | BBC Radio 4 | United Kingdom NPL |
Droitwich 52°17′44″N 2°06′23″W / 52.2955°N 2.1063°W |
T-aerial[s] | 500 kW[12] | Additional (50 kW) transmitters is at Burghead and Westerglen. The time signal is transmitted by 25 bit/s phase modulation.[13] |
2.5 MHz | BPM | China NTSC |
Pucheng, Shaanxi 34°56′56″N 109°32′35″E / 34.94889°N 109.54306°E |
(BCD time code on 125 Hz sub-carrier not yet activated) 07:30–01:00 UTC[14] | ||
WWV | United States NIST |
Near Fort Collins, Colorado 40°40′41″N 105°02′48″W / 40.67806°N 105.04667°W |
Broadband monopole | 2.5 kW | Binary-coded decimal (BCD) time code on 100 Hz sub-carrier | |
WWVH | United States NIST |
Kekaha, Hawaii 21°59′16″N 159°45′46″W / 21.98778°N 159.76278°W |
5 kW | |||
3.33 MHz | CHU | NRC |
Ottawa, Ontario 45°17′40″N 75°45′27″W / 45.29444°N 75.75750°W |
3 kW | 300 baud Bell 103 time code
| |
4.996 MHz | RWM | VNIIFTRI |
Taldom, Moscow 56°44′58″N 37°38′23″E / 56.74944°N 37.63972°E[j] |
10 kW | CW (1 Hz, 10 Hz) | |
5 MHz | BPM | China NTSC |
Pucheng, Shaanxi 34°56′56″N 109°32′35″E / 34.94889°N 109.54306°E |
BCD time code on 125 Hz sub-carrier. 00:00–24:00 UTC[14] | ||
HLA | South Korea KRISS |
Daejeon 36°23′14″N 127°21′59″E / 36.38722°N 127.36639°E |
2 kW | |||
WWV | United States NIST |
Near Fort Collins, Colorado 40°40′41″N 105°02′48″W / 40.67806°N 105.04667°W |
Broadband monopole | 10 kW[t] | BCD time code on 100 Hz sub-carrier | |
WWVH | United States NIST |
Kekaha, Hawaii 21°59′16″N 159°45′46″W / 21.98778°N 159.76278°W |
10 kW | |||
YVTO | Venezuela | Caracas 10°30′13″N 66°55′44″W / 10.50361°N 66.92889°W |
1 kW | |||
7.85 MHz | CHU | NRC |
Ottawa, Ontario 45°17′40″N 75°45′27″W / 45.29444°N 75.75750°W |
10 kW | 300 baud Bell 103 time code
| |
9.996 MHz | RWM | VNIIFTRI |
Taldom, Moscow 56°44′58″N 37°38′23″E / 56.74944°N 37.63972°E[j] |
10 kW | CW (1 Hz, 10 Hz) | |
10 MHz | BPM | China NTSC |
Pucheng, Shaanxi 34°56′56″N 109°32′35″E / 34.94889°N 109.54306°E |
(BCD time code on 125 Hz sub-carrier not yet activated) 00:00–24:00 UTC[14] | ||
LOL | Argentina SHN |
Buenos Aires[u] | 2 kW | Observatorio Naval Buenos Aires[15] | ||
WWV | United States NIST |
Near Fort Collins, Colorado 40°40′41″N 105°02′48″W / 40.67806°N 105.04667°W |
Broadband monopole | 10 kW | BCD time code on 100 Hz sub-carrier | |
WWVH | United States NIST |
Kekaha, Hawaii 21°59′16″N 159°45′46″W / 21.98778°N 159.76278°W |
10 kW | |||
PPE[16] | Brazil | Rio de Janeiro, RJ 22°53′44″S 43°13′27″W / 22.89556°S 43.22417°W[16] |
Horizontal half-wavelength dipole[16] | 1 kW[16] | Maintained by National Observatory (Brazil) | |
14.67 MHz | CHU | NRC |
Ottawa, Ontario 45°17′40″N 75°45′27″W / 45.29444°N 75.75750°W |
3 kW | 300 baud Bell 103 time code
| |
14.996 MHz | RWM | VNIIFTRI |
Taldom, Moscow 56°44′58″N 37°38′23″E / 56.74944°N 37.63972°E[j] |
10 kW | CW (1 Hz, 10 Hz) | |
15 MHz | BPM | China NTSC |
Pucheng, Shaanxi 34°56′56″N 109°32′35″E / 34.94889°N 109.54306°E |
(BCD time code on 125 Hz sub-carrier not yet activated) 01:00–09:00 UTC[14] | ||
WWV | United States NIST |
Near Fort Collins, Colorado 40°40′41″N 105°02′48″W / 40.67806°N 105.04667°W |
Broadband monopole | 10 kW | BCD time code on 100 Hz sub-carrier | |
WWVH | United States NIST |
Kekaha, Hawaii 21°59′16″N 159°45′46″W / 21.98778°N 159.76278°W |
10 kW | |||
20 MHz | WWV | United States NIST |
Near Fort Collins, Colorado 40°40′41″N 105°02′48″W / 40.67806°N 105.04667°W |
Broadband monopole | 2.5 kW | BCD time code on 100 Hz sub-carrier |
25 MHz | WWV | United States NIST |
Near Fort Collins, Colorado 40°40′41″N 105°02′48″W / 40.67806°N 105.04667°W |
Broadband monopole | 2.0 kW | Schedule: variable (experimental broadcast) |
MIKES |
Espoo, Finland 60°10′49″N 24°49′35″E / 60.18028°N 24.82639°E |
As of 2017 the transmission is discontinued until further notice.[18] "MIKES has a transmitter for time code and precise 25 MHz frequency for those near the Helsinki metropolitan area who need precise time and frequency."[19] |
Descriptions
- ^ 3 umbrella antennas, fixed on 3 guyed tubular masts, insulated against ground with a height of 305 metres (1000') and 15 guyed lattice masts with a height of 270 metres (885')
- ^ 3 umbrella antennas, fixed on 18 guyed lattice masts, height of central masts: 305 metres (1000')
- ^ umbrella antenna, fixed on 13 guyed lattice masts, height of central mast: 425 metres (1395')
- ^ 3 umbrella antennas, fixed on 3 guyed tubular masts, insulated against ground with a height of 205 metres (673') and 15 guyed lattice masts with a height of 170 metres (558')
- ^ in air RJH66
- ^ 3 umbrella antennas, fixed on 18 guyed lattice masts, height of central masts: 276 metres (905')
- ^ umbrella antenna, fixed on 18 guyed lattice masts arranged in 3 rows, height of central masts: 238 metres (780')
- ^ Before 1 April 2007, the signal was transmitted from Rugby, Warwickshire 52°21′33″N 01°11′21″W / 52.35917°N 1.18917°W
- ^ 3 T-antennas, spun 150 metres (492') above ground between two 227 metres (745') high guyed grounded masts in a distance of 655 metres (715 yards)
- ^ a b c d Before 2008, transmitter located at 55°44′14″N 38°09′04″E / 55.73722°N 38.15111°E
- ^ umbrella antenna, fixed on a 275 metres (902') high central tower insulated against ground and five 257 metres (843') high lattice masts insulated against ground in a distance of 324 metres (355 yards) from the central tower
- ^ T-antenna spun between two 125 metres (410') tall, grounded free-standing lattice towers in a distance of 227 metres (248 yards)
- ^ T-antenna spun between two telecommunication towers in a distance of 33 metres (36 yards)
- ^ Frequency for radio navigation system
- ^ a b c Frequency for radio teleswitch system
- ^ a b Frequency for AM-broadcasting
- ^ and requiring a more complex receiver for demodulating time signal
- ^ since 1988, before 200 kHz
- ^ Droitwich uses a T-aerial suspended between two 213 metres (699') guyed steel lattice radio masts, which stand 180 metres (197 yards) apart.
- ^ Time signal article says 2.5 kW
- ^ [15] says that the transmitter is located in Observatorio Naval Buenos Aires at Avenida España 2099, Buenos Aires; on Google Street View, some antenna structures can be seen both on and near the building, however, it's unclear where exactly the specific antenna is located. The coordinates here point to the building itself. 34°37′19″S 58°21′18″W / 34.62194°S 58.35500°W
Many other countries can receive these signals (JJY can sometimes be received in New Zealand, Western Australia, Tasmania, Southeast Asia, parts of Western Europe and the Pacific Northwest of North America at night), but success depends on the time of day, atmospheric conditions, and interference from intervening buildings. Reception is generally better if the clock is placed near a window facing the transmitter. There is also a propagation delay of approximately 1 ms for every 300 km (200 miles) the receiver is from the transmitter.
Clock receivers
A number of manufacturers and retailers sell radio clocks that receive coded time signals from a radio station, which, in turn, derives the time from a true atomic clock.
One of the first radio clocks was offered by
In the 2000s (decade) radio-based "atomic clocks" became common in retail stores; as of 2010 prices start at around US$15 in many countries.
The United States National Institute of Standards and Technology (NIST) has published guidelines recommending that radio clock movements keep time between synchronizations to within ±0.5 seconds to keep time correct when rounded to the nearest second.[23] Some of these movements can keep time between synchronizations to within ±0.2 seconds by synchronizing more than once spread over a day.[24]
Other broadcasts
- Attached to other broadcast stations
- Broadcast stations in many countries have carriers precisely synchronized to a standard phase and frequency, such as the BBC Radio 4 longwave service on 198 kHz, and some also transmit sub-audible or even inaudible time-code information, like the Radio France longwave transmitter on 162 kHz. Attached time signal systems generally use audible tones or phase modulation of the carrier wave.
- Teletext (TTX)
- Digital text pages embedded in television video also provide accurate time. Many modern TV sets and VCRs with TTX decoders can obtain accurate time from Teletext and set the internal clock. However, the TTX time can vary up to 5 minutes.[25]
Many digital radio and digital television schemes also include provisions for time-code transmission.
- Digital Terrestrial Television
- The ATSCstandards have 2 packet types that send time and date information to the receiver. Digital television systems can equal GPS stratum 2 accuracy (with short term clock discipline) and stratum 1 (with long term clock discipline) provided the transmitter site (or network) supports that level of functionality.
- VHF FM Radio Data System (RDS)
- RDS can send a clock signal with sub-second precision but with an accuracy no greater than 100 ms and with no indication of clock stratum. Not all RDS networks or stations using RDS send accurate time signals. The time stamp format for this technology is Modified Julian Date (MJD) plus UTC hours, UTC minutes and a local time offset.
- L-band and VHF Digital Audio Broadcasting
- DAB systems provide a time signal that has a precision equal to or better than Digital Radio Mondiale (DRM) but like FM RDS do not indicate clock stratum. DAB systems can equal GPS stratum 2 accuracy (short term clock discipline) and stratum 1 (long term clock discipline) provided the transmitter site (or network) supports that level of functionality. The time stamp format for this technology is BCD.
- Digital Radio Mondiale (DRM)
- DRM is able to send a clock signal, but one not as precise as navigation satelliteclock signals. DRM timestamps received via shortwave (or multiple hop mediumwave) can be up to 200 ms off due to path delay. The time stamp format for this technology is BCD.
Gallery
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LF time signal receiver
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World's first radio clock wrist watch, Junghans MEGA (analog model)
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Radio controlled analogwall clock
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The DCF77 time signal is used by organizations like the Deutsche Bahn railway company to synchronize their station clocks
Multiple transmitters
A radio clock receiver may combine multiple time sources to improve its accuracy. This is what is done in
GPS clocks
Many modern radio clocks use
GPS units intended primarily for time measurement as opposed to navigation can be set to assume the antenna position is fixed. In this mode, the device will average its position fixes. After approximately a day of operation, it will know its position to within a few meters. Once it has averaged its position, it can determine accurate time even if it can pick up signals from only one or two satellites.
GPS clocks provide the precise time needed for
Astronomy timekeeping
Although any
For serious precision timekeeping, a more specialized GPS device is needed. Some amateur astronomers, most notably those who time grazing lunar occultation events when the moon blocks the light from stars and planets, require the highest precision available for persons working outside large research institutions. The Web site of the International Occultation Timing Association[31] has detailed technical information about precision timekeeping for the amateur astronomer.
Daylight saving time
Various formats listed above include a flag indicating the status of daylight saving time (DST) in the home country of the transmitter. This signal is typically used by clocks to adjust the displayed time to meet user expectations.
See also
- Casio Wave Ceptor
- Clock network
- Speaking clock
- Standard frequency and time signal service
- Time from NPL
- Time transfer
- Time synchronization in North America
References
- ^ a b Lombardi, Michael A. (March 2010). "How Accurate is a Radio Controlled Clock?" (PDF). Horological Journal. 152 (3): 108–111. Archived (PDF) from the original on 2021-01-07. Retrieved 2023-12-01 – via National Institute of Standards and Technology website.
- ^ a b c d Standard Time and Frequency Signals (PDF) (in Russian), retrieved 2018-07-15 — official signal specification.
- ^ ISBN 3-527-40780-4page 257
- ^ "NIST Radio Station WWVB". NIST. March 2010. Archived from the original on 25 March 2014. Retrieved 18 March 2014.
- ^ "BPC". National Time Service Center, Chinese Academy of Sciences. Archived from the original on February 14, 2018. Retrieved 16 March 2013.
- ^ Yvonne Zimber (2007-05-09). "DCF77 transmitting facilities". Archived from the original on 2010-05-14. Retrieved 2010-05-02.
- ^ "Synchronizing time with DCF77 and MSF60". Archived from the original on 2011-01-12. Retrieved 2011-09-12. 090917 compuphase.com
- ^ "A Time Station Signal Project for Taiwan". Archived from the original on 2017-04-20. Retrieved 2018-07-09.
- ^ "长波授时 (Longwave time signal)". National Time Service Center, Chinese Academy of Sciences. Archived from the original on 10 January 2013. Retrieved 16 March 2013.
- ^ "科研成果 (Research achievements)". National Time Service Center, Chinese Academy of Sciences. Archived from the original on 17 April 2013. Retrieved 16 March 2013.
- ^ "PTB time monitor". Archived from the original on 2018-07-16. Retrieved 2018-07-16. — in German
- ^ "Radio stations in London, England". Archived from the original on 2016-04-19. Retrieved 2016-04-26.
Birmingham, Droitwich, 500 kW + Blackwall Tunnel + Rotherhithe Tunnel
- ^ "L.F. RADIO-DATA: Specification of BBC phase-modulated transmissions on long-wave" (PDF) (published 2006-10-24). December 1984. Archived (PDF) from the original on 2016-03-04. Retrieved 2016-04-25.
The BBC long-wave a.m. transmitter network carries a low bit-rate data signal, in addition to the normal programme signal modulation. The data signal is conveyed by phase-modulation of the carrier
- ^ a b c d "短波授时 (Shortwave time signal)". National Time Service Center, Chinese Academy of Sciences. Archived from the original on 2013-01-15. Retrieved 2013-03-16.
- ^ a b Information on the Official Time and Standard Frequency Archived 2018-08-28 at the Wayback Machine — in Spanish
- ^ a b c d "Rádio-Difusão de Sinais Horários". Observatório Nacional. Archived from the original on 2014-03-12. Retrieved 2012-02-23.
- ^ "QSL: MIKES Time Station, Espoo, Finland". SWL DX Blog. 14 May 2014. Archived from the original on 2016-10-12. Retrieved 2016-10-11. Reproduces a QSL letter from MIKES with technical details.
- ^ BIPM Annual Report on Time Activities – Time Signals Archived 2021-10-10 at the Wayback Machine, retrieved 2018 July 31.
- ^ "SI units in Finland, time and frequency |".
- ^ "Heathkit GC-1000-H Most Accurate Clock". Pestingers. Archived from the original on February 14, 2020.
- ^ US patent 4582434, David Plangger and Wayne K. Wilson, Heath Company, "Time corrected, continuously updated clock", issued April 15, 1986
- ^ " Radio controlled clock £19.95 Archived 2013-02-16 at archive.today
- ^ "How Accurate is a Radio Controlled Clock?" by Michael Lombardi (2010).
- ^ RADIO-CONTROLLED WALLCLOCK INSTRUCTION MANUAL
- ^ "How's your GHD8015F2 operating? — Personal Video Recorders — Digital Spy Forums". Digital Spy. 100506 digitalspy.co.uk
- ^ "datasheet i-Lotus TX Oncore" (PDF). Archived (PDF) from the original on 2015-10-16. Retrieved 2014-01-22.
- ^ "Symmetricom XL-GPS". Archived from the original on 2014-02-01. Retrieved 2014-01-22.
- ^ "datasheet Trimble Resolution SMT GG" (PDF). Archived (PDF) from the original on 2013-06-22. Retrieved 2014-01-22.
- ^ "datasheet u-blox NEO/LEA-M8T" (PDF). Archived (PDF) from the original on 2017-04-12. Retrieved 2017-04-11.
- ^ KEMA, Inc. (November 2006). "Substation Communications: Enabler of Automation / An Assessment of Communications Technologies". UTC — United Telecom Council: 3.
{{cite journal}}
: Cite journal requires|journal=
(help) - ^ "International Occultation Timing Association". Archived from the original on 2006-07-20. Retrieved 2006-07-19.
External links
- IOTA Observers Manual This manual from the International Occultation Timing Association has very extensive details on methods of accurate time measurement.
- NIST website: WWVB Radio Controlled Clocks
- NTP Project Development Website