# Radio clock

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Clock which synchronizes its time using radio transmitters

Not to be confused with [clock radio](/source/Alarm_clock#Clock_radio), an alarm clock incorporating a broadcast radio receiver or [Broadcast clock](/source/Broadcast_clock).

A modern [LF](/source/Low_frequency) radio-controlled clock

A **radio clock** or **radio-controlled clock** (RCC), and often colloquially (and incorrectly[1]) referred to as an "[atomic clock](/source/Atomic_clock)", is a type of [quartz](/source/Quartz_clock) [clock](/source/Clock) or watch that is automatically [synchronized](/source/Synchronization) to a [time code](/source/Time_code) transmitted by a radio transmitter connected to a [time standard](/source/Time_standard) such as an atomic clock. Such a clock may be synchronized to the time sent by a single transmitter, such as many national or regional time transmitters, or may use the multiple transmitters used by [satellite navigation](/source/Satellite_navigation) systems such as [Global Positioning System](/source/Global_Positioning_System). Such systems may be used to automatically set clocks or for any purpose where accurate time is needed. Radio clocks may include any feature available for a clock, such as alarm function, display of ambient temperature and humidity, broadcast radio reception, etc.

One common style of radio-controlled clock uses time signals transmitted by dedicated terrestrial [longwave](/source/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](/source/Shortwave_radio) bands. Systems using dedicated time signal stations can achieve accuracy of a few tens of milliseconds.

Satellite navigation 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. Timepieces with [Bluetooth](/source/Bluetooth) radio support, ranging from watches with basic control of functionality via a [mobile app](/source/Mobile_app) to full [smartwatches](/source/Smartwatch) obtain time information from a connected [phone](/source/Mobile_phone), with no need to receive time signal broadcasts.

## Single transmitter

Radio clocks synchronized to a terrestrial [time signal](/source/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](/source/Radio_propagation). Some timekeepers, particularly watches such as some [Casio Wave Ceptors](/source/Casio_Wave_Ceptor#Multi-Band_6) 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

List of radio time signal stations Frequency Callsign Country Authority Location Aerial type Power Remarks 25 kHz RJH69 Belarus VNIIFTRI Vileyka 54°27′47″N 26°46′37″E / 54.46306°N 26.77694°E / 54.46306; 26.77694 (RJH69) 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 Russia VNIIFTRI Arkhangelsk 64°21′29″N 41°33′58″E / 64.35806°N 41.56611°E / 64.35806; 41.56611 (RJH77) Triple umbrella antenna[b] 300 kW RJH63 Russia VNIIFTRI Krasnodar 44°46′25″N 39°32′50″E / 44.77361°N 39.54722°E / 44.77361; 39.54722 (RJH63) Umbrella antenna[c] 300 kW RJH90 Russia VNIIFTRI Nizhny Novgorod 56°10′20″N 43°55′38″E / 56.17222°N 43.92722°E / 56.17222; 43.92722 (RJH90) Triple umbrella antenna[d] 300 kW RJH86[2][e] Kyrgyzstan VNIIFTRI Bishkek 43°02′29″N 73°37′09″E / 43.04139°N 73.61917°E / 43.04139; 73.61917 (RJH86) Triple umbrella antenna[f] 300 kW RAB99 Russia VNIIFTRI Khabarovsk 48°29′29″N 134°48′59″E / 48.49139°N 134.81639°E / 48.49139; 134.81639 (RAB99) 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 / 37.37250; 140.84889 (JJY) Capacitance hat, height 250 m (820 ft) 50 kW Located near Fukushima[3] 50 kHz RTZ Russia VNIIFTRI Irkutsk 52°25′41″N 103°41′12″E / 52.42806°N 103.68667°E / 52.42806; 103.68667 (RTZ) 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 / 33.46500; 130.17556 (JJY) Capacitance hat, height 200 m (660 ft) 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 / 54.90750; -3.27333 (MSF)[h] Triple T-antenna[i] 17 kW Range up to 1,500 km (930 mi) WWVB United States NIST Near Fort Collins, Colorado[4] 40°40′41″N 105°02′48″W / 40.67806°N 105.04667°W / 40.67806; -105.04667 (WWVB) Two capacitance hats, height 122 m (400 ft) 70 kW Received through most of mainland U.S.[3] 66.66 kHz RBU Russia VNIIFTRI Taldom, Moscow 56°43′59″N 37°39′47″E / 56.73306°N 37.66306°E / 56.73306; 37.66306 (RBU)[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 / 34.45694; 115.83694 (BPC) 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] 75 kHz HBG Switzerland METAS Prangins 46°24′24″N 06°15′04″E / 46.40667°N 6.25111°E / 46.40667; 6.25111 (HBG) T-antenna[l] 20 kW Discontinued as of 1 January 2012 77.5 kHz DCF77 Germany PTB Mainflingen, Hessen 50°00′58″N 09°00′29″E / 50.01611°N 9.00806°E / 50.01611; 9.00806 (DCF77) Vertical omni-directional antennas with top-loading capacity, height 150 metres (490 ft)[6] 50 kW Located southeast of Frankfurt am Main with a range of up to 2,000 km (1,200 mi)[3][7] BSF Taiwan Zhongli 25°00′19″N 121°21′55″E / 25.00528°N 121.36528°E / 25.00528; 121.36528 (BSF) 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 / 34.94889; 109.54306 (BPL) 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 (1,900 mi)[10] RNS-E Russia VNIIFTRI Karachev (44 km from Bryansk) 53°07′49″N 34°54′37″E / 53.13028°N 34.91028°E / 53.13028; 34.91028 (RNS-E) 5 guyed masts 800 kW CHAYKA compatible format signal[2] 04:00–10:00 UTC and 14:00–18:00 UTC RNS-V Russia VNIIFTRI Alexandrovsk-Sakhalinsky 51°4′42.9″N 142°42′9.1″E / 51.078583°N 142.702528°E / 51.078583; 142.702528 (RNS-V) 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 [de] Germany PTB Mainflingen 50°00′58″N 09°00′29″E / 50.01611°N 9.00806°E / 50.01611; 9.00806 (DCF49) T-antenna 100 kW EFR radio teleswitch[11] time signal only (no reference frequency) FSK ± 170 Hz 200 baud 135.6 kHz[o] HGA22 [hu] Hungary PTB Lakihegy Tower 47°22′24″N 19°00′17″E / 47.37333°N 19.00472°E / 47.37333; 19.00472 (HGA22) Single guyed mast 100 kW 139 kHz[o] DCF39 [de] Germany PTB Burg bei Magdeburg 52°17′13″N 11°53′49″E / 52.28694°N 11.89694°E / 52.28694; 11.89694 (DCF39) Single guyed mast 50 kW 162 kHz[p] ALS162 France ANFR [fr] Allouis 47°10′10″N 02°12′16″E / 47.16944°N 2.20444°E / 47.16944; 2.20444 (ALS162) Two guyed steel lattice masts, height 350 m (1,150 ft), fed on the top 800 kW AM-broadcasting transmitter, located 150 km (93 mi) south of Paris with a range of up to 3,500 km (2,200 mi), 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 / 52.2955; -2.1063 (BBC4) 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] 225 kHz[p] Polskie Radio Poland Solec Kujawski 53°1′12.92″N 18°15′44.28″E / 53.0202556°N 18.2623000°E / 53.0202556; 18.2623000 Guyed mast 1000 kW Phase-modulated time signal[14][15] 2.5 MHz BPM China NTSC Pucheng, Shaanxi 34°56′56″N 109°32′35″E / 34.94889°N 109.54306°E / 34.94889; 109.54306 (BPM) (BCD time code on 125 Hz sub-carrier not yet activated) 07:30–01:00 UTC[16] WWV United States NIST Near Fort Collins, Colorado 40°40′41″N 105°02′48″W / 40.67806°N 105.04667°W / 40.67806; -105.04667 (WWV) 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 / 21.98778; -159.76278 (WWVH) 5 kW 3.33 MHz CHU Canada NRC Ottawa, Ontario 45°17′40″N 75°45′27″W / 45.29444°N 75.75750°W / 45.29444; -75.75750 (CHU) 3 kW 300 baud Bell 103 time code. Discontinued effective 22 June 2026.[17] 4.996 MHz RWM Russia VNIIFTRI Taldom, Moscow 56°44′58″N 37°38′23″E / 56.74944°N 37.63972°E / 56.74944; 37.63972 (RWM)[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 / 34.94889; 109.54306 (BPM) BCD time code on 125 Hz sub-carrier. 00:00–24:00 UTC[16] HLA Korea KRISS Daejeon 36°23′14″N 127°21′59″E / 36.38722°N 127.36639°E / 36.38722; 127.36639 (HLA) 2 kW WWV United States NIST Near Fort Collins, Colorado 40°40′41″N 105°02′48″W / 40.67806°N 105.04667°W / 40.67806; -105.04667 (WWV) 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 / 21.98778; -159.76278 (WWVH) 10 kW YVTO Venezuela Caracas 10°30′13″N 66°55′44″W / 10.50361°N 66.92889°W / 10.50361; -66.92889 (YVTO) 1 kW 7.85 MHz CHU Canada NRC Ottawa, Ontario 45°17′40″N 75°45′27″W / 45.29444°N 75.75750°W / 45.29444; -75.75750 (CHU) 10 kW 300 baud Bell 103 time code 9.996 MHz RWM Russia VNIIFTRI Taldom, Moscow 56°44′58″N 37°38′23″E / 56.74944°N 37.63972°E / 56.74944; 37.63972 (RWM)[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 / 34.94889; 109.54306 (BPM) (BCD time code on 125 Hz sub-carrier not yet activated) 00:00–24:00 UTC[16] LOL Argentina SHN Buenos Aires[u] 2 kW Observatorio Naval Buenos Aires[18] WWV United States NIST Near Fort Collins, Colorado 40°40′41″N 105°02′48″W / 40.67806°N 105.04667°W / 40.67806; -105.04667 (WWV) 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 / 21.98778; -159.76278 (WWVH) 10 kW PPE[19] Brazil Rio de Janeiro, RJ 22°53′44″S 43°13′27″W / 22.89556°S 43.22417°W / -22.89556; -43.22417 (PPE)[19] Horizontal half-wavelength dipole[19] 1 kW[19] Maintained by National Observatory (Brazil) 14.67 MHz CHU Canada NRC Ottawa, Ontario 45°17′40″N 75°45′27″W / 45.29444°N 75.75750°W / 45.29444; -75.75750 (CHU) 3 kW 300 baud Bell 103 time code 14.996 MHz RWM Russia VNIIFTRI Taldom, Moscow 56°44′58″N 37°38′23″E / 56.74944°N 37.63972°E / 56.74944; 37.63972 (RWM)[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 / 34.94889; 109.54306 (BPM) (BCD time code on 125 Hz sub-carrier not yet activated) 01:00–09:00 UTC[16] WWV United States NIST Near Fort Collins, Colorado 40°40′41″N 105°02′48″W / 40.67806°N 105.04667°W / 40.67806; -105.04667 (WWV) 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 / 21.98778; -159.76278 (WWVH) 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 / 40.67806; -105.04667 (WWV) 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 / 40.67806; -105.04667 (WWV) Broadband monopole 2.0 kW Schedule: variable (experimental broadcast) MIKES Finland MIKES Espoo, Finland 60°10′49″N 24°49′35″E / 60.18028°N 24.82639°E / 60.18028; 24.82639 (MIKES time signal transmitter) λ/4 sloper antenna 0.2 kW[20] 1 kHz amplitude modulation similar to DCF77. As of 2017 the transmission is discontinued until further notice.[21] "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."[22]

**Descriptions**

1. **[^](#cite_ref-2)** 3 umbrella antennas, fixed on 3 guyed tubular masts, insulated against ground with a height of 305 m (1,001 ft) and 15 guyed lattice masts with a height of 270 m (890 ft)

1. **[^](#cite_ref-4)** 3 umbrella antennas, fixed on 18 guyed lattice masts, height of central masts: 305 metres

1. **[^](#cite_ref-5)** umbrella antenna, fixed on 13 guyed lattice masts, height of central mast: 425 m (1,394 ft)

1. **[^](#cite_ref-6)** 3 umbrella antennas, fixed on 3 guyed tubular masts, insulated against ground with a height of 205 m (673 ft) and 15 guyed lattice masts with a height of 170 m (560 ft)

1. **[^](#cite_ref-7)** in air RJH66

1. **[^](#cite_ref-8)** 3 umbrella antennas, fixed on 18 guyed lattice masts, height of central masts: 276 m (906 ft)

1. **[^](#cite_ref-9)** umbrella antenna, fixed on 18 guyed lattice masts arranged in 3 rows, height of central masts: 238 m (781 ft)

1. **[^](#cite_ref-11)** Before 1 April 2007, the signal was transmitted from [Rugby, Warwickshire](/source/Rugby_Radio_Station) [52°21′33″N 01°11′21″W / 52.35917°N 1.18917°W / 52.35917; -1.18917](https://geohack.toolforge.org/geohack.php?pagename=Radio_clock&params=52_21_33_N_01_11_21_W_)

1. **[^](#cite_ref-12)** 3 T-antennas, spun 150 m (490 ft) above ground between two 227 m (745 ft) high guyed grounded masts in a distance of 655 m (716 yd)

1. ^ [***a***](#cite_ref-RBU_14-0) [***b***](#cite_ref-RBU_14-1) [***c***](#cite_ref-RBU_14-2) [***d***](#cite_ref-RBU_14-3) Before 2008, transmitter located at [55°44′14″N 38°09′04″E / 55.73722°N 38.15111°E / 55.73722; 38.15111](https://geohack.toolforge.org/geohack.php?pagename=Radio_clock&params=55_44_14_N_38_09_04_E_)

1. **[^](#cite_ref-15)** umbrella antenna, fixed on a 275 m (902 ft) high central tower insulated against ground and five 257 m (843 ft) high lattice masts insulated against ground in a distance of 324 metres (354 yards) from the central tower

1. **[^](#cite_ref-17)** T-antenna spun between two 125 m (410 ft) tall, grounded free-standing lattice towers in a distance of 227 m (248 yd)

1. **[^](#cite_ref-20)** T-antenna spun between two telecommunication towers in a distance of 33 m (36 yd)

1. **[^](#cite_ref-22)** Frequency for radio navigation system

1. ^ [***a***](#cite_ref-teleswitch_25-0) [***b***](#cite_ref-teleswitch_25-1) [***c***](#cite_ref-teleswitch_25-2) Frequency for radio teleswitch system

1. ^ [***a***](#cite_ref-AM_27-0) [***b***](#cite_ref-AM_27-1) [***c***](#cite_ref-AM_27-2) Frequency for AM-broadcasting

1. **[^](#cite_ref-28)** and requiring a more complex receiver for demodulating time signal

1. **[^](#cite_ref-29)** since 1988, before 200 kHz

1. **[^](#cite_ref-30)** Droitwich uses a T-aerial suspended between two 213 metres (699') guyed steel lattice [radio masts](/source/Radio_masts_and_towers), which stand 180 m (200 yd) apart.

1. **[^](#cite_ref-37)** Time signal article says 2.5 kW

1. **[^](#cite_ref-39)** [18] 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 / -34.62194; -58.35500 (LOL)](https://geohack.toolforge.org/geohack.php?pagename=Radio_clock&params=34_37_19_S_58_21_18_W_&title=LOL)

2300km
1429miles

DCF39DCF

[JJY (Ōtakadoyayama)](/source/%C5%8Ctakadoyayama_Transmitter)

[JJYJJY (Haganeyama)(Haganeyama)](/source/Haganeyama_Transmitter)

RNS-VRNS-V

RAB99RAB

HLA[HLA](/source/HLA_(radio_station))

BSF[BSF](/source/BSF_(time_service))

[BPC](/source/BPC_(time_signal))BPC

[BPM](/source/BPM_(time_service))

[BPL](/source/BPL_(time_service))

RTZ

RJH86RJH86

RJH90

RJH77

RJH63

[RBU](/source/RBU_(radio_station)), [RWM](/source/RWM)

[RNS-E](https://en.wikipedia.org/w/index.php?title=RNS-E&action=edit&redlink=1)

[RJH69](/source/RJH69)RJH69

[MIKES](https://en.wikipedia.org/w/index.php?title=MIKES_(radio_station)&action=edit&redlink=1)MIKES

GA22HGA22

DCF49, [DCF77](/source/DCF77)

[HBG](/source/HBG_(time_signal))

[ALS162](/source/ALS162_time_signal)
(formerly TDF)

[BBC Radio 4](/source/BBC_Radio_4)
([Droitwich](/source/Droitwich_Transmitting_Station))

[MSF](/source/Time_from_NPL_(MSF))

PPE[PPE](https://en.wikipedia.org/w/index.php?title=PPE_(radio_station)&action=edit&redlink=1)

LOL[LOL](https://en.wikipedia.org/w/index.php?title=LOL_(radio_station)&action=edit&redlink=1)

[YVTO](/source/YVTO)

[CHU](/source/CHU_(radio_station))C

[WWV](/source/WWV_(radio_station))

[WWVB](/source/WWVB)

[WWVH](/source/WWVH)H

Many other countries can receive these signals ([JJY](/source/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 (190 mi) 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 [Heathkit](/source/Heathkit) in late 1983. Their model GC-1000 "Most Accurate Clock" received shortwave time signals from radio station [WWV](/source/WWV_(radio_station)) in [Fort Collins, Colorado](/source/Fort_Collins%2C_Colorado). It automatically switched between WWV's 5, 10, and 15 MHz frequencies to find the strongest signal as conditions changed through the day and year. It kept time during periods of poor reception with a quartz-crystal [oscillator](/source/Oscillator). This oscillator was disciplined, meaning that the microprocessor-based clock used the highly accurate time signal received from WWV to trim the crystal oscillator. The timekeeping between updates was thus considerably more accurate than the crystal alone could have achieved. Time down to the tenth of a second was shown on an [LED](/source/LED) display. The GC-1000 originally sold for US$250 in kit form and US$400 preassembled, and was considered impressive at the time. Heath Company was granted a patent [Archived](https://web.archive.org/web/20151016222647/http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=4582434.PN.&OS=PN/4582434&RS=PN/4582434) 16 October 2015 at the [Wayback Machine](/source/Wayback_Machine) for its design.[23][24]

By 1990, engineers from German watchmaker [Junghans](/source/Junghans) had miniaturized this technology to fit into the case of a digital wristwatch. The following year the analog version [Junghans Mega](/source/Junghans_Mega) with hands was launched.

In the 2000s, radio-based "atomic clocks" became common in retail stores; as of 2010 prices start at around US$15 in many countries.[25] Clocks may have other features such as indoor thermometers and [weather station](/source/Weather_station) functionality. These use signals transmitted by the appropriate transmitter for the country in which they are to be used. Depending upon signal strength they may require placement in a location with a relatively unobstructed path to the transmitter and need fair to good atmospheric conditions to successfully update the time. Inexpensive clocks keep track of the time between updates, or in their absence, with a non-disciplined [quartz-crystal clock](/source/Quartz-crystal_clock), with the accuracy typical of non-radio-controlled quartz timepieces. Some clocks include indicators to alert users to possible inaccuracy when synchronization has not been recently successful.

The United States [National Institute of Standards and Technology](/source/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.[26] Some of these movements can keep time between synchronizations to within ±0.2 seconds by synchronizing more than once spread over a day.[27]

Timepieces with [Bluetooth](/source/Bluetooth) radio support, ranging from watches with basic control of functionality via a [mobile app](/source/Mobile_app) to full [smartwatches](/source/Smartwatch)[28] obtain time information from a connected [phone](/source/Mobile_phone), with no need to receive time signal broadcasts.

### Other broadcasts

Main article: [Time signal](/source/Time_signal)

**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](/source/BBC_Radio_4) [longwave](/source/Longwave) service on 198 kHz, and some also transmit sub-audible or even inaudible time-code information, like the [Radio France](/source/Radio_France) longwave transmitter on 162 kHz. Attached time signal systems generally use audible tones or phase modulation of the carrier wave.

**[Teletext](/source/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.[29]

Many [digital radio](/source/Digital_radio) and [digital television](/source/Digital_television) schemes also include provisions for time-code transmission.

**Digital Terrestrial Television**
- The [DVB](/source/Digital_Video_Broadcasting) and [ATSC](/source/ATSC) standards 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)](/source/Radio_Data_System)**
- 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](/source/Digital_Audio_Broadcasting)**
- DAB systems provide a time signal that has a precision equal to or better than [Digital Radio Mondiale (DRM)](/source/Digital_Radio_Mondiale) 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)](/source/Digital_Radio_Mondiale)**
- DRM is able to send a clock signal, but one not as precise as [navigation satellite](/source/Navigation_satellite) clock 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

		- [LF](/source/Low_frequency) time signal receiver

		- World's first radio clock wrist watch, [Junghans Mega](/source/Junghans_Mega) (analog model)

		- Radio controlled analog [wall clock](/source/Wall_clock)

		- The DCF77 time signal is used by organizations like the [Deutsche Bahn](/source/Deutsche_Bahn) railway company to synchronize their [station clocks](/source/Station_clock)

## Multiple transmitters

A radio clock receiver may combine multiple time sources to improve its accuracy. This is what is done in [satellite navigation systems](/source/Global_Navigation_Satellite_System) such as the [Global Positioning System](/source/Global_Positioning_System), [Galileo](/source/Galileo_positioning_system), and [GLONASS](/source/GLONASS). [Satellite navigation systems](/source/Satellite_navigation_system) have one or more caesium, rubidium or hydrogen maser atomic clocks on each satellite, referenced to a clock or clocks on the ground. Dedicated timing receivers can serve as local time standards, with a precision better than 50 ns.[30][31][32][33] The recent revival and enhancement of [LORAN](/source/LORAN), a land-based radio navigation system, will provide another multiple source time distribution system.

### GPS clocks

Main article: [GPS disciplined oscillator](/source/GPS_disciplined_oscillator)

Many modern radio clocks use [satellite navigation](/source/Satellite_navigation) systems such as [Global Positioning System](/source/Global_Positioning_System) to provide more accurate time than can be obtained from terrestrial radio stations. These *GPS clocks* combine time estimates from multiple satellite atomic clocks with error estimates maintained by a network of ground stations. Due to effects inherent in radio propagation and ionospheric spread and delay, GPS timing requires averaging of these phenomena over several periods. No GPS receiver directly computes time or frequency, rather they use GPS to discipline an oscillator that may range from a quartz crystal in a low-end navigation receiver, through oven-controlled [crystal oscillators](/source/Crystal_oscillators) (OCXO) in specialized units, to atomic oscillators ([rubidium](/source/Rubidium)) in some receivers used for [synchronization in telecommunications](/source/Synchronization_in_telecommunications). For this reason, these devices are technically referred to as [GPS-disciplined oscillators](/source/GPSDO).

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 [synchrophasor](/source/Synchrophasor) measurement of voltage and current on the commercial power grid to determine the health of the system.[34]

### Astronomy timekeeping

Although any [satellite navigation](/source/Satellite_navigation) receiver that is performing its primary navigational function must have an internal time reference accurate to a small fraction of a second, the displayed time is often not as precise as the internal clock. Most inexpensive navigation receivers have one [CPU](/source/CPU) that is multitasking. The highest-priority task for the CPU is maintaining satellite lock—not updating the display. Multicore CPUs for navigation systems can only be found on high end products.

For serious precision timekeeping, a more specialized GPS device is needed. Some amateur astronomers, most notably those who time [grazing lunar occultation](/source/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[35] 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](/source/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](/source/Casio_Wave_Ceptor)

- [Clock network](/source/Clock_network)

- [Speaking clock](/source/Speaking_clock)

- [Standard frequency and time signal service](/source/Standard_frequency_and_time_signal_service)

- [Time from NPL](/source/Time_from_NPL)

- [Time and frequency transfer](/source/Time_and_frequency_transfer)

- [Time synchronization in North America](/source/Time_synchronization_in_North_America)

## References

1. ^ [***a***](#cite_ref-Lombardi_1-0) [***b***](#cite_ref-Lombardi_1-1) Lombardi, Michael A. (March 2010). ["How Accurate is a Radio Controlled Clock?"](http://tf.nist.gov/general/pdf/2429.pdf) (PDF). *Horological Journal*. **152** (3): 108–111. [Archived](https://web.archive.org/web/20210107194406/https://tf.nist.gov/general/pdf/2429.pdf) (PDF) from the original on 7 January 2021. Retrieved 1 December 2023 – via National Institute of Standards and Technology website.

1. ^ [***a***](#cite_ref-vniiftri_3-0) [***b***](#cite_ref-vniiftri_3-1) [***c***](#cite_ref-vniiftri_3-2) [***d***](#cite_ref-vniiftri_3-3) ["Standard Time and Frequency Signals"](ftp://ftp.vniiftri.ru/BULLETINS/V/bull_b16_2018.pdf) (PDF). *FTP server* ([FTP](/source/FTP)) (in Russian). Retrieved 15 July 2018.[*dead ftp link*] (To view documents see [Help:FTP](https://en.wikipedia.org/wiki/Help:FTP)) — official signal specification.

1. ^ [***a***](#cite_ref-McCarthy09_10-0) [***b***](#cite_ref-McCarthy09_10-1) [***c***](#cite_ref-McCarthy09_10-2) [***d***](#cite_ref-McCarthy09_10-3) Dennis D. McCarthy, P. Kenneth Seidelmann *Time: From Earth Rotation to Atomic Physics* Wiley-VCH, 2009 [ISBN](/source/ISBN_(identifier)) [3-527-40780-4](https://en.wikipedia.org/wiki/Special:BookSources/3-527-40780-4) page 257

1. **[^](#cite_ref-13)** ["NIST Radio Station WWVB"](https://www.nist.gov/pml/div688/grp40/wwvb.cfm). *NIST*. March 2010. [Archived](https://web.archive.org/web/20140325181329/http://www.nist.gov/pml/div688/grp40/wwvb.cfm) from the original on 25 March 2014. Retrieved 18 March 2014.

1. **[^](#cite_ref-16)** ["BPC"](https://web.archive.org/web/20180214031330/http://www.time.ac.cn/serve/e_c.htm). *National Time Service Center, Chinese Academy of Sciences*. Archived from [the original](http://www.time.ac.cn/serve/e_c.htm) on 14 February 2018. Retrieved 16 March 2013.

1. **[^](#cite_ref-18)** Yvonne Zimber (9 May 2007). ["DCF77 transmitting facilities"](http://www.ptb.de/en/org/4/44/442/dcf77_sende_e.htm). [Archived](https://web.archive.org/web/20100514002918/http://www.ptb.de/en/org/4/44/442/dcf77_sende_e.htm) from the original on 14 May 2010. Retrieved 2 May 2010.

1. **[^](#cite_ref-compuphase_h0420_19-0)** ["Synchronizing time with DCF77 and MSF60"](http://www.compuphase.com/mp3/h0420_timecode.htm). [Archived](https://web.archive.org/web/20110112034340/http://www.compuphase.com/mp3/h0420_timecode.htm) from the original on 12 January 2011. Retrieved 12 September 2011. 090917 compuphase.com

1. **[^](#cite_ref-21)** ["A Time Station Signal Project for Taiwan"](https://lfintaiwan.bitbucket.io/overview.html). [Archived](https://web.archive.org/web/20170420145738/https://lfintaiwan.bitbucket.io/overview.html) from the original on 20 April 2017. Retrieved 9 July 2018.

1. **[^](#cite_ref-23)** ["长波授时 (Longwave time signal)"](https://web.archive.org/web/20130110210025/http://www.time.ac.cn/serve/BPL.htm). *National Time Service Center, Chinese Academy of Sciences*. Archived from [the original](http://www.time.ac.cn/serve/BPL.htm) on 10 January 2013. Retrieved 16 March 2013.

1. **[^](#cite_ref-24)** ["科研成果 (Research achievements)"](http://www.ntsc.cas.cn/kycg/). *National Time Service Center, Chinese Academy of Sciences*. [Archived](https://web.archive.org/web/20130417182930/http://www.ntsc.cas.cn/kycg/) from the original on 17 April 2013. Retrieved 16 March 2013.

1. **[^](#cite_ref-efr_26-0)** ["PTB time monitor"](http://www.efr.de/de/efr-system/#/PTB-Zeitmonitor). [Archived](https://web.archive.org/web/20180716194814/http://www.efr.de/de/efr-system/#/PTB-Zeitmonitor) from the original on 16 July 2018. Retrieved 16 July 2018. — in German

1. **[^](#cite_ref-31)** ["Radio stations in London, England"](https://radiomap.eu/uk/london). [Archived](https://web.archive.org/web/20160419145438/http://radiomap.eu/uk/london) from the original on 19 April 2016. Retrieved 26 April 2016. Birmingham, Droitwich, 500 kW + Blackwall Tunnel + Rotherhithe Tunnel

1. **[^](#cite_ref-32)** ["L.F. RADIO-DATA: Specification of BBC phase-modulated transmissions on long-wave"](https://downloads.bbc.co.uk/rd/pubs/reports/1984-19.pdf) (PDF) (published 24 October 2006). December 1984. [Archived](https://web.archive.org/web/20160304194431/http://downloads.bbc.co.uk/rd/pubs/reports/1984-19.pdf) (PDF) from the original on 4 March 2016. Retrieved 25 April 2016. 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

1. **[^](#cite_ref-33)** ["New timecode on Poland's 225 kHz signal"](https://pa3fwm.nl/signals/poland225kHz/). *pa3fwm.nl*. Retrieved 24 August 2025.

1. **[^](#cite_ref-34)** ["e-Czas Radio – e-CzasPL"](https://web.archive.org/web/20231229092027/https://e-czas.gum.gov.pl/e-czas-radio/). Archived from [the original](https://e-czas.gum.gov.pl/e-czas-radio/) on 29 December 2023. Retrieved 24 August 2025.

1. ^ [***a***](#cite_ref-bpm_35-0) [***b***](#cite_ref-bpm_35-1) [***c***](#cite_ref-bpm_35-2) [***d***](#cite_ref-bpm_35-3) ["短波授时 (Shortwave time signal)"](http://www.time.ac.cn/serve/BPM.htm). *National Time Service Center, Chinese Academy of Sciences*. [Archived](https://web.archive.org/web/20130115032133/http://www.time.ac.cn/serve/BPM.htm) from the original on 15 January 2013. Retrieved 16 March 2013.

1. **[^](#cite_ref-36)** ["NRC shortwave station broadcasts (CHU)"](https://nrc.canada.ca/en/certifications-evaluations-standards/canadas-official-time/nrc-shortwave-station-broadcasts-chu). *National Research Council*. Government of Canada. Retrieved 24 May 2026.

1. ^ [***a***](#cite_ref-lol_38-0) [***b***](#cite_ref-lol_38-1) [Information on the Official Time and Standard Frequency](http://www.hidro.gov.ar/Observatorio/LaHora.asp) [Archived](https://web.archive.org/web/20180828134617/http://www.hidro.gov.ar/Observatorio/LaHora.asp) 28 August 2018 at the [Wayback Machine](/source/Wayback_Machine) — in Spanish

1. ^ [***a***](#cite_ref-onrdsh_40-0) [***b***](#cite_ref-onrdsh_40-1) [***c***](#cite_ref-onrdsh_40-2) [***d***](#cite_ref-onrdsh_40-3) ["Rádio-Difusão de Sinais Horários"](http://pcdsh01.on.br/RadioDifusaoSinaisHorarios.html). Observatório Nacional. [Archived](https://web.archive.org/web/20140312212423/http://pcdsh01.on.br/RadioDifusaoSinaisHorarios.html) from the original on 12 March 2014. Retrieved 23 February 2012.

1. **[^](#cite_ref-MIKES_41-0)** ["QSL: MIKES Time Station, Espoo, Finland"](http://swldx.us/blog/?p=821). *SWL DX Blog*. 14 May 2014. [Archived](https://web.archive.org/web/20161012151307/http://swldx.us/blog/?p=821) from the original on 12 October 2016. Retrieved 11 October 2016. Reproduces a [QSL letter](/source/QSL_card) from MIKES with technical details.

1. **[^](#cite_ref-BIPM_42-0)** BIPM Annual Report on Time Activities – [Time Signals](https://web.archive.org/web/20211010023818/ftp://ftp2.bipm.org/pub/tai/scale/TIMESIGNALS/timesignals.pdf), Retrieved 31 July 2018.

1. **[^](#cite_ref-43)** ["SI units in Finland, time and frequency |"](https://www.vttresearch.com/en/si-units-finland-time-and-frequency).

1. **[^](#cite_ref-44)** ["Heathkit GC-1000-H Most Accurate Clock"](https://www.pestingers.net/pages-images/heathkit/radio-equipment/gc1000/gc1000.htm). *Pestingers*. [Archived](https://web.archive.org/web/20200214054036/https://www.pestingers.net/pages-images/heathkit/radio-equipment/gc1000/gc1000.htm) from the original on 14 February 2020.

1. **[^](#cite_ref-45)** [US patent 4582434](https://worldwide.espacenet.com/textdoc?DB=EPODOC&IDX=US4582434), David Plangger and Wayne K. Wilson, Heath Company, "Time corrected, continuously updated clock", issued 15 April 1986

1. **[^](#cite_ref-46)** [" Radio controlled clock £19.95](http://www.kleenezeshop.com/products/2988-radio-controlled-clock.aspx/?affiliateid=779) [Deprecated link](https://en.wikipedia.org/wiki/Wikipedia:Archive.today_guidance) archived 16 February 2013 at [archive.today](/source/Archive.today)

1. **[^](#cite_ref-lombardi2_47-0)** ["How Accurate is a Radio Controlled Clock?"](https://tf.nist.gov/general/pdf/2429.pdf) by Michael Lombardi (2010).

1. **[^](#cite_ref-48)** [RADIO-CONTROLLED WALLCLOCK INSTRUCTION MANUAL](https://cdn.nedis.com/datasheets/MAN_HE-CLOCK-89_EN.PDF)

1. **[^](#cite_ref-49)** ["Bluetooth"](https://www.casio.com/europe/watches/technology/bluetooth/). Casio. Retrieved 16 July 2024.

1. **[^](#cite_ref-digitalspy_co_uk-showthread_php_p_11057588_50-0)** ["How's your GHD8015F2 operating? — Personal Video Recorders — Digital Spy Forums"](http://www.digitalspy.co.uk/forums/showthread.php?p=11057588). *[Digital Spy](/source/Digital_Spy)*. 100506 digitalspy.co.uk

1. **[^](#cite_ref-51)** ["datasheet i-Lotus TX Oncore"](http://www.ilotus.com.sg/sites/all/themes/zeropoint/pdf/tx/TX%20Oncore%20-%20TDS%20(Ver%203.5.0).pdf) (PDF). [Archived](https://web.archive.org/web/20151016222646/http://www.ilotus.com.sg/sites/all/themes/zeropoint/pdf/tx/TX%20Oncore%20-%20TDS%20(Ver%203.5.0).pdf) (PDF) from the original on 16 October 2015. Retrieved 22 January 2014.

1. **[^](#cite_ref-52)** ["Symmetricom XL-GPS"](http://www.symmetricom.com/products/time-frequency-distribution/gps-instruments/xl-gps/). [Archived](https://web.archive.org/web/20140201153456/http://www.symmetricom.com/products/time-frequency-distribution/gps-instruments/xl-gps/) from the original on 1 February 2014. Retrieved 22 January 2014.

1. **[^](#cite_ref-53)** ["datasheet Trimble Resolution SMT GG"](http://www.trimble.com/timing/pdf/022542-039A_Resolution_SMT_GG_DS_0412_US_LR.pdf) (PDF). [Archived](https://web.archive.org/web/20130622223112/http://www.trimble.com/timing/pdf/022542-039A_Resolution_SMT_GG_DS_0412_US_LR.pdf) (PDF) from the original on 22 June 2013. Retrieved 22 January 2014.

1. **[^](#cite_ref-54)** ["datasheet u-blox NEO/LEA-M8T"](https://www.u-blox.com/sites/default/files/NEO-LEA-M8T-FW3_DataSheet_%28UBX-15025193%29.pdf) (PDF). [Archived](https://web.archive.org/web/20170412061545/https://www.u-blox.com/sites/default/files/NEO-LEA-M8T-FW3_DataSheet_%28UBX-15025193%29.pdf) (PDF) from the original on 12 April 2017. Retrieved 11 April 2017.

1. **[^](#cite_ref-55)** [KEMA, Inc.](/source/KEMA) (November 2006). "Substation Communications: Enabler of Automation / An Assessment of Communications Technologies". UTC — United Telecom Council. p. 3.

1. **[^](#cite_ref-56)** ["International Occultation Timing Association"](http://www.lunar-occultations.com/iota/). [Archived](https://web.archive.org/web/20060720062504/http://www.lunar-occultations.com/iota/) from the original on 20 July 2006. Retrieved 19 July 2006.

## External links

Look up ***[radio clock](https://en.wiktionary.org/wiki/Special:Search/radio_clock)*** in Wiktionary, the free dictionary.

- [IOTA Observers Manual](http://www.poyntsource.com/IOTAmanual/IOTA_Observers_Manual_all_pages.pdf) This manual from the *International Occultation Timing Association* has very extensive details on methods of accurate time measurement.

- [NIST website: WWVB Radio Controlled Clocks](https://www.nist.gov/pml/div688/grp40/radioclocks.cfm)

- [NTP Project Development Website](http://ntp.org)

v t e Time signal stations Longwave BPC BPL BSF Beta DCF77 JJY RBU RTZ ALS162 Time from NPL WWVB Shortwave BPM HD2IOA HLA JN53DV ROA Time RWM WWV WWVH YVTO VHF/FM/UHF Radio Data System Satellite BeiDou DORIS GLONASS Galileo Global Positioning System IRNSS Quasi-Zenith Satellite System Defunct BSF CHU HBG NAA OLB5 OMA Radio VNG WWVL Y3S

v t e Time signal authorities ANFR KRISS MIKES NICT NIST NPL NRC NTSC PTB ROA SHN VNIIFTRI Other ALS162 HLA MIKES JJY WWVB WWV WWVH MSF BBC (198 kHz) CHU BPC BPL BPM DCF77 DCF (EFR) EBC LOL RBU RJH (Beta) RNS (CHAYKA) RTZ RWM BSF HD2IOA JN53DV PPE YVTO

v t e Time Key concepts Past Present Future Eternity Measurement and standards Chronometry UTC Universal Time TAI Unit of time Orders of magnitude (time) Measurement systems Italian six-hour clock Thai six-hour clock 12-hour clock 24-hour clock Relative hour Daylight saving time Chinese Decimal Hexadecimal Hindu Jain Metric Roman Sidereal Solar Time zone Calendars Main types Solar Lunar Lunisolar Gregorian Julian Hebrew Islamic Solar Hijri Chinese Hindu Panchang Maya List Clocks Main types astronomical astrarium atomic quantum hourglass marine sundial watch 24-hour wristwatch mechanical stopwatch water-based Cuckoo clock Digital clock Grandfather clock History Timeline Chronology History Astronomical chronology Big History Calendar era Deep time Periodization Regnal year Timeline Philosophy of time A series and B series B-theory of time Chronocentrism Duration Endurantism Eternal return Eternalism Event Moving spotlight theory Perdurantism Presentism Temporal finitism Temporal parts "The Unreality of Time" Religion Mythology Ages of Man Destiny Immortality Dreamtime Kāla Time and fate deities Father Time Wheel of time Kalachakra Human experience and use of time Chronemics Generation time Mental chronometry Music tempo time signature Rosy retrospection Tense–aspect–mood Time management Yesterday – Today – Tomorrow Time in science Geology Geological time age chron eon epoch era period Geochronology Geological history of Earth Physics Absolute space and time Arrow of time Chronon Coordinate time Instant Proper time Spacetime Theory of relativity Time domain Time translation symmetry Time reversal symmetry Other fields Chronological dating Chronobiology Circadian rhythms Clock reaction Glottochronology Time geography Related Leap year Memory Moment Sabbath Space System time Tempus fugit Time capsule Time immemorial Time travel Time value of money Category Commons

v t e Time measurement and standards International standards Coordinated Universal Time offset UT ΔT DUT1 International Earth Rotation and Reference Systems Service ISO 31-1 ISO 8601 International Atomic Time 12-hour clock 24-hour clock Barycentric Coordinate Time Barycentric Dynamical Time Civil time Daylight saving time Geocentric Coordinate Time International Date Line IERS Reference Meridian Leap second Solar time Terrestrial Time Time zone 180th meridian Obsolete standards Ephemeris time Greenwich Mean Time Prime meridian Time in physics Absolute space and time Spacetime Chronon Coordinate time Discrete time and continuous time Proper time Theory of relativity Time dilation Gravitational time dilation Time domain Time-translation symmetry T-symmetry Chronometry Clock Astrarium Atomic clock Complication History of timekeeping devices Hourglass Marine chronometer Marine sandglass Radio clock Watch stopwatch Water clock Sundial Dialing scales Equation of time History of sundials Sundial markup schema Calendar Gregorian Hebrew Hindu Holocene Islamic (lunar Hijri) Julian Solar Hijri Astronomical Dominical letter Epact Equinox Intercalation Julian day Leap year Lunar Lunisolar Solar Solstice Tropical year Weekday determination Weekday names Archaeology and geology Chronological dating Geologic time scale International Commission on Stratigraphy Astronomical chronology Galactic year Nuclear timescale Precession Sidereal time Other units of time Instant Flick Shake Jiffy Second Minute Moment Hour Day Week Fortnight Month Year Olympiad Lustrum Decade Century Saeculum Millennium Related topics Orders of magnitude Chronology Duration music Mental chronometry Decimal time Metric time System time Time value of money Timekeeper

v t e Coordinated Universal Time (UTC) UTC offset for standard time and Daylight saving time (DST) Italics: historical or unofficial 180° to 90°W −12:00 −11:00 −10:30 −10:00 −09:30 −09:00 −08:30 −08:00 −07:00 90°W to 0° −06:00 −05:00 −04:30 −04:00 −03:30 −03:00 −02:30 −02:00 −01:00 −00:44 −00:25:21 0° to 90°E +00:00 +00:09:21 +00:20 +00:30 +01:00 +01:24 +01:30 +02:00 +02:30 +02:39:18 +03:00 +03:30 +04:00 +04:30 +04:51 +05:00 +05:30 +05:40 +05:45 90°E to 180° +06:00 +06:30 +07:00 +07:20 +07:30 +08:00 +08:30 +08:45 +09:00 +09:30 +09:45 +10:00 +10:30 +11:00 +11:30 180° to 90°W +12:00 +12:45 +13:00 +13:45 +14:00 Time zone data sources tz database Lists of time zones Time zones by country Time zones by UTC offset Military time zone Time zone abbreviations Daylight saving time by country Related topics Abolition of time zones

v t e Electric clock technology Powerline synchronized Synchronous Motor and the Master Clock Utility frequency Synchronous motor Electronic Quartz clock Atomic clock Radio clock

Authority control databases GND

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Adapted from the Wikipedia article [Radio clock](https://en.wikipedia.org/wiki/Radio_clock) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Radio_clock?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.