Question

What is the wavelength of the -Hz radio wave used by “radio-controlled” clocks and wristwatches?​

Answer 1

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	Belarus VNIIFTRI [ru]	Vileyka 54°27′47″N26°46′37″E	Triple umbrella antenna[a]	300 kW	This is Beta (time signal). The signal is transmitted in non-overlapping time: 2:00- 2:20 UTC RAB99 4:00- 4:25 UTC RJH86 6:00- 6:20 UTC RAB99 7:00- 7:25 UTC RJH69 8:00- 8:25 UTC RJH90 9:00- 9:25 UTC RJH77 10:00-10:25 UTC RJH86 11:00-11:20 UTC RJH63 [2]
	RJH77	Russia VNIIFTRI [ru]	Arkhangelsk 64°21′29″N41°33′58″E	Triple umbrella antenna[b]	300 kW
	RJH63	Russia VNIIFTRI [ru]	Krasnodar 44° 46′ 25″ N 39° 32′ 50″ E	Umbrella antenna[c]	300 kW
	RJH90	Russia VNIIFTRI [ru]	Nizhny Novgorod 56° 10′ 20″ N 43° 55′ 38″ E	Triple umbrella antenna[d]	300 kW
	RJH86[2][e]	Kyrgyzstan VNIIFTRI [ru]	Bishkek 43° 02′ 29″ N 73° 37′ 09″ E	Triple umbrella antenna[f]	300 kW
	RAB99	Russia VNIIFTRI [ru]	Khabarovsk     48° 29′ 29″ N 134° 48′ 59″ E	Umbrella antenna[g]	300 kW
40 kHz	JJY	Japan NICT [ja]	Mount Otakadoya, Fukushima     37° 22′ 21″ N 140° 50′ 56″ E	Capacitance hat, height 250 m	50 kW	[3] Located near Fukushima
50 kHz	RTZ	Russia VNIIFTRI [ru]	Irkutsk     52° 25′ 41″ N 103° 41′ 12″ E	Umbrella antenna	10 kW	Inactive
60 kHz	JJY	Japan NICT [ja]	Mount Hagane, Kyushu     33° 27′ 54″ N 130° 10′ 32″ E	Capacitance hat, height 200 m	50 kW	[3] Located on Kyūshū Island
	MSF	United Kingdom NPL	Anthorn 54° 54′ 27″ N 03° 16′ 24″ W	Triple T-antenna[h]	17 kW	Range up to 1500 km. Before 1 April 2007, the signal was transmitted from Rugby, Warwickshire 52° 21′ 33″ N01° 11′ 21″ W
	WWVB	United States NIST	Near Fort Collins, Colorado[4]     40° 40′ 41″ N 105° 02′ 48″ W	Two capacitance hats, height 122 m	70 kW	[3] Received through most of mainland USA
66.66 kHz	RBU	Russia VNIIFTRI [ru]	Taldom, Moscow 56° 43′ 59″ N 37° 39′ 47″ E	Umbrella antenna[i]	50 kW	before 2008, transmitter located at 55° 44′ 14″ N 38° 09′ 4″ E
68.5 kHz	BPC	China NTSC [zh]	Shangqiu, Henan     34° 56′ 54″ N 109° 32′ 34″ 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]
75 kHz	HBG	Switzerland	Prangins 46° 24′ 24″ N 06° 15′ 04″ E	T-antenna[j]	20 kW	Discontinued as of 1 January 2012
77.5 kHz	DCF77	Germany PTB [de]	Mainflingen, Hessen 50° 00′ 58″ N 09° 00′ 29″ E	Vertical omni-directional antennas with top-loading capacity, height 150 m[6]	50 kW	[3] Located southeast of Frankfurt am Main with a range of up to 2000 km[7]
	BSF	Taiwan	Zhongli     25° 00′ 19″ N 121° 21′ 55″ E	T-antenna[k]		[8]
100 kHz [l]	BPL	China NTSC [zh]	Pucheng, Shaanxi     34° 27′ 23″ N 115° 50′ 13″ E	Single guyed lattice steel mast	800 kW	Loran-C compatible format signal on air from 5:30 to 13:30 UTC,[9] with a reception radius up to 3000 km[10]
	RNS-E	Russia VNIIFTRI [ru]	Bryansk 53° 08′ 00″ N 34° 55′ 00″ E	5 guyed masts	800 kW	CHAYKA compatible format signal[2] 4:00-10:00 UTC and 14:00-18:00 UTC
	RNS-V	Russia VNIIFTRI [ru]	Aleksandrovsk-Sakhalinskiy 51° 05′ 00″ N 142° 43′ 00″ E	Single guyed mast	400 kW	CHAYKA compatible format signal[2] 23:00-5:00 UTC and 11:00-17:00 UTC
129.1 kHz [m]	DCF49	Germany PTB [de]	Mainflingen 50°00′58″N09°00′29″E	T-antenna	100 kW	EFR radio teleswitch[11] time signal only (no reference frequency) FSK ± 170 Hz 200 baud
135.6 kHz [m]	HGA22	Hungary PTB [de]	Lakihegy 47°22′24″N19°00′17″E	Single guyed mast	100 kW
139 kHz [m]	DCF39	Germany PTB [de]	Burg bei Magdeburg 52°17′13″N11°53′49″E	Single guyed mast	50 kW
162 kHz [n]	TDF	France ANFR [fr]	Allouis 47° 10′ 10″ N 02° 12′ 16″ E	Two guyed steel lattice masts, height 350 m, fed on the top	1100 kW	AM-broadcasting transmitter, located 150 km south of Paris with a range of up to 3500 km, using PM with encoding similar to DCF77[o]
198 kHz[n][p]	BBC Radio 4	United Kingdom NPL	Droitwich 52.2955°N 2.1063°W	T-aerial[q]	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 [zh]	Pucheng, Shaanxi     34° 56′ 54″ N 109° 32′ 34″ E			(BCD time code on 125 Hz sub-carrier not yet activated) 7:30-1:00 UTC[14]
	WWV	United States NIST	Near Fort Collins, Colorado     40° 40′ 41″ N 105° 02′ 48″ 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		5 kW
3.33 MHz	CHU	Canada NRC	Ottawa, Ontario 45° 17′ 40″ N 75° 45′ 27″ W		3 kW	300 baud Bell 103 time code
4.996 MHz	RWM	Russia VNIIFTRI [ru]	Taldom, Moscow 55° 44′ 14″ N 38° 09′ 4″ E		10 kW	CW
5 MHz	BPM	China NTSC [zh]	Pucheng, Shaanxi     34° 56′ 54″ N 109° 32′ 34″ E			BCD time code on 125 Hz sub-carrier. 0:00-24:00 UTC[14]
	HLA	South Korea KRISS [ko]	Taejon     36° 23′ 14″ N 127° 21′ 59″ E		2 kW
	WWV	United States NIST	Near Fort Collins, Colorado     40° 40′ 41″ N 105° 02′ 48″ W	Broadband monopole	10 kW[r]	BCD time code on 100 Hz sub-carrier
	WWVH	United States NIST	Kekaha, Hawaii     21° 59′ 16″ N 159° 45′ 46″ W		10 kW
	YVTO	Venezuela	Caracas		1 kW
7.85 MHz	CHU	Canada NRC	Ottawa, Ontario 45° 17′ 40″ N 75° 45′ 27″ W		10 kW	300 baud Bell 103 time code
9.996 MHz	RWM	Russia VNIIFTRI [ru]	Taldom, Moscow 55° 44′ 14″ N 38° 09′ 04″ E		10 kW	CW
10 MHz	BPM	China NTSC [zh]	Pucheng, Shaanxi     34° 56′ 54″ N 109° 32′ 34″ E			(BCD time code on 125 Hz sub-carrier not yet activated) 0:00-24:00 UTC[14]
	LOL	Argentina SHN [es]	Buenos Aires		2 kW	Observatorio Naval Buenos Aires[15]
	WWV	United States NIST	Near Fort Collins, Colorado     40° 40′ 41″ N 105° 02′ 48″ 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		10 kW
	PPE[16]	Brazil	Rio de Janeiro[16]	Horizontal half-wavelength dipole[16]	1 kW[16]	Observatório Nacional
14.67 MHz	CHU	Canada NRC	Ottawa, Ontario 45° 17′ 40″ N 75° 45′ 27″ W		3 kW	300 baud Bell 103 time code
14.996 MHz	RWM	Russia VNIIFTRI [ru]	Taldom, Moscow 55° 44′ 14″ N 38° 09′ 04″ E		10 kW	CW
15 MHz	BPM	China NTSC [zh]	Pucheng, Shaanxi     34° 56′ 54″ N 109° 32′ 34″ E			(BCD time code on 125 Hz sub-carrier not yet activated) 1:00-9:00 UTC[14]
	WWV	United States NIST	Near Fort Collins, Colorado     40° 40′ 41″ N 105° 02′ 48″ 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		10 kW
20 MHz	WWV	United States NIST	Near Fort Collins, Colorado     40° 40′ 41″ N 105° 02′ 48″ 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	Broadband monopole	1.0 kW	Schedule: variable (experimental broadcast)
	MIKES	Finland MIKES [fi]	Espoo, Finland 60°10′49″N24°49′35″E	λ/4 sloper antenna	200 W[17]	1 kHz amplitude modulation similar to DCF77. As of 2017 the transmission is discontinued until further notice.[18]