In radio, longwave, long wave or long-wave, and commonly abbreviated LW, refers to parts of the radio spectrum with wavelengths longer than what was originally called the medium-wave broadcasting band. The term is historic, dating from the early 20th century, when the radio spectrum was considered to consist of longwave (LW), medium-wave (MW), and short-wave (SW) radio bands. Most modern radio systems and devices use wavelengths which would then have been considered 'ultra-short'.
In contemporary usage, the term longwave is not defined precisely, and its intended meaning varies. It may be used for radio wavelengths longer than 1,000 m i.e. frequencies[note 1] up to 300 kilohertz (kHz), including the International Telecommunications Union's (ITU's) low frequency (LF, 30–300 kHz) and very low frequency (VLF, 3–30 kHz) bands. Sometimes the upper limit is taken to be higher than 300 kHz, but not above the start of the medium wave broadcast band at 525 kHz.
In Europe, Africa, and large parts of Asia (International Telecommunication Union Region 1), where a range of frequencies between 148.5 and 283.5 kHz is used for AM broadcasting in addition to the medium-wave band, the term longwave usually refers specifically to this broadcasting band, which falls wholly within the low frequency band of the radio spectrum (30–300 kHz). The "Longwave Club of America" (United States) is interested in "frequencies below the AM broadcast band" (i.e., all frequencies below 525 kHz).
Because of their long wavelength, radio waves in this frequency range can diffract over obstacles like mountain ranges and travel beyond the horizon, following the contour of the Earth. This mode of propagation, called ground wave, is the main mode in the longwave band. The attenuation of signal strength with distance by absorption in the ground is lower than at higher frequencies, and falls with frequency. Low frequency ground waves can be received up to 2,000 kilometres (1,200 mi) from the transmitting antenna. Very low frequency waves below 30 kHz can be used to communicate at transcontinental distances, and can penetrate saltwater to depths of hundreds of feet, and is used by the military to communicate with submerged submarines.
Low frequency waves can also occasionally travel long distances by reflecting from the ionosphere (the actual mechanism is one of refraction), although this method, called skywave or "skip" propagation, is not as common as at higher frequencies. Reflection occurs at the ionospheric E layer or F layers. Skywave signals can be detected at distances exceeding 300 kilometres (190 mi) from the transmitting antenna.
Non-directional beacons transmit continuously for the benefit of radio direction finders in marine and aeronautical navigation. They identify themselves by a callsign in Morse code. They can occupy any frequency in the range 190–1750 kHz. In North America, they occupy 190–535 kHz. In ITU Region 1 the lower limit is 280 kHz.
There are institutional broadcast stations in the range that transmit coded time signals to radio clocks. For example:
- WWVB in Colorado, United States, on 60 kHz
- DCF77 in Frankfurt am Main, Germany, on 77.5 kHz
- JJY in Japan, on 40 & 60 kHz
- 66.66 kHz in Taldom transmitter, Russia
- BPC in Lintong, China, 68.5 kHz
- MSF time and 60 kHz frequency standard transmitted from Anthorn in the UK.
- TDF from Allouis, France, on 162 kHz
Radio-controlled clocks receive their time calibration signals with built-in long-wave receivers. They use long-wave, rather than short-wave or medium-wave, because long-wave signals from the transmitter to the receiver always travel along the same direct path across the surface of the Earth, so the time delay correction for the signal travel time from the transmitting station to the receiver is always the same for any one receiving location.
Longwaves travel by groundwaves that hug the surface of the earth, unlike mediumwaves and shortwaves. Those higher-frequency signals do not follow the surface of the Earth beyond a few kilometers, but can travel as skywaves, ‘bouncing’ off different layers of the ionosphere at different times of day. These different propagation paths can make the time lag different for every signal received. The delay between when the long-wave signal was sent from the transmitter (when the coded time was correct) and when the signal is received by the clock (when the coded time is slightly late) depends on the overland distance between the clock and the transmitter and the speed of light through the air, which is also very nearly constant. Since the time lag is essentially the same, a single constant shift forward from the time coded in the signal can compensate for all long-wave signals received at any one location from the same time signal station.
The militaries of the United Kingdom, Russian Federation, United States, Germany, India and Sweden use frequencies below 50 kHz to communicate with submerged submarines.
In North America during the 1970s, the frequencies 167, 179 and 191 kHz were assigned to the short-lived Public Emergency Radio of the United States. Nowadays, in the United States, Part 15 of FCC regulations allow unlicensed use of 136 kHz and the 160–190 kHz band at output power up to 1 watt with up to a 15-meter antenna. This is called Low Frequency Experimental Radio (LowFER). The 190–435 kHz band is used for navigational beacons.
Swedish station SAQ, located at the Varberg Radio Station facility in Grimeton, is the last remaining operational Alexanderson alternator long-wave transmitter. Although the station ended regular service in 1996, it has been maintained as a World Heritage Site, and makes at least two demonstration transmissions yearly, on 17.2 kHz.
Longwave is used for broadcasting only within ITU Region 1. The long-wave broadcasters are located in western, northern, central, and southeastern Europe, the former Soviet Union, Mongolia, Algeria, and Morocco.
Typically, a larger geographic area can be covered by a long-wave broadcast transmitter compared to a medium-wave one. This is because ground-wave propagation suffers less attenuation due to limited ground conductivity at lower frequencies.
Long-wave carrier frequencies are exact multiples of 9 kHz; ranging from 153 to 279 kHz, except for a French-language station, Europe #1 in Germany. This station kept correctly spaced channels spacing for 4 months—only 7 years ago, and all Mongolian transmitters are 2 kHz above the internationally recognized channels.[clarification needed]
Until the 1970s, some long-wave stations in northern and eastern Europe and the Soviet Union operated on frequencies as high as 433 kHz.
Some radio broadcasters, for instance Droitwich transmitting station in the UK, derive their carrier frequencies from an atomic clock, allowing their use as frequency standards. Droitwich also broadcasts a low bit-rate data channel, using narrow-shift phase-shift keying of the carrier, for Radio Teleswitch Services.
In 2014 and 2015 Russia closed all of its LW broadcast transmitters.
Because long-wave signals can travel very long distances, some radio amateurs and shortwave listeners engage in an activity called DXing. DXers attempt to listen in to far away transmissions, and they will often send a reception report to the sending station to let them know where they were heard. After receiving a report, the sending station may mail the listener a QSL card to acknowledge this reception.
Reception of long-wave signals at distances in excess of 17,000 kilometres (11,000 mi) have been verified.
List of long-wave broadcasting transmitters
|153||Radio Antena Satelor||Romanian||Romania||Brașov||T-aerial on 2 guyed steel lattice masts, height: 250 metres (820 ft)||200|
|NRK P1||Norwegian||Norway||Ingøy||Omnidirectional aerial, guyed steel lattice mast 352 metres (1,155 ft) tall, fed at the top, ex-Omega equipment||100||The transmitter is important for the fishing fleet in the Barents Sea|
|Arabic||Algeria||Kénadsa||Three 357 metres (1,171 ft) tall guyed masts||500||Active with very low modulation and power|
|162||ANFR (TDF time signal)||French||France||Allouis||Two guyed lattice steel masts, height: 350 metres (1,150 ft) fed on the top||1000
|Time signal phase-modulated; the frequency broadcast France Inter until the end of 2016. Now only the time signal for public clocks is transmitted. The ANFR is in charge of this.|
|164||MNB Radio 1||Mongolian||Mongolia||Ulaanbaatar||259 metres (850 ft) tall cable-stayed steel truss mast||500||Broadcasts from 21:00 to 14:00 UTC|
|171||Médi 1||Arabic and French||Morocco||Nador||Directional aerial consisting of three guyed steel lattice masts, 380 metres (1,250 ft) tall||1600|
|183||Europe 1||French||Germany||Felsberg-Berus||Directional aerial, four ground insulated steel lattice masts 270 metres (890 ft), 276 metres (906 ft), 280 metres (920 ft) and 282 metres (925 ft) tall; spare aerial: two ground insulated steel lattice masts, height: 234 metres (768 ft)||2000||Main antenna:
|DRM tests after 00:00 UTC|
|189||RÚV Rás 1/RÚV Rás 2||Icelandic||Iceland||Gufuskalar near Hellissandur||Slight oval bi-directivity aerial, top loaded parallel connected triangular loops, mast as a common member, all guys insulated except two radiating diametrically opposed grounded top guys, loops closed by copper straps in the ground from two conducting guy grounding points to base of the guyed steel lattice mast insulated against ground, height: 412 metres (1,352 ft)||300|
|198||BBC Radio 4/BBC World Service||English||United Kingdom||Droitwich (SFN)||T-aerial on two guyed steel lattice masts insulated against ground with a height of 213 metres (699 ft)||500||All four transmitters carry Radio teleswitch PSK data; Droitwich relays BBC World Service from 01:00 to 05:20 UTC|
|Burghead (SFN)||Omnidirectional aerial, guyed steel lattice mast, height 154 metres (505 ft)||50|
|Westerglen (SFN)||Omnidirectional aerial, guyed steel lattice mast, height 152 metres (499 ft)|
|Dartford Tunnel (SFN)||0.004|
|207||RÚV Rás 1/RÚV Rás 2||Icelandic||Iceland||Eiðar near Egilsstaðir||Omnidirectional aerial, steel lattice mast insulated against ground, height 221 metres (725 ft)||100|
|209||MNB Radio 1||Mongolian||Mongolia||Choibalsan||Cable-stayed steel truss mast, height: 275.84 metres (905.0 ft)||75||Broadcasts from 21:00 to 14:00 UTC|
|Dalanzadgad||Broadcasts from 21:00 to 14:00 UTC|
|Olgii||Omnidirectional antenna, 352.5 metres (1,156 ft) high guyed mast||30||Broadcasts from 21:00 to 14:00 UTC|
|216||Radio Monte Carlo Info||French||France||Roumoules||Directional aerial, three 300 metres (980 ft) high guyed steel lattice masts, 330 metres (1,080 ft) high guyed steel lattice mast as backup aerial||700
|Transmitter located in France, in operation from 5:30 to 23:00 CET|
|225||Polskie Radio Jedynka||Polish||Poland||Solec Kujawski||Directional aerial, two guyed radio masts fed on the top, heights 330 metres (1,080 ft) and 289 metres (948 ft)||1000||Earlier Konstantynów was used ( )|
|227||MNB Radio 1||Mongolian||Mongolia||Altai||Cable-stayed steel truss mast||75||Broadcasts from 21:00 to 14:00 UTC|
|234||RTL||French||Luxembourg||Beidweiler||Directional aerial, three guyed grounded steel lattice masts, 290 metres (950 ft) high, with vertical cage aerials||1500
|Spare transmitter site Junglinster (
|243||DR Langbølge||Danish||Denmark||Kalundborg||Semi-directional Alexanderson antenna 153/333 degrees, two grounded 118 metres (387 ft) steel lattice radiating towers with interconnecting top wire capacitance||50||Transmitting in time slots only|
|Arabic||Algeria||Tipaza||Omnidirectional aerial, single guyed lattice steel mast, height 355 metres (1,165 ft)||750
|Half transmitter power during night|
|RTÉ Radio 1||English||Ireland||Clarkstown||Omnidirectional aerial, guyed steel lattice mast, insulated against ground, height 248 metres (814 ft)||100
|The only AM transmitter for RTÉ Radio 1, power is decreased at night to 100 kW, it is tentatively scheduled to cease broadcasting in June 2019|
|270||ČRo Radiožurnál||Czech||Czech Republic||Topolná||Directional aerial (maximum of radiation in east-west direction), two grounded 257 metres (843 ft) high guyed steel lattice mast with cage aerials||50||Broadcasting from Monday to Friday 5:00-24:00 CET and 6:00-24:00 CET at weekends|
|279||TR1 Watan Radio||Turkmen||Turkmenistan||Ashgabat||Cable-stayed steel truss mast||150||Almost no modulation|
|Deutschlandfunk||Germany||Donebach||Directional aerial, two guyed steel lattice masts, 363 m high, fed at the top||500||;||closed|
|YuFM||Russia||Taldom transmitter||Omnidirectional aerial, guyed steel lattice mast of 257 m height||300||closed|
|Radio Rossii||Popova near Komsomolsk-na-Amure||1200||closed|
|162||TRT Radyo 4||Turkey||Agri||Two guyed lattice steel masts, height 250 m||1000||;||inactive|
|Radio Rossii||Russia||Norilsk||Omnidirectional antenna, 205 m high antenna||150||?||closed|
|Radio Yuldash, Radio Rossii||Ufa||closed|
|Voice of Russia||Russia||Oktyabrsky||257 m metres tall antenna.||1200||closed|
|Radio Rossii||Russia||Bolshakovo near Kaliningrad||Omnidirectional antenna, 257 m high guyed lattice steel mast with cage antenna ( ARRT-antenna)||600||closed|
|Radio Ukraine 1||Ukraine||Krasne near Lviv||Omnidirectional antenna, 259 m high guyed lattice steel mast with cage antenna ( ARRT-antenna)||150/75||inactive|
|Radio Rossii||Russia||Raduga||Omnidirectional antenna, 255 m high guyed lattice steel mast with cage antenna ( ARRT-antenna)||250||closed|
|Radio 1||Russia||Murmansk||Omnidirectional antenna, 257 m high guyed lattice steel mast with cage antenna ( ARRT-antenna)||150||closed|
|Radio 1||Russia||Noginsk||Omnidirectional antenna, 242 m high guyed lattice steel mast with cage antenna ( ARRT-antenna)||150||closed|
|Radio 1||Russia||Ezhva near Syktyvkar||Omnidirectional antenna, 257 m high guyed lattice steel mast with cage antenna ( ARRT-antenna)||150||closed|
|Radio Rossii||Russia||Tulagino near Yakutsk||Omnidirectional antenna, circle antenna with 1 central and 6 ring masts||150||; ; ; ; ; ;||closed|
|Deutschlandradio Kultur||Germany||Zehlendorf near Oranienburg||Omnidirectional aerial, cage aerial mounted on 359.7 m high guyed mast, triangle aerial on 3 150 m high guyed steel lattice masts||500||closed|
|180||TRT Radyo 2||Turkey||Polatli||Omnidirectional antenna, 250 m high guyed latice steel mast||1200||inactive|
|Radio Rossii||Russia||Yelizovo near Petropavlovsk-Kamchatskiy||Omnidirectional antenna, 255 m high guyed lattice steel mast||150||closed|
|Radio Mayak||Russia||Kruchina near Chita||Omnidirectional antenna, 200 m high guyed lattice steel mast||150||inactive|
|Kazakh Radio 1||Kazakhstan||Alma-Ata||250||closed|
|Kazakh Radio 1||Kazakhstan||Aktyubinsk||150||closed|
|Kazakh Radio 1||Kazakhstan||Chimkent||50||closed|
|Rai Radio 1||Italy||Caltanissetta||Omnidirectional aerial, guyed steel lattice mast, height 282 m||10||closed|
|Sveriges Radio P1||Sweden||Orlunda||300||closed|
|Radio Rossii||Russia||Kostantinogradovka near Blagoveshchensk||Omnidirectional aerial, 257 m high guyed lattice steel mast with cage antenna ( ARRT-antenna)||1200||closed|
|Polskie Radio Parlament/Radio Polonia||Poland||Raszyn||Omnidirectional aerial, guyed steel lattice mast insulated against ground, 335 m high||200||closed|
|Radio Mayak||Russia||Saint Petersburg - Olgino||Omnidirectional aerial, 205 m high guyed steel lattice mast||150||inactive|
|Radio Mayak||Russia||Angarsk||Before 2001: T-antenna spun between 2 205 m tall guyed steel lattice mast||250||, possibly||closed|
|Radio Mayak||Russia||Avsyunino||Omnidirectional antenna, 257 m high guyed lattice steel mast with cage antenna ( ARRT-antenna)||150||inactive|
|Kyrgyzstan||Krasnaya Rechka near Bishkek||Radio-1||150||closed|
|RNE Radio 5||Spain||Logroño||Directional antenna, 300 metres tall.||>100||closed|
|Radio Ukraine 1||Ukraine||Brovary||Omnidirectional antenna, 259.6 m high guyed lattice steel mast with cage antenna ( ARRT-antenna)||600||closed|
|Jordan Radio||Jordan||Al Karanah||?||;||closed|
|Radio Mayak||Russia||Tynda||Omnidirectional aerial, steel lattice mast insulated against ground, height 244 m||150||closed|
|Deutschlandfunk||Germany||Aholming||Directional aerial, two guyed steel lattice masts, 265 m high, fed at the top||500||;||closed|
|SNRT Al Idaâ Al-Watania||Morocco||Azilal Demnate||304.8 metres (1,000 ft) tall guyed mast||400||inactive|
|NRK P1||Norway||Lambertseter near Oslo||200||closed|
|Radio Rossii||Russia||Krasnoyarsk||Omnidirectional antenna, guyed lattice steel mast, 210 m tall||150||closed|
|Radio Rossii||Russia||Atamanovka||Directional antenna||150||closed|
|Radio Rossii||Russia||Birobidzhan||2 guyed masts, 260 m high||30||;||closed|
|225||TRT GAP||Turkey||Van||Omnidirectional antenna, 250 m high guyed lattice steel mast||600||inactive|
|Radio Rossii||Russia||Surgut||Omnidirectional antenna, 257 m high guyed lattice steel mast with cage antenna ( ARRT-antenna)||1000||closed|
|Libya||Yafran near Tripoli||1000||closed|
|Radio 1||Russia||Krasny Bor transmitter near Sankt-Peterburg||Omnidirectional aerial, 271.5 metres tall guyed mast with cage antenna||1200||closed|
|Public Armenian Radio||Armenia||Kamo||?||500||?||closed|
|Radio Rossii||Russia||Koskovo near Murmansk||Omnidirectional aerial, 210 m tall guyed mast||250||inactive|
|Radio 1||Russia||Novosemeykino near Samara||Four 205 metres tall towers insulated against ground arranged in a square||2000||; ; ;||closed|
|Radio Rossii||Russia||Raduzhnyy near Magadan||Omnidirectional aerial, 259 m high guyed lattice steel mast with cage antenna ( ARRT-antenna)||1000||closed|
|Radio Rossii||Russia||Odinsk near Irkutsk||Omnidirectional aerial, 259 m high guyed lattice steel mast with cage antenna ( ARRT-antenna)||500||closed|
|Radio 1||Russia||Koskovo near Arkhangelsk||Omnidirectional aerial, 257 m high guyed lattice steel mast with cage antenna ( ARRT-antenna)||500||closed|
|243||TRT Radyo 4||Turkey||Erzurum||Omnidirectional antenna, 185 m high guyed lattice steel mast||200||inactive|
|Radio Rossii||Russia||Razdolnoye near Ussuriysk||Omnidirectional antenna, 259 m high guyed lattice steel mast with cage antenna ( ARRT-antenna)||1000||closed|
|Kazakh Radio 2 Shalkar||Kazakhstan||Karaganda||Omnidirectional aerial, guyed steel lattice mast of 254 m height||1000||closed|
|Kazakh Radio 2 Shalkar||Kazakhstan||Alma-Ata||1000||closed|
|Armenian Radio 1||Armenia||Kamo||150||?||closed|
|Yle Radio 1||Finland||Lahti||200||,||closed|
|Radio Rossii||Russia||Kazan||Omnidirectional aerial, 152 m high guyed lattice steel mast with cage antenna ( ARRT-antenna)||100||closed (9 January 2014)|
|Radioropa Info||Germany||Burg||Omnidirectional aerial, cage aerial on 324 m high guyed, grounded steel lattice mast, 210 m high steel tube mast, insulated against ground||200||closed|
|Radio Rossii||Russia||Taldom||Omnidirectional antenna, circle antenna with 1 central and 5 ring masts, height of central mast 275 m||2500||; ; ; ; ;||closed|
|Radio Rossii||Russia||Kruchina near Chita||Omnidirectional antenna, guyed lattice steel mast, 260 m high||150||closed|
|Radio Rossii||Russia||Tyumen||Omnidirectional antenna, guyed lattice steel mast, 220 m high||150||closed|
|Radio Rossii||Russia||Vorkuta||Omnidirectional antenna, guyed lattice steel mast, 220 m high||50||closed|
|Radio Horizont||Bulgaria||Vakarel||One of the few Blaw-Knox Towers in Europe, 215 m high||75||closed|
|Radio Rossii||Russia||Orenburg||Omnidirectional aerial, guyed steel lattice mast of 137 m height||25||closed|
|Radio 1||Russia||Khabarovsk||2 guyed steel lattice masts, height: 164 m||150||;||closed|
|Radio Rossii||Russia||Gorno-Altaisk||Omnidirectional antenna, 143m high guyed lattice steel mast||50||closed|
|Radio Rossii||Russia||Selenginsk||Omnidirectional aerial, 260 m high guyed lattice steel mast with cage antenna (ARRT-antenna)||150||closed|
|Radio Rossii||Russia||Vestochka near Yuzhno-Sakhalinsk||Omnidirectional antenna, guyed lattice steel mast, 258 m high||1000||closed|
|Radio Rossii||Russia||Yekaterinburg||Omnidirectional aerial, guyed steel lattice mast of 256 m height, fed at the top||150||closed|
|BR Pershy Kanal/BR Radyjo Stalitsa||Belarus||Sasnovy||353.5 metres tall guyed mast||500||closed|
- Low frequency: for other uses (military, commercial and amateur) of this part of the radio spectrum (30–300 kHz)
- Electromagnetic spectrum: Very low frequency, Shortwave, Ground wave, Skywave, Medium wave
- Radio broadcasting: AM broadcasting, BBC Radio 4, BBC Light Programme, Radio clock, Office de Radiodiffusion-Télévision Française, Warsaw radio mast, Digital Radio Mondiale, International broadcasting,
- Shipping: Global navigation satellite system, Navigation, Shipping Forecast
- Lists: Index of wave articles
- Other: 1 kilometre, National Institute of Standards and Technology, Fail-safe, WGU-20