Longwave

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Tuning dial on 1946 Dynatron Merlin T.69 console radio receiver, showing LW wavelengths between 800 and 2000 metres (375-150 kHz) Harumphy.radio dial.jpg
Tuning dial on 1946 Dynatron Merlin T.69 console radio receiver, showing LW wavelengths between 800 and 2000 metres (375–150 kHz)

In radio, longwave, long wave or long-wave, [1] and commonly abbreviated LW, [2] 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'.

Contents

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 [2] i.e. frequencies [note 1] up to 300  kilohertz (kHz), [3] [4] including the International Telecommunication 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 520 kHz. [5]

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 [6] 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" [5] (i.e., all frequencies below 520 kHz).

Propagation

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. [7] 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, can penetrate saltwater to depths of hundreds of feet, and are 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. [8]

Non-broadcast use

Non-directional beacons

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.

Time signals

There are institutional broadcast stations in the range that transmit coded time signals to radio clocks. For example:

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.

Submarine communication

The militaries of the United Kingdom, Russian Federation, United States, Germany, India and Sweden use frequencies below 50 kHz to communicate with submerged submarines.

Amateur radio

In the ITU Radio Regulations the band 135.7–137.8 kHz is allocated (on a secondary basis) to Amateur radio worldwide, subject to a power limit of 1 watt EIRP. Many countries' regulators license amateurs to use it.

LowFER

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 the 160–190 kHz band a transmitter / amplifier output power to the antenna of at most 1 watt, with an antenna at most 15 meters (49 feet) high; this is called Low Frequency Experimental Radio (LowFER). The 190–435 kHz band is used for navigational beacons.

Frequencies from 472–479 kHz are available to licensed amateurs as the new 630 m band, part of the now-defunct maritime band, but this is often considered a medium wave sub-band.

Historic

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. [9]

Broadcasting

Longwave is used for broadcasting only within ITU Region 1. The long-wave broadcasters are located in Europe, North Africa and Mongolia.

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 ground conductivity at lower frequencies. [10]

Many countries have stopped using LW for broadcasting because of low audience figures, a lack of LW on new consumer receivers, increasing interference levels, the energy inefficiency of AM and high electricity costs at transmitters.

In 2014 and 2015 Russia closed all of its LW broadcast transmitters. [11]

As of 2024 more than half of LW frequencies are unoccupied and some of the remaining services are scheduled for closure. BBC Radio 4 (UK) announced that it will stop LW broadcasts in 2024. [12]

Carrier frequencies

With the adoption of the Geneva Frequency Plan of 1975, long-wave carrier frequencies are exact multiples of 9 kHz; ranging from 153 to 279 kHz. One exception was a French-language station, Europe 1 in Germany, which retained its prior channel spacing until the long-wave service was terminated in 2019. Other exceptions are all Mongolian transmitters, which 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. [13]

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.

Long-distance reception

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. [14]

List of long-wave broadcasting transmitters

Height diagram1.gif
Height diagram of the antenna towers and antenna masts of long-wave broadcasting stations

See also

Notes

  1. ↑ Wave length and frequency are inversely related, with lower frequencies corresponding to longer wavelengths; 300 kHz corresponds to 1,000 m.

Related Research Articles

Ground waves are radio waves propagating parallel to and adjacent to the surface of the Earth, following the curvature of the Earth beyond the visible horizon. This radiation is known as Norton surface wave, or more properly Norton ground wave, because ground waves in radio propagation are not confined to the surface.

<span class="mw-page-title-main">Shortwave radio</span> Radio transmissions using wavelengths between 10 m and 100 m

Shortwave radio is radio transmission using radio frequencies in the shortwave bands (SW). There is no official definition of the band range, but it always includes all of the high frequency band (HF), which extends from 3 to 30 MHz ; above the medium frequency band (MF), to the bottom of the VHF band.

<span class="mw-page-title-main">Radio wave</span> Type of electromagnetic radiation

Radio waves are a type of electromagnetic radiation with the lowest frequencies and the longest wavelengths in the electromagnetic spectrum, typically with frequencies below 300 gigahertz (GHz) and wavelengths greater than 1 millimeter, about the diameter of a grain of rice. Like all electromagnetic waves, radio waves in a vacuum travel at the speed of light, and in the Earth's atmosphere at a slightly slower speed. Radio waves are generated by charged particles undergoing acceleration, such as time-varying electric currents. Naturally occurring radio waves are emitted by lightning and astronomical objects, and are part of the blackbody radiation emitted by all warm objects.

<span class="mw-page-title-main">Medium wave</span> Radio transmission using wavelengths 200-1000 m

Medium wave (MW) is a part of the medium frequency (MF) radio band used mainly for AM radio broadcasting. The spectrum provides about 120 channels with more limited sound quality than FM stations on the FM broadcast band. During the daytime, reception is usually limited to more local stations, though this is dependent on the signal conditions and quality of radio receiver used. Improved signal propagation at night allows the reception of much longer distance signals. This can cause increased interference because on most channels multiple transmitters operate simultaneously worldwide. In addition, amplitude modulation (AM) is often more prone to interference by various electronic devices, especially power supplies and computers. Strong transmitters cover larger areas than on the FM broadcast band but require more energy and longer antennas. Digital modes are possible but have not reached momentum yet.

<span class="mw-page-title-main">Very low frequency</span> The range 3–30 kHz of the electromagnetic spectrum

Very low frequency or VLF is the ITU designation for radio frequencies (RF) in the range of 3–30 kHz, corresponding to wavelengths from 100 to 10 km, respectively. The band is also known as the myriameter band or myriameter wave as the wavelengths range from one to ten myriameters. Due to its limited bandwidth, audio (voice) transmission is highly impractical in this band, and therefore only low data rate coded signals are used. The VLF band is used for a few radio navigation services, government time radio stations and for secure military communication. Since VLF waves can penetrate at least 40 meters (131 ft) into saltwater, they are used for military communication with submarines.

Low frequency (LF) is the ITU designation for radio frequencies (RF) in the range of 30–300 kHz. Since its wavelengths range from 10–1 km, respectively, it is also known as the kilometre band or kilometre waves.

<span class="mw-page-title-main">Medium frequency</span> The range 300-3000 kHz of the electromagnetic spectrum

Medium frequency (MF) is the ITU designation for radio frequencies (RF) in the range of 300 kilohertz (kHz) to 3 megahertz (MHz). Part of this band is the medium wave (MW) AM broadcast band. The MF band is also known as the hectometer band as the wavelengths range from ten to one hectometers. Frequencies immediately below MF are denoted as low frequency (LF), while the first band of higher frequencies is known as high frequency (HF). MF is mostly used for AM radio broadcasting, navigational radio beacons, maritime ship-to-shore communication, and transoceanic air traffic control.

<span class="mw-page-title-main">High frequency</span> The range 3-30 MHz of the electromagnetic spectrum

High frequency (HF) is the ITU designation for the range of radio frequency electromagnetic waves between 3 and 30 megahertz (MHz). It is also known as the decameter band or decameter wave as its wavelengths range from one to ten decameters. Frequencies immediately below HF are denoted medium frequency (MF), while the next band of higher frequencies is known as the very high frequency (VHF) band. The HF band is a major part of the shortwave band of frequencies, so communication at these frequencies is often called shortwave radio. Because radio waves in this band can be reflected back to Earth by the ionosphere layer in the atmosphere – a method known as "skip" or "skywave" propagation – these frequencies are suitable for long-distance communication across intercontinental distances and for mountainous terrains which prevent line-of-sight communications. The band is used by international shortwave broadcasting stations (3.95–25.82 MHz), aviation communication, government time stations, weather stations, amateur radio and citizens band services, among other uses.

Radio propagation is the behavior of radio waves as they travel, or are propagated, from one point to another in vacuum, or into various parts of the atmosphere. As a form of electromagnetic radiation, like light waves, radio waves are affected by the phenomena of reflection, refraction, diffraction, absorption, polarization, and scattering. Understanding the effects of varying conditions on radio propagation has many practical applications, from choosing frequencies for amateur radio communications, international shortwave broadcasters, to designing reliable mobile telephone systems, to radio navigation, to operation of radar systems.

<span class="mw-page-title-main">Digital Radio Mondiale</span> Digital radio broadcasting standard

Digital Radio Mondiale is a set of digital audio broadcasting technologies designed to work over the bands currently used for analogue radio broadcasting including AM broadcasting—particularly shortwave—and FM broadcasting. DRM is more spectrally efficient than AM and FM, allowing more stations, at higher quality, into a given amount of bandwidth, using xHE-AAC audio coding format. Various other MPEG-4 codecs and Opus are also compatible, but the standard now specifies xHE-AAC.

<span class="mw-page-title-main">Skywave</span> Propagation of radio waves beyond the radio horizon.

In radio communication, skywave or skip refers to the propagation of radio waves reflected or refracted back toward Earth from the ionosphere, an electrically charged layer of the upper atmosphere. Since it is not limited by the curvature of the Earth, skywave propagation can be used to communicate beyond the horizon, at intercontinental distances. It is mostly used in the shortwave frequency bands.

CHU is the call sign of a shortwave time signal radio station operated by the Institute for National Measurement Standards of the National Research Council. CHU's signal is used for continuous dissemination of official Canadian government time signals, derived from atomic clocks.

The radio spectrum is the part of the electromagnetic spectrum with frequencies from 3 Hz to 3,000 GHz (3 THz). Electromagnetic waves in this frequency range, called radio waves, are widely used in modern technology, particularly in telecommunication. To prevent interference between different users, the generation and transmission of radio waves is strictly regulated by national laws, coordinated by an international body, the International Telecommunication Union (ITU).

<span class="mw-page-title-main">Roumoules radio transmitter</span>

The Roumoules transmitter is the main broadcasting facility for longwave and mediumwave broadcasting of Radio Monte Carlo near Roumoules, France and is owned by Monaco Media Diffusion. The 1000 and 2000kW transmitters installed are among the most powerful in the world and can be received well at nighttime throughout Europe.

<span class="mw-page-title-main">Droitwich Transmitting Station</span> Longwave and mediumwave radio transmitter in England

The Droitwich transmitting station is a large broadcasting facility for long-wave and medium-wave transmissions, established in 1934 in the civil parish of Dodderhill, just outside the village of Wychbold, near Droitwich in Worcestershire, England. The site is the location of the British Broadcasting Corporation's most powerful long-wave transmitter, which together with the two Scottish long-wave transmitters at Burghead and Westerglen forms a network broadcasting on the same frequency. The masts can be seen to the east from the M5 motorway, between Droitwich and Bromsgrove, as well as to the west from the Herefordshire/Worcestershire border. At night, the two sets of aircraft warning lights are visible from a long distance. The station is owned and operated by Arqiva.

LowFER refers to experimental radio communication practiced by hobbyists on frequencies below 300 kHz, a part of the radio spectrum known as low frequency. The practitioners are known as "LowFERs".

Deutschlandfunk is a public-broadcasting radio station in Germany, concentrating on news and current affairs. It is one of the four national radio channels produced by Deutschlandradio.

Near vertical incidence skywave, or NVIS, is a skywave radio-wave propagation path that provides usable signals in the medium distances range — usually 0–650 km. It is used for military and paramilitary communications, broadcasting, especially in the tropics, and by radio amateurs for nearby contacts circumventing line-of-sight barriers. The radio waves travel near-vertically upwards into the ionosphere, where they are refracted back down and can be received within a circular region up to 650 km from the transmitter. If the frequency is too high, refraction is insufficient to return the signal to earth and if it is too low, absorption in the ionospheric D layer may reduce the signal strength.

MW DX, short for mediumwave DXing, is the hobby of receiving distant mediumwave radio stations. MW DX is similar to TV and FM DX in that broadcast band (BCB) stations are the reception targets. However, the nature of the lower frequencies used by mediumwave radio stations is very much different from that of the VHF and UHF bands used by FM and TV broadcast stations, and therefore involves different receiving equipment, signal propagation, and reception techniques.

<span class="mw-page-title-main">Radio</span> Use of radio waves to carry information

Radio is the technology of communicating using radio waves. Radio waves are electromagnetic waves of frequency between 3 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmitter connected to an antenna which radiates the waves. They are received by another antenna connected to a radio receiver. In addition to communication, radio is used for radar, radio navigation, remote control, remote sensing, and other applications.

References

  1. ↑ Graf, Rudolf F. (1999). Modern Dictionary of Electronics, 7th Ed. Boston MA: Newnes. p. 23. ISBN   0750698667.
  2. 1 2 "long wave". Macmillan Online Dictionary. Macmillan Publishers. Archived from the original on 11 August 2016. Retrieved 20 June 2016.
  3. ↑ "long wave". Cambridge Online Dictionary. Cambridge University Press. Archived from the original on 20 August 2016. Retrieved 20 June 2016– via Cambridge.org.
  4. ↑ Graf, Rudolf F. (1999). Modern Dictionary of Electronics (7th ed.). Newnes. p. 437. ISBN   0750698667.
  5. 1 2 "About LWCA". Longwave Club of America. Archived from the original on 27 June 2016. Retrieved 20 June 2016.
  6. ↑ Barun Roy (September 2009). Enter The World of Mass Media. Pustak Mahal. p. 21. ISBN   978-81-223-1080-1.
  7. ↑ Seybold, John S. (2005). Introduction to RF Propagation. John Wiley and Sons. pp. 55–58. ISBN   0471743682.
  8. ↑ Alan Melia, G3NYK. "Understanding LF Propagation". Radcom. 85 (9). Bedford, UK: Radio Society of Great Britain: 32.{{cite journal}}: CS1 maint: numeric names: authors list (link)
  9. ↑ SAQ Transmission. Archived 7 April 2015 at Wikiwix Radiostation Grimeton SAQ. Retrieved 5 April 2015.
  10. ↑ Ground-wave propagation curves for frequencies between 10 kHz and 30 MHz. Archived 24 August 2012 at the Wayback Machine ITU-R Recommendation P.368-9
  11. ↑ "Russia says 'So long, long-wave'". BBC News. 7 May 2018. Archived from the original on 23 February 2017. Retrieved 7 May 2018.
  12. ↑ BBC Radio 4 begins information campaign to transition listeners from Long Wave
  13. ↑ Guide to Broadcasting Stations (17th ed.). Butterworth. 1973. p. 18. ISBN   0-592-00081-8.
  14. ↑ http://www.classaxe.com/dx/ndb/rww/stats#top Archived 16 February 2016 at the Wayback Machine
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