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| longwave radio | |
|---|---|
| Name | Longwave radio |
| Wavelength | 100–1000 metres |
| Frequency | 30–300 kHz |
| First use | Early 20th century |
| Related | Very Low Frequency, Mediumwave, Shortwave, Radio navigation |
longwave radio is a radio spectrum band occupying frequencies from about 30 kHz to 300 kHz used for broadcasting, navigation, time signals, and submarine communication. Early pioneers such as Guglielmo Marconi, Reginald Fessenden, Edwin Armstrong, and institutions like the Marconi Company and the Radio Corporation of America advanced longwave transmission and receiver technology alongside developments at Bell Labs and Telefunken. Over the 20th century longwave services were shaped by international agreements including the International Telecommunication Union conferences and national broadcasters such as the BBC, Radio France, and Deutsche Welle.
Longwave origins trace to experiments by Heinrich Hertz and practical systems by Guglielmo Marconi and Reginald Fessenden that paralleled innovations at General Electric, Westinghouse Electric Corporation, and De Forest Company. Early maritime radiotelegraphy used longwave for transoceanic links in the era of the RMS Titanic and the Hundred Days' Campaign-era naval communications; nations like United Kingdom, United States, Germany, France, and Russia established coast stations. Interwar expansion involved broadcasters such as the BBC Home Service, the Radiodiffusion française, and the Reichssender network, while Cold War deployments included strategic links by United States Navy, Royal Navy, and Soviet Navy for submarine communication and by institutions like NATO and Warsaw Pact for coordination. Treaties and conferences such as the International Radiotelegraph Conference and later World Administrative Radio Conference influenced allocations and standards.
Longwave spans approximately 30–300 kHz, corresponding to wavelengths of about 10–1 kilometre to 1 kilometre, with typical broadcast allocations near 150–280 kHz. Transmitters use high-power vacuum tubes historically from Eimac and modern solid-state amplifiers from Rohde & Schwarz or Nokia Siemens Networks designs. Antenna systems often employ tall masts, T-antennas, folded monopoles, and ground systems requiring extensive radials; manufacturers and constructors have included firms like Leslie Green Engineering and AEG. Modulation modes include amplitude modulation (AM), single-sideband (SSB), and specialized minimum-shift keying used by agencies such as National Physical Laboratory time services. Receiver front-ends rely on tuned circuits, crystal detectors in early units by Atwater Kent, and later superheterodyne designs standardized by RCA and enhanced by integrated circuits from Texas Instruments.
Longwave allocations vary by region under frameworks set by the International Telecommunication Union Radiocommunication Sector and decisions from World Radiocommunication Conference. European broadcasters such as BBC Radio 4 and Radio France Internationale have used frequencies like 198 kHz and 162 kHz, while Russia Today and Polskie Radio have operated other channels. Aeronautical and maritime navigation services including Non-directional beacon (NDB) networks, LORAN-C, and successors have occupied portions of the band alongside time signal stations like MSF (time signal) and WWVB influence. National regulators—Ofcom, Federal Communications Commission, Agence Nationale des Fréquences, and Bundesnetzagentur—manage allocations and licensing, with some countries reallocating longwave spectrum for utility and research uses.
High-power longwave transmitters include historical complexes such as TANT transmitter, Rogers Point, and the Transmitter Nauen facilities; mast farms like those at Droitwich Transmitting Station, Nauen Transmitter Station, and Felsberg exemplify large installations. Construction involves civil engineering firms like Arup Group and tower specialists such as Dorman Long and large-scale grounding systems often modeled by researchers at CERN and MIT. Backup power, modulation control, and antenna tuning employ equipment from suppliers including Siemens, ABB, and Schneider Electric. Decommissionings and conversions have been carried out by broadcasters including the BBC and Radio Netherlands, with some sites preserved as heritage by organizations like English Heritage.
Longwave supports national broadcasting (e.g., BBC Radio 4 (LW)), maritime beacons like NON-Directional Beacon systems, aeronautical aids used historically by ICAO frameworks, time and frequency dissemination exemplified by MSF (time signal) and RBU (radio station), and submarine VLF communication practised by navies including the United States Navy and Russian Navy. Scientific services include ionospheric research at institutions such as Max Planck Institute for Solar System Research and National Oceanic and Atmospheric Administration facilities, while navigation systems like LORAN-C and proposed eLORAN implementations have been promoted by agencies such as UK Ministry of Defence and US Department of Transportation.
Longwave propagation involves groundwave and skywave mechanisms studied by groups like ITU-R and research labs at Imperial College London and Stanford University. Ground conductivity over terrains including Sahara Desert, North Sea, and Baltic Sea strongly affects range; seasonal and diurnal ionospheric variations driven by solar activity monitored by European Space Agency and NASA influence skywave reliability. Phenomena such as ducting, sporadic E, and absorption in the D-region have been analyzed in papers from Royal Society journals and conferences at URSI. Lightning noise from storms tracked by World Meteorological Organization networks and man-made interference from industrial sites regulated by International Electrotechnical Commission impact signal-to-noise ratios.
Receivers range from vintage sets by Atwater Kent and Philco to modern digital SDRs by FlexRadio Systems, Icom, and hobbyist platforms like RTL-SDR. Antenna options include longwire arrays, tuned loop antennas developed in designs from ARRL publications and active ferrite rod receivers by companies like Sony. Signal processing employs software projects such as GNU Radio and proprietary DSP suites from National Instruments; demodulation techniques and filtering use algorithms described in texts by Simon Haykin and standards from IEEE. Monitoring and logging communities include organizations like European DX Council and clubs such as North American Shortwave Association.
Category:Radio spectrum