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Longwave

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Longwave can also refer to the economics concept of Kondratiev waves, also called cycles, surges, or K-waves, or to the rock band Longwave.
The Longwave radio broadcasting band are those frequencies between 153 - 279 kHz, which correspond to wavelengths longer than 600 meters. This range is included within the low frequency band (but the low frequency band extends above and below longwave signals). Longwave signals have the property of following the curvature of the earth, making them ideal for continuous, continental communications. Unlike shortwave radio, longwave signals do not reflect or refract using the ionosphere, so there are fewer interference-caused fadeouts. Instead, the D-layer of the ionosphere and the surface of the earth serve as a waveguide directing the signal.

The earliest radio transmitters were all longwave transmitters, because propagation of radio waves of higher frequency was not yet understood. Radio alternator or spark gap transmitters were commonly used to generate the radio frequency carrier wave.

Contents

Broadcasting

In Europe, North Africa and Asia, longwave radio frequencies between 153 and 279 kHz are used for domestic and international broadcasting.

Radio navigation

In the Americas, frequencies between 200 and 430 kHz are used for non-directional beacons (NDBs), and do not necessarily follow the same 9 kHz spacing that other areas do.

Standard time signals

In the frequency range 40-80 kHz, there are several standard time and frequency stations, such as

In Europe and Japan, many low-cost consumer devices have since the late 1980s contained radio clocks with an LF receiver for these signals. Since these frequencies propagate by ground wave only, the precision of time signals is not affected by varying propagation paths between the transmitter, the ionosphere, and the receiver. In the United States, such devices became feasible for the mass market only after the output power of WWVB was increased in 1997 and 1999.

Military

Radio signals below 50 kHz are capable of penetrating ocean depths to approximately 200 meters, the longer the wavelength, the deeper. The British, German, Indian, Russian, Swedish, United States and probably more navies communicate with submarines on these frequencies.

In addition, Royal Navy nuclear submarines carrying ballistic missiles are allegedly under standing orders to monitor the BBC Radio 4 transmission on 198 kHz in waters near the UK. It is rumoured that they are to construe a sudden halt in transmission as an indicator that the UK is under attack, whereafter their sealed orders take effect.

For more details on this topic, see Communication with submarines.

Experimental and amateur

A 136 kHz allocation (135.7 to 137.8 kHz) band is available to amateur radio operators in most countries in Europe, New Zealand and French overseas dependencies. Activity levels are high, especially in Europe, with a world record distance for a two-way contact of over 10,000km from near Vladivostok to New Zealand. . Most activity uses very slow computer controlled morse code or specialised digital communications modes, although there is a reasonable amount of conventional morse used when signals are strong.

The UK allocated a 2.8 kHz sliver of spectrum from 71.6 to 74.4 kHz beginning in April 1996 to UK amateurs who applied for a Notice of Variation to use the band on a noninterference basis with a maximum output power of 1 W ERP (effective radiated power). This was withdrawn on 30 June 2003 after a number of extensions in favour of the European-harmonised 136 kHz band. A 1-watt transmission of very slow Morse Code between G3AQC (in the UK) and W1TAG (in the USA) spanned the Atlantic Ocean for 3275 miles on November 21-22, 2001.

In the United States there is a special licence free allocation in the longwave range called LowFER. This experimental allocation between 160 and 190 kHz is sometimes called the "Lost Band". Unlicensed operation by the public is permitted south of 60 degrees north latitude, except where interference would occur to 10 licensed location service stations located along the coasts. Regulations for use include a power output of no more than 1 watt, and an antenna/ground-lead length of no more than 15 meters, and a field strength of no more than 4.9 microvolts/meter. Also, emissions outside of the 160–190 kHz band must be attenuated by at least 20 dB below the level of the unmodulated carrier. Many experimenters in this band are amateur radio operators.

Antennas

Antennas used at these frequencies are usually mast radiators are used as antennas, which are fed at the bottom and which are insulated from ground, or mast antennas fed by the guy ropes (such masts are usually grounded), T-aerials, L-aerials and long wire aerials.

The height of aerials differ by usage. For NDBs the height is just around 10 metres, while for more powerful navigation transmitters such as DECCA, masts with a height around 100 metres are used. T-aerials have a height between 50 and 200 metres, while mast aerials are usually taller than 150 metres.

The height of mast aerials for LORAN-C is around 190 metres for transmitters with radiated power below 500 kW, and around 400 metres for transmitters greater than 1,000 kilowatts. The main type of LORAN-C aerial is insulated from ground.

Longwave broadcasting stations use mast antennas with heights of more than 150 metres or T-aerials. The mast antennas can be ground-fed insulated masts or upper-fed grounded masts. It is also possible to use cage aerials on grounded masts.

Nearly all longwave aerials are not as high as one quarter of the radiated wavelength. The only longwave transmission aerial realized with a height corresponding to a half radiated wavelength was Warszaw Radio Mast.

For broadcasting stations often directional aerials are required. They consist of multiple masts, which often have the same height. Some longwave aerials consist of multiple mast antennas arranged in a circle with or without a mast antenna in the centre. Such aerials focus the transmitted power toward ground and gave a large zone of fade-free reception. This aerial type is rarely used, because they are very expensive and require much space and because fading occurs on longwave much more rarely than in the medium wave range. One aerial of this kind was used by transmitter Orlunda in Sweden.

Longwave transmitting antennas for high power transmitters require large amounts of space, and have been the cause of controversy in the United States and Europe due to concerns about possible health hazards associated with exposure to high-power radio waves.

List of longwave broadcasting transmitters

List of the most important longwave broadcasting transmitters (Source: [http://de.wikipedia.org/wiki/Langwelle]).
Frequency Name of transmitter Country Location Kind of aerial Power Remarks
153 kHz Deutschlandfunk Germany Donebach directional aerial, two guyed steel framework masts, 363 m high, fed at the top 500 kW night 250 kW
Radio Romania Romania Braşov 1200 kW  
NRK Finnmark Norway Ingoy omnidirectional aerial, guyed steel framework mast of 362 m height 100 kW  
162 kHz France Inter France Allouis two guyed steel framework masts, height 350 m, fed on the top 2000 kW  
171 kHz Radio Medi Morocco Nador directional aerial consisting of at least two guyed steel framework masts, 380 metres high 2000 kW  
Radio Rossiya Russia Kaliningrad 1200 kW  
177 kHz Deutschlandradio Kultur Germany Zehlendorf near Oranienburg cage aerial mounted on 359.7 m high guyed mast, triangle aerial on 3 150 m high guyed steel framework masts 500 kW since August 29th, 2005 in DRM-Mode
183 kHz Europe 1 Germany Felsberg directional aerial, 4 insulated guyed steel framework masts, heights: 282 m, 280 m, 276 m and 270 m, 2 234 metre tall guyed steel framework masts, which are insulated against ground as backup antenna 2000 kW French Program
189 kHz RÚV Iceland Hellissandur omnidirectional aerial, guyed steel framework mast insulated against ground, height 412 m 300 kW
RAI Italia Caltanissetta omnidirectional aerial, guyed steel framework mast, height 282 m 10 kW inactive since August 2004
198 kHz BBC Radio 4 United Kingdom Droitwich T-aerial on 2 guyed steel framework masts with a height of 213 metre 500 kW BBC World Service
BBC Radio 4 United Kingdom Burghead Guyed steel framework mast 50 kW  
BBC Radio 4 United Kingdom Westerglen Guyed steel framework mast, height 152 m 50 kW  
Radio Polonia Poland Raszyn Guyed insulated mast, 335 m high 500 kW only active at daytime
207 kHz Deutschlandfunk Germany Aholming directional aerial, two guyed steel framework masts, 265 m high, fed at the top 500 kW night 250 kW
216 kHz Radio Monte Carlo France Roumoules directional aerial, 3 300 metre high guyed steel framework masts, 330 metre high guyed steel framework mast as backup aerial 1200 kW Transmitter site exterritorial, exclave of Monaco
225 kHz Radio Polonia Poland Solec Kujawski 2 guyed radio masts fed on the top, heights 330 m and 289 m 1000 kW Earlier tranmitter site Konstantynow
234 kHz RTL Luxemburg Beidweiler directional aerial, 3 guyed grounded steel framework masts, 290 m high, with vertikal cage aerials 2000 kW Spare transmitter site Junglinster
243 kHz Danmarks Radio Danmark Kalundborg Alexanderson aerial, carried from 2 118 Meter high freestanding steel framework towers 300 kW  
252 kHz RTA Algier Algeria Tipaza 1500 kW French programme; during nighttime half transmitter-power
RTÉ Radio 1 Ireland Clarkestown Guyed steel framework mast, insulated against ground, height 248 m 500 kW Earlier used by Atlantic 252 and TeamTalk 252, decreases power at night
261 kHz Transmitter Burg Germany Burg Cage aerial on 324 m high guyed steel framework mast, 210 m high steel tube mast, insulated against ground, omnidirectional radiation 200 kW inactive at the moment, former used by Radio Wolga and Radioropa Info
Radio Rossiya Russia Taldom 2500 kW Most powerful transmitter in the world
Radio Horizont Bulgaria Vakarel 60 kW
270 kHz ČRO 1 - Radiožurnál Czech Republic Topolna two grounded guyed steel framework mast with cage aerials, height 257 m, directional radiation with maximum of radiation in East-West direction 500 kW  
279 kHz Musicmann279 Isle of Man ± 5 km off Ramsey Crossed field antenna 500 kW Tests planned to begin in early 2005 pending a summer 2005 launch
BR1 Belarus Minsk 500 kW  

Height diagram of the antenna towers and antenna masts of longwave broadcasting stations
Enlarge
Height diagram of the antenna towers and antenna masts of longwave broadcasting stations

See also

External links

Radio spectrum
ELF SLF ULF VLF LF MF HF VHF UHF SHF EHF
3 Hz 30 Hz 300 Hz 3 kHz 30 kHz 300 kHz 3 MHz 30 MHz 300 MHz 3 GHz 30 GHz
30 Hz 300 Hz 3 kHz 30 kHz 300 kHz 3 MHz 30 MHz 300 MHz 3 GHz 30 GHz 300 GHz

 

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