Short Wave Frequency Bands
Introduction
The frequencies and bands used for short-wave radio broadcasting are agreed internationally by the International Telecommunications Union (ITU). Not all stations stick within these bands, indeed many choose to be just outside where there are fewer competing broadcast stations and thus less interference (this is known as 'out of band broadcasting'), but most do remain within the agreed limits. If you're just tuning around short wave and looking for stations, these are definitely the place to start. Also remember, radio frequencies below around 12000 kHz work best when it's dark (at night!) and those above around 9000 kHz work best during daylight hours. Most radio stations are on a 5 kHz raster meaning that their frequency in kHz will either end with a '5' or a '0' (eg 15205 or 6110 kHz).
The Short Wave Broadcasting Bands
There are fourteen discrete bands which are allocated for broadcasting over the short wave frequency range:
Band Frequency Range Notes
120 metres 2300-2495 kHz
Only used in tropical areas.
90 metres 3200-3400 kHz
Only used in tropical areas.
75 metres 3900-4000 kHz
Not used in the Americas. Restricted to 3950-4000 kHz in Europe, Africa and the Middle East.
60 metres 4750-4995 kHz
Only used in tropical areas.
48 metres 5900-6200 kHz
41 metres 7200-7450 kHz
Restricted to 7300-7450 kHz in the Americas.
31 metres 9400-9900 kHz
25 metres 11600-12100 kHz
22 metres 13570-13870 kHz
19 metres 15100-15800 kHz
16 metres 17480-17900 kHz Highest frequency band in common daily use.
15 metres 18900-19020 kHz Virtually empty! Only occasional use by WYFR Family Radio.
13 metres 21450-21850 kHz
11 metres 25670-26100 kHz Little activity other than tests of local digital services.
Other Short Wave Frequencies
There are lots of other short-wave frequencies outside of these specific broadcast bands which are used for all manner of purposes including ship-to-shore communications (maritime), air traffic control (aeronautical), radio amateurs, military and defence, weather information and even radio pirates. Broadcasters normally use amplitude modulation (AM), though some are now digital, whereas most of the other users are either digital or use single side band (SSB). It therefore requires specialist receivers to listen to these other services and indeed under some jurisdictions it is illegal to do so, however there is a world of fun to be had on short wave if you have the time and patience.
The only other short-wave frequencies which it is usually legal to receive and which require no specialist equipment are 'time and frequency standard stations'. These are stations which use very accurate transmitters controlled by atomic clocks, and thus serve as highly accurate references. They are very useful for checking the accuracy of your receiver. They also transmit time information, usually as a series of 'ticks' each second plus messages each minute.
The most commonly received stations are:
Station Location Frequencies
CHU
Ottawa, Canada 3330, 7850 and 14670 kHz
RWM
Moscow, Russia 4996, 9996 and 14996 kHz (note that RWM transmits pulses rather than ticks)
WWV
Colorado, USA 2500, 5000, 10000 and 15000 kHz
WWVH
Hawaii, USA 2500, 5000, 10000 and 15000 kHz
Note that time signal stations are not always listed in the main short-wave.info database.
Short-wave radio refers to the upper MF (medium frequency) and all of the HF (high frequency) portion of the radio spectrum, between 1,800–30,000 kHz. Short-wave radio received its name because the wavelengths in this band are shorter than 200 m (i.e. frequencies greater than 1500 kHz) which marked the original upper limit of the medium and low frequency bands first used for radio communications. These days, the broadcast medium-wave band reaches well above that 200 m/1500 kHz limit, and the amateur radio 1.8 MHz – 2.0 MHz band (known as top band) is the lowest-frequency band considered to be 'short-wave'.
Initially thought to be useless, short-wave radio now has many applications where the behaviour of radio waves in the Earth's atmosphere make long-range communication possible. Short-wave radio is used for broadcasting of voice and music, and long-distance communication to ships and aircraft, or to remote areas out of reach of wired communication or other radio services. Amateur radio on these frequencies can provide hobby, educational and emergency communication.
The discovery of long-distance shortwave propagation
Amateur radio operators are credited with the discovery of long-distance communication on the short-wave bands. Early long-distance services used surface wave propagation at very low frequencies, which are attenuated along the path. Longer distances and higher frequencies using this method meant more signal attenuation. This, and the difficulties of generating and detecting higher frequencies, made discovery of short-wave propagation difficult for commercial services.
Radio amateurs conducted the first successful transatlantic tests in December 1921, operating in the 200 meter medium-wave band (1500 kHz)—the shortest wavelength then available to amateurs. In 1922 hundreds of North American amateurs were heard in Europe at 200 meters and at least 20 North American amateurs heard amateur signals from Europe. The first two-way communications between North American and Hawaiian amateurs began in 1922 at 200 meters. Although operation on wavelengths shorter than 200 meters was technically illegal (but tolerated as the authorities mistakenly believed at first that such frequencies were useless for commercial or military use), amateurs began to experiment with those wavelengths using newly available vacuum tubes shortly after World War I.
Extreme interference at the upper edge of the 150-200 meter band—the official wavelengths allocated to amateurs by the Second National Radio Conference in 1923—forced amateurs to shift to shorter and shorter wavelengths; however, amateurs were limited by regulation to wavelengths longer than 150 meters (2 MHz). A few fortunate amateurs who obtained special permission for experimental communications below 150 meters completed hundreds of long distance two way contacts on 100 meters (3 MHz) in 1923 including the first transatlantic two way contacts in November 1923, on 110 meters (2.72 MHz)
By 1924 many additional specially licensed amateurs were routinely making transoceanic contacts at distances of 6000 miles (~9600 km) and more. On 21 September several amateurs in California completed two way contacts with an amateur in New Zealand. On 19 October amateurs in New Zealand and England completed a 90-minute two-way contact nearly halfway around the world. On October 10, the Third National Radio Conference made three short-wave bands available to U.S. amateurs[6] at 80 meters (3.75 MHz), 40 meters (7,5 MHz) and 20 meters (15 MHz). These were allocated worldwide, while the 10-meter band (30 MHz) was created by the Washington International Radiotelegraph Conference[7] on 25 November 1927. The 15-meter band (20 MHz) was opened to amateurs in the United States on 1 May 1952.
Marconi
In June and July 1923, Guglielmo Marconi's transmissions were completed during nights on 97 meters from Poldhu Wireless Station, Cornwall, to his yacht Elettra in the Cape Verde Islands. In September 1924, Marconi transmitted during daytime and nighttime on 32 meters from Poldhu to his yacht in Beirut. Marconi, in July 1924, entered into contracts with the British General Post Office (GPO) to install high speed short-wave telegraphy circuits from London to Australia, India, South Africa and Canada as the main element of the Imperial Wireless Chain. The UK-to-Canada short-wave "Beam Wireless Service" went into commercial operation on 25 October 1926. Beam Wireless Services from the UK to Australia, South Africa and India went into service in 1927.
Far more spectrum is available for long distance communication in the short-wave bands than in the long-wave bands; and short-wave transmitters, receivers and antennas were orders of magnitude less expensive than the multi-hundred kilowatt transmitters and monstrous antennas needed for long-wave.
Short-wave communications began to grow rapidly in the 1920s,[8] similar to the internet in the late 20th century. By 1928, more than half of long distance communications had moved from transoceanic cables and longwave wireless services to shortwave and the overall volume of transoceanic shortwave communications had vastly increased. Shortwave also ended the need for multi-million dollar investments in new transoceanic telegraph cables and massive long-wave wireless stations, although some existing transoceanic telegraph cables and commercial long-wave communications stations remained in use until the 1960s.
The cable companies began to lose large sums of money in 1927, and a serious financial crisis threatened the viability of cable companies that were vital to strategic British interests. The British government convened the Imperial Wireless and Cable Conference[9] in 1928 "to examine the situation that had arisen as a result of the competition of Beam Wireless with the Cable Services". It recommended and received Government approval for all overseas cable and wireless resources of the Empire to be merged into one system controlled by a newly-formed company in 1929, Imperial and International Communications Ltd. The name of the company was changed to Cable and Wireless Ltd. in 1934.
Shortwave propagation
Short-wave frequencies are capable of reaching any location on the Earth as they can be refracted downwards by the ionosphere (a phenomenon known as Skywave propagation). A typical phenomenon with short-wave propagation is the occurrence of a skip zone (see first figure on that page) where reception fails. With a fixed working frequency, large changes of the ionospheric characteristics may create a skip zone that appears at night.
As a result of the multi-layer structure of the ionosphere, propagation often simultaneously occurs on different paths, refracted by the E- or F-region and with different numbers of hops, a phenomenon that may be disturbing for certain techniques. Particularly for lower frequencies of the short-wave band, absorption of wave energy in the lowest ionospheric layer, the D-layer, may be a serious limit. This is due to many collisions of electrons with neutral molecules, absorbing energy from radio waves and turning it into heat.. Predictions of sky wave propagation depend on:
• The distance from the transmitter to the target receiver.
• Time of day. During the day, frequencies higher than approximately 12 MHz can travel longer distances than lower ones; at night, this property is reversed.
• With lower frequencies the dependence on the time of the day is mainly due to the lowest ionospheric layer, the D Layer, forming only during the day when photons from the sun break up atoms into ions and free electrons.
• Season. During the winter months the AM broadcast band tends to be more favorable because of longer hours of darkness.
• Solar flares produce a large increase of the D-region ionization causing, during periods of several minutes, an absorption in the D-region so high that all sky wave communications are extinguished.
Types of modulation
Further information: Modulation
Independent from frequency, the receiver must also be capable of receiving the modulation type being transmitted. AM, Single sideband and CW are common modulations. In the shortwave frequency range, these types of modulation are frequently used:
• AM: amplitude modulation. Most commonly used for shortwave broadcasting.
• SSB: Single sideband: This is used for long-range communications by ships and aircraft, for 11-meter CB, for voice transmissions by amateur radio operators, and for broadcasting. LSB (lower sideband) is generally used below 9 MHz and USB (upper sideband) above 9 MHz.
• CW: Continuous wave, which is used for Morse code communications.
• NBFM: Narrow-band frequency modulation. Primarily military NBFM transmissions occur in the higher HF frequencies (typically above 20 MHz). Because of the larger bandwidth required, NBFM is much more commonly used for VHF communication. NBFM is limited to short-range SW broadcasting due to the multiphasic distortions created by the ionosphere.
• DRM: Digital Radio Mondiale: digital modulation for use on bands below 30 MHz.
• Various radioteletype, fax, digital, slow-scan television—or other systems, which require software or special equipment to decode.
Uses
Some major uses of the shortwave radio band are:
• International broadcasting primarily by government-sponsored propaganda stations to foreign audiences: the most common use of all.
• Domestic broadcasting: to widely dispersed populations with few long-wave, medium-wave and FM stations serving them; or for specialty political, religious and alternative media networks; or of individual commercial and non-commercial paid broadcasts.
• Utility stations transmitting messages not intended for the general public, such as aircraft flying between continents, encrypted diplomatic messages, weather reporting, or ships at sea.
• Clandestine stations. These are stations that broadcast on behalf of various political movements, including rebel or insurrectionist forces, and are normally unauthorised by the government-in-charge of the country in question. Clandestine broadcasts may emanate from transmitters located in rebel-controlled territory or from outside the country entirely, using another country's transmission facilities. Clandestine stations were used during World War II to transmit news from the Allied point of view into Axis-controlled areas. Although the Nazis confiscated many radios and executed their owners, many people continued to listen.
• Numbers Stations These stations regularly appear and disappear all over the short-wave radio band but are unlicensed and untraceable. It is believed that Numbers Stations are operated by government agencies, and are used to communicate with clandestine operatives working within foreign countries. However, no definitive proof of such use has emerged. Because the vast majority of these broadcasts contain nothing but the recitation of blocks of numbers, in various languages, with occasional bursts of music, they have become known colloquially as "Number Stations". Perhaps the most noted Number Station is the "Lincolnshire Poacher", named after the 18th century English folk song, which is transmitted just before the sequences of numbers.
• Amateur radio operators.
• Time signal stations: In North America, WWV radio and WWVH radio transmit at these frequencies: 2500 kHz, 5000 kHz, 10000 kHz, and 15000 kHz; and WWV also transmits on 20000 kHz. The CHU radio station in Canada transmits on the following frequencies: 3330 kHz, 7850 kHz, and 14670 kHz. Other similar stations transmit on various short-wave and long-wave frequencies around the world.
• Over-the-horizon radar: From 1976 to 1989, the Soviet Union's Russian Woodpecker over-the-horizon radar system blotted out numerous shortwave broadcasts daily.
The term DXing, in the context of listening to radio signals of any user of the short-wave band, is the activity of monitoring distant stations. In the context of amateur radio operators, the term "DXing" refers to the two-way communications with a distant station, using short-wave radio frequencies.
The Asia-Pacific Telecommunity estimates that there are approximately 600,000,000 short-wave broadcast-radio receivers in use in 2002. WWCR claims that there are 1.5 billion short-wave receivers worldwide.
High frequency
High frequency (HF) radio frequencies are between 3 and 30 MHz. Also known as the decameter band or decameter wave as the wavelengths range from one to ten decameters (ten to one hundred metres). Frequencies immediately below HF are denoted Medium-frequency (MF), and the next higher frequencies are known as Very high frequency (VHF). The Short-wave range (2.310 - 25.820 MHz) used by international broadcasters is part of the HF frequency spectrum.
Since the ionosphere often refracts HF radio waves quite well (a phenomenon known as skywave propagation), this range is extensively used for medium and long range radio communication. However, suitability of this portion of the spectrum for such communication varies greatly with a complex combination of factors:
• Sunlight/darkness at site of transmission and reception
• Transmitter/receiver proximity to terminator
• Season
• Sunspot cycle
• Solar activity
• Polar aurora
These and other factors contribute, at each point in time for a given communication path, to a
• Maximum usable frequency (MUF)
• Lowest usable high frequency (LUF) and a
• Frequency of optimum transmission (FOT)
Exploitation of, and limits imposed by, these characteristics
When all factors are at their optimum, worldwide communication is possible on HF. At many other times it is possible to make contact across and between continents or oceans. At worst, when a band is 'dead', no communication beyond the limited ground-wave paths is possible no matter what powers, antennas or other technologies are brought to bear. When a transcontinental or worldwide path is open on a particular frequency, digital, SSB and CW communication is possible using surprisingly low transmission powers, often of the order of tens of watts, provided suitable antennas are in use at both ends and that there is little or no man-made or natural interference. On such an open band, interference originating over a wide area affects many potential users. These issues are significant to military, safety and amateur radio users of the HF bands
Uses
An amateur radio station incorporating two HF transceivers. The high frequency band is very popular with amateur radio operators, who can take advantage of direct, long-distance (often inter-continental) communications and the "thrill factor" resulting from making contacts in variable conditions. International short-wave broadcasting utilizes this set of frequencies, as well as a seemingly declining number of "utility" users (marine, aviation, military, and diplomatic interests), who have, in recent years, been swayed over to less volatile means of communication (for example, via satellites), but may maintain HF stations after switch-over for back-up purposes. However, the development of Automatic Link Establishment technology based on MIL-STD-188-141A and MIL-STD-188-141B for automated connectivity and frequency selection, along with the high costs of satellite usage, have led to a renaissance in HF usage among these communities. The development of higher speed modems such as those conforming to MIL-STD-188-110B which support data rates up to 9600 bit/s has also increased the usability of HF for data communications. Other standards development such as STANAG 5066 provides for error free data communications through the use of ARQ protocols.
CB radios operate in the higher portion of the range (around 27 MHz), as do some studio-to-transmitter (STL) radio links. Some modes of communication, such as continuous wave morse code transmissions (especially by amateur radio operators) and single sideband voice transmissions are more common in the HF range than on other frequencies, because of their bandwidth-conserving nature, but broadband modes, such as TV transmissions, are generally prohibited by HF's relatively small chunk of electromagnetic spectrum space.
Noise, especially man-made interference from electronic devices, tends to have a great effect on the HF bands. In recent years, concerns have risen among certain users of the HF spectrum over "broadband over power lines" (BPL) Internet access, which is believed to have an almost destructive effect on HF communications. This is due to the frequencies on which BPL operates (typically corresponding with the HF band) and the tendency for the BPL "signal" to leak from power lines. Some BPL providers have installed "notch filters" to block out certain portions of the spectrum (namely the amateur radio bands), but a great amount of controversy over the deployment of this access method remains. Some radio frequency identification (RFID) tags utilize HF. These tags are commonly known as HFID's or HighFID's (High Frequency Identification).
Radio propagation is the behavior of radio waves when they are transmitted, or propagated from one point on the Earth to another, or into various parts of the atmosphere. Like light waves, radio waves are affected by the phenomena of reflection, refraction, diffraction, absorption, polarization and scattering.
Radio propagation is affected by the daily changes of water vapor in the troposphere and ionization in the upper atmosphere, due to the Sun. Understanding the effects of varying conditions on radio propagation has many practical applications, from choosing frequencies for international shortwave broadcasters, to designing reliable mobile telephone systems, to radio navigation, to operation of radar systems. Radio propagation is also affected by several other factors determined by its path from point to point. This path can be a direct line of sight path or an over-the-horizon path aided by refraction in the ionosphere, which is a region between approximately 60 and 600 km.[3] Factors influencing ionospheric radio signal propagation can include sporadic-E, spread-F, solar flares, geomagnetic storms, ionospheric layer tilts, and solar proton events. Radio waves at different frequencies propagate in different ways. At extra low frequencies (ELF) and very low frequencies the wavelength is very much larger than the separation between the earth's surface and the D layer of the ionosphere, so electromagnetic waves may propagate in this region as a waveguide. Indeed, for frequencies below 20 kHz, the wave propagates as a single waveguide mode with a horizontal magnetic field and vertical electric field.[4] The interaction of radio waves with the ionized regions of the atmosphere makes radio propagation more complex to predict and analyze than in free space. Ionospheric radio propagation has a strong connection to space weather. A sudden ionospheric disturbance or short-wave fadeout is observed when the x-rays associated with a solar flare ionize the ionospheric D-region.[citation needed] Enhanced ionization in that region increases the absorption of radio signals passing through it. During the strongest solar x-ray flares, complete absorption of virtually all ionospherically propagated radio signals in the sunlit hemisphere can occur.[citation needed] These solar flares can disrupt HF radio propagation and affect GPS accuracy.[citation needed] Predictions of the average propagation conditions were needed and made during the Second world war. A most detailed code developed by Karl Rawer was applied in the German Wehrmacht, and after the war by the French Navy.[citation needed] Since radio propagation is not fully predictable, such services as emergency locator transmitters, in-flight communication with ocean-crossing aircraft, and some television broadcasting have been moved to communications satellites. A satellite link, though expensive, can offer highly predictable and stable line of sight coverage of a given area.
Low frequency
Low frequency or low freq or LF refers to radio frequencies (RF) in the range of 30 kHz–300 kHz. In Europe, and parts of Northern Africa and of Asia, part of the LF spectrum is used for AM broadcasting as the longwave band. In the western hemisphere, its main use is for aircraft beacon, navigation (LORAN), information, and weather systems. Time signal stations MSF, HBG, DCF77, JJY and WWVB are found in this band. Also known as the kilometre band or kilometre wave as the wavelengths range from one to ten kilometres.
Propagation of LF signals
Low frequency radio signals can follow the curvature of the Earth. Radio waves reaching the receiver by this route are called ground waves. Their strength is not reduced by absorption as much as in higher frequencies. Ground wave can cover an area with a radius of 2000 km about the transmitting antenna. Propagation by reflection (the actual mechanism is one of refraction) from the ionosphere is also possible. The refraction can take place at the E layer or F layers. These waves, called skywaves, can be detected at distances exceeding 300 km from the transmitting antenna.
Standard time signals
LF Radio clock
In the frequency range 40 kHz–80 kHz, there are several standard time and frequency stations, such as
• JJY in Japan (40 kHz and 60 kHz)
• MSF in Anthorn, England (60 kHz)
• WWVB in Fort Collins, Colorado, USA (60 kHz)
• HBG in Prangins, Switzerland (75 kHz) (to be closed down 31 December 2011)
• DCF77 in Mainflingen near Frankfurt am Main, Germany (77.5 kHz)
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 metres, the longer the wavelength, the deeper. The British, German, Indian, Russian, Swedish, United States and possibly other navies communicate with submarines on these frequencies. For more details on this topic, see Communication with submarines. 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, particularly of the morning news programme Today, as an indicator that the UK is under attack, whereafter their sealed orders take effect. In the USA, the Ground Wave Emergency Network or GWEN operated between 150 and 175 kHz, until replaced by satellite communications systems in 1999. GWEN was a land based military radio communications system, which could survive and continue to operate even in the case of a nuclear attack.
Experimental and amateur
An international 2.1 kHz allocation, the 2200-meter band (135.7 kHz to 137.8 kHz), is available to amateur radio operators in several countries in Europe, New Zealand, Canada and French overseas dependencies. The world record distance for a two-way contact is over 10,000 km from near Vladivostok to New Zealand.[5] As well as conventional Morse code many operators use very slow computer controlled Morse code (QRSS) or specialized digital communications modes. The 2007 World Radiocommunication Conference (WRC-07) made this band a worldwide amateur radio allocation.
The UK allocated a 2.8 kHz sliver of spectrum from 71.6 kHz 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 favor of the European-harmonized 136 kHz band.[6] A 1-watt transmission of very slow Morse Code between G3AQC (in the UK) and W1TAG (in the USA) spanned the Atlantic Ocean for 3,275 miles (5,271 km) on November 21–22, 2001.
In the United States there is a special license free allocation in the longwave range called LowFER. This experimental allocation between 160 kHz and 190 kHz is sometimes called the "Lost Band". Unlicensed operation by the public is permitted south of 60 degrees north latitude,[citation needed] except where interference would occur to ten licensed location service stations located along the coasts.[citation needed] Regulations for use include a power output of no more than 1 watt, a combined antenna/ground-lead length of no more than 15 meters, and a field strength of no more than 4.9 microvolts/meter.[citation needed] Also, emissions outside of the 160 kHz–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.
Meteorological information broadcasts
A regular service transmitting RTTY marine meteorological information on LF is the German Meteorological Service (Deutscher Wetterdienst or DWD). The DWD operates station DDH47 on 147.3 kHz using standard ITA-2 alphabet with a transmission speed of 50 baud and FSK modulation with 85 Hz shift..
Radio navigation signals
In parts of the world where there is no longwave broadcasting service, Non-directional beacons or NDB's used for aeronavigation operate on 190–300 kHz (and beyond into the MW band). In Europe, Asia and Africa, the NDB allocation starts on 283.5 kHz. The LORAN-C radio navigation system operates on 100 kHz. In the past, the Decca Navigator System operated between 70 kHz and 129 kHz. The last Decca chains were closed down in 2000. Differential GPS telemetry transmitters operate between 283.5 and 325 kHz. The commercial "DATATRAK" radio navigation system operates on a number of frequencies, varying by country, between 120 and 148 kHz.
Radio broadcasting
The long-wave radio broadcasting service operates on frequencies between 148.5 and 283.5 kHz in Europe and parts of Asia.
Other applications
Some radio frequency identification (RFID) tags utilize LF. These tags are commonly known as LFID's or LowFID's (Low Frequency Identification). The LF RFID tags are near field devices.
Antennas
Antennas (aerials) used at these low frequencies are usually mast radiators, 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-antennas and L-antennas are used when antenna height is an issue. Long wire antennas are also used in rare cases. Nearly all LF antennas are shorter than one quarter of the radiated wavelength. The only long-wave transmission antenna realized with a height corresponding to a half radiated wavelength was Warsaw Radio Mast. Low height antennas need loading coils of high inductance. These coils have high power losses due to ohmic heating of the coil wire. The addition of a horizontal section ("top hat") improves the efficiency of electrically short LF antennas without increasing the height of the antenna or its supporting structures. The height of antennas differ by usage. For some non-directional beacons (NDBs) the height can be as low as 10 meters, while for more powerful navigation transmitters such as DECCA, masts with a height around 100 meters are used. T-antennas have a height between 50 and 200 meters, while mast aerials are usually taller than 150 meters.
The height of mast antennas for LORAN-C is around 190 meters for transmitters with radiated power below 500 kW, and around 400 meters for transmitters greater than 1000 kilowatts. The main type of LORAN-C antenna is insulated from ground. LF (longwave) broadcasting stations use mast antennas with heights of more than 150 meters or T-aerials. The mast antennas can be ground-fed insulated masts or upper-fed grounded masts. It is also possible to use cage antennas on grounded masts. For broadcasting stations often directional antennas are required. They consist of multiple masts, which often have the same height. Some long-wave antennas consist of multiple mast antennas arranged in a circle with or without a mast antenna in the center. Such antennas focus the transmitted power toward ground and give a large zone of fade-free reception. This type of antenna 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 antenna of this kind was used by transmitter Orlunda in Sweden. LF transmitting antennas for high power transmitters require large amounts of space, and have been the cause of controversy in Europe and the United States due to concerns about possible health hazards associated with exposure to high-power radio waves.
de: 9M2AU....
Credit goes to 9W2TZ...for his contribution..