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Low Frequency or LF refers to Radio Frequencies (RF) in the range of 30 kHz–300 kHz. Radio frequency ( RF) is a Frequency or rate of Oscillation within the range of about 3 Hz to 300 GHz In Europe, and parts of Northern Africa and of Asia, part of the LF spectrum is used for AM broadcast service. North Africa or Northern Africa is the Northernmost Region of the African Continent, separated by the Sahara from Sub-Saharan The longwave Radio band is a range of frequencies used for AM broadcasting, which extends from 148 In the western hemisphere, its main use is for aircraft beacon, navigation (LORAN), information, and weather systems. LORAN ( LO ng R ange A id to N avigation is a terrestrial Radio navigation system using Low frequency Radio transmitters Time signal stations MSF, DCF77, JJY and WWVB are found in this band. The Time from NPL is a radio signal broadcast from the Anthorn VLF transmitter near Anthorn, Cumbria which serves as the United Kingdom DCF77 is a longwave Time signal and standard-frequency radio station JJY is the Call sign of a Low frequency Time signal Radio station. For the Virginia based broadcast radio station please see WWVB-FM. Also known as the kilometer band or kilometer wave as the wavelengths range from ten to one kilometers. The kilometre ( American spelling: kilometer) symbol km is a unit of Length in the Metric system, equal to one thousand

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Standard time signals

A LF Radio clock
A LF Radio clock

In the frequency range 40 kHz–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 contain radio clocks with an LF receiver for these signals. A radio clock is a Clock that is Synchronized by a Time code bit stream transmitted by a Radio transmitter connected to a Time standard 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 Physics, surface wave can refer to a Mechanical wave that propagates along the interface between differing media usually two fluids with different densities 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. For the Virginia based broadcast radio station please see WWVB-FM. Year 1997 ( MCMXCVII) was a Common year starting on Wednesday (link will display full 1997 Gregorian calendar Year 1999 ( MCMXCIX) was a Common year starting on Friday (link will display full 1999 Gregorian calendar)

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 [1] and probably more navies communicate with submarines on these frequencies. A submarine is a Watercraft that can operate independently below water as distinct from a Submersible that has only limited underwater capability

For more details on this topic, see Communication with submarines. Communication with submarines when they are submerged is a difficult technological task which requires specific techniques and devices

In the USA, the Ground Wave Emergency Network or GWEN operated between 150 and 175 kHz, until replaced by satellite communications systems in 1999. The Ground Wave Emergency Network ( GWEN) was a command and control communications system intended for use by the United States government to facilitate Military communications 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

A 2. 1 kHz allocation, the 136 kHz band (135. 7 kHz to 137. 8 kHz), is available to amateur radio operators in some countries in Europe [2] , New Zealand and French overseas dependencies. Amateur radio, often called ham radio, is both a Hobby and a service in which participants called "hams" use various types of Radio communications The world record distance for a two-way contact is over 10,000 km from near Vladivostok to New Zealand. Vladivostok ( is Russia 's largest port city on the Pacific Ocean and the administrative center of Primorsky Krai. New Zealand is an Island country in the south-western Pacific Ocean comprising two main landmasses (the North Island and the South Island [3] As well as conventional Morse code many operators use very slow computer controlled Morse code (QRSS) or specialized digital communications modes. Morse code is a Character encoding for transmitting telegraphic information using standardized sequences of short and long elements to represent the letters numerals A proposal at the WRC-07 World Radiocommunication Conference aims to make this a worldwide amateur radio allocation. World Radiocommunication Conference (WRC is organized by ITU to review and if necessary revise the Radio Regulations, the international treaty governing the use

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). In radio Telecommunications, effective radiated power or equivalent radiated power (ERP is a standardized theoretical measurement of radio frequency (RF This was withdrawn on 30 June 2003 after a number of extensions in favor of the European-harmonized 136 kHz band. [4] 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 license free allocation in the longwave range called LowFER. LowFER ( Low - F requency E xperimental R adio is a license-free form of two-way radio communications practiced on frequencies below 500 kHz 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, except where interference would occur to ten licensed location service stations located along the coasts. 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. 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). Radioteletype ( RTTY) is a Telecommunications system consisting of two or more Teleprinters using Radio as the Transmission medium. 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 [5].

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). A Non-directional beacon ( NDB) is a Radio transmitter at a known location used as an aviation or marine Navigational aid In Europe, Asia and Africa, the NDB allocation starts on 283. 5 kHz.

The LORAN-C radio navigation system operates on 100 kHz. LORAN ( LO ng R ange A id to N avigation is a terrestrial Radio navigation system using Low frequency Radio transmitters

In the past, the Decca Navigator System operated between 70 kHz and 129 kHz. The Decca Navigator System was a hyperbolic Low frequency Radio navigation system (also known as Multilateration) that was first deployed during The last Decca chains were closed down in 2000.

Differential GPS telemetry transmitters operate between 283. Differential Global Positioning System (DGPS is an enhancement to Global Positioning System that uses a network of fixed ground-based reference stations to broadcast the difference 5 and 325  kHz. [6]

The commercial "DATATRAK" radio navigation system operates on a number of frequencies, varying by country, between 120 and 148 kHz.

Radio broadcasting

Main article: Longwave

The longwave radio broadcasting service operates on frequencies between 148. The longwave Radio band is a range of frequencies used for AM broadcasting, which extends from 148 The longwave Radio band is a range of frequencies used for AM broadcasting, which extends from 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 RFUD tags are near field devices.

Antennas

Low cost LF time signal receiver
Low cost LF time signal receiver

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). A time signal is a visible audible mechanical or electronic signal used as a reference to determine the time of day A mast radiator (aka 'radiating tower' is a radio mast or tower in which the whole structure works 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 longwave transmission antenna realized with a height corresponding to a half radiated wavelength was Warsaw Radio Mast. The Warsaw radio mast was the world's tallest structure until its collapse on 8 August, 1991. 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. A Non-directional beacon ( NDB) is a Radio transmitter at a known location used as an aviation or marine Navigational aid The Decca Navigator System was a hyperbolic Low frequency Radio navigation system (also known as Multilateration) that was first deployed during 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. LORAN ( LO ng R ange A id to N avigation is a terrestrial Radio navigation system using Low frequency Radio transmitters 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 longwave Radio band is a range of frequencies used for AM broadcasting, which extends from 148 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 longwave 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. The Longwave transmitter Orlunda was a broadcast transmission facility for Longwave at Orlunda, Sweden near Motala, which

LF 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.

References

  1. ^ Very Low Frequency (VLF) - United States Nuclear Forces (1998).
  2. ^ CEPT/ERC Recommendation 62-01 E (Mainz 1997): Use of the band 135. 7-137. 8 kHz by the Amateur Service.
  3. ^ QSO ZL/UA0 on 136 kHz. The World of LF.
  4. ^ UK Spectrum Strategy 2002. Ofcom. The Office of Communications (Y Swyddfa Gyfathrebiadau or as it is more often known Ofcom is the independent regulator and competition authority for the Communication
  5. ^ DWD Sendeplan. Retrieved on 2008-01-08. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 871 - Battle of Ashdown - Ethelred of Wessex defeats a Danish invasion army
  6. ^ Alan Gale, G4TMV (2008). World DGPS database for DXers (PDF). Retrieved on 2008-01-14. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 1129 - Formal approval of the Order of the Templar at the Council of Troyes.

See also

Further reading

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