Airband or aircraft band is the name for a group of

frequencies Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is e ...

in the

VHF Very high frequency (VHF) is the ITU designation for the range of radio frequency electromagnetic waves (radio waves) from 30 to 300 megahertz (MHz), with corresponding wavelengths of ten meters to one meter. Frequencies immediately below VHF ...

radio spectrum The radio spectrum is the part of the electromagnetic spectrum with frequencies from 0 Hz to 3,000 GHz (3 THz). Electromagnetic waves in this frequency range, called radio waves, are widely used in modern technology, particul ...

allocated to radio communication in civil

aviation Aviation includes the activities surrounding mechanical flight and the aircraft industry. ''Aircraft'' includes airplane, fixed-wing and helicopter, rotary-wing types, morphable wings, wing-less lifting bodies, as well as aerostat, lighter- ...

, sometimes also referred to as ''VHF'', or phonetically as ''"Victor"''. Different sections of the band are used for radionavigational aids and

air traffic control Air traffic control (ATC) is a service provided by ground-based air traffic controllers who direct aircraft on the ground and through a given section of controlled airspace, and can provide advisory services to aircraft in non-controlled airsp ...

. In most countries a license to operate airband equipment is required and the operator is tested on competency in procedures, language and the use of the phonetic alphabet.

Spectrum usage

The VHF airband uses the frequencies between 108 and 137 MHz. The lowest 10 MHz of the band, from 108 to 117.95 MHz, is split into 200 narrow-band channels of 50 kHz. These are reserved for navigational aids such as

VOR VOR or vor may refer to: Organizations * Vale of Rheidol Railway in Wales * Voice of Russia, a radio broadcaster * Volvo Ocean Race, a yacht race Science, technology and medicine * VHF omnidirectional range, a radio navigation aid used in ...

beacon A beacon is an intentionally conspicuous device designed to attract attention to a specific location. A common example is the lighthouse, which draws attention to a fixed point that can be used to navigate around obstacles or into port. More mode ...

s, and precision approach systems such as ILS localizers. , most countries divide the upper 19 MHz into 760 channels for

amplitude modulation Amplitude modulation (AM) is a modulation technique used in electronic communication, most commonly for transmitting messages with a radio wave. In amplitude modulation, the amplitude (signal strength) of the wave is varied in proportion to ...

voice transmissions, on frequencies from 118 to 136.975 MHz, in steps of 25 kHz. In Europe, it is becoming common to further divide those channels into three (8.33 kHz channel spacing), potentially permitting 2,280 channels. Some channels between 123.100 and 135.950 are available in the US to other users such as government agencies, commercial company advisory,

search and rescue Search and rescue (SAR) is the search for and provision of aid to people who are in distress or imminent danger. The general field of search and rescue includes many specialty sub-fields, typically determined by the type of terrain the search ...

, military aircraft, glider and ballooning air-to-ground, flight test and national aviation authority use. A typical transmission range of an aircraft flying at cruise altitude (), is about in good weather conditions.

Other bands

Aeronautical voice communication is also conducted in other frequency bands, including satellite voice on Inmarsat,

Globalstar Globalstar, Inc. is an American satellite communications company that operates a low Earth orbit (LEO) satellite constellation for satellite phone and low-speed data communications. The Globalstar second-generation constellation consists of 24 lo ...

Iridium Iridium is a chemical element with the symbol Ir and atomic number 77. A very hard, brittle, silvery-white transition metal of the platinum group, it is considered the second-densest naturally occurring metal (after osmium) with a density o ...

, and

high frequency High frequency (HF) is the ITU designation for the range of radio frequency electromagnetic waves (radio 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 ...

voice. Usually these other frequency bands are only used in oceanic and remote areas, though they work over wider areas or even globally. Military aircraft also use a dedicated UHF-AM band from 225.0 to 399.95 MHz for air-to-air and air-to-ground, including air traffic control communication. This band has a designated emergency and guard channel of 243.0 MHz.DAOT 5: ''C-12-118-000/MB-000 Operating Instructions CH118 Helicopter'' (unclassified), Change 2, 23 April 1987, Page 1-51. Department of National Defence Radio aeronautical navigation aids ( navaids) use other frequencies.

Non-directional beacon A non-directional beacon (NDB) or non-directional radio beacon is a radio beacon which does not include directional information. Radio beacons are radio transmitters at a known location, used as an aviation or marine navigational aid. NDB are ...

s (NDB)s operate on

low frequency 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 wave. LF radio waves e ...

and

medium frequency 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 h ...

bands 190–415 kHz and 510–535 kHz. The

instrument landing system In aviation, the instrument landing system (ILS) is a precision radio navigation system that provides short-range guidance to aircraft to allow them to approach a runway at night or in bad weather. In its original form, it allows an aircraft to ...

(ILS) glide path operates in the

UHF Ultra high frequency (UHF) is the ITU designation for radio frequencies in the range between 300 megahertz (MHz) and 3 gigahertz (GHz), also known as the decimetre band as the wavelengths range from one meter to one tenth of a meter (on ...

range of 329.3–335.0 MHz with

marker beacon A marker beacon is a particular type of VHF radio beacon used in aviation, usually in conjunction with an instrument landing system (ILS), to give pilots a means to determine position along an established route to a destination such as a runway. ...

s at 75 MHz.

Distance measuring equipment In aviation, distance measuring equipment (DME) is a radio navigation technology that measures the slant range (distance) between an aircraft and a ground station by timing the propagation delay of radio signals in the frequency band betwee ...

(DME) also uses UHF from 962 to 1150 MHz.

Channel spacing

Channel spacing for voice communication on the airband was originally 200 kHz until 1947, providing 70 channels from 118 to 132 MHz. Some radios of that time provided receive-only coverage below 118 MHz for a total of 90 channels. From 1947 to 1958 the spacing became 100 kHz; from 1954 split once again to 50 kHz and the upper limit extended to 135.95 MHz (360 channels), and then to 25 kHz in 1972 to provide 720 usable channels. On 1 January 1990 the frequencies between 136.000 and 136.975 MHz were added, resulting in 760 channels. Increasing air traffic congestion has led to further subdivision into narrow-band 8.33 kHz channels in the

ICAO The International Civil Aviation Organization (ICAO, ) is a specialized agency of the United Nations that coordinates the principles and techniques of international air navigation, and fosters the planning and development of international a ...

European region; since 2007, all aircraft flying above FL195 are required to have communication equipment for this channel spacing. Outside of Europe, 8.33 kHz channels are permitted in many countries but not widely used as of 2012. The emergency communication channel 121.5 MHz is the only channel that retains 100 kHz channel spacing in the US; there are no channel allocations between 121.4 and 121.5 or between 121.5 and 121.6

Modulation

Aircraft communications radio operations worldwide use

, predominantly

A3E The International Telecommunication Union uses an internationally agreed system for classifying radio frequency signals. Each type of radio emission is classified according to its Bandwidth (signal processing), bandwidth, method of modulation, na ...

double sideband with full carrier on VHF and UHF, and

J3E The International Telecommunication Union uses an internationally agreed system for classifying radio frequency signals. Each type of radio emission is classified according to its bandwidth, method of modulation, nature of the modulating signal, ...

single sideband with suppressed carrier on HF. Besides being simple, power-efficient and compatible with legacy equipment, AM and SSB permit stronger stations to override weaker or interfering stations. Additionally, this method does not suffer from the

capture effect In a radio receiver, the capture effect, or FM capture effect, is a phenomenon associated with FM reception in which only the stronger of two signals at, or near, the same frequency or channel will be demodulated. FM phenomenon The capture ...

found in FM. Even if a pilot is transmitting, a control tower can "talk over" that transmission and other aircraft will hear a somewhat garbled mixture of both transmissions, rather than just one or the other. Even if both transmissions are received with identical signal strength, a

heterodyne A heterodyne is a signal frequency that is created by combining or mixing two other frequencies using a signal processing technique called ''heterodyning'', which was invented by Canadian inventor-engineer Reginald Fessenden. Heterodyning is u ...

will be heard where no such indication of blockage would be evident in an FM system. Alternative analog modulation schemes are under discussion, such as the "CLIMAX" multi-carrier system and offset carrier techniques to permit more efficient utilization of spectrum.

Audio properties

The

audio Audio most commonly refers to sound, as it is transmitted in signal form. It may also refer to: Sound *Audio signal, an electrical representation of sound *Audio frequency, a frequency in the audio spectrum * Digital audio, representation of sou ...

quality in the airband is limited by the RF

bandwidth Bandwidth commonly refers to: * Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range * Bandwidth (computing), the rate of data transfer, bit rate or thr ...

used. In the newer channel spacing scheme, the largest bandwidth of an airband channel is limited to 8.33 kHz, so the highest possible

audio frequency An audio frequency or audible frequency (AF) is a periodic vibration whose frequency is audible to the average human. The SI unit of frequency is the hertz (Hz). It is the property of sound that most determines pitch. The generally accepted ...

is 4.166 kHz. In the 25 kHz channel spacing scheme, an upper audio frequency of 12.5 kHz would be theoretically possible. However, most airband voice transmissions never actually reach these limits. Usually, the whole transmission is contained within a 6 kHz to 8 kHz bandwidth, corresponding to an upper audio frequency of 3 kHz to 4 kHz. This frequency, while low compared to the top of the human hearing range, is sufficient to convey

speech Speech is a human vocal communication using language. Each language uses phonetic combinations of vowel and consonant sounds that form the sound of its words (that is, all English words sound different from all French words, even if they are th ...

. Different aircraft, control towers and other users transmit with different bandwidths and audio characteristics.

Digital radio

A switch to

digital radio Digital radio is the use of digital technology to transmit or receive across the radio spectrum. Digital transmission by radio waves includes digital broadcasting, and especially digital audio radio services. Types In digital broadcasting s ...

s has been contemplated, as this would greatly increase capacity by reducing the bandwidth required to transmit speech. Other benefits from digital coding of voice transmissions include decreased susceptibility to electrical interference and jamming. The change-over to digital radio has yet to happen, partly because the mobility of aircraft necessitates complete international cooperation to move to a new system and also the time implementation for subsequent changeover.

Unauthorised use

It is illegal in most countries to transmit on the airband frequencies without a suitable license, although an individual license may not be required, for instance in the US where aircraft stations are "licensed by rule". Many countries' regulations also restrict communications in the airband. For instance, in

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by to ...

, airband communications are limited to those required for "the safety and navigation of an aircraft; the general operation of the aircraft; and the exchange of messages on behalf of the public. In addition, a person may operate radio apparatus only to transmit a non-superfluous signal or a signal containing non-profane or non-obscene radiocommunications." Listening to airband frequencies without a license is also an offense in some countries. However, in certain countries, such as the UK, it is permissible to listen to as it is covered under navigational and weather related transmissions. Such activity has been the subject of international situations between governments when tourists bring airband equipment into countries which ban the possession and use of such equipment."Plane-spotters 'ignored warnings'."
''BBC News'', 25 April 2002. Retrieved: 14 March 2007. Quote: "Note-taking in conjunction with other activities may be detrimental (to Greek security)."

References

{{Telecommunications Airbands