Acceptable interference

Interference at a higher level than that defined as permissible interference and which has been agreed upon between two or more administrations without prejudice to other administrations.

Actual antenna height (above see level)

The height of the antenna centre of radiation above mean sea level.

Actual antenna height (above terrain)

The height of the antenna centre of radiation above terrain (ground) surrounding the antenna.

Adjacent channel

In a given set of radio frequency channels, the radio channel whose characteristic frequency is situated next above or next below that of a given channel.

Adjacent-channel interference

Interference caused by extraneous power from a signal in an adjacent channel.

Administration (regulator)

Any governmental department or service responsible for discharging the obligations undertaken in the Constitution of the International Telecommunication Union, in the Convention of the International Telecommunication Union and in the Administrative Regulations.

Aeronautical fixed service

A radiocommunication service between specified fixed points provided primarily for the safety of air navigation and for the regular, efficient and economical operation of air services.

Aeronautical mobile service

A mobile service between aeronautical stations and aircraft stations, or between aircraft stations, in which survival craft stations may participate; emergency position-indicating radiobeacon stations may also participate in this service on designated distress and emergency frequencies.


Entry in the Table of Frequency Allocations of a given frequency band for the purpose of its use by one or more terrestrial or space radiocommunication services or the radio astronomy service under specified conditions. This term shall also be applied to the frequency band concerned.

Allotment (of a radio frequency or radio frequency channel)

Entry of a designated frequency channel in an agreed plan, adopted by a competent conference, for use by one or more administrations for a terrestrial or space radiocommunication service in one or more identified countries or geographical areas and under specified conditions.


Electrical device which converts electric currents into electromagnetic waves, and vice versa.

Antenna aperture

In a directional antenna, the portion of a plane surface very near antenna normal to the direction of maximum radiant intensity , through which major part of the radiation passes.

Antenna effective aperture

Ratio of the time average power delivered to a conjugate matched load connected to a lossless receiving antenna to the time average power density of an incident wave illuminating the antenna.

Antenna effective area

The ratio of the available power at the terminals of receiving antenna to the power flux density of a plane wave incident from that, the wave being polarization matched to the antenna direction.

Antenna effective height

The height of the centre of radiation of an antenna above the average terrain level.

Antenna efficiency

The ratio of the total power radiated by an antenna to the net power accepted by the antenna from the connected transmitter.

Antenna pattern lobe

An identifiable segment of an antenna radiation pattern. The radiation of many antennas shows a pattern of maxima or "lobes" at various angles, separated by "nulls", angles where the radiation falls to zero. There are the main lobe, opposite side lobe and side lobes.

Antenna polarisation

Orientation of the electric vector of the radio wave with respect to the Earth's surface determined by the physical structure of the antenna and by its orientation.

Antenna radiation pattern

Variation of the power radiated by an antenna as a function of the direction away from the antenna (usually related to maximum value).

Assigned frequency

The centre of the assigned frequency band.


Authorization given by an administration for a radio station to use a radio frequency or radio frequency channel under specified conditions.


1) Direction of a celestial point from a terrestrial point, expressed as the angle in the horizontal plane between a reference line and the horizontal projection of the line joining the two points. True North is usually implied as reference direction. 2) Angle between horizontal reference direction and the horizontal of the direction of boresight of the antenna.

Azimuth of (antenna) maximum radiation

For a directional antenna, the direction of maximum radiation azimuth antenna defined with respect to True North.