NCAA Aeronautical Station Operator key terms

An authorisation issued by a national administration permitting a station to conduct aeronautical mobile or fixed service communications, specifying the frequencies, classes of emission, power and operator qualifications allowed under that authorisation.

A personal credential, often issued under ITU Radio Regulations provisions, certifying that the holder has passed examinations in radio theory, regulations and operating procedures and may therefore staff an aeronautical station.

A radiocommunication service between aircraft stations and aeronautical stations, or between aircraft stations, including stations on board aircraft and stations on the ground serving flight safety and regularity.

A radiocommunication service between specified fixed points providing telecommunications for air navigation safety, regularity and efficiency, typically carrying flight and safety messages rather than direct pilot speech.

A standardised designation describing a transmission's characteristics, including modulation type, nature of the modulating signal and type of information carried, such as A3E for double-sideband telephony.

The binding international treaty instrument governing use of the radio spectrum, covering frequency allocations, station licensing, interference avoidance, distress procedures and operator obligations that national rules implement.

A modulation technique in which the instantaneous amplitude of a radio-frequency carrier is varied in proportion to an information signal, producing a carrier plus upper and lower sidebands.

An amplitude modulation variant that transmits only one sideband and suppresses or reduces the carrier, saving power and bandwidth; aeronautical HF voice commonly uses upper sideband.

A modulation method in which the carrier's instantaneous frequency deviates in step with the modulating signal while amplitude stays constant, giving good immunity to amplitude noise and used for VHF voice.

The ratio of maximum to minimum voltage or current along a transmission line, indicating how well the antenna and line impedances match; a value near one to one means a good match.

The intrinsic impedance of a transmission line, determined by its conductor geometry and dielectric, that governs how power flows and what load impedance gives a reflection-free match.

An adjustable matching network placed between transmitter and feed line that transforms the antenna's impedance to the value the transmitter expects, reducing reflected power and protecting the output stage.

A radio wave that travels along or near the earth's surface, following its curvature and attenuating more at higher frequencies, useful for medium-frequency and lower HF coverage.

A radio wave radiated upward and returned to earth by refraction in the ionosphere, enabling long-distance HF communication whose usable frequencies vary with time of day and solar activity.

Layers of ionised gas in the upper atmosphere, produced mainly by solar radiation, that refract high-frequency radio waves and thereby make over-the-horizon HF communication possible.

The highest frequency that a sky wave can use for a given path and time while still being refracted back to earth, above which the signal passes through the ionosphere.

A receiver circuit that mutes audio output unless the incoming signal exceeds a chosen threshold, suppressing background noise during silence on a voice channel.

The peak shift of a frequency-modulated carrier away from its assigned centre frequency, which must stay within the channel limits to avoid splatter into adjacent channels.

The weakest input signal at which a receiver still delivers usable, intelligible output at a stated signal-to-noise ratio, usually expressed in microvolts or decibels relative to one milliwatt.

A receiver's ability to accept the wanted signal while rejecting strong signals on adjacent or nearby frequencies, determined largely by its intermediate-frequency filter characteristics.

Spurious mixing of two or more strong signals in a non-linear stage, producing unwanted products at sums and differences of the originals that can fall on and disrupt other channels.

A standard three-part reporting scale used on radiotelephony and radiotelegraph circuits to describe reception quality, signal strength and, for Morse, the quality of the note.

Two-way voice communication by radio, in aviation normally using standardised phraseology, spelling alphabets and readback procedures to keep exchanges brief and unambiguous.

The repetition by a receiving station of a clearance or instruction as understood, allowing the issuing station to detect and correct any error before the instruction is acted upon.

The standard set of spoken code words, such as Alfa, Bravo and Charlie, used to spell out letters and letter groups so that they survive noise and accent differences.

The worldwide network of fixed circuits and message switches that carries aeronautical fixed service traffic such as flight plans, meteorological data and NOTAMs between aviation organisations.

A classification assigned to a message that determines its order of transmission and handling, with distress and urgency traffic preceding safety, flight-regularity and routine categories.

A notice distributed by means of telecommunication containing information on the establishment, condition or change of any facility, service or procedure whose timely knowledge is essential to flight operations.

A state-published document containing aeronautical information of lasting relevance, such as regulations, procedures and facility descriptions, which must be amended and kept current.

A routine coded weather report for an aerodrome, issued at fixed intervals, giving wind, visibility, weather, cloud, temperature and pressure information for aviation users.

A special aerodrome weather report issued when specified significant changes occur between routine reports, such as rapid deterioration of visibility or the onset of a significant weather phenomenon.

A transmission concerning a grave and imminent danger requiring immediate assistance, sent with the spoken signal MAYDAY and given absolute priority over all other communications on the frequency.

A transmission concerning the safety of a station, aircraft or person but not requiring immediate assistance, introduced by the spoken signal PAN PAN and handled ahead of routine traffic.

A transmission containing important navigational or meteorological information, such as a hazard to navigation, introduced by the spoken signal SECURITE and given priority below distress and urgency traffic.

The continuous listening duty maintained on an assigned frequency during specified hours, ensuring distress, urgency and safety calls are heard and answered promptly by the station on duty.

Radiation or induction that endangers the functioning of a radio navigation or safety service or seriously degrades, obstructs or repeatedly interrupts a radiocommunication service operating under regulation.

The chronological record a station keeps of communications, frequencies used, times, correspondents and irregularities, serving as evidence of compliance and an aid to investigating incidents.

A concise assessment of a received transmission's quality, commonly given in readability and strength terms, allowing the other station to judge propagation and adjust power or frequency.