Commonly used radio terminology

This is a brief list of some commonly used terms and expressions used by radio enthusiasts and resellers. It is not an exhaustive list and many of the terms can be found in greater detail in the Wikipedia.

http://www.wikipedia.org

You can use your browser’s Find on Page feature to search for a term on the current page. Click any column heading to sort the entries by that column. Click it again to reverse the sort order.

term	meaning
10 MHz Reference	A commonly used external frequency reference for synchronising radio equipment and test instruments.
50 Ohm	A common characteristic impedance used by radio-frequency equipment and many amateur radio systems.
75 Ohm	A common characteristic impedance used in broadcast, television and some other RF systems.
A Index	A daily measure derived from geomagnetic observations and used as an indicator of longer-term geomagnetic activity.
ACARS	Aircraft Communications Addressing and Reporting System – a digital data communication system used by aircraft and ground stations.
Active Antenna	An antenna incorporating an electronic amplifier, allowing a physically small antenna to provide useful output to a receiver.
Adjacent Channel	A channel immediately above or below the desired channel frequency.
Adjacent Channel Interference	Interference caused by a strong signal on a nearby radio channel.
Adjacent Channel Rejection	The ability of a receiver to reject an unwanted signal on a nearby channel.
Aerial	Another name for an antenna.
AGC	Automatic Gain Control – a circuit that automatically adjusts receiver gain as signal strength changes.
AGC Attack	The speed at which an AGC system reduces receiver gain after detecting a strong signal.
AGC Fast	An AGC setting that responds quickly to changes in received signal strength.
AGC Hang	An AGC mode in which reduced receiver gain is held for a period after a strong signal disappears.
AGC Pumping	An audible effect caused by rapid AGC gain changes, often producing noticeable changes in background noise or audio level.
AGC Release	The speed at which an AGC system restores receiver gain after a strong signal decreases or disappears.
AGC Slow	An AGC setting that responds more gradually to changes in received signal strength, often giving smoother audio with fading signals.
AGC Threshold	The signal level at which an automatic gain control system begins to adjust receiver gain.
AGC Time Constant	The response characteristic determining how quickly an automatic gain control system changes receiver gain.
AIS	Automatic Identification System – a maritime radio-based system that exchanges vessel identification, position, course and other information.
AM	Amplitude Modulation – a method of encoding information by varying the amplitude of a carrier wave. AM is commonly used on longwave, medium-wave and shortwave broadcasting, and is also used for aviation communications.
AM Broadcast	Radio broadcasting using amplitude modulation, commonly used on longwave and medium-wave frequencies.
AM Sidebands	The upper and lower frequency components produced when an AM carrier is modulated. These sidebands contain the modulation information.
Amateur Radio	A radio service in which licensed operators use designated frequencies for communication, experimentation, education and technical activities.
Antenna	A device used to transmit or receive radio-frequency electromagnetic waves.
Antenna Diversity	A reception technique using multiple antennas and selecting or combining their signals to improve reliability.
Antenna Efficiency	The proportion of radio-frequency power supplied to an antenna that is actually radiated as electromagnetic energy.
Antenna Farm	A site containing multiple antennas, commonly associated with broadcasting or communications.
Antenna Gain	A measure of how effectively an antenna concentrates transmitted or received energy in a particular direction compared with a reference antenna.
Antenna Impedance	The electrical impedance presented by an antenna at a particular frequency.
Antenna Lobe	A region of relatively strong radiation or reception in an antenna radiation pattern.
Antenna Mast	A pole, tower or supporting structure used to elevate an antenna.
Antenna Matching	The process of obtaining a suitable impedance relationship between an antenna, transmission line and transmitter or receiver.
Antenna Polarisation	The orientation of the electric field of a radio wave, commonly described as vertical, horizontal or circular.
Antenna Preamp	A low-noise amplifier placed near an antenna to increase weak received signals before feedline losses.
Antenna Resonance	A condition where an antenna has a suitable relationship between inductive and capacitive reactance at a particular frequency.
Antenna Rotator	A motorised device used to turn a directional antenna toward a selected direction.
Antenna Tuner	A device used to transform the impedance presented by an antenna system so that it more closely matches the transmitter or transmission line.
Antenna Tuning Unit	Another name for an antenna tuner.
Approach Frequency	A radio frequency used by aircraft to communicate with an air traffic control approach service.
ATC	Air Traffic Control – a service responsible for managing aircraft movements and maintaining safe separation.
ATIS	Automatic Terminal Information Service – a recorded aviation broadcast providing information such as weather, runway and airport conditions.
Atmospheric Ducting	A propagation condition in which atmospheric layers guide radio waves and allow unusually long-distance VHF, UHF or microwave communication.
Atmospheric Noise	Natural radio noise produced by sources such as lightning and electrical storms.
Atmospheric Static	Natural radio-frequency noise, particularly from lightning and thunderstorms.
ATU	Antenna Tuning Unit – a device used to match an antenna system to a transmitter or transmission line.
Audio AGC	Automatic gain control applied to an audio signal to maintain a relatively consistent listening level.
Audio Clipping	Distortion caused when an audio signal exceeds the maximum level that an amplifier or processing stage can reproduce.
Audio Distortion	Unwanted changes introduced into an audio signal by a receiver, transmitter, amplifier or other equipment.
Audio Filter	A filter applied to received audio to reduce unwanted frequencies or improve intelligibility.
Audio Gain	The amplification level applied to an audio signal.
Audio Gain Control	A control used to adjust the level or amplification of an audio signal.
Aurora	A natural luminous phenomenon caused by charged particles interacting with Earth's upper atmosphere. It can also influence VHF radio propagation.
Auroral Propagation	Radio propagation associated with auroral regions that can enable unusual long-distance VHF communications.
Automatic Notch	A receiver function that automatically detects and suppresses interfering tones or carriers.
Aviation Band	The VHF frequency range used for civil aviation voice communications, normally using AM.
Azimuth	The horizontal direction from an observer toward a location, normally measured in degrees from north.
Backlight	Illumination provided behind or around a radio display or controls to improve visibility in low light.
Balun	A device used to connect balanced and unbalanced radio-frequency circuits or transmission lines.
Band Plan	A published arrangement showing how frequencies within a radio band are intended to be used.
Band Scan	A scanning function that searches through a defined range of frequencies.
Band-Pass Filter	A filter that allows a specified range of frequencies to pass while attenuating frequencies outside that range.
Bandwidth	The range of frequencies occupied by a signal or allowed through a receiver or filter, normally expressed in hertz.
Bandwidth Control	A receiver control used to adjust the width of the received signal passband and improve selectivity.
Base Station	A fixed radio station operating from a permanent location.
Battery Saver	A feature that reduces portable radio power consumption by placing parts of the receiver into a low-power state when inactive.
Baud	The number of symbols transmitted per second in a communication system.
Beacon	A radio transmitter that periodically or continuously sends an identifying signal or information.
Beacon Frequency	A designated frequency used by a beacon transmitter.
Beacon Monitoring	The practice of listening for known beacons to assess radio propagation conditions.
Beacon Network	A collection of radio beacons used to provide identifying or propagation information.
Beamwidth	The angular width of the main lobe of an antenna radiation pattern, commonly measured between points 3 dB below the peak.
Bearing	The direction from one location toward another, normally expressed in degrees relative to north.
Beat Note	An audible tone produced when two signals with slightly different frequencies are mixed.
BER	Bit Error Rate – the proportion of received digital bits containing errors.
BFO	Beat Frequency Oscillator – an oscillator used to create an audible beat note when receiving CW or SSB signals.
BFO Pitch	The audio pitch produced by a beat frequency oscillator when receiving CW or SSB.
Birdie	An unwanted internally generated signal appearing at a particular frequency in a receiver, often caused by oscillator harmonics or digital circuitry.
Bitrate	The amount of digital information transmitted or processed per second.
Blocking	A receiver condition where a strong unwanted signal reduces the ability to receive a weaker desired signal.
Break-In	A method of operation allowing a transmitter to switch between transmit and receive during Morse code operation.
Broadcast	A radio transmission intended to be received by multiple listeners rather than a single specified station.
Broadcast Band	A frequency range allocated for radio broadcasting to the general public.
Broadcast Monitoring	The practice of monitoring radio broadcasting services for reception, content or technical performance.
Broadcast Schedule	A timetable showing when a radio service is expected to transmit on particular frequencies.
Busy Channel	A radio channel on which a signal is currently being detected.
Busy Lockout	A feature preventing transmission while another signal is detected on the selected channel.
Bypass Capacitor	A capacitor used to provide a low-impedance path for unwanted high-frequency signals.
Cable Loss	The reduction in radio-frequency signal power as it travels through a transmission cable.
Calibration	The process of checking and adjusting radio equipment against known standards.
Call Sign	A unique sequence of letters, numbers or both used to identify a radio station or operator.
Callsign	Another spelling of call sign, the identifying letters or numbers assigned to a radio station or operator.
Capture Ratio	The minimum strength difference between two FM signals that allows the receiver to effectively capture the stronger one.
Carrier	A radio-frequency signal that is modulated to carry information such as speech, music or digital data.
Carrier Detect	A receiver indication showing that a signal above a defined threshold has been detected.
Carrier Frequency	The nominal frequency of a radio-frequency carrier before modulation is applied.
Carrier Reinsertion	The process of generating a local replacement carrier in a receiver to demodulate a suppressed-carrier signal.
Carrier Reinsertion Oscillator	A locally generated oscillator used to provide a replacement carrier when receiving suppressed-carrier modes.
Carrier Squelch	A squelch system that opens receiver audio when a received RF signal exceeds a preset strength.
Carrier-Off	A condition in which a radio-frequency carrier is absent.
Carrier-On	A condition in which a radio-frequency carrier is present.
CB Radio	Citizens Band radio – a short-range two-way radio service intended for personal and general communications on designated frequencies.
Centre Frequency	The nominal frequency at the centre of a channel, filter passband or modulated signal.
Ceramic Filter	A filter using ceramic resonators to provide a defined frequency response and bandwidth.
Channel	A designated radio frequency or range of frequencies used for a particular communication service or transmission.
Channel Allocation	The assignment of specific radio frequencies or frequency ranges to particular services or users.
Channel Bandwidth	The total frequency range allocated to or occupied by a radio channel.
Channel Busy	A condition in which a radio channel contains detectable radio activity.
Channel Busy Indicator	A display, light or icon showing that a radio receiver detects activity on the current channel.
Channel Guard	A general term for tone or digital signalling used to control access to a radio channel.
Channel Spacing	The frequency separation between adjacent radio channels. Suitable spacing helps reduce interference between neighbouring channels.
Characteristic Impedance	The characteristic impedance of a transmission line, commonly 50 or 75 ohms in radio systems.
Chirp	An unwanted change in transmitter frequency occurring during the beginning of a transmission.
Circular Polarisation	Polarisation in which the electric field rotates as the wave travels.
Clipping	Distortion caused when an amplifier or signal-processing stage is driven beyond its available signal range.
Co-channel Interference	Interference caused by two or more stations using the same or very similar frequencies.
Coax	Common abbreviation for coaxial cable.
Coaxial Cable	A transmission line consisting of a central conductor surrounded by dielectric insulation and an outer conductive shield.
Codec	A system or algorithm used to encode and decode digital audio or other information.
Common-Mode Choke	A device designed to suppress unwanted common-mode currents on cables.
Common-Mode Noise	Unwanted electrical noise appearing in the same direction on multiple conductors.
Connector Loss	Signal loss caused by connectors, adapters and junctions in an RF system.
Control Channel	A channel carrying signalling information used by a trunked radio system to manage communications.
Counterpoise	A conductive wire or structure used as an RF reference or return path for an antenna system.
Courtesy Tone	A short tone transmitted by some repeaters to indicate that a transmission has ended and the channel is available.
Coverage Area	The geographical area in which a radio transmission can be received at an acceptable level.
Coverage Prediction	An estimate of the geographical area expected to receive a radio transmission at a specified quality.
CRC	Cyclic Redundancy Check – an error-detection method used to determine whether digital data has been corrupted.
Critical Frequency	The highest frequency that an ionospheric layer can return to Earth when a signal is transmitted vertically.
Cross-Band	A radio operating method in which a station receives on one frequency band and transmits on another.
Crystal Filter	A highly selective filter using quartz crystal resonators to provide a narrow and stable frequency response.
Crystal Oscillator	An oscillator using a quartz crystal to provide a highly stable reference frequency.
CTCSS	Continuous Tone-Coded Squelch System – a system using low-frequency tones to control access to a compatible receiver or repeater.
CTCSS Tone	A sub-audible tone transmitted with a radio signal to control access to compatible equipment.
Cutoff Frequency	The frequency defining the transition between a filter passband and stopband according to a specified criterion.
CW	Continuous Wave – a radio transmission method traditionally used for Morse code, in which a carrier is switched on and off to form dots and dashes.
CW Pitch	The audible tone selected for reception of a CW signal.
D Layer	The lowest major ionospheric region involved in HF propagation. It can strongly absorb lower-frequency signals, especially during daylight.
DAB	Digital Audio Broadcasting – a digital radio broadcasting system transmitting audio and data using digital modulation.
DAB+	An enhanced version of DAB using the HE-AAC audio codec for more efficient digital audio broadcasting.
Data Burst	A short, discrete transmission of digital information.
Data Rate	The rate at which digital information is transmitted, normally expressed in bits per second.
dBd	Decibels relative to a half-wave dipole antenna, used to express antenna gain.
dBi	Decibels relative to an ideal isotropic antenna, commonly used to express antenna gain.
dBm	Decibels relative to one milliwatt, commonly used to express RF power levels.
dBµV	Decibels relative to one microvolt, commonly used to describe RF signal levels.
DCS	Digital-Coded Squelch – a system using a digital code to control receiver squelch or repeater access.
DCS Code	A digital code used to control access to compatible radio receivers or repeaters.
De-emphasis	A receiver process that reduces higher audio frequencies after FM reception to complement transmitter pre-emphasis.
De-multiplexing	The process of separating combined signals or services from a multiplexed transmission.
Dead Air	A period during which a radio channel or station carries no intended programme audio or information.
Dead Carrier	A transmitted RF carrier containing little or no intended modulation or information.
Dead Spot	An area where a normally usable radio signal becomes unusually weak or unavailable.
Decibel	A logarithmic unit used to express ratios of power, voltage, signal level and other quantities.
Decoupling	The process of preventing unwanted electrical or RF signals from passing between circuits through shared connections.
Demodulation	The process of recovering information from a modulated radio-frequency signal.
Desensitisation	A reduction in receiver sensitivity caused by a strong nearby signal or other interference.
Digital AGC	Automatic gain control implemented using digital signal processing.
Digital Audio	Audio represented as digital data rather than as a continuously varying analogue signal.
Digital Mode	A radio communication mode in which information is transmitted using digitally encoded signals.
Digital Modulation	A modulation method in which digital information is represented by controlled changes in a radio-frequency carrier.
Dipole	A simple antenna consisting of two conductive elements arranged around a feed point. A half-wave dipole is approximately half a wavelength long.
Directional Antenna	An antenna designed to transmit or receive signals more strongly in particular directions.
Discriminator	A circuit used in FM receivers to convert frequency variations into corresponding voltage variations.
Distress Signal	A radio signal indicating that a person, vessel, aircraft or station is in serious danger and requires assistance.
Doppler Shift	A change in apparent received frequency caused by relative movement between transmitter and receiver or by movement of a reflecting medium.
Downlink	A radio transmission from a satellite or other elevated system to a receiving station on Earth.
DSC	Digital Selective Calling – a digital signalling system used particularly in maritime communications for automated calling and distress alerts.
DSP	Digital Signal Processing – the use of digital computation to filter, analyse, demodulate and otherwise process signals.
DSP Filter	A digitally implemented filter used to control bandwidth, remove interference or improve reception.
Dual Receive	A function allowing a radio to monitor two frequencies or channels, either simultaneously or alternately depending on the equipment.
Dual Watch	A function that monitors two selected frequencies or channels.
Dummy Antenna	Another term sometimes used for a dummy load.
Dummy Load	A non-radiating load designed to absorb transmitter power and provide a suitable impedance for testing.
Duplex	A communication method using separate transmit and receive frequencies.
DX	Long-distance radio communication or reception. A DX station is a distant station.
DX Listener	A shortwave listener who concentrates on receiving distant radio stations.
DX Opening	A period of favourable propagation allowing reception or communication with distant stations.
DXing	The activity of attempting to receive or contact distant radio stations.
Dynamic Range	The range between the weakest useful signal a receiver can detect and the strongest signal it can handle without unacceptable degradation.
E Layer	An ionospheric region above the D layer that can reflect some radio signals. Sporadic E occurs in this region.
ECSS	Exalted Carrier Single Sideband – a reception technique using a locally generated carrier together with a selected sideband to improve reception of AM signals.
EHF	Extremely High Frequency – radio frequencies from 30 GHz to 300 GHz.
EIRP	Effective Isotropic Radiated Power – the equivalent power that would need to be supplied to an ideal isotropic antenna to produce the same maximum power density.
Electromagnetic Interference	Interference caused by unwanted electromagnetic energy from another source.
Electromagnetic Spectrum	The complete range of electromagnetic radiation, including radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays.
Elevation	The angle above the horizon toward a target such as a satellite or radio source.
ELF	Extremely Low Frequency – radio frequencies from 3 Hz to 30 Hz.
ELT	Emergency Locator Transmitter – an aviation emergency transmitter intended to help locate an aircraft after an accident or emergency.
EME	Earth-Moon-Earth – another name for moonbounce communication.
Emergency Beacon	A radio transmitter designed to send an emergency or distress signal to aid rescue or location.
Emergency Broadcast	A radio transmission used to distribute urgent information concerning emergencies or public safety.
Emergency Frequency	A designated frequency used for emergency or distress communications within a radio service.
EMI	Electromagnetic Interference – unwanted electromagnetic energy that disrupts electronic equipment.
End-Fed Antenna	An antenna fed at or near one end rather than at its centre.
Ensemble	In DAB, a group of digital radio services transmitted together within a single multiplex.
Envelope Detector	A detector commonly used for AM that extracts the varying envelope of the modulated carrier.
EON	Enhanced Other Networks – an RDS feature allowing a receiver to obtain information about traffic or other programme services on different networks.
EPIRB	Emergency Position-Indicating Radio Beacon – a maritime distress beacon designed to transmit an emergency signal and, depending on the system, position information.
ERP	Effective Radiated Power – transmitter power taking antenna gain and system losses into account in a specified direction.
Error Correction	Techniques used in digital systems to detect and correct errors introduced during transmission.
External Reference	A stable frequency signal supplied from outside a radio to improve frequency accuracy and stability.
External Speaker	A separate loudspeaker connected to a radio receiver or transceiver.
F Layer	The upper major ionospheric region responsible for much long-distance HF propagation. It can divide into F1 and F2 regions during daylight.
Factory Reset	A function that restores a radio to its original manufacturer settings.
Fade Margin	The amount of signal strength available above the minimum required level, providing protection against fading.
Fade-In	A gradual increase in received signal strength or audio level.
Fade-Out	A gradual reduction in received signal strength or audio level.
Fading	Variation in received signal strength caused by changes in radio propagation.
Far Field	The region sufficiently far from an antenna where the radiation pattern is substantially established.
FEC	Forward Error Correction – additional information transmitted so that some errors in received digital data can be detected and corrected.
Feedline	A transmission line carrying RF energy between radio equipment and an antenna.
Ferrite Bead	A small ferrite component used to suppress unwanted high-frequency electrical noise.
Ferrite Choke	A component or assembly using ferrite material to suppress unwanted radio-frequency currents.
Ferrite Rod Antenna	A compact antenna using a coil wound around a ferrite rod, commonly used in medium-wave broadcast receivers.
Field Strength	The strength of an electromagnetic radio signal at a particular location.
Field Strength Meter	An instrument used to measure the strength of a radio signal at a location.
Fine Tuning	Small adjustments to the operating frequency used to accurately tune a signal, particularly useful for SSB and CW.
Firmware	Software stored inside a radio device that controls its hardware and operating functions.
Firmware Update	An update to the software controlling a radio device.
First Hop	The first propagation segment between a transmitter and the point where an ionospherically propagated signal returns to Earth.
FM	Frequency Modulation – a method of encoding information by varying the frequency of a carrier wave. FM is widely used for VHF broadcasting and two-way communications.
FM Broadcast	Radio broadcasting using frequency modulation, commonly used in the VHF broadcast band.
FM Capture Effect	The tendency of an FM receiver to favour the stronger of two signals received on or near the same frequency.
FM Detector	A circuit that converts frequency variations in an FM signal into a corresponding audio or data signal.
FM Deviation	The amount by which the instantaneous frequency of an FM signal moves above and below its centre frequency.
FM Stereo	A system for transmitting left and right audio channels using an FM broadcast signal.
Forward Power	Radio-frequency power travelling from a transmitter toward an antenna or other load.
FOT	Frequency of Optimum Transmission – a practical operating frequency normally chosen below the predicted MUF.
Free-Space Path Loss	The theoretical reduction in signal strength caused by spreading of a radio wave through free space.
Free-Space Propagation	Ideal radio propagation through unobstructed space without reflections or environmental losses.
Frequency	The number of complete cycles of a periodic signal occurring each second. Frequency is measured in hertz.
Frequency Accuracy	How closely an actual operating frequency corresponds to its specified or intended frequency.
Frequency Allocation	The designation of a frequency band for use by one or more radio communication services.
Frequency Assignment	The designation or authorisation of a particular radio frequency for a specific station or service.
Frequency Band	A defined range of radio frequencies identified by its limits or by a conventional name such as HF, VHF or UHF.
Frequency Coordination	The process of selecting and managing frequencies to reduce interference between radio systems.
Frequency Display	A display showing the currently selected or tuned radio frequency.
Frequency Drift	An unwanted change in operating frequency over time.
Frequency Memory	A receiver memory location containing a stored operating frequency.
Frequency Monitoring	The practice of observing or listening to activity on specified radio frequencies.
Frequency Reference Lock	A condition where a radio oscillator or synthesizer is locked to a stable reference.
Frequency Response	The range of frequencies an audio or radio system can reproduce or process and the relative response at each frequency.
Frequency Stability	The ability of a frequency source to maintain its frequency despite temperature, voltage, ageing and other changes.
Frequency Synthesizer	An electronic circuit capable of generating many selectable frequencies from one or more stable reference frequencies.
Front-End Overload	A condition in which a strong signal overwhelms the input stages of a receiver, potentially producing distortion or false signals.
Front-to-Back Ratio	A measurement comparing antenna response in the main direction with response in the opposite direction.
FSK	Frequency Shift Keying – a digital modulation method in which different frequencies represent different digital states or symbols.
Geomagnetic Activity	The level of disturbance in Earth's magnetic field caused by solar activity.
Geomagnetic Storm	A disturbance in Earth's magnetic environment caused by solar activity that can significantly affect HF propagation.
Gigahertz	One billion hertz, abbreviated GHz.
GMDSS	Global Maritime Distress and Safety System – an international system using radio and satellite communications for maritime distress and safety.
GPSDO	GPS Disciplined Oscillator – a highly stable frequency source disciplined using timing information from a satellite navigation system.
Great Circle	The shortest surface path between two points on a sphere, commonly used when considering long-distance radio paths.
Greyline	The boundary region between daylight and darkness around the Earth. Propagation can sometimes be enhanced along this region.
Greyline Propagation	Long-distance HF propagation occurring along or near the boundary between daylight and darkness.
Ground Control	An air traffic control service managing aircraft and vehicles on airport movement areas.
Ground Loop	An unwanted electrical connection between equipment grounds that can introduce circulating currents, hum or interference.
Ground Plane	A conductive surface forming part of an antenna system, commonly used with vertical antennas.
Ground Radials	Conductive wires arranged around the base of a vertical antenna to improve its RF ground system.
Ground Station	A radio station located on Earth that communicates with satellites, spacecraft or other remote systems.
Ground Wave	Radio propagation in which a signal travels along or close to the Earth's surface.
Guard Band	A frequency range separating channels or services to reduce interference.
Guard Channel	A designated radio channel monitored for important, emergency or distress communications.
Guard Frequency	A designated frequency monitored for distress or emergency communications.
Half-Wave Antenna	An antenna approximately half a wavelength long, such as a conventional dipole.
Ham Radio	Another name for amateur radio.
Handheld Transceiver	A small portable transceiver designed to be operated while held in the hand.
Harmonic	A signal occurring at an integer multiple of a fundamental frequency. Unwanted harmonics can cause interference.
Harmonic Distortion	Distortion caused by the generation of unwanted harmonic frequencies.
Headphone Output	An audio output connection provided by a receiver for headphones.
Hertz	The unit of frequency equal to one cycle per second, abbreviated Hz.
Heterodyne	The process of mixing two frequencies together to produce new frequencies equal to their sum and difference.
HF	High Frequency – radio frequencies from 3 MHz to 30 MHz. HF is commonly associated with shortwave broadcasting and long-distance communications.
High-Pass Filter	A filter that allows frequencies above a selected cutoff frequency to pass while attenuating lower frequencies.
Horizontal Antenna	An antenna whose main radiating element is oriented horizontally.
Horizontal Polarisation	Radio-wave polarisation in which the electric field is predominantly horizontal.
Hum	Low-frequency unwanted audio, commonly caused by mains-frequency interference or grounding problems.
IF	Intermediate Frequency – a fixed frequency used inside many receivers for filtering and amplification.
IF Filter	A filter operating at a receiver intermediate frequency to determine bandwidth and selectivity.
IF Rejection	The ability of a receiver to reject unwanted signals occurring at or near its intermediate frequency.
ILS	Instrument Landing System – an aviation navigation system providing guidance during approach to a runway.
Image Frequency	An unwanted frequency that can also produce the receiver intermediate frequency and therefore appear as a false reception in a superheterodyne receiver.
Image Rejection	The ability of a receiver to reject unwanted signals at the image frequency.
Insertion Loss	Signal loss caused by inserting a component such as a filter or connector into a signal path.
Interference	An unwanted signal or electrical disturbance that makes a desired radio signal harder to receive or decode.
Interference Margin	The amount by which a desired signal exceeds an interfering signal or noise level.
Interference-Limited	A condition where reception quality is primarily limited by unwanted signals.
Intermodulation	The creation of unwanted signals at new frequencies when two or more signals interact in a non-linear circuit.
International Broadcaster	A broadcaster transmitting programmes across national or regional boundaries.
Interval Signal	A distinctive musical phrase, tone or other signal transmitted by a broadcaster before or between programmes.
Ionosphere	A region of the upper atmosphere containing significant concentrations of charged particles. It strongly influences radio propagation, particularly at HF.
Ionospheric Absorption	Reduction in radio signal strength caused by absorption of RF energy within the ionosphere.
Ionospheric Layer	A region within the ionosphere with particular electrical characteristics affecting radio propagation.
Ionospheric Storm	A period of disturbed ionospheric conditions caused by solar or geomagnetic activity.
IP3	Third-Order Intercept Point – a specification used to describe the linearity of RF amplifiers and receivers.
IQ	In-phase and Quadrature – two components used to represent the amplitude and phase information of a radio signal.
Isotropic Antenna	An ideal theoretical antenna radiating equally in all directions and used as a reference for antenna gain.
K Index	A numerical indicator of short-term geomagnetic activity used when assessing conditions affecting HF propagation.
Key Clicks	Unwanted short RF or audio transients produced when a Morse transmitter switches rapidly.
Keypad Entry	Entering a frequency, channel or configuration using the controls on a radio keypad.
Kilohertz	One thousand hertz, abbreviated kHz.
KiwiSDR	A network-connected software-defined radio platform commonly used to provide remote access to HF and other radio signals.
L-Match	An impedance matching network using reactive components arranged in an L configuration.
LCD	Liquid Crystal Display – a display technology commonly used in radios, scanners and other electronic equipment.
LF	Low Frequency – radio frequencies from 30 kHz to 300 kHz.
Licence	An official authorisation allowing operation of a radio transmitter under specified conditions.
Licence-Free	Describes a radio service that may be operated without an individual licence, subject to applicable regulations and equipment requirements.
Limiter	A circuit that restricts signal amplitude, commonly used in FM receivers to reduce the effect of amplitude noise.
Limiter Stage	A receiver stage that restricts amplitude variations, commonly used in FM reception.
Line of Sight	A propagation path with a largely unobstructed direct path between transmitting and receiving antennas.
Linked Repeater	A repeater connected to one or more other repeaters.
Listen Before Transmit	The practice of checking a radio channel for existing activity before transmitting.
Listening Post	A location primarily used for monitoring and receiving radio transmissions.
LNA	Low Noise Amplifier – an amplifier used near the receiver input or antenna to increase weak signals with relatively little added noise.
Local Noise	Radio-frequency interference generated near a receiving location by electrical or electronic equipment.
Local Oscillator	An oscillator inside a receiver that generates a frequency used for mixing with the incoming signal.
Local Station	A radio station primarily intended to provide coverage to a particular local geographical area.
Lockout	A scanner function that prevents a selected frequency or channel from being included in a scan.
Logbook	A record of radio contacts or reception details.
Long Path	The longer great-circle route between two locations around the Earth.
Long Wire	A wire antenna relatively long compared with the wavelength of the received signal.
Longwave	A commonly used term for radio transmissions in the LF range, particularly for broadcasting services below the medium-wave band.
Longwire Antenna	A relatively long wire antenna commonly used for receiving or transmitting radio signals.
Loop Antenna	An antenna consisting of one or more loops of wire or conductor.
Low Battery Alert	A warning produced by a radio when battery voltage or remaining capacity becomes low.
Low Noise Amplifier	An amplifier designed to increase weak RF signals while adding as little noise as practical.
Low-Pass Filter	A filter that allows frequencies below a selected cutoff frequency to pass while attenuating higher frequencies.
LSB	Lower Sideband – the lower sideband component of an SSB transmission.
LUF	Lowest Usable Frequency – the lowest frequency expected to provide acceptable communication over a specified path, often limited by noise and absorption.
Magnetic Loop	A small loop antenna designed primarily to respond to the magnetic component of a radio wave and often providing useful directional nulls.
Man-Made Noise	Radio-frequency interference generated by electrical equipment, vehicles, power supplies and other human-made sources.
Marine VHF	A VHF radio service used for communication between ships, boats and shore stations.
Matching Network	A circuit used to transform one impedance into another in a radio-frequency system.
Mayday	An internationally recognised distress call indicating grave and imminent danger requiring immediate assistance.
Megahertz	One million hertz, abbreviated MHz.
Memory Channel	A stored receiver configuration containing a frequency and possibly other settings.
Memory Recall	The process of retrieving a stored frequency or radio configuration.
Memory Scan	A scanning function that checks only frequencies or channels stored in memory.
Meteor Scatter	Propagation using ionised trails created by meteors in the upper atmosphere to reflect or scatter radio signals.
MF	Medium Frequency – radio frequencies from 300 kHz to 3 MHz. The medium-wave AM broadcast band is located within this range.
Mic Gain	A control that adjusts the audio level supplied from a microphone to a transmitter.
Microphone	A device that converts sound into an electrical audio signal.
Microvolt	One millionth of a volt. Receiver sensitivity and RF signal levels may be specified in microvolts.
Microwave	Radio-frequency electromagnetic waves commonly associated with frequencies above approximately 1 GHz.
Microwave Link	A point-to-point communication link using microwave frequencies, usually with highly directional antennas.
Mixer	A circuit that combines two frequencies and produces sum and difference frequencies.
Mobile Station	A radio station installed in or carried by a vehicle or other mobile platform.
Mode	The particular transmission or reception method used by a radio system, such as AM, FM, SSB or CW.
Modem	A device or system that modulates and demodulates signals to allow digital information to be transmitted over radio.
Modulation	The process of varying a radio-frequency carrier to encode information such as speech, music or digital data.
Modulation Depth	A measure of the extent to which an AM carrier is varied by its modulation signal.
Modulation Index	In FM, a measure related to frequency deviation divided by the frequency of the modulating signal.
Monitor	A function allowing an operator to listen to transmitted or internally processed audio.
Monitoring Receiver	A receiver used primarily to monitor radio frequencies or communications.
Mono	Monaural audio consisting of a single audio channel.
Moonbounce	Radio communication using the Moon as a natural reflector for radio signals.
Morse Code	A communication code representing letters, numbers and punctuation using combinations of short and long signals.
MUF	Maximum Usable Frequency – the highest frequency generally expected to support reliable ionospheric communication over a specified path.
Multi-Hop	Propagation in which a signal makes multiple ionospheric reflections or hops to reach a distant receiver.
Multipath	A condition where a radio signal reaches the receiver by multiple propagation paths, potentially causing fading or distortion.
Multiplex	A combined digital broadcast stream containing multiple radio services and associated data.
Multiplexing	The process of combining multiple signals or services into a single transmission channel.
Narrow/Wide Switch	A control allowing the receiver to select between narrower and wider filtering, helping balance selectivity and audio quality.
Navigation Beacon	A radio beacon transmitting signals used by aircraft, ships or other users for navigation.
NAVTEX	A maritime information service that automatically broadcasts navigational and meteorological safety information to ships.
NDB	Non-Directional Beacon – a radio navigation beacon used by aircraft to determine direction to the beacon.
Near Field	The region close to an antenna where electromagnetic fields behave differently from the far-field radiation pattern.
Network Radio	A radio communication system in which stations or repeaters are connected through a communications network.
Networked SDR	A software-defined radio receiver accessible remotely over a computer network.
Noise	Unwanted random electrical or radio-frequency energy that can obscure or degrade a desired signal.
Noise Blanker	A receiver circuit designed to reduce short-duration interference pulses such as ignition or electrical switching noise.
Noise Figure	A measurement of the amount of noise added by an electronic circuit or receiver. Lower values generally indicate better weak-signal performance.
Noise Floor	The background noise level present in a receiver or radio system when no desired signal is being received.
Noise Floor Rise	An increase in the receiver background noise level caused by interference or changing environmental conditions.
Noise Reduction	Signal processing designed to reduce unwanted noise while retaining as much of the desired signal as possible.
Noise-Limited	A condition where reception quality is primarily limited by background noise.
Notch Filter	A filter designed to strongly attenuate a narrow range of frequencies while allowing frequencies outside that range to pass.
Null	A direction or frequency at which the response of an antenna, filter or receiver becomes particularly weak.
Occupied Bandwidth	The frequency range containing most of the power of a transmitted signal according to a specified measurement criterion.
OCXO	Oven Controlled Crystal Oscillator – a crystal oscillator maintained at a controlled temperature for very high frequency stability.
OFDM	Orthogonal Frequency Division Multiplexing – a digital transmission technique that divides information among many closely spaced orthogonal subcarriers.
Offset Frequency	The frequency difference between transmit and receive frequencies in a duplex radio system.
Omnidirectional	Describes an antenna or radiation pattern providing approximately equal coverage in all horizontal directions.
One-Way Propagation	A propagation path in which a signal can be received in one direction more effectively than the reverse direction.
Open Carrier	A transmitter operating with its carrier present without necessarily carrying useful audio or information.
Operating Frequency	The frequency at which a transmitter, receiver or transceiver is intended to operate.
Overload	A condition in which a signal is too strong for a receiver or circuit to handle correctly, potentially causing distortion or unwanted responses.
Overmodulation	A condition where modulation exceeds the permitted or intended limits of a transmission system, potentially producing distortion and splatter.
Packet	A formatted block of digital data transmitted as a unit.
Packet Radio	A digital radio communication system in which information is divided into packets for transmission.
Pan-Pan	An internationally recognised urgency call indicating a serious situation requiring assistance but not constituting immediate grave danger.
Panadapter	A display showing RF activity across a range of frequencies around the tuned frequency.
Passband	The range of frequencies that a filter or receiver allows to pass with relatively little attenuation.
Path Loss	The reduction in radio signal power as a signal travels from transmitter to receiver.
Path Profile	A representation of terrain and other obstacles along a radio communication path.
Payload	The useful information carried within a digital data packet, excluding protocol information.
Peak Deviation	The maximum frequency deviation from the centre frequency of an FM signal.
Phase Noise	Unwanted short-term fluctuations in the phase of an oscillator signal that can degrade receiver or transmitter performance.
Phase Noise Floor	The level of unwanted oscillator phase noise surrounding a carrier signal.
Pi Network	A matching or filtering circuit using three reactive components arranged in a pi configuration.
Pilot Tone	A reference tone transmitted by some radio systems to allow the receiver to identify or recover additional information.
PLB	Personal Locator Beacon – a personal emergency beacon transmitting a distress signal to appropriate rescue systems.
PLL	Phase-Locked Loop – an electronic circuit that locks the phase and frequency of an oscillator to a reference signal.
PLL Synthesizer	A frequency synthesizer using a phase-locked loop to generate stable selectable frequencies.
PMR446	A European licence-exempt personal mobile radio service using designated UHF frequencies for short-range communication.
Point-to-Point	A radio communication link established between two specific locations.
Polarisation	The orientation of the electric field of an electromagnetic wave.
Polarisation Diversity	A diversity technique using antennas with different polarisation orientations.
Portable Station	A radio station designed to be operated temporarily away from its normal fixed location.
Pre-emphasis	A transmitter process that increases higher audio frequencies before FM transmission to improve the signal-to-noise ratio.
Pre-sets	Stored frequencies or stations that can be quickly selected by the user.
Preamp	A preamplifier used to increase the level of a weak signal before further processing.
Preselector	A filter placed before the main receiver circuitry to reduce unwanted signals and improve resistance to overload.
Priority Channel	A channel given special treatment by a scanning receiver and checked periodically while other channels are scanned.
Priority Scan	A scanning function that periodically checks a designated priority channel while scanning other channels.
Product Detector	A detector that mixes a received signal with a local oscillator signal to recover information from SSB or CW transmissions.
Programme Service	The audio programme or radio service transmitted by a broadcaster.
Propagation	The way radio waves travel from a transmitting antenna to a receiving location.
Propagation Forecast	A prediction of expected radio propagation conditions for particular frequencies, locations and times.
Propagation Opening	A period when radio propagation conditions allow signals to be received over a path that is not normally available.
Propagation Path	The route taken by a radio signal between its transmitting and receiving locations.
PSK	Phase Shift Keying – a digital modulation method in which information is represented by controlled changes in carrier phase.
PTT	Push-To-Talk – a control used to switch a radio from receive to transmit.
PTT Lockout	A function preventing the push-to-talk control from activating the transmitter under specified conditions.
QPSK	Quadrature Phase Shift Keying – a digital modulation scheme using four carrier phase states to represent digital symbols.
QRM	Amateur radio shorthand for interference from other radio stations.
QRN	Amateur radio shorthand for natural or electrical radio noise.
QRP	Amateur radio terminology generally referring to low-power operation.
QSB	Amateur radio shorthand for fading or variation in signal strength.
QSL	A confirmation that a radio contact or reception has taken place.
QSL Bureau	A service that forwards QSL cards between radio operators.
QSL Card	A physical or electronic card or message confirming a radio contact or reception.
QSL Manager	A person or organisation responsible for handling QSL confirmations for a station or operator.
QSL Report	A report confirming reception or a radio contact, commonly including frequency, time, date and signal information.
QSY	Amateur radio shorthand meaning to change frequency.
QTH	Amateur radio shorthand for the location of a radio station or operator.
Quarter-Wave Antenna	An antenna approximately one quarter of a wavelength long, commonly used as a vertical antenna with a suitable ground or counterpoise.
Radial	A conductive element extending from an antenna base and forming part of the antenna ground or counterpoise system.
Radiated Power	The radio-frequency power actually radiated by an antenna system.
Radiation Pattern	A graphical or descriptive representation of the relative strength of an antenna in different directions.
Radio Amateur	A person authorised to operate an amateur radio station under the applicable regulations.
Radio Beacon	A transmitter sending a known identifying signal that can be used for navigation, identification or propagation monitoring.
Radio Gateway	Equipment that connects a radio system to another communications network or service.
Radio Horizon	The approximate maximum distance for direct radio communication caused by the curvature of the Earth and atmospheric refraction.
Radio Link	A communication path between two or more locations using radio signals.
Radio Monitoring	The practice of listening to or observing radio-frequency transmissions.
Radio Observatory	A location equipped for systematic observation and measurement of radio signals or propagation.
Radio Regulation	Rules governing the use of radio frequencies, transmitters, power levels and emissions.
Radio Relay	A system in which a radio signal is received and retransmitted to extend coverage.
Radio Scanner	A receiver capable of automatically scanning multiple programmed frequencies or channels.
Radio Silence	A period during which radio transmissions are intentionally prohibited or avoided.
Radio Spectrum	The portion of the electromagnetic spectrum used for radio-frequency communications and related applications.
Radio Wave	An electromagnetic wave used to transmit energy and information through space or other propagation environments.
Random Wire	A wire antenna of arbitrary length used for radio reception or transmission, normally with suitable matching when required.
RDS	Radio Data System – a system used mainly on FM broadcasts to transmit station identification, programme information, traffic information and other data.
RDS AF	Alternative Frequencies information in RDS, allowing receivers to identify other frequencies carrying the same programme.
RDS PI Code	Programme Identification code used by RDS to identify a particular radio programme or service.
RDS PS	Programme Service information in RDS, allowing compatible receivers to display a station or programme name.
RDS PTY	Programme Type information in RDS identifying the general type of programme being broadcast.
RDS TA	Traffic Announcement indicator in RDS, identifying when traffic information is being broadcast.
RDS TP	Traffic Programme indicator in RDS, identifying stations that regularly carry traffic announcements.
Receive Indicator	A visual or audible indication that a radio is receiving a signal.
Receive Mode	The modulation or demodulation mode selected by a receiver.
Receiver	A radio device designed to receive, select, amplify and demodulate radio signals.
Receiver Bandwidth	The range of frequencies allowed through a receiver around its tuned frequency.
Receiver Desense	A reduction in receiver sensitivity caused by a strong nearby transmission or other interfering signal.
Receiver Diversity	A technique using multiple receiving paths to improve reception during fading and multipath conditions.
Receiver Front End	The portion of a receiver containing the initial RF filtering, amplification and mixing circuitry.
Receiver Overload	A condition where excessive RF input causes a receiver to behave non-linearly or produce unwanted responses.
Receiver Sensitivity Threshold	The minimum signal level at which a receiver provides a specified quality of reception.
Receiver Site	The location where radio receiving equipment and antennas are installed.
Reception Report	A report sent to a broadcaster or station describing when and how well its transmission was received.
Reciprocal Mixing	Unwanted mixing between a strong signal and phase noise from a receiver oscillator, potentially degrading reception of weak signals.
Reciprocity	The general principle that, under equivalent conditions, a radio propagation path behaves similarly in both directions.
Reference Frequency	A stable frequency used as a standard from which other frequencies are generated or measured.
Reflected Power	Radio-frequency power travelling back toward a transmitter because of an impedance mismatch.
Reflected Wave	Radio-frequency energy travelling back toward its source after reflection from an impedance mismatch.
Reflection Coefficient	A measure of the proportion and phase of a wave reflected from a load because of impedance mismatch.
Relay	A radio station or system that receives a signal and retransmits it to another location or network.
Remote Control	A method of controlling a radio receiver, transmitter or repeater from another location.
Remote Monitoring	The process of monitoring a radio system or receiver from another location.
Remote Receiver	A receiver located away from the operator and controlled or monitored remotely.
Repeater	A radio station that receives a signal and retransmits it, usually on another frequency, to extend communication range.
Repeater Controller	Equipment controlling repeater functions such as identification, timers, tones and transmit switching.
Repeater Courtesy Tone	A tone transmitted by a repeater after a transmission to indicate that the channel is available.
Repeater Coverage	The geographical area in which a repeater can reliably receive or transmit signals.
Repeater ID	An identification transmitted by a repeater to identify the repeater station.
Repeater Input	The frequency on which a repeater receives transmissions from users.
Repeater Link	A communication connection between repeaters or between a repeater and another radio network.
Repeater Linking	Connecting two or more repeaters so transmissions received by one can be retransmitted by another.
Repeater Offset	The frequency difference between a repeater input and output frequency.
Repeater Output	The frequency on which a repeater retransmits signals to users.
Repeater Station	A station that receives and retransmits radio signals to extend communication coverage.
Return Loss	A measurement of reflected RF power caused by impedance mismatch. Higher return loss generally indicates a better match.
RF	Radio Frequency – electromagnetic frequencies used for radio transmission and reception.
RF Amplifier	An amplifier designed to increase the strength of radio-frequency signals.
RF Choke	A component designed to impede unwanted radio-frequency currents.
RF Front End	The input section of a receiver that handles incoming radio-frequency signals before further processing.
RF Gain	A receiver control that adjusts the amplification applied to incoming radio-frequency signals.
RF Gain Control	A control that allows the operator to vary receiver radio-frequency gain, useful for optimising weak-signal reception or reducing overload.
RF Shield	A conductive enclosure or barrier designed to reduce unwanted radio-frequency coupling.
RF Spectrum	The distribution of radio-frequency energy across a range of frequencies.
RFI	Radio Frequency Interference – unwanted RF energy that interferes with radio reception or operation.
Roger Beep	A tone transmitted at the end of a transmission, commonly associated with some CB radios.
Rotary Encoder	An electronic rotary control commonly used as a tuning knob on modern radios.
RSSI	Received Signal Strength Indicator – a measurement or indication of received radio signal strength.
RX	Common abbreviation for receive or receiver.
S-Meter	A receiver meter or display indicating the approximate strength of a received signal.
Satellite Communication	Radio communication using artificial satellites to relay signals between locations.
SAW Filter	Surface Acoustic Wave filter – a filter using acoustic waves travelling across a specially designed surface to provide precise frequency filtering.
Scan List	A programmed list of frequencies or channels that a scanner checks automatically.
Scanner Lockout	A scanner function that excludes a selected frequency or channel from scanning.
Scanning	A receiver function that automatically checks a series of frequencies or channels and stops when activity is detected.
Scatter Propagation	Propagation in which radio signals are scattered by atmospheric or other irregularities.
SDR	Software Defined Radio – a radio system in which functions traditionally implemented using dedicated analogue circuits are performed largely using digital processing and software.
SDR Dongle	A small USB-connected software-defined radio receiver used with a computer or other host device.
SDR Receiver	A software-defined radio receiver using digital processing and software to receive and process radio signals.
Search Scan	A function that searches a specified frequency range and pauses when an active signal is detected.
Selcall	Selective Calling – a signalling system used to call a particular station or group using encoded information.
Selective Calling	A system allowing a receiver to respond only when a particular tone, code or address is detected.
Selectivity	The ability of a receiver to receive a desired signal while rejecting unwanted signals on nearby frequencies.
Selectivity Curve	A representation of receiver response showing how signals at different frequencies are attenuated around the tuned frequency.
Selectivity Skirt	The region outside a receiver passband where unwanted signals become increasingly attenuated.
Sensitivity	The ability of a receiver to detect weak signals. Receiver sensitivity may be specified in microvolts, dBm, dBµV or by measurements such as SINAD.
Shadowing	Reduction in radio signal strength caused by terrain, buildings or other obstacles.
SHF	Super High Frequency – radio frequencies from 3 GHz to 30 GHz.
Shielding	The use of conductive or magnetic material to reduce unwanted electromagnetic coupling.
Short Path	The shorter great-circle route between two locations when discussing long-distance radio propagation.
Shortwave	A commonly used name for radio frequencies in the HF range from 3 MHz to 30 MHz. Shortwave signals can travel very long distances through ionospheric propagation.
Shortwave Broadcast	A radio broadcast transmitted in the HF range and often intended for reception over very long distances.
Shortwave Listener	A person who listens to shortwave radio transmissions.
Side Lobe	A secondary region of radiation or reception outside the main lobe of a directional antenna.
Sideband	A band of frequencies produced on either side of a carrier when it is modulated.
Signal Detect	A function that identifies when a radio-frequency signal exceeds a specified threshold.
Signal Report	Information describing the strength and quality of a received radio signal.
Signal Strength	A measure of the strength of a received radio signal at a particular location.
Signal Trace	A displayed or recorded representation of signal strength or frequency over time.
Signal-to-Noise Ratio	The ratio between the strength of a desired signal and the level of unwanted noise, normally expressed in decibels.
Simplex	A communication method in which stations transmit and receive on the same frequency, with only one station transmitting at a time.
Simplex Frequency	A frequency used for direct communication without separate repeater input and output frequencies.
SINAD	Signal-to-Noise and Distortion ratio – a measurement commonly used to assess analogue receiver performance.
SINPO	A reception-report system describing Signal strength, Interference, Noise, Propagation and Overall reception quality.
SIO	A reception-report system describing Signal strength, Interference and Overall quality.
Skip	A term describing long-distance propagation where a signal leaves the local area and returns to Earth after ionospheric propagation.
Skip Distance	The approximate distance from a transmitter at which an ionospherically propagated signal first returns to Earth.
Skip Zone	An area between the limit of ground-wave reception and the point where skywave signals return to Earth.
Skywave	Radio propagation in which signals travel through the ionosphere and return to Earth, enabling long-distance communication.
Smith Chart	A graphical tool used to analyse impedance, transmission lines and RF matching networks.
Solar Cycle	The approximately 11-year cycle of changing solar activity that influences ionospheric conditions and HF propagation.
Solar Disturbance	A solar event or condition capable of changing ionospheric and radio propagation conditions.
Solar Flare	A sudden eruption of energy from the Sun that can alter ionospheric conditions and sometimes disrupt HF communications.
Solar Flux	A measurement of solar radio emission used as an indicator of solar activity and HF propagation conditions.
Solar Maximum	A period near the peak of the solar cycle when solar activity and sunspot numbers are relatively high.
Solar Minimum	A period near the low point of the solar cycle when solar activity and sunspot numbers are relatively low.
Solar Wind	A stream of charged particles flowing outward from the Sun. Variations can affect Earth's ionosphere and magnetic environment.
Space Diversity	A diversity technique using physically separated antennas so that they experience different fading conditions.
Speaker	An electroacoustic device that converts an electrical audio signal into audible sound.
Spectrum	The range of radio frequencies available for or used by radio services.
Spectrum Analyser	An instrument that displays signal strength across a range of frequencies.
Spectrum Display	A visual representation of radio-frequency activity across a range of frequencies.
Spectrum Management	The planning and regulation of radio-frequency spectrum use to minimise interference and improve efficient use.
Splatter	Unwanted transmitter energy appearing outside the intended bandwidth, often caused by excessive modulation or poor transmitter adjustment.
Sporadic E	A temporary region of intense ionisation in the E layer that can enable unusually long-distance VHF reception.
Sporadic-E Opening	A period when enhanced sporadic-E ionisation permits unusual long-distance VHF propagation.
Spurious Emission	An unwanted RF emission occurring outside the intended transmission frequency or bandwidth.
Spurious Response	An unwanted receiver response to a signal at a frequency other than the desired tuned frequency.
Squelch	A receiver function that mutes audio when the received signal falls below a preset threshold.
Squelch Tail	A brief burst of noise heard when receiver squelch closes after a transmission.
Squelch Threshold	The signal level at which a squelch system opens or closes receiver audio.
SSB	Single Sideband – a form of amplitude modulation in which one sideband is transmitted while the carrier is normally suppressed. It is widely used for HF voice communications.
Standing Wave	A fixed pattern of voltage and current along a transmission line caused by the interaction of forward and reflected energy.
Station ID	An abbreviation for station identification.
Station Identification	A transmission used to identify a radio station, commonly using its name, call sign or other identifying information.
Station Log	A record of radio stations received or contacted, commonly including frequency, date, time, mode and signal report.
Station Site	The physical location where radio equipment and antennas are installed.
Stereo	Audio reproduced using separate left and right channels.
Stereo Pilot	The pilot signal transmitted as part of an FM stereo broadcast system.
Stereo Separation	The ability of an FM stereo receiver to distinguish the left and right audio channels.
Stopband	The range of frequencies that a filter is designed to attenuate significantly.
Subcarrier	A secondary carrier or frequency component used to transmit additional information within a larger signal.
Sunspot	A relatively dark region on the Sun associated with strong magnetic activity.
Sunspot Number	A numerical measure of solar sunspot activity historically used as an indicator of solar activity and HF propagation conditions.
Suppressed Carrier	A carrier that has been greatly reduced or removed from a transmission to improve transmission efficiency, as used by many SSB systems.
SWL	Shortwave Listening – the hobby of listening to shortwave broadcasts, utility stations and other HF transmissions.
SWR	Standing Wave Ratio – a measurement of the relationship between forward and reflected waves on a transmission line.
Symbol Rate	The number of symbols transmitted per second in a digital communication system.
Synchronous AM	AM reception using a locally generated carrier synchronised to the incoming carrier.
Synchronous Detection	A detection technique using a locally generated carrier synchronised with the received signal, often improving AM reception during fading.
T-Network	An impedance matching network using three reactive components arranged in a T configuration.
Talkaround	A mode allowing direct radio-to-radio communication without using a repeater.
Talkgroup	A logical group of users within a trunked or digital radio system who share communications.
Talkgroup ID	A numerical or digital identifier associated with a talkgroup in a digital or trunked radio system.
TCXO	Temperature Compensated Crystal Oscillator – a crystal oscillator designed to maintain improved frequency stability as temperature changes.
Telemetry	Automatic transmission of measurements or status information from remote equipment to a receiving station.
Telemetry Link	A radio link used to transmit measurements or status information from remote equipment.
Temperature Inversion	An atmospheric condition in which temperature increases with altitude over a layer, potentially contributing to radio ducting.
Test Transmission	A transmission made to test equipment, coverage, signal quality or a new radio service.
Thermal Drift	A change in frequency or electrical characteristics caused by temperature changes.
Third-Order Intercept	A measurement associated with the linearity of an RF circuit and its resistance to third-order intermodulation.
Time Signal	A radio transmission providing an accurate reference for the current time.
Timebase	A stable frequency or timing reference used by radio equipment or test instruments.
Tone Squelch	A squelch system that opens the receiver audio only when a specified tone or code is detected.
TOT	Time-Out Timer – a feature that automatically stops transmission after a preset period.
Tower Frequency	A radio frequency used for communication between aircraft and an airport control tower.
Traffic Announcement	A broadcast announcement containing information about traffic conditions, delays, accidents or road conditions.
Transceiver	A radio device combining a transmitter and receiver in a single unit.
Transmission Line	A cable or electrical path designed to carry radio-frequency energy between a transmitter or receiver and an antenna.
Transmit Indicator	A visual or audible indication that a radio is transmitting.
Transmit Inhibit	A feature or condition that prevents a radio from transmitting.
Transmit Mode	The modulation method selected by a transmitter or transceiver.
Transmit Power	The radio-frequency power produced by a transmitter before losses in cables, connectors and other components.
Transmitter	A radio device that generates and amplifies a radio-frequency signal and supplies it to an antenna for transmission.
Transmitter Site	The location where a radio transmitter and associated antenna equipment are installed.
Troposphere	The lowest major layer of Earth's atmosphere. Conditions within it can affect radio propagation.
Tropospheric Propagation	Propagation through the lower atmosphere that can allow VHF and UHF signals to travel unusually long distances.
Trunked Radio	A radio communication system in which a pool of frequencies is dynamically assigned to users or groups.
Tuning	The process of adjusting a receiver to the frequency of a desired station or transmission.
Tuning Knob	A physical control used to change the operating frequency of a receiver or transceiver.
Tuning Step	The frequency increment by which a receiver or transceiver changes frequency when its tuning control is adjusted.
TX	Common abbreviation for transmit or transmitter.
UHF	Ultra High Frequency – radio frequencies from 300 MHz to 3 GHz.
Under-Modulation	A condition where the modulation level is significantly below the intended operating level.
Unun	An impedance-transforming device used between unbalanced radio-frequency circuits or antenna systems.
Uplink	A radio transmission from a ground station or other lower location to a satellite or elevated communication system.
Urgency Signal	A radio signal indicating a serious situation requiring assistance but not necessarily immediate distress response.
Usable Sensitivity	The minimum received signal level producing acceptable reception according to a defined criterion.
USB	Upper Sideband – the upper sideband component of an SSB transmission.
Utility Monitoring	The practice of listening to non-broadcast services such as aviation, maritime, weather and other radio services.
Utility Station	A radio station providing communications or information services other than conventional entertainment broadcasting.
Variable Bandwidth Tuning	A receiver feature that allows the operator to continuously or incrementally adjust the receiver bandwidth.
Vertical Antenna	An antenna whose main radiating element is oriented vertically.
Vertical Polarisation	Radio-wave polarisation in which the electric field is predominantly vertical.
VFO	Variable Frequency Oscillator – a frequency source whose operating frequency can be varied for tuning a radio.
VHF	Very High Frequency – radio frequencies from 30 MHz to 300 MHz.
VLF	Very Low Frequency – radio frequencies from 3 kHz to 30 kHz.
VOLMET	Aviation radio broadcasts providing meteorological information for aircraft in flight.
VOR	VHF Omnidirectional Range – an aviation radio navigation system allowing aircraft to determine bearing from a ground station.
VOX	Voice Operated Transmit – a system that automatically switches a transmitter on when speech or another audio signal is detected.
VOX Delay	The time a transmitter remains active after detected speech has stopped.
VOX Sensitivity	A control determining how much audio is required to activate VOX.
VSWR	Voltage Standing Wave Ratio – another name for SWR.
Warm-Up Drift	Frequency change occurring while radio equipment warms to its normal operating temperature.
Waterfall	A scrolling graphical representation of radio-frequency activity over time.
Waterfall Display	A graphical display commonly used with SDR software showing radio activity over time, with frequency represented horizontally.
Waterfall History	The accumulated historical display of RF activity in a waterfall spectrum display.
Wavelength	The distance between corresponding points on successive cycles of a radio wave. For a wave travelling at a given speed, wavelength decreases as frequency increases.
WebSDR	A remotely accessible software-defined radio receiver that allows users to listen to radio signals through a web interface.
Whine	A high-pitched unwanted audio or RF interference often associated with switching power supplies or digital electronics.
Whip Antenna	A simple vertical antenna consisting of a flexible or rigid metal rod, commonly used on portable radios and mobile equipment.
World Band	Another name commonly used for the HF or shortwave range, particularly on consumer multiband receivers.
Yagi	A directional antenna consisting of a driven element and one or more parasitic elements.

Home | Tables | Radio Frequencies