A-F

A

Absorption: The reduction in strength of a radio signal due to refraction in the ionosphere.

Active antenna: A physically short or small antenna with a high gain preamplifier; designed for use indoors or in limited space areas.

Active filter: A circuit that eliminates unwanted audio frequencies from the audio output of a receiver.

Address: The information in a packet specifying the intended receiving station.

Aeronautical station: A radio station aboard an airplane or a ground station that communicates with aircraft.

AGC: Abbreviation for automatic gain control. 

Amplitude modulation: A modulation technique that varies the power output of a transmitter in accordance with the variations in the modulating audio signal.

AM: Abbreviation for amplitude modulation.

Amplification: The process of increasing the strength of a radio signal.

AMTOR: Acronym for "amateur teleprinting over radio," a mode that uses FSK to send messages containing error detection capabilities and the ability request retransmission of missing or corrupted data. 

ANARC: Acronym for "Association of North American Radio Clubs," an association of radio listener clubs in the United States and Canada.

Antenna tuning unit: A device installed between a receiver or transmitter and the antenna to match the radio impedance to the antenna impedance for maximum power transfer. 

ARQ: Abbreviation for automatic repeat request. In AMTOR, an ARQ is sent back to the transmitting station by the receiving station to request retransmission of missing or corrupted portions. 

ARRL: Acronym for "American Radio Relay League," the national association for ham radio operators in the United States.

ASCII: Acronym for "American standard code for information interchange," a method of representing upper and lower letters in addition to numbers and special symbols.

Attended operation: Operation of a radio station with a human operator at the control point. 

Attenuator: A circuit to reduce the sensitivity of a receiver in fixed steps measured in decibels. 

ATU: Abbreviation for antenna tuning unit.

Auroral propagation: Propagation of signals above 30 MHz via refraction by highly ionized regions around the Earth's poles. 

Automatic gain control: A receiver circuit that adjust the amount of amplification given to a received signal so that the volume from the speaker stays relatively constant. 

B

Balun: A device used with to match an unbalanced feedline, like coaxial cable, to a balanced antenna, like a dipole.

Bandpass: The frequency range that a receiver is currently tuning or that a filter permits to pass through it. 

Band pass filter: A filter that allows a certain range of frequencies to pass but which will reject frequencies below and above the desired range. 

Band plan: A plan to allocate different frequencies within a range for specific purposes and users.

Band spread: A form of electronic (not mechanical) fine tuning common on tube-era general coverage receivers. Usually the ham bands were "spread" to achieve better frequency display accuracy than the main tuning dial could provide. The proper setting of the main dial was critical. 

Bandwidth: The amount of frequency space occupied by a radio signal.

Bank: A storage area for channels in a radio.

Base loading: Placing a loading coil at the base of an antenna in order to lower the antenna's resonant frequency.

Baud: The rate at which data is transmitted measured in bits per second.

BCB: Abbreviation for the AM " broadcast band" running from 540 to 1700 kHz. 

BCL: Abbreviation for "broadcast listener," someone who listens to shortwave radio strictly for program content.

Beacon: A station making one-way transmissions for navigation, homing, and propagation indication purposes.

Beam antenna: An outdoor antenna, usually mounted on a rotor, that concentrates more transmitter power (or receives better) in a certain direction. 

Beat frequency oscillator: A receiver circuit that generates a replacement carrier to enable intelligible reception of CW, FSK, and SSB signals.

BFO: Abbreviation for beat frequency oscillator.

Birdie: A false or spurious signal in a receiver inadvertently produced by the receiver's circuitry.

Bureau: A clearinghouse for QSL cards sent to and received from ham operators in other countries.

Burst: Reception of a signal for a few seconds via meteor scatter.

C

Calling frequency: An agreed-upon frequency where stations attempt to contact each other; once contact is made, stations move to a working frequency.

Call sign: A group of letters and numbers used to identify a station and the country authorizing its operation. 

Carrier: The unmodulated output of a radio transmitter.

Center frequency: The unmodulated carrier frequency of a FM transmitter.

Center loading: Placing a loading coil at the center of an antenna in order to lower the antenna's resonant frequency.

Channel: The frequency on which a radio transmission takes place, or the input and output frequency pair used by a repeater station.

Chief engineer: The person at a broadcasting station responsible for proper and legal operation of a station and maintenance of all required records.

Chirp: Changes in the carrier frequency of a Morse code transmitter, usually due to power supply problems.

Circular polarization: An antenna design where polarization switches rapidly between horizontal and vertical. 

Closed repeater: A repeater station that may be used only by stations belonging to a certain organization or group; access is usually restricted by tone access.

Closing: 1) When a station ends its operations and shuts down; 2) When a frequency can no longer support propagation to a desired station or location.

Co-channel interference: Interference from stations on frequencies adjacent to the desired signal.

Coded access: A method of restricting access to a repeater station to stations that begin their transmission with a special sequence of tones. 

Collision: When two or more packet radio stations simultaneously attempt to transmit on the same frequency.

Connected: Term used to describe a successful contact between two packet radio stations and exchange of packets between them. 

Continuous wave: The constant output of a radio transmitter that can be periodically interrupted to send messages by morse code.

Control operator: The person responsible for all functions and correct operation of a radio station.

Control point: The physical location from which a radio station's functions (setting frequency, turning the station off and on, etc.) are controlled.

Coordinated universal time: An international time and date system derived from the 0-degree meridian at Greenwich. 

Coordinator: A non-governmental group that works to voluntarily assign frequencies to users in order to prevent interference, especially for repeater stations. 

CQ: A general call sent by a station to any other station that may receive it. Hams and other stations "call CQ" to indicate they will answer any station replies to their call. 

Critical angle: An angle defined in reference to the Earth at which a radio signal is refracted in the ionosphere. The lower the angle, the greater distance the radio signal will travel through ionospheric refraction. 

Critical frequency: The frequency at or near the MUF at which the maximum sky wave propagation range is obtained. 

Crystal filter: A filter that uses a network of piezoelectric crystals to obtain high rejection of unwanted signals.

Cut numbers: A system of sending numbers via Morse code by substituting shorter letter characters for the longer number characters. 

Cutoff frequency: The frequency at which a filter will begin to reject signals.

CW: Abbreviation for continuous wave. 

D

D-layer: The lowest region of the ionosphere found approximately 25 to 55 miles above Earth; it fades away quickly after sunset and sometimes does not form at all on short winter days. The main impact of the D-layer on radio propagation is to absorb energy from signals passing through it.

dB: Abbreviation for decibel. 

Dead zone: A region where a radio signal cannot be received due to propagation difficulties.

Decibel: The ratio between two power levels on a logarithmic scale. A 3-decibel increase is a doubling of power; a 20-decibel increase is a power increase of 100 times. 

Delay: How long a radio pauses on a channel to await another transmission.

Deviation: The change in the carrier frequency of a FM transmitter produced by the modulating signal.

Digipeater: A packet radio station that receives and retransmits packets intended for other stations. 

Dipole: An antenna one half-wavelength long at the desired operation frequency that is divided into two quarter-wavelength sections; it transmits and receives in a figure-8 pattern. 

Direct: To communicate with another station without using a repeater. 

Direct wave: A radio signal propagated via line of sight. 

Drift: Slow, gradual change in the frequency of a transmitter or receiver. 

Dummy load: A device used in transmitter testing and adjustment that dissipates the transmitter's energy without radiating it. 

Duplex: To transmit on one frequency while listening for replies on another. 

DX: Any station that is hard to hear or contact on a particular frequency or is rarely heard or contacted on a particular frequency. "DX" is the old telegraph abbreviation for "distant."

DXCC: Abbreviation for "DX Century Club," an award given by the ARRL to hams who contact other hams in at least 100 different countries. 

DXpedition: An organized effort by ham radio operators to put a rare location on the air, or a trip by shortwave listeners to a site for favorable DX reception. 

Dynamic range: How well a receiver can handle strong signals with overloading; any measure of over 100 decibels is considered excellent.

E

E-layer: The region of the ionosphere found approximately 55 to 90 miles above Earth; it fades away a few hours after sunset. The main impact of the E-layer on radio propagation is to absorb energy from signals passing through it, although sporadic-E propagation makes possible distant communications on frequencies above 30 MHz.

Effective radiated power: The output of a transmitter multiplied by the gain of an antenna. 

Elmer: An experienced ham radio operator who mentors new hams and prospective hams. 

EME: Abbreviation for "Earth-Moon-Earth," a method of communication on UHF frequencies by bouncing radio signals off the Moon. 

ERP: Abbreviation for effective radiated power. 

Exalted carrier reception: A reception technique where the carrier produced by a receiver's BFO circuit or product detector is used to replace the carrier of an AM signal for better reception.

Exchange: The passing of all necessary information between two stations during a contact. 

Eyeball: Slang for a face-to-face meeting between two ham radio operators or radio hobbyists.

F

FHSS: Frequency-hopping spread spectrum. A new way to make your radio not transmit or receive. FHSS - First seen in Baofeng UV-88 radio

F-layer: The region of the ionosphere found approximately 90 to 400 miles above Earth, and which is responsible for most long-distance propagation on frequencies below 30 MHz. During the daytime (especially in summer), solar heating can cause the F-layer to split into two separate layers, the F1-layer and the F2-layer. 

FEC: Abbreviation for forward error correction, a FSK mode that transmits each character twice to avoid errors. If the first character is received correctly, the retransmission of it is ignored. 

Feedline: The cable connecting a radio to an antenna. 

FHSS: Frequency

Filter: A circuit or device that will allow certain frequencies to pass while rejecting others. 

Final: The last transmission by a station during a contact, or the last amplifying stage of a radio transmitter.

Fixed station: A station that always operates from a constant, specified land location. 

Flutter: The rapid variation in the signal strength of a station, usually due to propagation variations. 

FM: Abbreviation for frequency modulation. 

Frequency modulation: A modulation technique that varies the carrier frequency of a transmitter in accordance with the variations in the strength of the modulating audio signal. 

Frequency shift keying: A mode that shifts the station's carrier between two fixed frequencies to form characters.

Frequency synthesis: A tuning method in transmitters and receivers which uses a few piezoelectric crystals to generate a wide range of frequencies. 

FSK: Abbreviation for frequency shift keying. 

Full Quieting: A FM radio signal strong enough to completely quiet the receiver background noise.