Glossary
An alphabetical reference of common amateur radio terms. This glossary covers fundamental concepts, equipment terminology, operating practices, and technical vocabulary encountered throughout amateur radio.
AC (Alternating Current) -- Electrical current that periodically reverses direction. Household power (mains) is AC, typically 120V/60Hz (North America) or 230V/50Hz (Europe and much of the world).
AFSK (Audio Frequency Shift Keying) -- A digital modulation method where two audio tones represent binary 0 and 1. Used in AX.25 packet radio and APRS (Bell 202 standard: 1200 Hz and 2200 Hz).
AGC (Automatic Gain Control) -- A circuit in a receiver that automatically adjusts the gain to maintain a consistent audio output level despite variations in incoming signal strength. Prevents strong signals from being painfully loud and weak signals from being inaudible.
AMBE (Advanced Multi-Band Excitation) -- A proprietary voice codec used in DMR, D-STAR, and other digital voice systems to compress speech into low bitrate digital streams. Developed by DVSI (Digital Voice Systems, Inc.).
ARES (Amateur Radio Emergency Service) -- An ARRL-organized group of licensed amateur radio operators who volunteer their skills and equipment for public service communications during emergencies.
ARRL (American Radio Relay League) -- The national association for amateur radio in the United States, founded in 1914. Publishes QST magazine, administers the Logbook of The World (LoTW), and advocates for amateur radio interests.
ALC (Automatic Level Control) -- A feedback circuit in a transmitter that reduces drive level to prevent over-modulation and excessive power output. On digital modes, ALC action should be minimized or eliminated to prevent signal distortion.
Antenna Tuner (ATU) -- A device that matches the impedance of an antenna system to the transmitter's output impedance (typically 50 ohms). Does not actually "tune" the antenna; rather, it transforms the impedance presented at the transmitter end of the feed line.
APRS (Automatic Packet Reporting System) -- A tactical amateur radio communication system that combines packet radio with GPS for real-time position tracking, messaging, weather reporting, and telemetry.
Attenuator -- A passive device that reduces signal strength by a fixed or variable amount (measured in dB). Used in receivers to prevent overloading by strong signals, or in test setups to reduce power.
Balun (Balanced-Unbalanced) -- A device that connects a balanced antenna (like a dipole) to an unbalanced feed line (like coaxial cable). Prevents common-mode current on the feed line, which can cause interference and distort antenna patterns.
Band Plan -- A voluntary (and sometimes regulatory) allocation of specific frequency ranges within an amateur band for different modes and activities. For example, the lower portion of the 20-meter band is allocated for CW, the middle for digital modes, and the upper for SSB voice.
Bandwidth -- The range of frequencies occupied by a signal. A narrow-band FM signal occupies approximately 12.5 kHz, while an SSB signal occupies about 2.4 kHz, and an FT8 signal occupies only about 50 Hz.
Beacon -- A station that transmits continuously or at regular intervals, typically for propagation monitoring purposes. The NCDXF/IARU international beacon network transmits on multiple HF bands to help operators assess propagation conditions worldwide.
BNC (Bayonet Neill-Concelman) -- A quick-connect/disconnect coaxial connector commonly used in amateur radio for test equipment, handheld antennas, and some mobile installations. Rated for frequencies up to several GHz.
CAT (Computer-Aided Transceiver) -- A serial communication protocol that allows a computer to control a radio transceiver (change frequency, mode, etc.). Each manufacturer has its own CAT protocol (ICOM CI-V, Yaesu CAT, Kenwood command set).
CQ -- A general call inviting any station to respond. Derived from "seek you" or, more likely, from early telegraph and maritime convention.
CTCSS (Continuous Tone-Coded Squelch System) -- A sub-audible tone (67.0--254.1 Hz) transmitted alongside voice audio. Used by repeaters to prevent activation by noise or unintended signals. Also known as PL tone (Motorola's trademark "Private Line").
CW (Continuous Wave) -- Morse code transmission, where the carrier is keyed on and off to form dots and dashes. The oldest and most spectrum-efficient voice-communication mode in amateur radio, requiring only about 150 Hz of bandwidth.
DC (Direct Current) -- Electrical current that flows in only one direction. Batteries and most amateur radio power supplies provide DC. Most amateur radio equipment operates on 12--13.8V DC.
DCS (Digital-Coded Squelch) -- A digital access control system that serves the same purpose as CTCSS but uses a continuous digital code instead of an analog tone. Also called DPL (Digital Private Line).
DMR (Digital Mobile Radio) -- An open digital radio standard using TDMA (time division multiple access) to carry two simultaneous voice channels on one 12.5 kHz channel. Widely adopted in amateur radio for networked digital voice communication.
Dipole -- A fundamental antenna type consisting of two conductive elements (usually wire) fed at the center. A half-wave dipole for a given frequency has a total length of approximately one-half wavelength and presents an impedance of approximately 73 ohms at its feed point.
D-STAR (Digital Smart Technologies for Amateur Radio) -- A digital voice and data protocol developed by JARL and implemented primarily by ICOM. Features callsign-based routing and internet linking.
Dummy Load -- A resistive load (typically 50 ohms) that absorbs RF energy without radiating it. Used for transmitter testing and adjustment without causing interference. Also called a "dry load."
Duplex -- A mode of communication where a station transmits on one frequency and receives on another simultaneously (or in rapid alternation). Repeater operation is the most common form of duplex in amateur radio.
DX -- Long-distance communication, or a distant station. On HF, DX typically means contacts with stations in other countries or continents. On VHF/UHF, DX may refer to contacts beyond the normal range.
DXCC (DX Century Club) -- The most prestigious amateur radio operating award. Requires confirmed contacts with 100 or more DXCC entities (countries and territories). Administered by the ARRL.
Elmer -- An experienced amateur radio operator who mentors a newcomer. The term is unique to amateur radio culture.
Feed Line -- The cable that connects a radio to its antenna. Common types include coaxial cable (RG-58, RG-8X, LMR-400), ladder line (450-ohm window line), and twin-lead (300-ohm).
FT8 -- A digital mode designed for weak-signal communication, created by Joe Taylor (K1JT) and Steve Franke (K9AN). Uses 15-second transmit/receive cycles and can decode signals 24 dB below the noise floor.
Ground Plane -- A conductive surface (or set of radial wires) beneath a vertical antenna that serves as the "other half" of the antenna system. A quarter-wave vertical with ground radials is called a ground-plane antenna.
Hamfest -- A gathering of amateur radio operators, typically including equipment sales (flea market), forums, license exam sessions, and social activities.
HF (High Frequency) -- The portion of the radio spectrum from 3 MHz to 30 MHz, used for long-distance (skywave) amateur radio communication. Often loosely includes 1.8 MHz (160 meters, technically MF).
Hotspot -- A low-power personal gateway device that connects a digital voice radio (DMR, D-STAR, C4FM) to the internet, providing access to digital networks without a nearby repeater.
Impedance -- The total opposition to alternating current flow in a circuit, measured in ohms. In amateur radio, most systems are designed around 50-ohm impedance (transmitters, coaxial cable, antennas).
Ionosphere -- Layers of the Earth's upper atmosphere (60--1000 km altitude) where solar radiation ionizes gas molecules, creating regions that can refract (bend) radio waves back to Earth. This refraction is the mechanism behind HF long-distance propagation.
ITU (International Telecommunication Union) -- The United Nations agency responsible for global radio spectrum allocation. Divides the world into three regions for frequency allocation purposes.
Key (CW Key) -- The device used to generate Morse code. Types include straight keys (manual up-down), paddles (semi-automatic with an electronic keyer), and bugs (mechanical semi-automatic keys).
Linked Repeater -- A repeater connected to other repeaters via radio links or the internet (IRLP, EchoLink, AllStar), extending communication range beyond a single repeater's coverage area.
LoTW (Logbook of The World) -- The ARRL's electronic QSL confirmation system. Stations upload their logs, and the system automatically confirms matching contacts. Required for DXCC and other ARRL awards.
NVIS (Near Vertical Incidence Skywave) -- A propagation technique using low antennas (typically less than 1/4 wavelength high) to launch signals nearly straight up, reflecting off the ionosphere for reliable regional coverage (0--500 km). Used extensively in emergency communications on 40m and 80m.
NEC (Numerical Electromagnetics Code) -- Software for modeling the electromagnetic response of antennas and other structures. Used in antenna design programs like EZNEC, 4nec2, and xnec2c.
Net -- A scheduled, organized on-air meeting of amateur radio operators, usually on a specific frequency. Nets may serve social, training, traffic handling, or emergency communication purposes. A Net Control Station (NCS) manages the net.
Offset -- The frequency difference between a repeater's transmit (output) and receive (input) frequencies. Standard offsets vary by band (e.g., 600 kHz on 2 meters, 5 MHz on 70 centimeters).
PL Tone -- See CTCSS.
Propagation -- The behavior of radio waves as they travel from transmitter to receiver. Includes ground wave, skywave (ionospheric), tropospheric, and line-of-sight propagation.
QSL Card -- A written (physical or electronic) confirmation of a two-way radio contact. Exchange of QSL cards is an amateur radio tradition and is required for most operating awards.
QSO -- A two-way radio contact between amateur stations. From the Q-code "QSO" meaning "I can communicate with... directly."
Ragchew -- An informal, extended conversation on amateur radio. The amateur radio equivalent of a long phone call with a friend.
Repeater -- A station that receives a signal on one frequency and simultaneously retransmits it on another, typically from a high location with higher power than the stations it serves. Extends the range of handheld and mobile radios.
RF (Radio Frequency) -- Electromagnetic energy in the frequency range used for radio communication (roughly 3 kHz to 300 GHz). Also used as an adjective to describe anything related to radio signals ("RF energy," "RF exposure").
RST (Readability, Strength, Tone) -- The standard system for reporting signal quality. Readability (1--5), Strength (1--9), and Tone (1--9, CW only). A report of "59" means perfectly readable and extremely strong.
SDR (Software-Defined Radio) -- A radio system where signal processing functions traditionally performed by analog hardware (mixing, filtering, demodulation) are instead performed by software on a computer or embedded processor. SDR receivers (e.g., RTL-SDR) have made wideband radio reception accessible and inexpensive.
Simplex -- Communication where both stations transmit and receive on the same frequency (as opposed to duplex/repeater operation).
SMA (SubMiniature version A) -- A small threaded coaxial connector used on many handheld radios and small devices. Rated for frequencies up to 18 GHz or higher depending on construction.
S-Meter -- A signal strength meter on a receiver, calibrated in S-units (S1 through S9, then dB over S9). Each S-unit nominally represents 6 dB of signal level difference. S9 is defined as 50 microvolts at the antenna terminal on HF.
SO-239 -- The female panel-mount UHF coaxial connector commonly found on amateur radio base and mobile equipment. Mates with the PL-259 male connector. Despite the name "UHF connector," it is most commonly used at HF and VHF frequencies.
SSB (Single Sideband) -- A modulation technique that transmits only one sideband of an AM signal, suppressing the carrier and the other sideband. More power-efficient and spectrum-efficient than AM. The dominant voice mode on HF amateur radio. USB (Upper Sideband) is used on 20m and above; LSB (Lower Sideband) on 40m and below.
SWR (Standing Wave Ratio) -- A measure of impedance matching between a transmitter, feed line, and antenna. An SWR of 1:1 is a perfect match (all power delivered to the antenna). SWR above 2:1 indicates significant mismatch; above 3:1 risks damage to the transmitter.
UHF (Ultra High Frequency) -- The portion of the radio spectrum from 300 MHz to 3 GHz. In amateur radio, the primary UHF band is 70 centimeters (420--450 MHz).
UTC (Coordinated Universal Time) -- The global time standard used in amateur radio for logging, scheduling, and synchronization. Formerly called GMT (Greenwich Mean Time). All amateur radio logs should record times in UTC.
VFO (Variable Frequency Oscillator) -- The tunable oscillator in a radio that determines the operating frequency. In modern radios, the VFO is typically a digitally synthesized oscillator controlled by a tuning knob or keypad.
VHF (Very High Frequency) -- The portion of the radio spectrum from 30 MHz to 300 MHz. In amateur radio, the primary VHF band is 2 meters (144--148 MHz).
VOX (Voice-Operated Transmit) -- A circuit that automatically keys the transmitter when the operator speaks into the microphone, and releases it during pauses. Allows hands-free operation.
VSWR -- See SWR. The "V" stands for "Voltage" (Voltage Standing Wave Ratio), the most common method of measuring SWR.
Watt -- The unit of electrical power. In amateur radio, transmitter output power is measured in watts. Common amateur power levels range from milliwatts (QRP) to 1500 watts (US legal maximum for amateur stations).
Yagi (Yagi-Uda Antenna) -- A directional antenna consisting of a driven element, a reflector, and one or more directors. Provides gain in one direction at the expense of others. Named after Hidetsugu Yagi and Shintaro Uda. Commonly used on VHF/UHF and also on HF (often on rotatable masts).
73 -- An amateur radio shorthand meaning "best regards." Used as a sign-off at the end of a contact. Not pluralized ("73" not "73s"). One of the oldest telegraph abbreviations still in common use.
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