Glossary

How to use the glossary

Short definitions of the terms you will meet in this compendium and on the air, in alphabetical order. Terms that have their own article are links: follow one when the one-line definition is not enough. For on-air shorthand such as 73 or OM, see Ham abbreviations and numbers; for Q-codes, see Q-codes; for formulas, see Formula sheet.

A to D

Term	Meaning
AC	Alternating current: current that reverses direction many times a second, as in household power and in radio signals.
ADIF	Amateur Data Interchange Format: a plain-text file format for exchanging log data between programs.
AGC	Automatic gain control: a receiver circuit that turns the gain down on strong signals to keep the audio level steady.
AM	Amplitude modulation: information carried by varying the strength of the carrier.
Amplifier	A circuit that makes a signal stronger by drawing power from a supply.
Antenna	The conductor system that turns RF current into radio waves, and radio waves back into current.
Antenna tuner	A matching network between radio and feed line that presents the radio with the impedance it wants. It does not change the antenna itself.
APRS	Automatic Packet Reporting System: position, weather and short messages sent by packet radio.
ARES	Amateur Radio Emergency Service: volunteer operators who support emergency response, sponsored by the ARRL.
ARRL	The American Radio Relay League: the US national amateur radio association, which represents US operators and publishes handbooks and a band plan.
Attenuator	A circuit that reduces signal level by a fixed or adjustable amount while keeping the impedance matched.
AWG	American Wire Gauge: the wire-size numbering in which a smaller number means thicker wire.
Balun	A device that joins a balanced antenna or line to an unbalanced one (coax), such as a dipole to coax.
Band	A range of frequencies allocated for a service, such as the 20-meter amateur band.
Band plan	A voluntary agreement on which modes use which parts of a band.
Bandwidth	The width of spectrum a signal occupies, or a filter or antenna passes, in hertz.
Beacon	A station that transmits a repeating identification or signal so others can judge propagation.
Break-in (QSK)	Operating so you can hear the other station between your own CW characters.
Call sign	The unique identifier assigned to a licensed station, made of a prefix, a number and a suffix.
Capacitance	The ability to store energy in an electric field, measured in farads.
Carrier	The steady radio-frequency signal that is varied (modulated) to carry information.
CAT	Computer Aided Transceiver control: a link that lets software control a radio's frequency, mode and more.
Characteristic impedance	The impedance a transmission line presents to a signal travelling along it, set by its geometry (Z0).
Coaxial cable	A feed line with a center conductor inside an insulator, surrounded by a shield.
Common-mode current	Current flowing in the same direction on both conductors of a line, or on the outside of coax, where it should not.
Control operator	The licensed amateur designated to be responsible for a station's transmissions.
CQ	A general call meaning: calling any station.
CTCSS	Continuous Tone-Coded Squelch System: a sub-audible tone that opens a repeater (the PL tone).
CW	Continuous wave: Morse code sent by turning a carrier on and off.
dB	Decibel: a logarithmic ratio. 3 dB is double the power, 10 dB is ten times.
dBi	Antenna gain in decibels compared with an isotropic radiator. A dipole is 2.15 dBi.
DC	Direct current: current that flows in one direction only.
Deviation	How far an FM signal's frequency swings away from the carrier frequency.
Digital mode	A mode that sends data as discrete tones or phase shifts, usually with a computer: FT8, PSK31, RTTY.
Dipole	An antenna of two equal conductors fed at the center between them; the half-wave dipole is the reference for dBd.
Doppler shift	The change in received frequency caused by relative motion, important for satellite work.
DSP	Digital signal processing: filtering and demodulating with mathematics instead of analog parts.
Dummy load	A resistor that absorbs transmitter power without radiating it, for testing.
Duty cycle	The share of time a transmitter is on; it determines average power.
DX	A distant station; chasing such contacts is called DXing.
DXCC	DX Century Club: the ARRL award for confirming contacts with many countries and entities.

E to L

Term	Meaning
EIRP	Effective isotropic radiated power: transmit power times antenna gain, compared with an isotropic antenna.
Elmer	A mentor who helps newcomers learn the hobby.
EME	Earth-Moon-Earth: communicating by reflecting signals off the Moon, also called moonbounce.
ERP	Effective radiated power: transmit power times antenna gain, compared with a dipole.
Feed line	The cable or line that carries RF between radio and antenna.
Feed point	The place on an antenna where the feed line connects.
FM	Frequency modulation: information carried by varying the carrier's frequency.
Frequency	The number of cycles per second, in hertz (Hz).
Front-to-back ratio	The strength of an antenna's forward lobe compared with the opposite direction.
FT8	A weak-signal digital mode using 15-second transmissions, widely used on HF.
Fuse	A protective device that melts to open a circuit when current exceeds its rating; it protects the wire.
Gain	How much stronger a signal becomes, in an amplifier (more power) or an antenna (more focus).
General	The middle US license class, with most HF privileges.
Grey line	The band around the Earth between day and night, where HF propagation is often enhanced.
Ground plane	A conducting surface or set of radials that a vertical antenna works against.
Ground wave	A signal that follows the Earth's surface rather than bouncing off the ionosphere.
Ham	A licensed amateur radio operator.
Hamfest	A gathering with a swap meet, exams and talks for radio amateurs.
Harmonic	A multiple of a signal's frequency; unwanted harmonics from a transmitter must be filtered.
Hertz (Hz)	The unit of frequency: one cycle per second.
HF	High frequency: 3 to 30 MHz, the shortwave range for worldwide communication.
HT	Handheld transceiver: a portable VHF/UHF radio.
IF	Intermediate frequency: the fixed frequency a superheterodyne receiver converts signals to for filtering and amplification.
Impedance	Total opposition to AC, combining resistance and reactance, in ohms.
Inductance	The ability to store energy in a magnetic field, measured in henries.
Ionosphere	The electrically charged upper atmosphere that reflects (refracts) HF radio waves.
J-pole	A simple half-wave antenna, end-fed through a quarter-wave matching stub, common on VHF and UHF.
Key	The switch used to send Morse code: straight key, paddle or bug.
kHz	Kilohertz: a thousand cycles per second.
Linear amplifier	An amplifier that raises power without distorting the signal, used for SSB and CW.
Long path	A signal that reaches you the long way around the Earth, rather than by the shortest route.
LoTW	Logbook of The World: the ARRL's online system for confirming contacts.
LSB	Lower sideband: the SSB mode that keeps the sideband below the carrier.
LUF	Lowest usable frequency: below it, signals are too weak to use, mainly from D-layer absorption.

M to R

Term	Meaning
Mixer	A circuit that combines two frequencies to produce their sum and difference.
Mode	The type of signal or emission: CW, SSB, FM, digital and so on.
Modulation	Putting information onto a carrier by varying its amplitude, frequency or phase.
MUF	Maximum usable frequency: the highest frequency the ionosphere will return for a path.
Net	A scheduled, organized on-air gathering of operators.
Noise floor	The level of background noise in a receiver; signals near or below it are hard or impossible to hear.
NVIS	Near-vertical incidence skywave: steep-angle HF used for reliable regional contacts.
Ohm (Ω)	The unit of resistance, reactance and impedance.
Open-wire line	A feed line of two parallel wires held apart by spacers, with very low loss; also called ladder line.
Oscillator	A circuit that generates a repeating signal at a set frequency.
Part 97	The FCC rules governing the Amateur Radio Service.
PEP	Peak envelope power: the average power during the strongest part of a modulated signal.
Phonetic alphabet	Standard words for letters (Alfa, Bravo, Charlie) that make spelling clear over a radio link.
Pileup	Many stations calling a rare or wanted station at the same moment.
PLL	Phase-locked loop: a circuit that locks an oscillator to a reference, the basis of frequency synthesis.
Polarization	The orientation of a wave's electric field: horizontal, vertical or circular.
Propagation	The ways radio signals travel from one place to another.
PSK31	A narrow, keyboard-to-keyboard digital mode using phase shifts at 31 baud.
PTT	Push to talk: the switch or control that makes the radio transmit.
Q	The quality factor of a resonant circuit: higher Q means a sharper, narrower response.
Q-code	A three-letter code starting with Q that stands for a phrase, such as QTH for location.
QRP	Low-power operation, commonly 5 watts or less.
QSL	A confirmation of a contact, or the card or electronic record that proves it.
QSO	A radio contact between two stations.
Radials	Wires laid on or above the ground to give a vertical antenna its counterpoise.
Reactance	The opposition to AC offered by capacitors and inductors, in ohms.
Repeater	A station that receives on one frequency and retransmits on another, extending VHF/UHF range.
Resonance	The frequency at which the inductive and capacitive reactance of a circuit cancel.
RF	Radio frequency: alternating currents and fields at frequencies used for radio.
RFI	Radio-frequency interference: unwanted RF disturbing a receiver or electronic device.
RIT	Receiver incremental tuning: shifts the receive frequency without moving the transmit frequency.
RST	Readability, Strength, Tone: the signal report scale (phone omits the tone).
RTTY	Radioteletype: the long-standing text mode that shifts between two tones.

S to Z

Term	Meaning
SDR	Software-defined radio: a radio where most signal processing is done by software.
Sidebands	The frequency bands above and below a carrier created by modulation.
Simplex	Transmit and receive on the same frequency; used for direct contacts without a repeater.
Skin effect	The tendency of RF current to flow near a conductor's surface.
Skip	The way HF signals return to Earth beyond the range of the ground wave; the area they miss is the skip zone.
S meter	A receiver meter showing signal strength, where each S unit is 6 dB.
Solar flux	A measure of solar radio noise at 10.7 cm that tracks HF conditions.
SOTA	Summits on the Air: an award program for operating from mountaintops.
Split	Transmitting on a different frequency from the one you receive on.
Sporadic E	Patches of ionization in the E layer that briefly reflect VHF signals over long distances.
Squelch	A circuit that mutes the receiver until a signal is present.
SSB	Single sideband: a voice mode that transmits one sideband and suppresses the carrier.
Superheterodyne	A receiver that mixes the incoming signal down to a fixed intermediate frequency.
SWR	Standing wave ratio: a measure of how well a load matches the feed line. 1:1 is a perfect match.
Technician	The entry-level US license class, with privileges on VHF/UHF and some HF.
Time constant	How quickly an RC or RL circuit charges or decays, equal to R × C or L ÷ R.
Transceiver	A radio that combines a transmitter and a receiver in one unit.
Tropo	Short for tropospheric propagation: weather-driven bending of VHF/UHF signals beyond the horizon.
TVI	Interference to television reception from a transmitter, extended to other consumer electronics.
UHF	Ultra high frequency: 300 MHz to 3 GHz.
Unun	An unbalanced-to-unbalanced transformer, used to change impedance.
USB	Upper sideband: the SSB mode that keeps the sideband above the carrier.
UTC	Coordinated Universal Time: the worldwide time standard used for logs; also called Zulu.
Velocity factor	How fast a signal travels in a line compared with free space, as a fraction (0.66 for solid-polyethylene coax).
VFO	Variable-frequency oscillator: the tunable oscillator that sets a radio's frequency.
VHF	Very high frequency: 30 to 300 MHz.
Wavelength	The distance a wave travels in one cycle: 300 divided by frequency in MHz gives meters.
Winlink	A radio email system with a global network of gateways.
WPM	Words per minute: Morse speed, measured using the word PARIS.
WSPR	Weak Signal Propagation Reporter: a mode for low-power propagation beacons.
XIT	Transmitter incremental tuning: shifts the transmit frequency without moving the receive frequency.
XYL	Wife, in ham slang; YL is a young lady, or any female operator.
Yagi	A directional antenna with a driven element, a reflector and one or more directors.
Z0	Symbol for a transmission line's characteristic impedance, commonly 50 Ω in amateur radio.
Zulu	The military name for UTC, from the phonetic word for Z.

Related

• What is amateur radio?A licensed radio service for self-training, experimentation and public service, never for money.
• Ham abbreviations and numbers73, 88, CQ, DX, QSO and other jargon, decoded.
• Q-codesThree-letter shorthand like QTH, QSL and QRM, and what each means.
• Formula sheetThe formulas an operator uses.
• Amateur band chartThe bands and their ranges.
• The radio spectrumLF to microwaves: where the bands sit and what each is good for.