Glossary

This glossary explains the words, abbreviations and slang that amateur radio operators use on the air, in club meetings and in magazines and manuals. Each entry gives a short, plain-language definition; where HamWiki has a full article on the subject, the entry links to it. Terms are listed alphabetically, with numbers first. Alternative names and spellings are shown in parentheses.

For the shorthand used in Morse code and on voice, see also Q-codes, Prosigns, Ham radio slang and the Phonetic alphabet.

Jump to: 0–9 · A · B · C · D · E · F · G · H · I · J · K · L · M · N · O · P · Q · R · S · T · U · V · W · X · Y · Z

0–9

2200 meters: The lowest US amateur band, 135.7 to 137.8 kHz, open to General and higher licensees at very low power after notifying the utilities' coordinating body. See 2200-meter band.
5 by 9: A signal report meaning perfectly readable (5) and very strong (9). Contesters give it to nearly everyone, so it often says little about the real signal. See Signal reports.
5/8-wave: A vertical antenna about five-eighths of a wavelength tall, with a matching coil at the base. It radiates lower than a quarter-wave whip, making it a favorite 2-meter mobile antenna. See Vertical antenna.
60 meters: A small HF allocation near 5.3 MHz, shared with government users, where US hams follow special limits on frequencies, power and bandwidth. It fills the gap between 80 and 40 meters. See 60-meter band.
630 meters: A low-frequency band at 472 to 479 kHz for General and higher licensees, with tight power limits and advance notification required. Popular for WSPR and other weak-signal experiments. See 630-meter band.
73: Morse and voice shorthand for "best regards," used to sign off a contact. It is already plural, so "73s" is redundant. See Ham radio slang.
88: Shorthand for "love and kisses," a friendly sign-off traditionally used between couples or close friends rather than in ordinary contacts. See Ham radio slang.
8JK (8JK beam, W8JK beam): A bidirectional flat-top beam made of two closely spaced half-wave elements fed out of phase, designed by John Kraus, W8JK. It gives modest gain without needing a rotator for two directions.

A

A index: A daily number summarizing geomagnetic activity, derived from the K index. Low values mean a quiet field and generally better HF propagation; high values mean storms and poor conditions. See Space weather.
AC (alternating current): Current that reverses direction many times per second. US household power is 120 volts AC at 60 Hz, and radio signals themselves are AC at far higher frequencies. See AC and DC.
Access tone: A subaudible tone, or on some older systems a tone burst, that a repeater must hear before it will retransmit your signal. Program it into your radio along with the offset. See CTCSS and DCS.
Activator: The operator who travels to a park, summit or other qualifying site and makes contacts from there, giving others the chance to log it. See Parks on the Air.
ADC (analog-to-digital converter): A chip that measures a voltage many times per second and turns each reading into a number. It is the heart of every software-defined radio.
ADIF: Amateur Data Interchange Format, the standard text file format for moving contact logs between programs, award services and online confirmation systems. See Logging software.
Admittance: The reciprocal of impedance, measured in siemens: how easily a circuit passes alternating current. It makes calculations for parallel circuits simpler. See Impedance.
AFSK (audio frequency-shift keying): Sending data by switching between two audio tones fed into a voice transmitter. Common 1200-baud packet and APRS use 1200 and 2200 Hz tones over FM.
AGC: Automatic gain control, a receiver circuit that turns gain down for strong signals and up for weak ones, keeping the audio level steady. See AGC.
Air core: A coil wound without an iron or ferrite core. It cannot saturate and has low loss, so it is used in antenna tuners, traps and high-power circuits. See Inductors.
ALC: Automatic level control, a feedback signal that limits a transmitter's drive to prevent overdriving. Keep ALC action minimal on digital modes to avoid a distorted, splattering signal. See ALC.
ALE (automatic link establishment): An HF system in which radios automatically scan channels, test paths and pick the best frequency to connect. Used by government, MARS and some amateur emergency groups.
Aliasing: A sampling error in which signals above half the sample rate show up as false lower frequencies. Filters ahead of the converter in a software-defined radio prevent it.
Alligator: Slang for a station that is "all mouth and no ears," transmitting loudly but unable to hear well. The word also commonly means a spring-loaded alligator clip. See Ham radio slang.
AllStarLink: A network that links repeaters and personal nodes over the internet using Asterisk telephone software, with full-duplex audio and many connection options. See AllStarLink.
AM (amplitude modulation): The oldest voice mode, in which the strength of the carrier varies with the audio. It uses more bandwidth than SSB but has a loyal following for its natural sound. See AM.
Amateur Extra (Extra): The highest US license class, earned by passing the Element 4 written exam after the Technician and General. It grants all amateur privileges on every band. See Amateur Extra license.
Amateur radio: A licensed, noncommercial radio service for personal communication, experimentation, public service and emergency support, using frequency bands set aside for hams. See Amateur radio.
Amateur satellite (Bird): A satellite built by and for radio amateurs, often carrying an FM or linear transponder. Many can be worked with a handheld and a small handheld beam. See Amateur satellites.
AMBE: A proprietary digital voice codec used in D-STAR, DMR and System Fusion radios. Its licensing is one reason open alternatives such as M17 use Codec 2 instead.
Ammeter: A meter that measures current in amperes. It must be wired in series with the circuit, and most hams use the current range of a multimeter.
Amp-hour (Ah): A battery's charge capacity: one amp supplied for one hour. A 50 Ah battery can, in theory, power a 5-amp load for about 10 hours. See Batteries.
Ampere (Amp, A): The unit of electric current, equal to one coulomb of charge passing a point each second. Rigs draw roughly 20 amps when transmitting at 100 watts. See Ohm's law.
Amplifier: A circuit that makes a signal larger. To hams it usually means a linear amplifier that boosts a transceiver's output from about 100 watts to higher power. See Amplifiers.
Amplifier classes (Class A, AB, B, C, D): Labels for how much of each cycle an amplifier's device conducts. Class A is cleanest, AB suits SSB linears, C suits FM and CW but not SSB, and D is efficient switching. See Amplifiers.
AMSAT: The Radio Amateur Satellite Corporation, the volunteer group in North America that builds amateur satellites and publishes tracking data and operating guidance. See Amateur satellites.
Anderson Powerpole (Powerpole): A genderless, color-coded DC connector that has become the standard for 12-volt ham gear, so any radio can plug into any supply or battery. See Power supplies.
Antenna analyzer: An instrument that measures SWR, impedance and resonance across a band without needing to transmit, making antenna tuning quick and safe. See Antenna analyzer.
Antenna efficiency: The share of power reaching an antenna that is actually radiated rather than lost as heat in ground, coils or wires. Short mobile and loaded antennas are often quite inefficient. See Antenna gain.
Antenna farm: Slang for a property covered with towers, wire antennas and beams, usually belonging to a serious DX or contest station. See Ham radio slang.
Antenna gain: How strongly an antenna concentrates signal in a favored direction compared with a reference, stated in dBi or dBd. Gain comes from focusing, not from creating power. See Antenna gain.
Antenna modeling (NEC, EZNEC): Using software, usually built on the NEC engine, to predict an antenna's pattern, gain and impedance before building it. EZNEC is a popular program. See Antenna modeling.
Apogee: The point in an orbit farthest from Earth. Satellites in elliptical orbits move slowly near apogee, giving long passes and wide coverage. See Amateur satellites.
Apparent power: Voltage times current in a circuit, measured in volt-amperes, without accounting for phase. It equals real power only when the load is purely resistive. See Impedance.
Appliance operator: A mildly disparaging term for a ham who uses only factory-built gear and has little interest in how it works. Most operators start this way. See Ham radio slang.
APRS: Automatic Packet Reporting System, a packet-based network for sharing position, weather, messages and status, operating on 144.390 MHz in North America. See APRS.
Arduino: A family of inexpensive open-source microcontroller boards. Hams use them for homebrew keyers, rotator controllers, beacons and station automation projects. See Homebrewing.
AREDN (Amateur Radio Emergency Data Network): A high-speed mesh network built from commercial Wi-Fi equipment reflashed to operate on amateur microwave frequencies, carrying video, voice and data for emergencies. See AREDN.
ARES: Amateur Radio Emergency Service, the ARRL's program of trained volunteers who provide communications to served agencies during disasters and public events. See ARES.
ARISS: Amateur Radio on the International Space Station, a program that arranges school contacts with astronauts and supports ham equipment aboard the station. See Amateur satellites.
Armchair copy: A signal so strong and clear that you can copy it while leaning back and relaxing, with no strain at all. See Ham radio slang.
ARQ (automatic repeat request): An error-control method in which the receiving station acknowledges each data block and asks for repeats of bad ones. It makes Pactor, VARA and packet links error-free.
ARRL (American Radio Relay League): The national association for amateur radio in the US, founded in 1914 by Hiram Percy Maxim. It publishes QST and advocates for hams. See ARRL.
ASCII: A standard 7-bit code that assigns numbers to letters, digits and symbols. Packet radio and many computer-based digital modes send text as ASCII. See Packet radio.
Astable multivibrator (Astable): An oscillator circuit with no stable state that flips continuously between two states, producing a square wave. A 555 timer is a common example. See Oscillators.
Atom: The smallest unit of an element, made of a nucleus surrounded by electrons. Electric current is the movement of loosely held electrons from atom to atom. See Semiconductors.
Attenuation: Loss of signal strength, usually stated in decibels. Feed line attenuation rises with frequency and length, which matters most at VHF and UHF. See Coaxial cable.
Attenuator: A circuit that reduces signal level by a known number of decibels. Receivers use one to prevent overload, and fox hunters use one near the hidden transmitter. See Fox hunting.
Attic antenna: An antenna installed under the roof, a popular answer to HOA rules. It works surprisingly well but loses some signal and puts RF closer to people. See Stealth antennas.
Aurora: The northern and southern lights, caused by solar particles striking the upper atmosphere during geomagnetic storms. Aurora can reflect VHF signals with a distinctive raspy tone. See Auroral propagation.
Auroral propagation: Long-distance VHF and upper-HF contacts made by bouncing signals off an active aurora. Signals sound buzzy, so CW and SSB work best. See Auroral propagation.
Automatic control: Operating a station without a control operator present at the control point, as repeaters commonly do. FCC rules allow it only for certain station types and frequencies. See Part 97.
Autotuner: An antenna tuner that measures SWR and adjusts itself to a match automatically. It can be built into the rig or mounted outdoors at the antenna. See Antenna tuner.
AUXCOMM (Auxiliary Communications): The federal term for volunteer radio support, often by hams, that is integrated into government emergency communications under the Incident Command System. See AUXCOMM.
Auxiliary station: An FCC station type that sends point-to-point communications within a system, such as repeater links and remote control. It may operate only on 2 meters and shorter wavelengths, with exclusions. See Part 97.
Average power: Power averaged over time. For SSB voice it is far below peak envelope power, while FM, RTTY and FT8 run near full power continuously. See PEP and power measurement.
Average value: The mean of an AC waveform's magnitude over a half cycle. For a sine wave it is about 0.637 times the peak value. See RMS and peak values.
AWG (American Wire Gauge): The US system of wire sizes, in which a smaller number means thicker wire. Use heavy gauge, such as 10 or 12 AWG, for 100-watt radio power leads. See Power supplies.
AX.25: The link-layer protocol used by amateur packet radio and APRS, adapted from the commercial X.25 standard. It carries callsigns in every frame. See Packet radio.
Azimuth plot: A chart of an antenna's radiation pattern viewed from above, showing gain in each compass direction. Check it to see a beam's front-to-back ratio. See Antenna modeling.

B

Backscatter: Weak, hollow-sounding signals scattered back from the ground or ionosphere beyond the skip distance. It lets you hear stations that would otherwise sit in your skip zone.
Balun: A device that connects a balanced antenna or line to an unbalanced one such as coax, often transforming impedance as well. See Balun.
Band: A range of frequencies allocated to amateurs, usually named by its approximate wavelength, such as 20 meters or 70 centimeters. See Amateur radio bands.
Band edge: The upper or lower limit of a band or license subband. Keep your entire signal inside it, not just the dial frequency, since sidebands extend several kilohertz. See Band plan.
Band opening: A period when propagation suddenly makes a normally quiet band usable for long-distance contacts, as when Sporadic E opens 6 meters in summer.
Band plan: A voluntary agreement on which parts of a band are used for which modes and activities, layered on top of the FCC rules. See Band plan.
Band-pass filter: A filter that passes a chosen range of frequencies and blocks those above and below. Multi-station events like Field Day rely on them to reduce interference. See Band-pass filter.
Band-stop filter (Band-reject filter): A filter that blocks a narrow range of frequencies while passing everything else, such as a notch that keeps a strong broadcast station out of a receiver. See Radio frequency interference.
Bandwidth: The width of the frequency range a signal occupies or a filter passes. An SSB voice signal needs about 3 kHz, while an FT8 signal needs only about 50 Hz. See Single sideband.
Barefoot: Running a transceiver without an external amplifier, typically at about 100 watts. Many DX contacts are made barefoot with a good antenna. See Amplifiers.
Base station: A station operated from a fixed location, such as a home shack, as opposed to mobile or portable. See Ham shack.
Battery: One or more electrochemical cells that store energy. Hams commonly use sealed lead-acid and lithium iron phosphate batteries for portable and backup power. See Batteries.
Battery management system (BMS): The circuit inside a lithium battery pack that balances cells and disconnects them on overcharge, deep discharge, overcurrent or extreme temperature. See Batteries.
Baud: The number of signal symbols sent per second. It equals bits per second only when each symbol carries one bit; standard amateur RTTY runs at 45.45 baud.
BBS (bulletin board system): A computer system that stores messages and files for users to read and post. Packet BBSs still relay amateur mail and bulletins over radio. See Packet radio.
Beacon: A transmitter that repeatedly sends its identification on a known frequency so hams can judge propagation. The NCDXF/IARU network cycles 18 beacons worldwide on five HF frequencies. See Radio propagation.
Beacon station: In FCC rules, an amateur station transmitting for propagation and reception studies. Beacons are limited to 100 watts and to specific segments when under automatic control. See Part 97.
Beam: A directional antenna that concentrates signal in one direction, such as a Yagi, quad or hex beam, usually turned with a rotator. See Yagi antenna.
Beamwidth: The angle between the points where an antenna's main lobe drops 3 dB from its peak. Higher-gain antennas have narrower beamwidths and need more accurate aiming. See Antenna gain.
Beta (hFE): A bipolar transistor's current gain, the ratio of collector current to base current. It varies widely even between parts of the same type. See Transistors.
Beverage: A long, low, terminated wire receiving antenna, usually a wavelength or more long, that pulls weak signals out of noise on 160 and 80 meters. See Beverage antenna.
BFO (beat frequency oscillator): A receiver oscillator that mixes with the intermediate frequency to make CW signals audible as tones and to recover SSB voice. See Superheterodyne receiver.
Bias: A steady DC voltage or current applied to a transistor or tube to set its operating point. Bias determines an amplifier's class and linearity. See Transistors.
Big gun: A station with large antennas, maximum legal power and skilled operators that dominates contests and pileups. See Contesting.
Birdie: A steady, unwanted carrier generated inside a receiver by its own oscillators and mixing, heard at the same frequency regardless of the antenna. See Receiver performance.
Bit depth (Resolution): The number of bits an analog-to-digital converter uses for each sample. Each added bit gives about 6 dB more potential dynamic range. See Software-defined radio.
BK: A Morse abbreviation meaning "break," used to hand the frequency back quickly to the other station without sending full call signs. See Prosigns.
Bleeder resistor: A resistor across a power supply's filter capacitors that drains their charge after power is removed. Never trust it blindly; high-voltage capacitors can still be deadly. See Power supplies.
Blocking: Loss of receiver sensitivity when a very strong nearby signal overloads the front end, burying weaker signals even on other frequencies. See Receiver performance.
BNC: A small bayonet coax connector that locks with a quarter turn, common on test equipment, scanners and some handhelds. See RF connectors.
Boat anchor: Affectionate slang for heavy vintage gear, usually tube equipment, from the era when radios weighed as much as an anchor. See Boat anchors.
Bonding: Connecting all station equipment, ground rods and the electrical service ground together with heavy conductors so they stay at the same potential during a lightning strike. See Grounding and lightning protection.
Boost converter: A switching circuit that raises a DC voltage, for example keeping a radio at 13.8 volts as a battery sags. Cheap ones can produce strong RF noise. See Power supplies.
BPQ32 (LinBPQ): Packet node, BBS and Winlink gateway software written by John Wiseman, G8BPQ. BPQ32 runs on Windows and LinBPQ on Linux, including Raspberry Pi. See LinBPQ.
BrandMeister: A worldwide network of servers that links DMR repeaters and hotspots, letting users talk through shared talkgroups. See DMR.
Breadboard: A solderless board with spring contacts for building and testing circuits quickly, or more loosely any rough prototype layout. See Homebrewing.
Break: A word used to interrupt or join a conversation during a pause between transmissions. On repeaters, saying your call sign is usually enough; "break break" signals urgent traffic. See Operating etiquette.
Brick: Slang for a small solid-state RF power amplifier, often used to boost a VHF or UHF handheld or mobile radio. See Amplifiers.
Bridge rectifier: Four diodes arranged to convert both halves of an AC cycle into pulsating DC, the usual first stage in a linear power supply. See Diodes.
Broadband-Hamnet: A mesh networking firmware for repurposed Wi-Fi routers operating in the amateur 2.4 GHz band, an early relative of AREDN.
Buck converter: A switching circuit that efficiently lowers a DC voltage, such as stepping 12 volts down to 5 volts for USB devices. Poorly filtered ones cause RF noise. See Power supplies.
Bug: A semi-automatic mechanical key whose vibrating arm sends strings of dits automatically while the operator forms dahs by hand. Vibroplex made the best-known models. See Morse keys and paddles.
Busted call (Bust): A call sign copied or logged incorrectly. In contests, a busted call loses the contact's points and may bring an extra penalty. See Contesting.
Bypass capacitor (Decoupling capacitor): A capacitor from a supply line to ground that shunts RF and noise away, keeping circuit stages from interacting through shared power. See Capacitors.

C

C rate: A battery's charge or discharge current relative to its capacity. A 1C rate on a 20 Ah battery is 20 amps; 0.5C is 10 amps. See Batteries.
Cabrillo: The standard text file format for submitting contest logs to sponsors, generated automatically by most contest logging programs. See Contesting.
Call area (Call district): One of the ten numbered regions of the US, 0 through 9, reflected in call signs. Hams who move may keep their old call. See Call signs.
Callbook: A directory of licensed amateurs with names and addresses. Once a thick printed book, it has been replaced by online lookups drawing on the Universal Licensing System.
Calling frequency: A frequency where stations call and meet before moving elsewhere to talk, such as 146.520 MHz, the national 2-meter FM simplex calling frequency. See Simplex.
Callsign: The unique identifier the FCC assigns to each amateur station, made of a prefix, a digit and a suffix, which you must send regularly. See Call signs.
Callsign-SSID (SSID): A number from 0 to 15 appended to a call sign in packet and APRS, such as W1AW-9, so one operator can run several stations. See APRS.
Cans: Slang for headphones, which help copy weak signals and keep the shack quieter for everyone else in the house. See Ham radio slang.
Capacitance: The ability to store energy in an electric field between two conductors, measured in farads. Most radio circuits use picofarads to microfarads. See Capacitors.
Capacitor: A component of two conductors separated by an insulator that stores charge, blocks DC and passes AC. Used in filters, tuned circuits and power supplies. See Capacitors.
Capacity hat: Wires or a disk at the top of a vertical antenna that add capacitance, letting a shorter antenna resonate lower with better efficiency. See Vertical antenna.
Carrier: The steady radio wave that a transmitter modulates to carry information. AM keeps it, CW switches it on and off, and SSB removes it. See Single sideband.
CAT control: Computer Aided Transceiver control, a serial or USB link that lets software read and set a radio's frequency, mode and other settings. See Digital mode interface.
Catenary: The curve a wire takes when hung between two supports. Wire antennas always sag somewhat, so the center sits lower than the ends. See Dipole antenna.
CB (Citizens Band): A license-free service with 40 channels near 27 MHz, used by truckers and hobbyists. It is not amateur radio, though many hams started there. See GMRS, FRS and CB.
Cell: A single electrochemical unit within a battery. Four lithium iron phosphate cells at 3.2 volts each make a 12.8-volt battery. See Batteries.
CEPT: The European Conference of Postal and Telecommunications Administrations. Its arrangements let US citizens holding General or higher licenses operate in many member countries without a separate license. See Operating abroad.
Ceramic capacitor: A small, inexpensive capacitor with a ceramic insulator, widely used for RF bypassing. Types labeled C0G or NP0 stay stable enough for tuned circuits. See Capacitors.
CERT (Community Emergency Response Team): A FEMA-backed program that trains neighborhood volunteers in basic disaster response. Many teams welcome hams to provide radio links. See Emergency communications.
Characteristic impedance: The impedance a feed line presents, set by its conductor size, spacing and insulation. Most coax is 50 ohms, while ladder line is often 450 ohms. See Feed line.
Charge controller: A device that regulates current from a solar panel into a battery to prevent overcharging. MPPT types harvest more power than simpler PWM types. See Batteries.
Cheat sheet: A quick-reference card at the operating position listing band privileges, frequencies, Q-codes or contest exchanges. See Q-codes.
Check-in: A station reporting into a net, or the act of doing so. Wait for net control to call for check-ins, then give your call sign clearly. See Nets.
Chirp (CHIRP): A CW signal whose frequency shifts each time the key closes, a sign of an unstable transmitter. In capitals, CHIRP is free radio programming software. See CHIRP.
Choke (RF choke): An inductor that passes DC or low frequencies while blocking RF, used to keep radio energy out of power and bias lines. See Inductors.
Choke balun (Common-mode choke, current balun): Coax coiled or wound on ferrite to block current flowing on the outside of the shield, curing RF in the shack and feed line radiation. See Common-mode choke.
Chordal hop: HF propagation in which a signal bounces between ionospheric regions without returning to Earth in between, giving low-loss paths, especially across the equator. See Trans-equatorial propagation.
Circuit: A closed path through which current flows from a source, through a load, and back. An open circuit has a break; a short circuit bypasses the load. See Ohm's law.
Circuit breaker: A resettable switch that opens automatically when current exceeds its rating, protecting wiring and equipment from overloads. See Power supplies.
Circular polarization: Radio waves whose electric field rotates as they travel, either right- or left-hand. Satellite operators use it to reduce fading from tumbling spacecraft. See Polarization.
Claimed score: The score a contestant calculates and submits with a log. The sponsor's checked score is often lower after dupes and busted calls are removed. See Contesting.
Clear: Said at the end of a final transmission to show you are leaving the air or the frequency. In Morse it is sent as CL. See Prosigns.
Clock sync (NTP, time sync): Keeping a computer's clock accurate, usually through internet time servers. FT8 and similar modes fail if the clock is off by more than about a second.
Club callsign (Club station license): A call sign issued to a radio club through a licensed trustee, used at club events, Field Day and shared stations. See Club stations.
CME (coronal mass ejection): A huge eruption of solar plasma. When one reaches Earth, typically a day or more later, it can trigger geomagnetic storms, poor HF conditions and aurora. See Space weather.
CMOS (complementary metal-oxide semiconductor): A low-power integrated circuit technology used in most digital logic and microcontrollers. CMOS parts are easily damaged by static, so handle them carefully. See Digital logic.
Coax (Coaxial cable): Feed line with a center conductor surrounded by insulation and a shield, the most common way to connect radios to antennas. See Coaxial cable.
Code plug: A configuration file holding a digital radio's channels, talkgroups, zones and contacts, written to the radio with programming software. See DMR.
Code test: The Morse code exam once required for US licenses. The FCC dropped it for all classes in February 2007, though many hams still learn code. See Learning Morse code.
Coil loading: Adding a coil to an electrically short antenna so it resonates at a lower frequency, as in mobile HF whips. Some efficiency is lost. See Loading coil.
Cold solder joint: A dull, grainy solder connection where the solder did not flow properly, causing intermittent faults. Reheat it with fresh solder and enough heat. See Homebrewing.
Collinear: An antenna made of several elements stacked end to end and fed in phase, giving gain in all horizontal directions. Common for VHF and UHF base stations. See Collinear antenna.
Color code: The system of colored bands marking resistor values and tolerance, and more generally any color convention for wires or parts. See Resistors.
Common-mode current: Unwanted current flowing on the outside of a coax shield or equally on both feed line wires, causing RF in the shack and noise pickup. See Common-mode choke.
Complex impedance: Impedance written as resistance plus reactance, such as 50 + j25 ohms. Antenna analyzers display both parts. See Impedance.
Conductance (Siemens): The reciprocal of resistance, showing how easily a material carries current. It is measured in siemens, once called mhos. See Ohm's law.
Conductor: A material that carries electric current easily because its electrons move freely. Copper is most common in radio wiring; aluminum is popular for antenna elements. See Resistors.
Contest: An on-air competition to make as many contacts as possible, with specific stations or areas, within a set time. See Contesting.
Continuity: An unbroken electrical path. A meter's continuity setting beeps when it finds one, quickly confirming cables, fuses and solder joints. See Multimeter.
Control operator: The licensed amateur responsible for a station's transmissions. The control operator's license class sets which privileges may be used. See Part 97.
Control point: The location where the control operator controls a station's transmissions, which for remote operation may be far from the transmitter. See Remote operation.
Controlled environment: An RF exposure category for people who know about the exposure and can control it, such as a ham. Its limits are higher than for the general public. See RF exposure.
Cootie: A sideswiper key moved side to side, making contact on each side, with the operator timing every dit and dah by hand. See Morse keys and paddles.
Copy: To receive and understand a transmission. "Do you copy?" asks whether the message got through, and "solid copy" means fully received. See Ham radio slang.
Core saturation (Saturation): The point at which a magnetic core can carry no more flux, so inductance collapses. Saturated baluns and chokes overheat and distort at high power. See Inductors.
Coulomb: The unit of electric charge, about 6.24 billion billion electrons. One ampere is one coulomb flowing past a point each second.
Counterpoise: A wire or set of wires that serves as the missing half of an antenna, such as a vertical or end-fed wire, in place of earth ground. See Radials and counterpoises.
Courtesy tone: The beep a repeater sends after a user unkeys. Wait for it before transmitting, which leaves a gap for others to join. See Repeaters.
CQ: A general call meaning "any station, please answer," usually repeated with your call sign several times. See Calling CQ.
CQ zone: One of 40 geographic zones, originally defined by CQ magazine, used for the Worked All Zones award and the CQ contests. See Amateur radio awards.
Crest factor: The ratio of a waveform's peak value to its RMS value. A sine wave's is about 1.414; speech is much higher, which speech processing reduces. See RMS and peak values.
Crimp: To attach a connector by squeezing it onto wire with a special tool instead of soldering. Powerpoles and many coax connectors are crimped. See RF connectors.
Critical angle: The highest takeoff angle at which an ionospheric layer still bends a signal of a given frequency back to Earth. Steeper waves pass into space. See Ionosphere.
Critical frequency: The highest frequency an ionospheric layer reflects straight back down. It sets the upper limit for NVIS operating and changes with time of day and the solar cycle.
Cross-modulation: Interference in which a strong unwanted signal's modulation gets imposed on the station you are listening to, a sign of receiver overload. See Receiver performance.
Cross-polarization: A mismatch between transmitting and receiving antenna polarization, such as horizontal versus vertical. On VHF line-of-sight paths it can cost 20 dB or more. See Polarization.
Crystal: A thin slice of quartz that vibrates at a very precise frequency, used to control oscillators and build sharp filters. See Oscillators.
Crystal lattice filter: Several quartz crystals combined into a narrow band-pass filter, used in a receiver's IF stage to separate SSB and CW signals. See Superheterodyne receiver.
CSCE: Certificate of Successful Completion of Examination, given by volunteer examiners after you pass. It proves your exam credit for 365 days. See Volunteer examiners.
CTCSS (PL tone, tone): Continuous Tone-Coded Squelch System, a subaudible tone sent with FM voice that many repeaters require for access. See CTCSS and DCS.
CUL: Morse abbreviation for "see you later," often sent near the end of a CW contact before 73. See Ham radio slang.
Current: The flow of electric charge through a conductor, measured in amperes. Current is what heats wires, so size cables for the current they carry. See Ohm's law.
Current clamp: A meter with jaws that close around a wire to measure current without breaking the circuit. RF versions help find common-mode current on feed lines. See Multimeter.
Cut numbers: Morse letters substituted for digits to save time, such as T for 0 and N for 9, used mostly in contest exchanges. See Cut numbers.
CW: Continuous wave, the on-off keyed carrier used to send Morse code. It is simple, narrow and gets through when voice cannot. See Morse code.
Cycle life: How many charge and discharge cycles a battery delivers before its capacity falls to a set level. Lithium iron phosphate lasts far longer than lead-acid. See Batteries.

D

D layer: The lowest ionospheric layer, present mainly in daylight, which absorbs lower HF signals. It fades after sunset, opening 160, 80 and 40 meters for distance. See Ionosphere.
D-STAR: A digital voice and data standard developed by the Japan Amateur Radio League, supported mainly by Icom radios, with internet-linked repeaters and reflectors. See D-STAR.
DAC (digital-to-analog converter): A chip that turns a stream of numbers into a varying voltage, used to generate transmit signals and audio in a software-defined radio.
dBd: Antenna gain in decibels relative to a half-wave dipole. A figure in dBd is 2.15 dB lower than the same antenna's gain in dBi. See Antenna gain.
dBi: Antenna gain in decibels relative to an imaginary isotropic antenna radiating equally in all directions. Watch which unit advertised gain figures use. See Antenna gain.
dBm: Power in decibels relative to one milliwatt. Zero dBm is 1 milliwatt and +30 dBm is 1 watt; receiver sensitivity is usually stated this way. See Decibels.
dBW: Power in decibels relative to one watt. A 100-watt transmitter puts out 20 dBW, and a 1,000-watt amplifier 30 dBW. See Decibels.
DC (direct current): Current that flows in one direction only, as from batteries and power supplies. Most transceivers run on about 13.8 volts DC. See AC and DC.
DCS (digital-coded squelch): A squelch system that sends a continuous low-speed digital code instead of a CTCSS tone, used for repeater access on some systems. See CTCSS and DCS.
DDS (direct digital synthesis): Generating a signal by computing its waveform digitally and converting it with a DAC. DDS chips make stable, quickly tunable VFOs for homebrew rigs. See Oscillators.
Dead band: A band that seems empty because propagation is poor. Often stations are listening but not calling, so a CQ may reveal an opening. See Radio propagation.
Decade: A range spanning a factor of ten, such as 1 to 10 MHz. In power, one decade equals 10 dB. See Decibels.
Decibel (dB): A logarithmic unit comparing two power or voltage levels. Doubling power adds 3 dB, and ten times the power adds 10 dB. See Decibels.
Decimation: Reducing a digital signal's sample rate after filtering, so a software-defined radio can process a narrow slice of spectrum with less computing power. See Software-defined radio.
Delta loop: A full-wavelength wire loop shaped like a triangle, which needs only one tall support. It is quiet on receive and works well for DX. See Delta loop antenna.
Depth of discharge (DoD): How much of a battery's capacity has been used. Lead-acid batteries last longer if kept above half charge; lithium iron phosphate tolerates deeper use. See Batteries.
Derating: Running a component or amplifier below its maximum rating for reliability, such as reducing power for continuous-duty modes like RTTY and FT8. See Amplifiers.
Desense: Reduced receiver sensitivity caused by a strong nearby signal, such as a repeater hearing its own transmitter through an inadequate duplexer. See Repeaters.
Desoldering braid (Solder wick): Fine copper braid coated with flux that soaks up molten solder when heated, used to clean pads and remove parts. See Homebrewing.
Deviation: How far an FM signal's frequency swings with modulation. Amateur FM typically uses about 5 kHz; narrowband radios use about 2.5 kHz. See FM.
Dielectric: An insulating material between conductors, as in capacitors and coax. The dielectric sets coax's velocity factor and much of its loss. See Coaxial cable.
Digipeater: A digital repeater that receives and retransmits packets on the same frequency, extending the range of APRS and packet stations. See APRS.
Digirig: A compact USB interface that combines a sound card and a serial CAT port, connecting a radio to a computer for digital modes. See Digital mode interface.
Digital electronics: Circuits that work with discrete on and off states rather than continuously varying signals. Microcontrollers, logic chips and SDR processing are digital. See Digital logic.
Digital mode: Any mode that sends data through a computer or digital radio, from FT8 and RTTY to digital voice. Most need a digital mode interface between radio and computer.
Diode: A two-terminal semiconductor that lets current flow in one direction only, used for rectifiers, detectors, mixers and protection. See Diodes.
Dip meter (Grid dip meter): A tunable oscillator whose meter reading dips when held near a circuit resonant at the same frequency, used to check coils, traps and antennas. See Dip meter.
Diplexer: A filter that lets two different bands share one feed line or antenna, such as a 2-meter and 70-centimeter radio on one dual-band antenna. See Feed line.
Dipole: A center-fed antenna made of two equal halves, about a half wavelength long overall, the reference standard for wire antennas. See Dipole antenna.
Direct sampling: An SDR design that digitizes the antenna signal directly with a very fast ADC, without mixing it down first. See Software-defined radio.
Directed net: A net in which the net control station runs the frequency and all stations must get permission before transmitting. See Net control station.
Directional coupler: A device that samples power flowing in each direction on a feed line separately, the core of SWR meters and wattmeters. See SWR meter.
Directional wattmeter: A meter that reads forward and reflected power on a feed line, letting you check transmitter output and SWR together. See PEP and power measurement.
Director: A parasitic element, slightly shorter than the driven element, placed in front of it in a beam to pull the pattern forward. See Yagi antenna.
Direwolf: Free software that turns a computer and sound card into a packet TNC, APRS digipeater or iGate. See Direwolf.
Discone: A wideband vertical antenna made of a disk above a cone, popular for scanners and multiband VHF and UHF use. See Discone antenna.
Dit and dah: The spoken names for the Morse dot and dash; a dah is three dits long. Learning code by sound uses these words. See Learning Morse code.
DMR (Digital Mobile Radio): A commercial two-slot TDMA digital voice standard widely adopted by hams, using talkgroups to route conversations across linked networks. See DMR.
Doppler shift: The change in received frequency caused by motion between stations. Satellite signals can shift up to about 10 kHz on 70 centimeters during a pass, so retune as it goes. See Amateur satellites.
Doublet: A center-fed wire antenna of any convenient length, fed with ladder line and an antenna tuner for multiband use. See Antenna tuner.
Doubling: Two stations transmitting at the same time, usually on a repeater or net, so neither is heard clearly. Pause between transmissions to prevent it. See Operating etiquette.
Driven element: The element in a beam antenna that connects directly to the feed line; the other elements are parasitic. See Yagi antenna.
Dropout voltage: The minimum difference between input and output a linear voltage regulator needs to keep regulating. Low-dropout (LDO) regulators need less. See Power supplies.
DSP (digital signal processing): Using software or dedicated chips to filter, demodulate and clean up signals. In receivers it provides sharp filters, notches and noise reduction. See Noise blanker and noise reduction.
DTMF (Touch-tone): Dual-tone multi-frequency signaling, the tones a telephone keypad makes. Hams use them to control repeaters, links and remote equipment. See Repeaters.
Ducting (Tropospheric ducting): VHF and UHF signals trapped in a layer of the lower atmosphere, sometimes carrying them hundreds of miles. See Tropospheric ducting.
Dummy load: A resistor that absorbs transmitter power without radiating, used for testing and adjustment off the air. See Dummy load.
Dupe: A duplicate contact with a station already logged on the same band and mode in a contest, worth no extra points. Logging software flags dupes. See Contesting.
Duplex: Transmitting and receiving on different frequencies, as through a repeater. Full duplex means both happen at once, as on many satellites. See Repeaters.
Duplexer: A set of tuned cavity filters that lets a repeater transmit and receive at the same time through one antenna without desensing itself. See Repeaters.
Duty cycle: The share of time a transmitter is keyed at full power. FT8 and RTTY run near 100 percent, stressing equipment and raising RF exposure. See RF exposure.
DX: Long-distance contacts or stations, especially in other countries. Chasing DX is one of the hobby's oldest pursuits. See DXing.
DX cluster: An internet network where hams post spots of DX stations heard, shown as live lists in logging software. See DX cluster.
DX window: A band-plan segment set aside for long-distance contacts, such as 50.100 to 50.125 MHz on 6 meters. Avoid local ragchews there. See Band plan.
DXCC: The DX Century Club, the ARRL award for confirmed contacts with 100 or more DXCC entities, which are countries and other recognized areas. See Amateur radio awards.
DXpedition: A trip to a rare or uninhabited location to put it on the air for others. Expect huge pileups, usually worked using split operation.
Dynamic range: The span between the weakest and strongest signals a receiver handles at once without distortion, in decibels. It matters most in crowded contests. See Receiver performance.

E

E layer: The ionospheric layer about 60 to 90 miles up, strongest in daytime. It refracts lower HF signals over shorter skip distances, and dense patches cause Sporadic E. See Ionosphere.
Ears: Slang for a station's receiving ability, as in "he has good ears." A quiet location and a good receive antenna often matter more than power for working weak stations.
Earth station: An amateur station on or near the Earth's surface that communicates through satellites or with space stations. Any license class may operate one; see Amateur satellites.
EchoLink: A free system that links amateur stations and repeaters over the internet, letting licensed hams talk worldwide from a computer, phone app or radio node. See EchoLink.
Eddy current: A circulating current induced in a metal core or nearby metal by a changing magnetic field. It wastes power as heat, which is why transformer cores are laminated or made of ferrite.
EFHW (end-fed half-wave): A half-wavelength wire fed at one end through a high-ratio transformer, usually 49:1. Popular for portable use since it needs one support and covers several harmonic bands. See End-fed half-wave antenna.
EIRP (effective isotropic radiated power): Transmitter power minus feed line loss plus antenna gain in dBi, compared with an isotropic radiator. Power limits on the 2200- and 630-meter bands are stated as EIRP.
Electric charge (charge): A basic property of matter, positive on protons and negative on electrons, measured in coulombs. Moving charge is current, and separated charge creates voltage.
Electric field: The region of force around a charged object or between points at different voltages, measured in volts per meter. Capacitors store energy in it, and RF exposure limits cover its strength.
Electricity: The behavior of electric charges at rest and in motion, which powers every radio. Hams mostly work with voltage, current, resistance and power, tied together by Ohm's law.
Electrolytic capacitor: A polarized capacitor that packs large capacitance into a small case, used for power supply filtering and audio coupling. Installed backward, it can fail violently. See also Capacitors.
Electromagnet: A coil of wire, often wound on an iron core, that becomes a magnet while current flows through it. Relays, speakers and solenoids all rely on electromagnets.
Electromagnetic spectrum: The full range of electromagnetic waves, from radio through microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays. Amateur radio bands occupy small slices of the radio portion.
Electromagnetic wave: Electric and magnetic fields, at right angles to each other, traveling through space at the speed of light. Radio signals are electromagnetic waves; see Wavelength and frequency.
Electron: A negatively charged particle surrounding the nucleus of an atom. The flow of electrons through a conductor is electric current, and loosely held electrons make metals good conductors.
Electronics: The field dealing with circuits that use active parts such as transistors, tubes and integrated circuits to control current. Basic electronics helps with exams, repairs and homebrewing.
Electrostatic discharge (ESD): A sudden spark of static electricity, often from your body, that can destroy sensitive parts such as MOSFETs and ICs. Wear a grounded wrist strap when handling circuit boards.
Element: Either a numbered license exam (Element 2 is Technician, 3 is General, 4 is Amateur Extra) or one conductor of an antenna, such as a Yagi's director.
Element credit: Credit for an exam element you have already passed, shown on your CSCE and valid for 365 days. It lets you skip that element at a later session. See also Volunteer examiners.
Elevation plot: A side view of an antenna's radiation pattern, showing signal strength at each vertical angle. Low angles favor DX, while high angles favor NVIS and nearby contacts.
Elmer: An experienced ham who mentors newcomers with licensing, station building and operating. Many clubs pair new licensees with an Elmer. See Elmers.
EmComm (emergency communications): Amateur radio support for public safety and served agencies when normal systems fail during disasters. Groups such as ARES and RACES train for it. See Emergency communications.
EME (moonbounce): Earth-Moon-Earth communication, bouncing VHF, UHF or microwave signals off the Moon. Path loss is enormous, so it needs big antennas or weak-signal digital modes such as Q65. See Moonbounce.
Emission type: The FCC's classification of a signal by its modulation and content, such as CW, phone, RTTY, data or image. Part 97 specifies which emission types are allowed in each band segment.
eQSL: An online service, eQSL.cc, for exchanging electronic QSL cards. It is popular for casual confirmations, but ARRL awards such as DXCC accept Logbook of the World confirmations instead.
ERP (effective radiated power): Transmitter power minus feed line loss plus antenna gain in dBd, compared with a half-wave dipole. It is 2.15 dB lower than EIRP for the same station and is often used to describe repeater coverage.
Error correction: Techniques that detect and fix data errors caused by noise or fading, either by retransmission (ARQ) or by added redundancy (FEC). Modes such as PACTOR, VARA and FT8 depend on it.
ES: Morse and digital-mode shorthand for "and," as in "NAME BOB ES QTH OHIO." It comes from the American Morse character for "&".
Exchange: The information stations trade to complete a contest contact, such as a signal report and state, a serial number, or class and section on Field Day. Accurate copy matters for scoring.

F

F layer: The highest ionospheric layer, roughly 90 to 250 miles up, and the most important for HF DX. By day it splits into F1 and F2; F2 supports most long-distance skip. See Ionosphere.
F region: The upper part of the ionosphere containing the F1 and F2 layers, which merge into one F layer at night. A single F2 hop can cover about 2,500 miles; see Radio propagation.
Far field: The region more than a few wavelengths from an antenna, where its radiation pattern is fully formed and field strength falls predictably with distance. Published gain and patterns describe far-field behavior.
Farad (F): The unit of capacitance. One farad is enormous, so radio circuits use microfarads (µF) and picofarads (pF); see Capacitors.
Faraday rotation: A slow twisting of a radio wave's polarization as it passes through the ionosphere in Earth's magnetic field. It causes fading on satellite and moonbounce signals; circular polarization helps.
Farnsworth: A Morse teaching method that sends each character at a higher speed, such as 18 WPM, with extra space between characters, so learners hear sounds rather than count dots. See Learning Morse code.
Fast-scan television (ATV): Amateur television using broadcast-style analog or digital video, usually on 70 centimeters and higher because of its wide bandwidth. See Amateur television.
FB (fine business): CW and voice shorthand meaning "excellent" or "great," as in "FB OM, your signal is solid copy here." See also Ham radio slang.
FCC (Federal Communications Commission): The US agency that regulates civilian radio, writes the amateur rules in Part 97, and issues amateur licenses through the Universal Licensing System.
FEC (forward error correction): Redundant bits added to transmitted data so the receiver can repair errors without asking for a resend. It helps FT8 decode signals buried deep in noise.
Feedback: Returning part of a circuit's output to its input. Negative feedback stabilizes amplifiers; positive feedback causes oscillation, like the squeal when a microphone gets too close to a speaker.
Feedline: The cable that carries RF between the radio and the antenna, usually coaxial cable or balanced line such as ladder line. See Feed line.
Feedline loss (line loss): Power lost as heat in a feed line, usually given in dB per 100 feet. It rises with frequency, length and high SWR, so VHF and UHF runs need low-loss coax.
Feedpoint impedance: The impedance where the feed line connects to an antenna. Matching it to 50 ohms keeps SWR low; a half-wave dipole measures roughly 50 to 75 ohms depending on height.
FEMA: The Federal Emergency Management Agency, which coordinates federal disaster response. Its free online Incident Command System courses, such as IS-100, are often required for ARES members.
Ferrite: A ceramic magnetic material made from iron oxide blended with other metals. Formed into toroids, rods and beads, it is used for chokes, transformers and RFI suppression; see Common-mode choke.
Ferrite bead: A small ferrite sleeve or clamp-on core placed over a cable to block common-mode RF. On HF, several turns through a larger core work better than a single bead; see Radio frequency interference.
Ferrite mix: The material formula of a ferrite core, identified by a number, which sets the frequencies where it works best. Mix 31 is popular for HF chokes, and mix 43 suits upper HF and VHF.
FET (field-effect transistor): A transistor whose current is controlled by the voltage on its gate rather than by base current. Its very high input impedance suits receiver front ends and amplifiers. See Transistors.
FFT (fast Fourier transform): A fast algorithm that converts sampled signals into their frequency components. It drives the spectrum and waterfall displays in SDRs and digital-mode software.
Field Day: ARRL's annual emergency-preparedness exercise and operating event, held the fourth full weekend of June, when clubs set up temporary stations, often on emergency power. See Field Day.
Field strength meter: A simple instrument with a short antenna that shows relative RF field strength nearby. Useful for comparing antenna patterns, confirming a transmitter has output, or finding a radiating feed line.
Film capacitor: A capacitor that uses a plastic film such as polyester or polypropylene as its dielectric. Stable and low in loss, it suits audio, timing and filter circuits; see Capacitors.
Filter: A circuit that passes some frequencies and rejects others. Low-pass, high-pass, band-pass and notch filters reduce interference, sharpen receivers and keep harmonics off the air.
Firmware: Software stored inside a radio or other device. Manufacturers release updates that fix bugs or add features, but an interrupted update can disable a radio, so follow the instructions carefully.
Fist: An operator's individual sending style on a Morse key. Experienced operators can often recognize friends by their fist alone; see Morse code.
fldigi: A free, open-source program for many digital modes, including PSK31, RTTY, Olivia and MFSK, with logging and rig control. It is widely used for emergency messaging. See fldigi.
Flip-flop: A digital circuit with two stable states that stores a single bit. Flip-flops are the building blocks of counters, frequency dividers, shift registers and memory; see Digital logic.
Float charge: Holding a fully charged battery at a constant, slightly lower voltage to offset self-discharge. It suits lead-acid backup batteries, but lithium batteries generally should not be floated indefinitely. See Batteries.
Flutter: Rapid, irregular fading on signals that pass through the auroral zone or reflect off moving objects such as aircraft. It makes CW sound raspy; see Auroral propagation.
Flux: A chemical that cleans metal surfaces so solder flows and bonds; most electronic solder has a rosin flux core. In physics, flux also means the magnetic field passing through an area.
FM (frequency modulation): A mode that varies the carrier's frequency with the audio signal. It gives clear, noise-resistant audio and is the standard mode for VHF and UHF repeaters. See FM.
Folded dipole: A half-wave dipole made of two parallel conductors joined at both ends, with one fed at the center. Its feedpoint impedance is about 300 ohms, and it has wider bandwidth.
Frequency: The number of cycles per second of an alternating signal, measured in hertz. Frequency and wavelength are inversely related, so higher frequencies have shorter waves. See Wavelength and frequency.
Frequency coordination: Assigning repeater input and output pairs so nearby repeaters do not interfere. It is voluntary, but FCC rules put the burden on an uncoordinated repeater in an interference dispute.
Frequency coordinator (coordination): The volunteer person or group, recognized by local amateurs, that assigns repeater frequencies and keeps records for a state or region. Contact them before putting a repeater on the air.
Frequency counter: An instrument that measures and digitally displays the frequency of a signal. Useful for checking oscillators, transmitters and homebrew projects. See Frequency counter.
Frequency multiplier: A circuit that produces a harmonic of its input, such as a doubler or tripler, to reach a higher frequency. Older VHF transmitters and some microwave gear use multiplier chains.
Frequency response: How evenly a device passes signals across a range of frequencies. SSB transmit audio is typically limited to roughly 300 to 3,000 Hz to save bandwidth while staying intelligible.
FRN (FCC Registration Number): A 10-digit number the FCC assigns to identify you in its systems. You need one before taking a license exam, and you use it for all later filings. See Getting licensed.
Front-to-back ratio: The difference, in dB, between a directional antenna's signal in its forward direction and directly behind it. A high ratio helps reject interference from behind; see Yagi antenna.
FRS (Family Radio Service): A license-free UHF two-way radio service with 22 channels near 462 and 467 MHz and a 2-watt maximum. Handy for families, but not amateur radio. See FRS and CB.
FSK (frequency-shift keying): A digital technique that shifts the carrier between two frequencies to send ones and zeros. Amateur RTTY uses FSK with a 170 Hz shift.
FST4: A WSJT-X weak-signal mode with selectable transmit periods from 15 seconds to 30 minutes. Longer periods give extreme sensitivity, making it popular on the 2200- and 630-meter bands.
FT4: A fast WSJT-X digital mode with 7.5-second transmit periods, designed for contesting. It gives up a few dB of sensitivity compared with FT8 for quicker contacts. See FT4.
FT8: The most popular HF digital mode, using 15-second transmit periods and automatic sequencing. It decodes signals well below the noise, bringing DX within reach of modest stations. See FT8.
Full gallon (full legal limit): Slang for running the maximum legal power, 1,500 watts PEP output in the United States, usually through a large amplifier.
Full quieting: An FM signal strong enough to completely silence the receiver's background noise. Being told "you're full quieting" means your signal is getting into the repeater well.
Fuse: A protective device whose metal link melts and opens the circuit when current exceeds its rating. Replace a blown fuse only with one of the same rating; see Power supplies.

G

G5RV: A multiband wire dipole 102 feet long, fed through a ladder-line matching section, designed by Louis Varney, G5RV. Most installations need a tuner on some bands. See G5RV antenna.
Gain: An increase in signal level, expressed in dB. For antennas, gain means concentrating power in one direction rather than creating more power; see Antenna gain.
General: The middle US license class, earned by passing the Element 3 exam. It opens most HF privileges, making worldwide contacts practical. See General license.
Geomagnetic storm: A disturbance of Earth's magnetic field caused by solar wind or coronal mass ejections. It degrades HF propagation, especially on polar paths, but can bring VHF aurora; see Space weather.
GFCI: Ground-fault circuit interrupter, an outlet or breaker that cuts power when it senses current leaking to ground. Electrical codes require them in damp locations, and they are wise for outdoor operating.
GMRS (General Mobile Radio Service): A licensed UHF personal radio service that shares frequencies with FRS but allows higher power and repeaters. The license requires no exam and covers immediate family. See GMRS, FRS and CB.
Go-kit (go-box): A packed radio kit ready for quick deployment, typically holding a transceiver, antenna, power source, cables and paperwork. Common among emergency communications volunteers.
GPSDO: GPS-disciplined oscillator, a reference oscillator locked to GPS satellite timing for extremely accurate frequency. Valuable for microwave and narrow weak-signal work, where tiny drift matters.
Grace period: The two years after a US amateur license expires during which it can be renewed without retesting. You may not transmit until it is renewed. See License renewal.
Gray line (grey line, terminator): The band of twilight circling Earth between day and night. Low-band signals along it often travel unusually far because D-layer absorption is low. See Gray line.
Great circle: The shortest path between two points on a globe. Beam headings come from great-circle bearings, best shown on an azimuthal map centered on your location; see Long path and short path.
Green stamp: Slang for a US dollar bill sent with a QSL request to help cover a DX station's return postage. Some countries prohibit cash in the mail; see QSL cards and logging.
Grid square (Maidenhead locator): A location code from the Maidenhead system, such as FN31, covering 1 degree of latitude by 2 degrees of longitude. Used in VHF contests, digital modes and awards. See Grid squares.
GridTracker: A free program that maps stations decoded by WSJT-X or JTDX and highlights the grids, states or countries you still need. See GridTracker.
Ground: A shared zero-volt reference point, or a connection to the earth. Stations need safety, lightning and RF grounds, which have different requirements. See Grounding and lightning protection.
Ground conductivity: How well the soil conducts electricity. It affects ground-wave range and vertical antenna efficiency; salt water is best, while dry, rocky or sandy soil is poor.
Ground loop: An unwanted current path created when equipment is grounded at more than one point. It causes hum, noise or RF problems, often between a computer and a digital mode interface.
Ground plane: A conducting surface, or a set of radials, that acts as the missing half of a vertical antenna. A car roof makes a good ground plane for mobile antennas.
Ground radial (radial system): A wire running outward from the base of a vertical antenna, on or under the ground. More and longer radials reduce ground losses and improve efficiency. See Radials and counterpoises.
Ground rod: A copper-clad steel rod, usually 8 feet long, driven into the earth for lightning and safety grounding. The electrical code requires bonding it to the building's service ground; see Grounding and lightning protection.
Ground wave: Propagation that follows Earth's surface, strongest on the MF and low HF bands. It provides reliable local and regional coverage regardless of ionospheric conditions. See Ground wave.
Gutter antenna: A stealth antenna that uses a metal rain gutter and downspout as the radiator, fed through a tuner. Useful where antenna restrictions rule out anything visible.

H

Half-power point (3 dB point): The frequency or angle at which power falls to half its peak, 3 dB down. Filter bandwidth and antenna beamwidth are measured between half-power points; see Decibels.
Half-wave: A length equal to half a wavelength at the operating frequency. A half-wave dipole's length in feet is roughly 468 divided by the frequency in MHz.
Hall effect device: A sensor that produces a voltage proportional to the magnetic field passing through it. Clamp meters use one to measure DC current without breaking the circuit.
Ham: An amateur radio operator. The word's origin is uncertain; it was once an insult for clumsy telegraph operators before hams adopted it with pride. See Amateur radio.
Ham cram: A one-day class that reviews the question pool, followed immediately by an exam session. Fast and effective, though critics say it favors memorization over understanding.
Hamfest: A gathering of hams with a flea market, vendors, forums and often license exams. A great place to find used gear and meet local operators. See Hamfests.
Hamvention: The largest US hamfest, held each May near Dayton, Ohio, and run by the Dayton Amateur Radio Association. It draws visitors and vendors from around the world; see Hamfests.
Handheld (HT, handie-talkie): A small battery-powered transceiver held in the hand, usually covering 2 meters and 70 centimeters FM. Many newcomers start with one. See Handheld transceiver.
Handie-talkie: Ham slang for a handheld radio, usually shortened to HT. The name was Motorola's for its SCR-536 handheld of World War II. See Handheld above.
Hardline: Coax with a solid or corrugated metal outer conductor, offering very low loss. Used for long VHF and UHF runs, but stiff and requires special connectors.
Harmonic distortion: Unwanted energy at multiples of the input frequency, created when a circuit does not respond linearly. In transmitters it causes interference; in audio it muddies the sound.
Harmonics: Signals at whole-number multiples of a fundamental frequency, such as 14 MHz from a 7 MHz signal. Transmitters must suppress them, often with low-pass filters. See Harmonics and spurious emissions.
Heat shrink: Plastic tubing that shrinks tightly when heated, used to insulate and protect splices and connectors. Adhesive-lined types seal outdoor coax connections against water.
Heat sink: A metal part, usually finned aluminum, that draws heat away from transistors, regulators and other components. Keep a radio's heat sink unobstructed during long transmissions.
Henry (H): The unit of inductance. Radio circuits mostly use microhenries (µH) and millihenries (mH); see Inductors.
Hertz (Hz, kHz, MHz): The unit of frequency, one cycle per second. A kilohertz is 1,000 Hz and a megahertz is 1,000,000 Hz; radio frequencies are usually given in kHz or MHz. See Wavelength and frequency.
Heterodyne: Mixing two frequencies to produce their sum and difference. The principle underlies the superheterodyne receiver, frequency conversion and the BFO used to hear CW.
Hex beam: A lightweight, six-sided wire beam that covers several HF bands with modest gain and a small turning radius. Popular where a full-size Yagi is impractical. See Hex beam.
HF: High frequency, 3 to 30 MHz, home of the bands that use ionospheric skip for worldwide contacts. See HF.
Hi hi: Laughter in Morse code, sent as "HI HI." Also heard in voice contacts as a friendly nod to CW tradition; see Ham radio slang.
High bands: The upper HF bands, usually 20 through 10 meters, which open in daylight and thrive during high solar activity. Some operators include 6 meters.
High-altitude balloon (ham balloon, pico balloon): A balloon carrying a small amateur transmitter into the stratosphere. Tiny pico balloons can circle the globe for weeks, reporting position by WSPR or APRS. See High-altitude balloons.
High-pass filter: A filter that passes frequencies above its cutoff and blocks those below. Often added to a TV or receiver input to reject strong HF signals; see Radio frequency interference.
HOA (homeowners association): A community organization whose deed restrictions often limit or ban outdoor antennas. FCC protections against local government antenna rules do not cover private HOA covenants. See Antenna restrictions.
Homebrew: Equipment a ham designs or builds personally, from simple antennas to complete transceivers. A long-standing tradition of the hobby. See Homebrewing.
Horizontal loop (skywire): A large horizontal wire loop, often a full wavelength on 80 meters, fed with ladder line and a tuner for multiband use. Often quieter on receive than a dipole. See Horizontal loop antenna.
Hotspot: A small, low-power device that links a radio to digital voice networks such as DMR, D-STAR or System Fusion over the internet. See Hotspots.
HT: Short for handie-talkie: a handheld transceiver. See Handheld above.
Hunter (chaser): An operator who contacts activators in programs such as Parks on the Air and Summits on the Air. Hunters earn their own awards for parks or summits worked.
Hysteresis: A lag in which a system's output depends on its past state. Magnetic cores show it as energy loss; in circuits it prevents rapid toggling near a threshold, such as squelch chatter.

I

Iambic: A keying method using a dual-lever paddle: squeezing both levers sends alternating dits and dahs. Keyers offer iambic Mode A and Mode B. See Morse keys and paddles.
IARU (International Amateur Radio Union): The worldwide federation of national amateur radio societies, organized into three regions. It represents hams at the ITU, and the ARRL is its US member society.
IC (integrated circuit): A chip containing many transistors and other components on one piece of silicon. Op-amps, microcontrollers and audio amplifiers are common ICs in ham gear.
ICS (Incident Command System): The standard management structure US agencies use for emergencies. Emergency communicators learn it, often through free FEMA courses, to fit into a served agency's operation. See Incident Command System.
IF (intermediate frequency): The fixed frequency a superheterodyne receiver converts incoming signals to for filtering and amplification. Common IFs include 455 kHz and 9 MHz. See Superheterodyne receiver.
Image rejection: A receiver's ability to reject image signals, given in dB. Good front-end filtering or a high first IF improves it; see Receiver performance.
Image response (image): An unwanted signal received at a frequency twice the IF away from the desired one, on the opposite side of the local oscillator. See Superheterodyne receiver.
Impedance: The total opposition to alternating current, combining resistance and reactance, measured in ohms. Most ham gear is designed for 50 ohms. See Impedance.
Inductance: The property of a conductor or coil that opposes changes in current by storing energy in a magnetic field. It is measured in henries. See Inductors.
Inductor (coil): A component, usually a coil of wire, that stores energy in its magnetic field. Used in filters, tuned circuits, chokes and loading coils. See Inductors.
Insertion loss: The signal loss, in dB, caused by inserting a device such as a filter, connector or switch into a line. Lower is better, especially in receive preamp and filter chains.
Insulator: A material that resists current flow, such as glass, plastic or ceramic. Antenna insulators separate wires from supports and must withstand the high RF voltage at wire ends.
Interlock: A safety switch that cuts dangerous high voltage when an amplifier or power supply cabinet is opened. Never defeat one on energized equipment; see Amplifiers.
Intermodulation (IMD, intermod): Unwanted signals created when two or more signals mix in a nonlinear circuit. It produces phantom signals in receivers and plagues crowded repeater sites; see Receiver performance.
Inverted L: A vertical wire that bends to run horizontally at the top, forming an L, fed against radials. Popular on 160 and 80 meters where a full-size vertical is impractical. See Inverted L antenna.
Inverted V: A dipole supported at its center by a single mast, with both ends sloping down toward the ground. Easy to put up and needs only one tall support. See Inverted V antenna.
Inverter: A device that converts DC battery power to AC for household equipment; many generate strong RF noise. In digital logic, an inverter is a NOT gate.
Ionosphere: Layers of electrically charged gas in the upper atmosphere, ionized by solar radiation, that bend HF signals back to Earth for long-distance contacts. See Ionosphere.
IOTA (Islands on the Air): An awards program for contacting islands, grouped under reference numbers. Rare island groups are favorite DXpedition destinations. See Islands on the Air.
IRLP (Internet Radio Linking Project): A system linking repeaters and simplex nodes worldwide through the internet. Users connect to other nodes by sending DTMF codes from their radios. See IRLP.
Isotropic antenna: A theoretical antenna that radiates equally in all directions. It does not exist in practice but serves as the reference for gain in dBi.
ISS (International Space Station): The crewed space station, which carries amateur equipment for school contacts through the ARISS program and often runs an FM repeater or APRS digipeater. See Amateur satellites.
ITU (International Telecommunication Union): The United Nations agency that allocates radio spectrum worldwide through its Radio Regulations. National rules such as Part 97 are built on its allocations.
ITU region: One of three areas the ITU uses for frequency allocations. The Americas are Region 2, which is why US band edges differ from Europe's; see Operating abroad.
ITU zone: One of 90 zones the ITU divides the world into, used for some contests and awards. The IARU HF Championship uses the ITU zone as its exchange; see Contesting.

J

J-pole: An end-fed half-wave vertical matched by a quarter-wave stub, forming a J shape. Cheap and easy to build, it is especially popular on 2 meters. See J-pole antenna.
JOTA (Jamboree on the Air): An annual Scouting event, held the third full weekend of October, when hams help Scouts talk with other Scouts around the world. See Jamboree on the Air.
JS8Call: A keyboard-to-keyboard digital mode built on FT8's modulation, adding free-form chat, relaying and store-and-forward messaging for weak-signal conditions. See JS8Call.
JT65: An older WSJT weak-signal mode with one-minute transmit periods. Largely replaced by FT8 on HF, it is still used for moonbounce; see WSJT-X.
JT9: A narrow-bandwidth WSJT-X weak-signal mode with one-minute transmit periods, suited to HF and the low-frequency bands. It sees little use since FT8 arrived.
JTAlert: A Windows companion program for WSJT-X and JTDX that flags new and needed stations, sounds alerts and passes contacts to logging software.
JTDX: A program forked from WSJT-X, focused on strong FT8 decoding performance in crowded bands. Many DX chasers prefer it. See JTDX.
Junk box: A ham's stash of salvaged and spare parts, kept for repairs and homebrewing. Many projects start with whatever is in the junk box.

K

K and KN: Morse prosigns that end a transmission. K invites any station to reply, while KN means only the station already in contact should answer. See Prosigns.
K index: A 0-to-9 scale of geomagnetic disturbance over a three-hour period. Low values mean quiet conditions, while 5 or higher marks a storm that degrades HF; see Space weather.
Keplerian elements (keps, TLE): Numbers describing a satellite's orbit, usually distributed in two-line element (TLE) format. Tracking software uses them to predict passes, so update them regularly; see Amateur satellites.
Kerchunk: Keying up a repeater briefly without identifying, just to hear it respond. Unidentified transmissions break FCC rules and annoy listeners; see Repeaters.
Key: A switch for sending Morse code by hand, such as a straight key, bug or paddle. As a verb, it means to turn on a transmitter. See Morse keys and paddles.
Key clicks: Broadband clicks heard on either side of a CW signal, caused by keying with rise and fall times that are too fast. They interfere with nearby stations and signal a poorly adjusted transmitter.
Keyboard-to-keyboard: Live, typed conversation between operators using digital modes such as RTTY, PSK31 or JS8Call, as opposed to the brief, automated exchanges of FT8.
Keyer: An electronic circuit that turns paddle movements into perfectly timed dits and dahs. Many radios have one built in, and memory keyers store messages. See Morse keys and paddles.
Kirchhoff's laws: Two circuit rules: the currents entering a junction equal the currents leaving it, and the voltages around any closed loop add to zero. Used with Ohm's law to analyze circuits.
Kit: A package of parts and instructions for building equipment yourself. Kits range from simple keyers to full transceivers and are a popular way into homebrewing.
Knife-edge diffraction: The bending of VHF and UHF signals over a sharp obstacle such as a mountain ridge, letting them reach areas beyond line of sight. See also Radio propagation.
Koch method: A Morse learning method that starts with two characters at full speed and adds one more each time you reach about 90 percent accuracy. See Learning Morse code.

L

Ladder line: Balanced feed line made of two parallel wires held apart by spacers, usually 300 to 600 ohms. Its very low loss suits multiband antennas used with a tuner. See Feed line.
Learning net: A slow-paced, friendly net where newcomers practice check-ins, procedures and traffic handling without pressure. See also Nets.
LED (light-emitting diode): A diode that emits light when forward current flows. It needs a series resistor to limit current, and some LED bulbs and drivers generate RF noise.
Legal limit: The maximum transmitter power allowed, 1,500 watts PEP output on most US amateur bands. Some bands, including 30 and 60 meters, have lower limits; see Part 97.
LEO (low Earth orbit): An orbit below about 1,200 miles, where most amateur satellites and the ISS fly. Passes are short, typically 10 to 15 minutes; see Amateur satellites.
License term: The period a US amateur license is valid, currently 10 years. You can renew online through ULS within 90 days before it expires. See License renewal.
Lid: Slang for a poor or inconsiderate operator, such as one who transmits over others or tunes up on a busy frequency. See Operating etiquette.
LiFePO4 (lithium iron phosphate): A lithium battery chemistry that is safer and longer-lived than other lithium types. A four-cell pack gives about 13 volts, ideal for 12-volt radios. See Batteries.
Lightning arrester (surge arrester): A device in a feed line that diverts lightning-induced surges to ground. It must connect to a solid ground at the building entry point. See Grounding and lightning protection.
Line of sight: A direct, unobstructed path between two antennas. VHF and UHF signals mostly travel line of sight, so antenna height greatly extends range; see Radio propagation.
Linear: Short for linear amplifier, an RF power amplifier that boosts a signal without distorting it. "Running a linear" means using an amplifier after the transceiver. See Amplifiers.
Linear power supply: A power supply built from a transformer, rectifier and linear regulator. Heavy and inefficient, but electrically quiet compared with switching supplies. See Power supplies.
Linearity: How faithfully a circuit's output follows its input. Poor linearity in an SSB transmitter or amplifier causes splatter and intermodulation that bother nearby stations.
Link budget: A tally of all gains and losses between transmitter and receiver, used to predict received signal strength. Essential for satellite, microwave and moonbounce planning.
Link layer: The protocol layer that frames data, addresses stations and checks for errors over a single link. In packet radio, AX.25 is the link-layer protocol.
Link margin: How many dB the received signal exceeds the minimum needed for reliable communication. Extra margin keeps a link working through fading and other losses.
Linked repeaters: Repeaters connected by radio or internet so that a transmission on one is heard on all. Linked systems can cover a whole state or region.
Listening (monitoring): Receiving without transmitting, the best way to learn band conditions and operating practice. Always listen first to make sure a frequency is clear; see Operating etiquette.
Lithium-ion (Li-ion): A rechargeable battery with high energy density, used in handhelds and portable packs. It needs proper charging and protection circuits, since damaged cells can catch fire. See Batteries.
Little pistol: Slang for a modest station with low power and simple antennas, the opposite of a big gun. Little pistols work plenty of DX with patience; see Ham radio slang.
LMR-400: A popular low-loss 50-ohm coaxial cable about 0.4 inches in diameter, widely used for VHF and UHF feed lines. See Coaxial cable.
LO (local oscillator): The oscillator in a receiver or transmitter whose signal is mixed with another to convert it to a different frequency. See Oscillators.
Load: Whatever receives power from a source, such as an antenna or a dummy load. On tube amplifiers, the load control adjusts output coupling for best power transfer.
Loaded Q: The Q of a resonant circuit when it is connected to its load. It is lower than unloaded Q and sets the circuit's real bandwidth. See Resonance and Q.
Loading coil: An inductor added to an electrically short antenna to bring it to resonance. Common in mobile whips and shortened verticals. See Loading coil.
Local control: Operating a station with the control operator physically present at the station's control point, the most common arrangement. Compare remote control.
Log: A record of contacts, typically date, time, frequency, mode and callsign. FCC rules no longer require most logging, but logs are needed for QSLs and awards. See QSL cards and logging.
Log periodic (LPDA): A directional antenna with progressively sized elements that covers a wide frequency range with moderate gain. See Log-periodic antenna.
Logic gate: A digital circuit that performs a basic logical operation such as AND, OR or NOT on its inputs. Gates are combined to build every digital device. See Digital logic.
Logic level: The voltage ranges that represent a digital 1 and 0, such as 0 and 3.3 volts. Mixing 5-volt and 3.3-volt logic without conversion can damage chips; see Digital logic.
Long path: A signal path taking the longer way around the great circle between two stations. It sometimes beats the short path at dawn or dusk. See Long path and short path.
Long wire: A wire antenna at least one wavelength long at the operating frequency, though the term is often used loosely for any end-fed wire. See Random wire antenna.
LoRa: A low-power spread-spectrum modulation that carries small amounts of data over long distances. Meshtastic uses it, often in the 902 to 928 MHz band.
LoTW (Logbook of the World): ARRL's free online system for confirming contacts electronically. Its confirmations count toward DXCC, WAS and other major awards. See Logbook of the World.
Low bands: The lower HF and MF bands, usually 160, 80 and 40 meters, which work best at night. Big antennas and low noise help most here; see 160-meter band.
Low-pass filter: A filter that passes frequencies below its cutoff and blocks those above. Placed after an HF transmitter, it reduces harmonics; see Harmonics and spurious emissions.
LUF (lowest usable frequency): The lowest frequency that works on a given path, below which D-layer absorption weakens signals too much. Operate between the LUF and MUF; see Propagation prediction.

M

M17: An open-source digital voice mode that uses the free Codec 2 vocoder instead of proprietary codecs. It runs on modified radios, hotspots and dedicated hardware. See M17.
Machine: Slang for a repeater, as in "meet you on the machine after dinner." See also Repeaters.
Mag mount (magnet mount): A magnetic antenna base that attaches to a vehicle's steel roof without drilling. Good for temporary installs, though it can scratch paint. See Mobile antennas.
Magic band: Nickname for 6 meters, because of its sudden, unpredictable openings via sporadic E and other propagation. See 6-meter band.
Magnetic field: The region of force around a magnet or a current-carrying conductor. Inductors and transformers store and transfer energy through it; see Inductors.
Magnetic loop (mag loop, small transmitting loop): A small loop antenna tuned to resonance by a capacitor. It has very narrow bandwidth and develops high voltage across the capacitor, but performs well in tight spaces. See Magnetic loop antenna.
Maidenhead: The worldwide locator system that divides Earth into fields, squares and subsquares identified by letters and numbers, such as FN31pr. See Grid squares.
Malicious interference: Deliberately interfering with other stations' communications, which FCC rules prohibit. Do not respond on the air; report persistent cases. See Volunteer Monitor program.
Maritime mobile: Operating from a boat or ship, often signing "/MM" after the callsign. Maritime mobile nets help sailors with weather and position reports; see Mobile operating.
MARS (Military Auxiliary Radio System): A Defense Department program in which licensed hams train and pass traffic on military frequencies to support emergency communications. See MARS.
Mast: A pole that supports antennas, lighter and simpler than a tower. Telescoping fiberglass masts are popular for portable operating and Field Day.
MDS (minimum discernible signal): The weakest signal a receiver can detect above its own noise, given in dBm. Lower numbers mean better sensitivity; see Receiver performance.
Memory channel: A stored frequency together with settings such as offset, tone and mode. Programming software such as CHIRP makes loading many channels easy.
Meshtastic: An open-source system for off-grid text messaging over inexpensive LoRa radios, which relay messages for each other. See Meshtastic.
Meteor scatter: Reflecting VHF signals off the ionized trails of meteors, allowing brief contacts out to about 1,400 miles. Best during major meteor showers. See Meteor scatter.
Metric prefixes: Prefixes that scale units, such as kilo (thousand), mega (million), milli (thousandth), micro (millionth) and pico (trillionth). For example, 14,250 kHz equals 14.250 MHz.
MF (medium frequency): The range from 300 kHz to 3 MHz, which includes the 630-meter and 160-meter amateur bands and AM broadcasting.
MFSK (multiple frequency-shift keying): A family of digital modes that send data using many tones rather than two. It resists fading and noise; Olivia and FT8 are examples.
Mic gain: The setting that controls microphone amplification. Too much causes distorted audio and splatter; set it so ALC action stays within the recommended range.
Mica capacitor: A capacitor using mica as its dielectric, prized for stability and low loss. Silver mica types are common in RF tuned circuits and filters; see Capacitors.
Microcontroller: A small computer on a single chip, with processor, memory and inputs and outputs. Boards such as Arduino put them in keyers, controllers and many homebrew projects.
Microvolt: One millionth of a volt, written µV. Receiver sensitivity is often given in microvolts, and an S9 signal on HF is defined as 50 µV; see Signal reports.
Microwave: Radio frequencies above about 1 GHz. Amateur microwave bands start at 23 centimeters and need careful construction and low-loss feed lines; see 23-centimeter band.
Mixer: A circuit that combines two signals to produce their sum and difference frequencies. Mixers are central to superheterodyne receivers and transverters. See Mixers.
Mobile: Operating while in a vehicle, whether in motion or temporarily stopped. Most mobile stations run 2-meter and 70-centimeter FM, and many also run HF. See Mobile operating.
Mobile whip: A vertical antenna for a vehicle, such as a quarter-wave 2-meter whip or a loaded HF whip. See Mobile antennas.
Mode: The type of transmission, such as CW, SSB, FM, RTTY or FT8. Band plans assign different segments to different modes. See also Band plan.
Mode (satellite): A designation of the bands a satellite uses for uplink and downlink, written as uplink then downlink, such as V/U. See Amateur satellites.
Mode V/U (Mode J): A satellite configuration with the uplink on 2 meters (VHF) and the downlink on 70 centimeters (UHF). Many FM and linear transponder satellites use it.
Modulation: Impressing information onto a carrier by varying its amplitude, frequency or phase. AM, FM, SSB and digital modes are all forms of modulation.
Monopole: An antenna with a single radiating element, using the ground or radials as its other half. A quarter-wave vertical is the most common example.
Monostable multivibrator (one-shot): A circuit that produces a single output pulse of fixed length each time it is triggered. The 555 timer is often wired as one; see Digital logic.
MOSFET: Metal-oxide-semiconductor field-effect transistor, widely used in RF power amplifiers and switching supplies. MOSFETs are easily damaged by static discharge. See Transistors.
Moxon: A two-element wire beam shaped like a rectangle with folded-in ends. It gives good gain and an excellent front-to-back ratio in a compact size. See Moxon antenna.
MPE (maximum permissible exposure): The FCC limits on human exposure to RF energy, which vary with frequency. Hams must evaluate their stations to make sure people nearby stay within them. See RF exposure.
MPPT (maximum power point tracking): A solar charge controller technique that continuously adjusts its load to draw the most power from a panel. MPPT controllers are efficient but can generate RF noise.
MSHV: A free Windows and Linux program supporting FT8, FT4, MSK144 and other WSJT-style modes. Its multi-stream feature lets DXpeditions work several stations at once; see DXing.
MSK144: A WSJT-X digital mode designed for meteor scatter, decoding the brief pings from meteor trails. It is used mainly on 6 and 2 meters; see Meteor scatter.
MUF (maximum usable frequency): The highest frequency that the ionosphere will return to Earth on a given path. The best signals are usually just below it; see Propagation prediction.
Multi-hop: Propagation in which a signal bounces between the ionosphere and the ground several times, carrying it beyond single-hop range. Each hop adds loss. See also Radio propagation.
Multimeter: A test instrument that measures voltage, current and resistance, often with continuity and other functions. It is the first tool most hams buy. See Multimeter.
Multipath: Reception of the same signal over several paths of different lengths. The arrivals interfere, causing fading, distortion and mobile "picket fencing."
Multiplexer (mux): A circuit that selects one of several inputs and routes it to a single output. In RF work, a multiplexer also combines several bands onto one feed line.
Multiplier: In contests, a unique item such as a state, zone or country that multiplies your total contact points. Working new multipliers raises scores fastest.

N

N connector (N-type): A threaded, weatherproof coaxial connector with low loss well into the microwave range. Among RF connectors, it is the usual choice for UHF antennas and outdoor runs.
N1MM Logger+: A free Windows program and one of the most widely used kinds of Logging software for Contesting. It checks dupes, tracks multipliers, sends CW and voice messages, and controls the radio.
NAND gate: A Digital logic gate whose output goes low only when every input is high. Because any logic function can be built from NAND gates alone, they are a staple of homebrew circuits.
NanoVNA: A low-cost, open-source handheld vector network analyzer. It measures SWR, impedance, and filter response, making it a popular budget alternative to a commercial Antenna analyzer.
Narrowband: A signal or channel that occupies little bandwidth. On VHF and UHF FM, narrowband usually means 12.5 kHz channels with about 2.5 kHz deviation, versus 25 kHz wideband channels.
NCVEC: The National Conference of Volunteer Examiner Coordinators, the body through which US VECs work together. Its Question Pool Committee writes the Question pools used on every US license exam.
Near field: The region close to an antenna, within a wavelength or so, where electric and magnetic fields have not yet settled into a radiated wave. It complicates RF exposure evaluations at close range.
Net: A scheduled on-air gathering where stations check in, usually under a net control station, to pass traffic, share information, or practice emergency procedures. See Nets.
Net control: The station that runs a net: it opens the session, takes check-ins, keeps order, and decides who transmits when. See Net control station.
Net script (Preamble): The written text a net control station reads to open and run a net, explaining its purpose, rules, and check-in procedure. Many Nets share theirs so new operators can take a turn.
Neutron: An uncharged particle found alongside protons in an atom's nucleus. Neutrons add mass but play no direct part in electric current, which is carried by electrons.
NMO mount: A widely used permanent mobile antenna base that needs a hole drilled in the vehicle's roof. Its standard thread lets you swap among many Mobile antennas in seconds.
Node: A connection point in a radio or internet network, such as a Packet radio station, an AllStarLink link, or a mesh radio that relays traffic for others.
Noise blanker: A receiver circuit that removes short, sharp pulses, such as ignition or electric fence noise, by briefly silencing the receiver during each pulse. See Noise blanker and noise reduction.
Noise figure: A measure, in decibels, of how much noise a receiver or amplifier adds to a signal. A low noise figure matters most on VHF and up, where a good Preamplifier helps.
Noise floor: The level of background noise, from the receiver and its surroundings, below which signals vanish. On HF, local man-made noise usually sets it, so tackling Radio frequency interference often helps more than a new radio.
Non-resonant antenna (Non-resonant dipole): An antenna not cut to resonate on the operating frequency, such as a doublet fed with ladder line. It needs an Antenna tuner but can cover several bands with one wire.
NOR gate: A Digital logic gate whose output is high only when every input is low. Like the NAND gate, it can be combined to build any other logic function.
Notch filter: A filter that removes a narrow slice of frequencies while passing everything else. Hams use it to cut a steady carrier or heterodyne whistle out of a Single sideband signal.
Novice and Advanced: Former US license classes. The FCC stopped issuing new Novice and Advanced licenses in 2000, but existing holders can still renew them and keep their privileges. Today's path is described in Getting licensed.
NR (noise reduction): DSP processing that reduces random hiss and background noise so weak voice or CW signals are easier to hear. Too much makes audio sound watery. See Noise blanker and noise reduction.
NTS (National Traffic System): The ARRL's organized network of nets that relays formal written messages, called radiograms, across the country and supports emergency message handling. See National Traffic System.
NTSC: The analog color television standard long used in North America. Most analog fast-scan Amateur television in the US uses NTSC video, typically on 70 centimeters and higher bands.
NVIS: Near vertical incidence skywave: signals sent nearly straight up and reflected back down, giving gap-free coverage out to a few hundred miles on 40, 60, and 80 meters. See NVIS.
NXDN: A narrowband digital voice and data protocol developed by Icom and Kenwood, used in commercial radio and on some ham repeaters. It cannot talk to DMR or D-STAR radios.
Nyquist rate: The minimum sampling rate, twice the highest frequency being captured, needed to digitize a signal without aliasing. It sets how much spectrum a Software-defined radio can show at once.

O

Occupied bandwidth: The width of spectrum a transmitted signal actually takes up. It matters near band edges, since your whole signal, not just the dial frequency, must stay inside your privileges.
Octave: A doubling or halving of frequency, such as from 7 MHz to 14 MHz. Filter steepness is often stated in decibels per octave, and harmonics fall an octave apart.
OFDM: Orthogonal frequency-division multiplexing: data spread across many closely spaced carriers sent at once. It resists fading and multipath and is used by HF data modes such as VARA.
Off-center-fed dipole (OCF, Windom): A dipole fed about one-third of the way from one end, usually through a 4:1 balun, so it presents a manageable impedance on several bands. See Off-center-fed dipole.
Offset (Repeater offset, shift): The frequency difference between what Repeaters receive and transmit. Standard US offsets are 600 kHz on 2 meters and 5 MHz on 70 centimeters; set it wrong and the repeater won't hear you.
Ohm (Ω): The unit of resistance, reactance, and Impedance. One volt across one ohm drives one amp; most ham radios, coax, and antennas are designed around 50 ohms.
Ohm's law: The relationship between voltage, current, and resistance, written E = I × R. It is the most-used formula in ham electronics and appears on the license exams. See Ohm's law.
Old timer (OT): A ham who has been licensed for many years. In Ham radio slang it is usually a term of respect for an operator with deep experience and good stories.
Olivia: A robust MFSK digital mode that copies through heavy noise and fading, popular for keyboard chats and nets on HF when conditions are poor. See Olivia.
OM (old man): Classic Ham radio slang for any male operator, whatever his age, as in "thanks for the call, OM." Hams often refer to a fellow operator as "the OM."
Op-amp (Operational amplifier): A high-gain integrated amplifier with two inputs, used with a few external parts to build audio filters, preamps, and comparators. See Operational amplifiers.
Open circuit: A break in a circuit, such as a broken wire, loose connector, or blown fuse, so no current can flow. A meter reads infinite resistance across it.
Open collector (Open drain): An output that can pull a line to ground but needs an external pull-up resistor to go high. It is a common way to key PTT or CW in a Digital mode interface.
Optoisolator (Optocoupler): A part that passes a signal through an LED and light sensor with no electrical connection between sides. In a Digital mode interface it isolates computer from radio, helping prevent ground loops.
OQRS (Online QSL Request Service): An online form, most often on Club Log, that lets a caller request a DX station's paper QSL card, direct for a fee or through the bureau, without sending a card first. See QSL cards and logging.
Orbital period: The time a satellite takes to complete one orbit. Most Amateur satellites are in low Earth orbit and circle the planet in roughly 90 to 120 minutes.
Oscillator: A circuit that generates a steady signal at a set frequency. Every transmitter and receiver relies on oscillators for tuning, mixing, and producing the carrier. See Oscillators.
Oscilloscope (Scope): An instrument that draws voltage against time as a trace on a screen. Hams use it to check waveforms, audio, power supply ripple, and transmitter modulation. See Oscilloscope.
Out: A procedural word meaning "I am finished and expect no reply." Saying "over and out" together is contradictory and best avoided, as Operating etiquette guides point out.
Out-of-band emission: Unwanted energy just outside a signal's necessary bandwidth, caused by the modulation itself, such as splatter from overdriving. It is distinct from Harmonics and spurious emissions that land farther away.
Over: A procedural word meaning "I'm done; your turn to reply." Useful on simplex voice, but rarely needed on repeaters, where the courtesy tone does the same job.
Overdrive: Feeding more signal into an amplifier or transmitter stage than it can handle cleanly. Overdriving Amplifiers causes distortion and splatter, so watch your ALC reading.
Overmodulation: Modulating a transmitter beyond 100 percent, or driving it too hard, which distorts the signal and spreads it onto neighboring frequencies. Keep mic gain moderate, especially on AM.

P

P25: Project 25, a digital radio standard built for US public safety agencies. Some hams use surplus P25 radios and run P25 repeaters, mostly on VHF and UHF.
Packet: Digital data sent in short, error-checked bundles, usually AX.25 at 1200 baud on VHF. It carries APRS, bulletin boards, and keyboard messaging. See Packet radio.
PACTOR: A family of HF data modes that use error correction to deliver files and email reliably, especially through Winlink. Its higher versions require a commercial modem. See Pactor.
Paddle: A Morse key with one or two levers pressed sideways, used with an electronic keyer that forms the dits and dahs automatically. See Morse keys and paddles.
Panadapter (Spectrum scope): A live graph of signals across a slice of band, often with a waterfall below, so you can spot activity and click to tune. See Panadapter.
Parallel circuit: A circuit where components connect across the same two points, so each gets the same voltage and their currents add. Total resistance is lower than that of any single resistor.
Parasitic element: An antenna element not connected to the feed line that reradiates energy to shape the pattern, such as a director or reflector on a Yagi antenna.
Parasitic oscillation: Unwanted self-oscillation in an amplifier, often far from the operating frequency. It can cause spurious signals, overheating, and ruined tubes or transistors in Amplifiers.
Part 97: The section of FCC rules that governs the US Amateur Radio Service, covering licensing, operating practices, technical standards, and station identification. See Part 97.
Passband: The range of frequencies a filter lets through with little loss. A receiver's passband, such as 2.4 kHz for SSB, sets how much spectrum you hear at once.
Passband ripple (Ripple): Small ups and downs in a filter's response across its passband; less ripple means a flatter, more natural sound. Ripple also means leftover AC on a DC supply's output.
Patch lead (Jumper, patch cable): A short cable with connectors on both ends linking station gear, such as radio to SWR meter. Use good Coaxial cable and connectors, since cheap jumpers can add loss and faults.
Payload: The equipment a satellite, balloon, or rocket carries to do its job, such as a transponder, tracker, or camera. High-altitude balloons often carry APRS or WSPR payloads.
PCB (printed circuit board): A board with copper traces that connect components in place of loose wires. Most kits use one, and cheap online fabrication puts custom boards within reach for Homebrewing.
Peak value (Peak voltage): The highest instantaneous voltage or current in a waveform. For a sine wave the peak is about 1.414 times the RMS value, a ratio explained in RMS and peak values.
Peak-to-peak: The voltage difference between a waveform's positive and negative peaks, the easiest value to read on an Oscilloscope. For a sine wave it is twice the peak value.
PEP (peak envelope power): The average power a transmitter delivers during the highest crest of its modulation. Most US amateur power limits, including the 1,500-watt maximum, are stated in PEP. See PEP and power measurement.
Perfboard (Protoboard): A board with a grid of pre-drilled holes, sometimes with copper pads, for building permanent circuits by soldering parts and wires. It suits one-off Homebrewing projects.
Perigee: The point in an orbit where a satellite comes closest to Earth. Satellites in elliptical orbits move fastest near perigee, so passes there are short.
Permeability: How easily a material carries magnetic flux. Ferrite and powdered-iron cores have high permeability, so coils wound on them need fewer turns for the same inductance; see Inductors.
Phase: The position of a point within a wave's cycle, measured in degrees. Two equal signals in phase add together, while signals 180 degrees out of phase cancel.
Phase noise: Random jitter in an oscillator that spreads its signal slightly. In a receiver it lets strong nearby signals mask weak ones; in a transmitter it adds noise beside the signal. See Receiver performance.
Phased array: Two or more antennas fed with controlled phase differences so their signals reinforce in some directions and cancel in others. Switching the phasing steers the pattern, as in four-square Vertical antenna arrays.
Phasor: An arrow representing a sine wave's amplitude and phase. Phasors make it easy to add AC voltages and currents or to combine resistance and reactance into Impedance.
Phillips Code: A system of abbreviations created in 1879 so press telegraphers could move news faster by Morse code. Terms such as POTUS and SCOTUS come from it.
Phone: Any voice mode, such as SSB, AM, or FM. "Phone privileges" and "phone segments" refer to the parts of the Amateur radio bands where voice is allowed.
Phonetic alphabet: Standard words for each letter, such as Alfa, Bravo, and Charlie, used to spell callsigns clearly on voice. Hams use the ITU set. See Phonetic alphabet.
Photodiode: A diode that conducts current in proportion to the light falling on it. Photodiodes are used in light sensors, optical links, and inside optoisolators; see Diodes.
Photon: A single packet of electromagnetic energy. Radio waves, light, and X-rays all consist of photons that differ only in frequency, and each radio photon carries very little energy.
Picket fencing: Rapid fluttering of a VHF or UHF FM signal, usually heard when a moving station passes through reflections and shadows. It is worst near the edge of range during Mobile operating.
Pileup (Pile-up): Many stations calling one station at once, typically a rare DX station or DXpedition. In DXing, careful listening and well-timed calls beat calling nonstop.
PIN diode: A diode with an undoped middle layer that acts as a variable resistor at RF. It switches antennas and handles transmit/receive switching in amplifiers; see Diodes.
PL-259: The male UHF coaxial plug used on most HF and many VHF cables, mating with the SO-239 jack. Soldering one properly is a classic skill among RF connectors.
PLL (phase-locked loop): A feedback circuit that locks an oscillator to a stable reference, letting a radio tune in precise, stable steps. Most synthesized radios use PLLs, DDS, or both; see Oscillators.
Polarity: Which side of a circuit is positive and which is negative. Reversing DC power polarity can destroy a radio instantly, so check leads carefully when connecting Power supplies.
Polarization: The orientation of an antenna's electric field: vertical, horizontal, or circular. Matching it matters on VHF and UHF, where a mismatch can cost 20 dB or more. See Polarization.
Portable: Operating away from home with gear you carry and set up, such as in a park, campsite, or on a summit. See Portable operating.
Portable designator: An indicator added to a callsign, such as /P, /M, or /KH6, showing portable, mobile, or out-of-area operation. US hams may use one but usually need not within the country; see Call signs.
POTA: Parks on the Air, a popular program in which activators operate portable from parks and hunters contact them from home or elsewhere. See Parks on the Air.
Potentiometer: A variable resistor with a sliding contact, used for volume, gain, and other adjustable controls. It also works as an adjustable voltage divider; see Resistors.
Powdered iron core: A magnetic core made of fine iron particles bound together, common in toroids for RF coils. It is more stable than ferrite in tuned circuits but has lower permeability; see Inductors.
Power: The rate at which energy is used or delivered, measured in watts. In a DC circuit, power equals voltage times current, a companion to Ohm's law.
Power factor: In AC circuits, the ratio of true power to apparent power. A power factor of 1 means voltage and current are in phase, with no reactive power circulating; see AC and DC.
Power supply: A unit that converts AC mains to the steady DC a radio needs, typically 13.8 volts. Choose one rated for your rig's full transmit current. See Power supplies.
Preamp: A low-noise amplifier placed ahead of a receiver to boost weak signals. It helps most on VHF and up; on the lower HF bands it often just amplifies noise. See Preamplifier.
Prefix: The first part of a callsign, letters plus a digit, that identifies the country and often the region. US prefixes begin with A, K, N, or W; see Call signs.
Preselector: A tunable filter ahead of a receiver that passes the wanted band and rejects strong out-of-band signals, reducing overload and images. See Receiver performance for related measures.
Primary allocation: A band or segment where a radio service has first rights to the spectrum. Amateurs are primary on bands such as the 20-meter band; secondary users must not interfere with primary ones.
Privileges: The bands, modes, and power a license class allows you to use. Technician, General, and Amateur Extra privileges differ mainly on HF; see Getting licensed.
Product detector: A receiver stage that mixes the incoming signal with a local carrier to recover audio from Single sideband and CW. It replaced the simple diode detector used for AM.
Programming cable: A USB cable that connects a radio, usually a handheld, to a computer so you can load channels and settings with software like CHIRP. Cheap clones sometimes need special drivers.
Propagation: How radio waves travel from transmitter to receiver, whether by line of sight, ground wave, ionospheric skip, or other paths. See Radio propagation.
Prosign: A Morse character sent as one run-together symbol to signal procedure, such as AR for end of message or SK for end of contact. See Prosigns.
Proton: A positively charged particle in an atom's nucleus. Its charge equals the electron's but is opposite in sign, and the number of protons defines the element.
PSK (phase-shift keying): A digital modulation that sends data by shifting a carrier's phase. It is efficient and narrow, and it underlies many modes, including PSK31.
PSK Reporter: A website that maps automatic reception reports from digital mode software worldwide. Call CQ on FT8 and you can see where you are heard within minutes. See PSK Reporter.
PSK31: A narrow keyboard-to-keyboard digital mode using phase-shift keying, popular for low-power HF chats. Each signal is only about 60 Hz wide. See PSK31.
PTT (push to talk): The switch that keys a transmitter while pressed. It may sit on a microphone or foot switch, or be controlled by computer software. See VOX and PTT.
Pull-up resistor: A resistor that holds a digital input at its high voltage when nothing else drives it, preventing erratic readings. It is required with open-collector outputs; see Digital logic.

Q

Q factor (Q): A measure of how sharply a component or resonant circuit responds: reactance divided by resistance. High Q means low loss and narrow bandwidth. See Resonance and Q.
Q-code: Three-letter codes beginning with Q, such as QTH for location and QRM for interference, used as shorthand on CW and often on voice. See Q-codes.
Q65: A weak-signal digital mode in WSJT-X built for tough paths such as moonbounce, ionospheric scatter, and rain scatter on VHF and up. It decodes signals far below audibility.
QAM (quadrature amplitude modulation): A modulation that varies both amplitude and phase to pack several bits into each symbol. It gives high data rates but needs clean, strong signals.
QRO: The Q-code for "increase power"; in slang, high-power operation, usually with an amplifier. It is the opposite of QRP.
QRP: Low-power operating, commonly defined as 5 watts or less on CW and 10 watts or less on SSB. Operators enjoy the challenge and the small, portable gear. See QRP.
QSL bureau (Buro): A service that collects and sorts QSL cards in bulk, cutting postage costs for international exchanges. The ARRL runs the outgoing bureau for its members. See QSL bureau.
QSL card: A postcard confirming a contact, showing callsigns, date, time, band, and mode. Cards are collected for awards and kept as souvenirs. See QSL cards and logging.
QSL manager: A ham who handles QSL replies for another station, often a DXpedition or busy DX operator. Look for "QSL via" notes before sending a card; see QSL cards and logging.
QSO party: A contest centered on a state, province, or region, where everyone tries to work as many in-area stations and counties as possible. See QSO parties.
Quad: A directional antenna made of square or diamond-shaped wire loops, each about one wavelength around, with gain similar to a somewhat larger Yagi. See Cubical quad antenna.
Quantization: Rounding each sample of an analog signal to the nearest digital level during conversion. More bits mean finer steps, less noise, and more dynamic range in a Software-defined radio.
Quarter-wave vertical: A vertical radiator one-quarter wavelength long, worked against Radials and counterpoises or a ground plane. Simple and omnidirectional, it is a classic first antenna.
Question pool: The public bank of questions from which every US license exam is drawn. Each pool is revised on a four-year cycle. See Question pools.
Question pool committee (QPC): The NCVEC committee that writes and updates the three US exam Question pools, releasing each new version well before it takes effect.

R

RAC (Radio Amateurs of Canada): Canada's national amateur radio association, comparable to the ARRL in the US. It represents Canadian hams to government and sponsors contests and awards.
RACES: The Radio Amateur Civil Emergency Service, in which hams register with government emergency management agencies to provide communications during emergencies. See RACES.
Radial: A wire laid on or above the ground, running outward from a vertical antenna's base to form the return path that makes the antenna efficient. See Radials and counterpoises.
Radiation pattern: A plot showing how strongly an antenna radiates in each direction, either around the horizon or at different elevation angles. Antenna modeling software calculates it.
Radiation resistance: The part of an antenna's feedpoint resistance that represents power actually radiated. Small antennas have very low radiation resistance, which is why a Magnetic loop antenna needs thick, low-loss conductors.
Radio blackout: A loss of HF signals on the sunlit side of Earth caused by X-rays from a solar flare. NOAA rates blackouts on a scale from R1 to R5; see Space weather.
Radio direction finding (RDF, fox hunting): Locating a transmitter by taking bearings with directional antennas. Hams do it for sport and to track down interference or stuck transmitters. See Fox hunting.
Radio horizon: The farthest distance a VHF or UHF signal reaches by line of sight. Slight bending in the atmosphere makes it about 15 percent farther than the visual horizon; see VHF.
Radiogram: A formal written message in the ARRL standard format, with preamble, address, text, and signature, passed through the National Traffic System.
Rag chew: A relaxed, open-ended conversation on the air, as opposed to a quick contest or DX exchange. See Ragchewing.
Random wire: A wire antenna of convenient length, not cut for resonance, usually fed through a 9:1 unun and a tuner. It is easy to deploy for portable, multiband work. See Random wire antenna.
Raspberry Pi: A small, low-cost Linux computer popular with hams. It runs Hotspots, APRS gateways, logging programs, and digital mode software.
RBN (Reverse Beacon Network): A worldwide network of automated receivers that decode CW and RTTY signals and report who is heard where. Use it to check propagation and your own signal. See Reverse Beacon Network.
REACT: REACT International, a volunteer group long known for monitoring CB emergency channel 9 that now also uses GMRS and ham radio, often supporting community events; see FRS and CB.
Reactance: Opposition to AC from capacitors and inductors, measured in ohms. Unlike resistance, it stores and returns energy instead of turning it into heat, and it changes with frequency; see Impedance.
Reactive power: Power that flows back and forth between source and a reactive load each cycle without being consumed, measured in volt-amperes reactive (VAR); see AC and DC.
Reciprocal mixing: Receiver noise created when a strong nearby signal mixes with the phase noise of the local oscillator. It masks weak signals even without overload; see Receiver performance.
Reciprocal operating: Operating in another country under its rules using your home license, through arrangements such as CEPT, IARP, or bilateral agreements. See Operating abroad.
Rectifier: A diode or circuit that converts AC to pulsating DC, the first stage in most linear power supplies. Bridge rectifiers use four Diodes to use both halves of the cycle.
Reflected power: Power returned from a mismatched antenna or feed line toward the transmitter. A high SWR means more reflected power, and many radios cut output to protect themselves.
Reflector: A parasitic element slightly longer than the driven element, placed behind it in a beam antenna to push the signal forward, as on a Yagi antenna.
Relay: An electrically operated switch in which a coil pulls contacts open or closed. Hams use relays for antenna switching, amplifier keying, and transmit/receive changeover.
Remote control: Operating a station from another location over the internet or a radio link. Part 97 allows it, with the control operator as responsible as if on site. See Remote operation.
Remote tuner (Remote auto tuner): An automatic Antenna tuner mounted outdoors at the antenna feedpoint instead of in the shack. It avoids feed-line loss from high SWR on multiband wire antennas.
Repeater: A station, usually on a hill or tower, that receives on one frequency and retransmits on another, greatly extending handheld and mobile range. See Repeaters.
Resistance: Opposition to current flow, measured in ohms, which turns electrical energy into heat. It ties voltage and current together through Ohm's law.
Resistor: A component that adds a set amount of resistance to a circuit, used to limit current, divide voltage, and bias transistors. See Resistors.
Resonance: The frequency at which an antenna or tuned circuit's inductive and capacitive reactances cancel, leaving pure resistance. A resonant antenna is usually easy to match. See Resonance and Q.
Resonant circuit (Tuned circuit): An inductor and capacitor combined to respond strongly at one frequency. Tuned circuits select stations in receivers and filter harmonics in transmitters; Resonance and Q covers the basics.
Return loss: How much weaker the reflected signal is than the forward signal, in decibels. Higher return loss is better; 20 dB equals an SWR of about 1.22:1.
Reverse split: Swapping transmit and receive frequencies, usually with a radio's REV button, to listen on a repeater's input. If you hear the other station directly, move to Simplex.
RF burn: A burn from touching an antenna or conductor carrying RF current. RF burns can be deep and painful even at modest power, so keep antennas out of reach; see RF exposure.
RF exposure: The absorption of radio energy by the body. The FCC requires hams to evaluate their stations to keep exposure within safe limits. See RF exposure.
RF in the shack: Stray RF from your own transmitter showing up on mic cables, computers, and chassis, causing distorted audio, glitches, or tingly metal. A Common-mode choke on the feed line often cures it.
RF power meter: An instrument that measures transmitter output, often reading forward and reflected power and sometimes PEP. See PEP and power measurement for how readings differ.
RF safety: Practices that protect people from RF burns and excessive exposure, such as keeping antennas high and away from people and evaluating your station's RF exposure.
RFI (radio frequency interference): Unwanted signals that disrupt radio reception or electronic equipment, whether your signal affecting a neighbor's TV or a noisy device ruining your reception. See Radio frequency interference.
RG-213: A thick 50-ohm Coaxial cable about 0.4 inch across that handles high power with moderate loss. A durable choice for HF feed lines.
RG-58: A thin, flexible 50-ohm Coaxial cable that is easy to handle but lossy at VHF and up. Best for short jumpers and low-power HF.
RG-8X: A medium-size 50-ohm Coaxial cable, thinner than RG-213 but lower loss than RG-58. A popular compromise for portable work and moderate HF runs.
Rig: Ham radio slang for a radio, especially a transceiver. "My rig" usually means the main radio in your station.
RIT (Clarifier): Receiver incremental tuning: shifts your receive frequency slightly without moving your transmit frequency, to tune in a station that is a bit off frequency. See RIT and XIT.
RMS (root mean square): The effective value of an AC voltage or current, equal to the DC value that would produce the same heating. For a sine wave it is 0.707 of peak. See RMS and peak values.
Roger: Voice procedure meaning "message received and understood." Strictly it does not mean yes or agreement, though hams often use it casually that way; see Operating etiquette.
Roofing filter: A filter placed early in a receiver, right after the first mixer, that blocks strong signals outside the wanted range before they cause overload. It matters most in crowded contests; see Receiver performance.
Rotator (Rotor): A motorized unit that turns a beam antenna to point it in any direction, controlled from the shack. See Rotators.
Rover: A station that travels between Grid squares during a VHF contest, giving others new multipliers. Rovers often carry antennas for several bands.
RR73: FT8 and FT4 shorthand meaning "roger, report received, and 73," sent to close a contact. Many operators consider an FT8 QSO complete once it is sent.
RSGB (Radio Society of Great Britain): The national amateur radio society of the United Kingdom, publisher of RadCom magazine and many technical books, and a sponsor of contests and awards.
RST: The classic signal report: Readability 1–5, Strength 1–9, and Tone 1–9 (CW only). "599" is the best and most common report. See Signal reports.
RTTY: Radioteletype, an older digital mode using frequency-shift keying at 45.45 baud. It remains popular in contests and on DXpeditions. See RTTY.
Rubber duck: The short, flexible antenna supplied with most handheld radios. It is convenient but inefficient, so a longer antenna often improves range noticeably; see Handheld antennas.
Rubber-stamp contact: A brief, formulaic QSO exchanging only signal report, name, location, and rig before 73. Fine for a quick contact; Ragchewing goes further.
Run: In contesting, holding one frequency and calling CQ while others answer you. A good run can produce well over a hundred contacts per hour; see Contesting.

S

S unit (S point): A step on a receiver's S meter. By convention one S unit is 6 dB and S9 is a 50-microvolt signal on HF, though few radios are calibrated accurately; see Signal reports.
Safety ground: The green-wire connection to equipment chassis that carries fault current to trip a breaker, protecting people from shock. It is distinct from an RF ground; see Grounding and lightning protection.
Sampling rate: How many times per second an analog signal is measured during digitizing. In a Software-defined radio it sets how much spectrum you can see at once.
SASE: A self-addressed stamped envelope, sent with your QSL card so the other station can reply at no cost. International cards often need extra return postage; see QSL cards and logging.
Satellite pass (Pass): The period when a satellite is above your horizon and usable, often only 10 to 15 minutes for low-orbit Amateur satellites. Tracking apps predict pass times.
SATERN: The Salvation Army Team Emergency Radio Network, a ham volunteer network supporting Salvation Army disaster relief with communications and health-and-welfare traffic; see Emergency communications.
Scatter: Propagation in which signals bounce off irregularities in the atmosphere or ionosphere, reaching stations otherwise out of range, such as the ionized trails used for Meteor scatter.
Schematic: A diagram showing a circuit's components and connections with standard symbols. Learning to read schematics is a key Homebrewing skill.
Schottky diode: A diode with a low forward voltage drop, about 0.3 volts, and fast switching. It is used in power supplies, reverse-polarity protection, and RF detectors; see Diodes.
SCR (silicon-controlled rectifier): A semiconductor switch that latches on when triggered and stays on until current stops. Power supplies use one as a crowbar to protect radios from overvoltage.
Screwdriver antenna: An HF mobile antenna with a motor-driven coil that changes its electrical length, letting you tune across bands from the driver's seat; see Mobile antennas.
SDR (software-defined radio): A radio that digitizes signals and processes them in software, allowing flexible modes, filters, and a live spectrum display. See Software-defined radio.
Search and pounce (S&P): A Contesting technique of tuning the band to find and call stations, rather than calling CQ on one frequency.
Secondary allocation: A band where amateurs share spectrum with a primary service and must not interfere with it, while accepting interference from it. The 30-meter band is one example.
Selectivity: A receiver's ability to separate a wanted signal from others close in frequency, determined mostly by its filters; see Receiver performance.
Semiconductor: A material such as silicon whose conductivity falls between conductors and insulators and can be controlled. It is the basis of diodes, transistors, and chips. See Semiconductors.
Sensitivity: How weak a signal a receiver can detect. Modern receivers are sensitive enough that on HF, outside noise usually limits reception first; see Receiver performance.
Sequential callsign: A callsign the FCC assigns automatically, in order, from those available for your license class and region. You can change it later through the Vanity call signs program.
Series circuit: A circuit where components connect end to end, so the same current passes through each and their voltages add. Total resistance is the sum of each resistor.
Service monitor: A test set combining a signal generator, receiver, deviation meter, and often a spectrum analyzer. It is used for aligning FM radios and maintaining Repeaters.
Shack: The room or space where a ham keeps their station, whether a dedicated room, a closet, a desk corner, or a car. See Ham shack.
Shack in a box: A compact transceiver covering HF through VHF and UHF with many modes in one unit, ideal for Portable operating or small stations.
Shielding: A conductive enclosure or braid that keeps RF in or out of a circuit or cable. Good shielding reduces Radio frequency interference in both directions.
Shift register: A Digital logic circuit of chained flip-flops that moves bits one position per clock pulse, often used to convert serial data to parallel.
Short circuit (Short): An unintended low-resistance path that lets excessive current flow, blowing fuses or damaging parts. Fuse DC leads close to the battery or Power supplies they connect to.
Short path: The direct, shorter great-circle route between two stations, the usual path for signals. Its opposite is long path. See Long path and short path.
Shunt: A low-value resistor placed in parallel to carry most of a current, letting a meter measure large currents safely, as in a Multimeter. Shunt also means any parallel-connected part.
Sideswiper (Cootie): A Morse key with a single lever that moves side to side, sending each element manually in either direction for a distinctive rhythm; see Morse keys and paddles.
Sidetone: The tone a radio produces so you can hear your own CW as you send it. Its pitch and volume are adjustable; see Morse code.
Signal generator: A test instrument that produces a controllable RF or audio signal at a known frequency and level, used for aligning and testing receivers. See Signal generator.
Signal tracer: A simple troubleshooting tool, basically an amplifier with a probe and speaker, used to follow a signal stage by stage until it disappears; handy in Homebrewing.
SignaLink: A popular USB sound card interface from Tigertronics that connects a radio to a computer for digital modes, with a built-in audio codec and automatic PTT; see Digital mode interface.
Simplex: Communicating directly between stations on one frequency, without a repeater. Common simplex calling frequencies are 146.52 MHz on 2 meters and 446.0 MHz on 70 centimeters. See Simplex.
Sine wave: The smooth, regular waveform of pure AC or a single-frequency signal. A clean carrier is a sine wave with no harmonics; see AC and DC.
Single-op (Single operator): A Contesting category where one person does all the operating and logging. Subcategories cover power levels and whether spotting assistance is used.
Single-point ground: A grounding scheme where all station equipment and entry cables bond to one common point, preventing ground loops and dangerous lightning voltage differences; see Grounding and lightning protection.
SK (Silent Key): A ham who has died. SK is also the Morse prosign sent at the end of a contact. See Silent Key.
Sked (Schedule): An arranged contact at a set time and frequency, common for difficult paths such as Moonbounce or meteor scatter, or for keeping in touch with friends.
Skin effect: The tendency of RF current to flow near a conductor's surface, raising loss as frequency increases. That is why thick or hollow conductors work well in Feed line and antennas.
Skip: Signals bent back to Earth by the Ionosphere, often in several hops, letting HF contacts span continents. "The band is skipping" means distant stations are coming through.
Skip zone: The gap between where ground wave ends and where sky-wave signals first return, in which a station may not be heard at all. See Skip zone.
Sky wave: A signal that reaches distant points after refraction by the ionosphere. It is the main path for long-distance HF contacts; see Radio propagation.
SKYWARN: The National Weather Service's volunteer storm spotter program, in which many hams report severe weather by radio. See SKYWARN.
SLA (sealed lead-acid): A maintenance-free lead-acid battery, such as AGM or gel. Heavy but cheap and tolerant, it is common for backup power, though LiFePO4 is replacing it; see Batteries.
Slim Jim: A folded variant of the J-pole, made from twin-lead or tubing, that gives a low-angle, omnidirectional pattern on VHF and UHF. See Slim Jim antenna.
Sloper: A wire antenna run at a slant from a high point down toward the ground, giving some directivity toward its low end. See Sloper antenna.
SMA: A small threaded coaxial connector used on most handheld radios and SDR dongles. Check the gender before buying antennas, as some brands reverse it; see RF connectors.
Smith chart: A circular graph that plots complex Impedance, used to design matching networks and read antenna analyzer data. NanoVNAs display it live.
SNR (signal-to-noise ratio): How much stronger a signal is than the background noise, usually in decibels. Digital modes such as FT8 report SNR, often well below zero.
SO-239: The female UHF chassis jack found on most HF radios and many antennas, mating with the PL-259 plug; see RF connectors.
Solar cycle: The roughly 11-year rise and fall of sunspot activity. Higher activity improves conditions on the upper HF bands, such as 10 and 15 meters. See Solar cycle.
Solar flare: A sudden burst of radiation from the Sun. X-rays from large flares can black out HF on the daylit side of Earth within minutes; see Space weather.
Solar flux (SFI, solar flux index): A daily measurement of the Sun's radio output at 10.7 centimeters (2800 MHz). Higher numbers mean stronger ionization and generally better upper HF conditions; see Solar cycle.
Solar panel: A panel of photovoltaic cells that converts sunlight into DC power. With a charge controller it keeps Batteries topped up for portable or emergency operation.
Solder: A low-melting metal alloy, either tin-lead or lead-free, used to join electrical connections. Rosin-core solder includes flux for clean joints; see Homebrewing.
Soldering iron: A heated tool for melting solder onto joints. A temperature-controlled iron with a clean, tinned tip makes reliable connections for Homebrewing.
Solid state: Equipment that uses transistors and integrated circuits instead of vacuum tubes. Nearly all modern radios are solid state, unlike the tube-era Boat anchors.
SOTA: Summits on the Air, an awards program for operating portable from mountain summits and for the chasers who contact them. See Summits on the Air.
Sound card interface: A device linking a radio's audio and PTT to a computer sound card so software can send and receive digital modes such as FT8. See Digital mode interface.
Space station: In FCC rules, an amateur station located more than 50 km above Earth's surface, including satellites and the ham station aboard the ISS; see Amateur satellites.
Space weather: Conditions on the Sun and in near-Earth space, including flares, solar wind, and geomagnetic storms, that affect radio propagation. See Space weather.
Special event station: A station set up to mark an event or anniversary, often with a special callsign and commemorative QSL card. See Special event stations.
Spectrum analyzer: An instrument that displays signal strength against frequency, used to check transmitters for harmonics and spurious signals. See Spectrum analyzer.
Speech processor (Compression): A circuit that raises average voice power relative to peaks, helping SSB signals punch through noise. Too much makes audio harsh and splattery. See Speech processing.
Spin fading: Regular fading of a satellite's signal as the satellite rotates. Circularly polarized ground antennas help reduce it; see Amateur satellites.
Splatter: Distortion products that spread a signal well beyond its normal bandwidth, usually from overdriving or overmodulation, interfering with nearby stations. Watch your ALC to prevent it.
Split operation (Working split): Transmitting on one frequency and listening on another, commonly used by DX stations to manage pileups. See Split operation.
Sporadic E (Es): Unpredictable propagation off dense patches in the E layer, mostly in summer, opening 6 and 10 meters for contacts of roughly 500 to 1,400 miles. See Sporadic E.
Spotting (Spot): Posting a station's callsign and frequency to a DX cluster or website so others can find it. Self-spotting is prohibited in many contests.
Spread spectrum: A technique that spreads a signal over a wide bandwidth, making it resistant to interference. US amateurs may use it on 222 MHz and higher bands under Part 97.
Spurious emission: Unwanted signals outside a transmitter's necessary bandwidth, such as harmonics. FCC rules limit them strictly. See Harmonics and spurious emissions.
Squelch: A circuit that mutes the receiver until a signal is strong enough to hear. Tone squelch opens only for signals carrying the right tone; see CTCSS and DCS.
SSB: Single sideband, a voice mode that transmits one sideband without the carrier, and the main voice mode on HF. See Single sideband.
SSTV: Slow-scan television, sending still images over voice-bandwidth radio channels. The ISS sometimes transmits SSTV images for anyone to receive. See SSTV.
STA (special temporary authority): FCC permission for temporary operation not normally allowed by the rules, such as an experiment or unusual special event. See Special temporary authority.
Standing wave: Stationary voltage and current peaks along a feed line, caused by forward and reflected waves combining when there is a mismatch; see SWR.
State of charge (SoC): How much energy remains in a battery, as a percentage of full. Lithium batteries hold a flat voltage, so an SoC meter tells more than a voltmeter; see Batteries.
Static electricity (Static): Electric charge built up on an object and released as a spark, which can damage sensitive parts like MOSFETs. On the air, static also means crackling atmospheric noise.
Station identification (ID): Transmitting your callsign as required, at least every 10 minutes during a contact and at its end. See Station identification.
Stealth antenna: An antenna designed to be unobtrusive, used where restrictions or neighbors limit visible antennas. See Stealth antennas.
STEM (science, technology, engineering and mathematics): Education in science and technical fields. Ham radio supports STEM through school stations, kit building, and contacts with astronauts, often with help from Ham radio clubs.
Stopband: The range of frequencies a filter blocks. A good low-pass filter has deep attenuation in its stopband to suppress a transmitter's harmonics.
Straight key: The simplest Morse key, an up-and-down lever with which you form each dit and dah by hand. Many operators learn on one; see Morse keys and paddles.
Stub: A short section of feed line, open or shorted at its end, used as a filter or matching device. Quarter-wave stubs can notch out harmonics; see Feed line.
Suffix: The letters after the digit in a callsign. Short suffixes are prized for contest and CW use, since they are quicker to send; see Call signs.
Sunspots: Dark, cooler areas on the Sun's surface linked to solar activity. More sunspots generally mean better HF propagation, especially on higher bands; see Solar cycle.
Superheterodyne (Superhet): A receiver design that converts signals to a fixed intermediate frequency for filtering and amplification. Most analog radios use it. See Superheterodyne receiver.
Surface-mount (SMD, SMT): Components soldered directly onto PCB pads instead of through holes. They are smaller and cheaper but harder to solder by hand; see Homebrewing.
Susceptance: The imaginary part of admittance, measured in siemens. It plays the role in parallel circuits that reactance plays in series ones, useful in Impedance matching.
Swapfest: A gathering where hams buy, sell, and trade equipment, often smaller and less formal than a hamfest; see Hamfests.
Sweepstakes: The ARRL's November contest for US and Canadian stations, with separate CW and phone weekends and a long exchange. See ARRL Sweepstakes.
Switching power supply (Switcher): A power supply that converts power at high frequency, making it light and efficient. Cheap ones can radiate RF noise; see Power supplies.
SWL (shortwave listener): Someone who listens to shortwave broadcasts and ham stations without transmitting. Many hams started as SWLs. See Shortwave listening.
SWR: Standing wave ratio, a measure of how well an antenna system matches the transmitter. 1:1 is perfect, and below 2:1 is generally acceptable. See SWR.
SWR meter: An instrument placed in the feed line to measure SWR, usually by comparing forward and reflected power. See SWR meter.
System Fusion (C4FM, YSF): Yaesu's digital voice and data system using C4FM modulation, with repeaters that can pass both digital and analog FM. See System Fusion.

T

Tactical call: A functional name such as "Shelter 3" or "Net Control" used during events or emergencies. You must still give your FCC callsign every 10 minutes; see Emergency communications.
Tail-ending: Calling a station right after it finishes another contact, instead of calling CQ. Wait until the first QSO clearly ends; see Operating etiquette.
Tailgating: Keying up immediately after another station stops, with no pause. On Repeaters, leaving a second or two lets others break in, especially in emergencies.
Takeoff angle (Radiation angle): The vertical angle at which most of an antenna's energy leaves. Lower angles give longer hops for DX; higher angles suit regional and NVIS work; see Radio propagation.
Talkgroup: A virtual channel on DMR and other digital systems, letting a group of users talk without hearing other users of the same repeater.
TCXO: A temperature-compensated crystal oscillator, which holds frequency steady as temperature changes. It matters for digital modes and VHF/UHF stability; see Oscillators.
TDMA: Time-division multiple access, dividing a channel into time slots so several users can share it. DMR uses two-slot TDMA.
TDR (time-domain reflectometry): A method of finding faults in cables by sending a pulse and timing its reflections. Many NanoVNAs offer a TDR mode for checking Coaxial cable.
Technician: The entry-level US license, earned by passing a 35-question exam. It grants all amateur privileges above 50 MHz and limited HF privileges. See Technician license.
Telecommand: Remote control commands sent to an amateur space station, such as a satellite. Only stations designated by the satellite's licensee may send them; see Amateur satellites.
Telemetry: Data transmitted by a remote station about its own condition, such as a satellite's battery voltage or a balloon's altitude; see Amateur satellites.
Temperature coefficient: How much a component's value changes with temperature, often in parts per million per degree. Low values matter for stable oscillators; see Capacitors.
Temperature inversion: An atmospheric layer where warm air sits above cooler air, bending VHF and UHF signals back toward Earth and causing Tropospheric ducting.
Temporary identifier: A suffix such as /AG or /AE added to your callsign after passing an upgrade exam, used until the FCC database shows your new class; see Universal Licensing System.
Thermal resistance: How strongly a component resists the flow of heat to its surroundings, measured in degrees Celsius per watt. Lower values mean better cooling, as with a good heat sink.
Thermal runaway: A cycle in which heating increases current, which causes more heating, until a part fails. It can affect Transistors and lithium batteries.
Thermistor: A resistor whose resistance changes strongly with temperature, used for temperature sensing and to limit inrush current in power circuits.
Third party: A person who is not the control operator but on whose behalf a message is sent, or who speaks over an amateur station; see Third-party traffic.
Third-order intercept (IP3): A measurement of how well a receiver handles strong signals without creating intermodulation products. Higher IP3 means better strong-signal performance; see Receiver performance.
Third-party traffic: Messages sent on behalf of unlicensed people, including letting them talk over your station. International third-party traffic is allowed only with countries that have agreements with the US. See Third-party traffic.
Through-hole: Components with wire leads inserted through holes in a circuit board and soldered on the other side. They are easier to hand-solder than surface-mount parts; see Homebrewing.
Tiger tail (Rat tail): A short wire attached to a handheld's antenna base that acts as a counterpoise, often improving range; see Handheld antennas.
Time constant: The time a resistor-capacitor or resistor-inductor circuit takes to reach about 63 percent of its final change. It sets timing and filtering behavior; see Capacitors.
Time slot: One of the divisions of a TDMA channel. DMR repeaters offer two time slots, each carrying a separate conversation.
Time-out timer: A timer that shuts off a transmitter after a set limit, preventing stuck microphones. On Repeaters, it reminds long-winded users to keep transmissions short.
TNC: Terminal node controller, a modem that converts data to Packet radio signals and back. Sound card software has replaced many of them.
TNX (TU): Abbreviations for "thanks" and "thank you," common on CW and digital modes; see Ham radio slang.
Tolerance: How far a component's actual value may differ from its marked value, usually as a percentage. Common Resistors are 5 percent or 1 percent.
Tone squelch (TSQL): A squelch mode that opens only for signals carrying a matching CTCSS tone, so you don't hear other users on the frequency; see CTCSS and DCS.
Top band: Nickname for the 160-meter band, 1.8 to 2.0 MHz, prized for nighttime DX and demanding large antennas. See 160-meter band.
Toroid: A doughnut-shaped magnetic core of ferrite or powdered iron, used to wind inductors, transformers, and chokes with little stray field; see Inductors.
Tower: A sturdy metal structure that supports antennas high above the ground. Building permits, zoning, and HOA rules may apply; see Antenna restrictions.
Trace: The line drawn on an Oscilloscope or analyzer screen showing a signal. Trace also means a copper conductor path on a printed circuit board.
Traffic: Messages passed on behalf of others, especially formal written messages handled on nets of the National Traffic System.
Trans-equatorial propagation (TEP): A VHF propagation mode in which signals travel across the geomagnetic equator, often in the afternoon and evening. See Trans-equatorial propagation.
Transceiver: A radio that combines a transmitter and receiver in one unit, the standard in modern ham radio, from handhelds to the HF transceiver.
Transconductance: A measure of how much output current changes with input voltage in a transistor or tube, in siemens. Higher values mean more gain; see Transistors.
Transformer: A device that uses magnetic coupling between windings to change voltage, current, or impedance levels. See Transformers.
Transistor: A semiconductor device that amplifies or switches signals, the building block of nearly all modern electronics. See Transistors.
Transverter: A device that converts signals between a transceiver's band and another band, often used for VHF, UHF, and microwave operation. See Transverter.
Trap: A parallel inductor-capacitor circuit inserted in an antenna to block RF on one band, letting one antenna work on several bands, as in a Trap dipole.
Trap dipole: A dipole with traps that electrically shorten it on higher bands, making it a simple multiband antenna. See Trap dipole.
Triac: A semiconductor switch that conducts in both directions once triggered, used to control AC power in dimmers and motor controls. Triac dimmers often cause Radio frequency interference.
Trickle charge: A low-current charge that keeps a battery topped up over long periods. It suits lead-acid but is not recommended for lithium Batteries.
Tropospheric ducting (Tropo, ducting): VHF and UHF signals trapped in atmospheric layers and carried hundreds of miles or more, often during stable summer and fall weather. See Tropospheric ducting.
True power (Real power): The power actually consumed in a circuit's resistance, measured in watts. It is less than apparent power when current and voltage are out of phase; see AC and DC.
Trustee: The licensee responsible for a club station or repeater callsign and its compliance with FCC rules; see Club stations.
Truth table: A table listing a logic circuit's output for every combination of inputs. It is the standard way to describe gates in Digital logic.
TTL (transistor-transistor logic): A Digital logic family built from bipolar transistors and powered at 5 volts. Hams also say TTL for logic-level serial signals on radio interfaces.
Tube (Valve): A vacuum tube, which controls current using a heated cathode and electrodes sealed in a vacuum. Tubes are still used in some high-power Amplifiers.
Tuner (ATU, antenna tuner, matcher): A device that transforms the impedance a transmitter sees so it delivers full power into a mismatched antenna system. It does not change SWR on the feed line. See Antenna tuner.
Tuning up: Adjusting a transmitter or tuner for proper output. Do it into a Dummy load when possible, or briefly on a clear frequency with your callsign.
Tunnel diode: A diode that shows negative resistance over part of its range, letting it oscillate at very high frequencies. It is rare in today's ham gear; see Diodes.
Twin-lead: Flat two-conductor Feed line, usually 300 ohms, once common for TV antennas and still used for some ham antennas, such as twin-lead J-poles.

U

UHF: Ultra high frequency, 300 MHz to 3 GHz, which includes the popular 70-centimeter band and the 33 and 23 centimeter bands. See UHF.
UHF connector: The common PL-259 and SO-239 connector family. Despite the name, it works best at HF and VHF, and N connectors are preferred for UHF and above; see RF connectors.
ULS (Universal Licensing System): The FCC's online licensing database, where you can look up callsigns, renew your license, and update your address. See Universal Licensing System.
Uncontrolled environment: An area where people, such as neighbors or the public, may be exposed to RF without knowing it. FCC exposure limits are stricter there; see RF exposure.
Unloaded Q: The Q of a resonant circuit or component by itself, without any external load connected. It shows the component's inherent losses; see Resonance and Q.
Unun: An unbalanced-to-unbalanced transformer used to match coaxial cable to an end-fed wire. Common ratios are 9:1 for random wires and 49:1 for the End-fed half-wave antenna.
Up: A DX station's request that callers transmit above its frequency. "Up 5" means call about 5 kHz higher; see Split operation.
Upgrade: Moving to a higher license class by passing additional exams, earning more privileges, mainly on HF; see Getting licensed.
Uplink (Downlink): The uplink is the frequency you transmit on to reach a satellite or repeater; the downlink is the frequency it transmits back on. See Amateur satellites for typical pairs.
UR: Shorthand for "your" or "you are" on CW and digital modes, as in "UR RST 599"; see Ham radio slang.
USB and LSB (Upper and lower sideband): The two choices for Single sideband. By convention, hams use LSB below 10 MHz and USB above, except on 60 meters, where USB is standard.
UTC (Zulu): Coordinated Universal Time, the worldwide time standard hams use for logging contacts and scheduling. See UTC.

V

Vanity callsign: A callsign you choose, subject to availability and your license class, through the FCC vanity program. See Vanity call signs.
VARA: Proprietary HF and FM modem software used mainly with Winlink for fast, reliable data transfer. See VARA.
VarAC: A chat and messaging program that runs over the VARA HF modem for keyboard-to-keyboard contacts and file exchange. See VarAC.
Varactor (Varicap): A diode whose capacitance changes with applied voltage, used to tune oscillators and filters electronically; see Diodes.
VE (Volunteer Examiner): A licensed ham, General class or higher, accredited by a VEC to give license exams. At least three VEs must be present at each session. See Volunteer examiners.
VE team: The group of at least three VEs who run an exam session, grade the tests, and file the paperwork; see Volunteer examiners.
VEC (Volunteer Examiner Coordinator): An organization that accredits VEs, coordinates exam sessions, and submits results to the FCC; see Volunteer examiners.
Velocity factor: The speed of signals in a feed line compared with free space. Solid polyethylene Coaxial cable is about 0.66; it matters when cutting phasing lines and stubs.
Vertical: An antenna with a vertical radiator, usually omnidirectional, popular for DX, mobile, and small lots. See Vertical antenna.
VFO: Variable-frequency oscillator, the tuning circuit behind a radio's main dial. Many radios have two VFOs for split operation; see Oscillators.
VHF: Very high frequency, 30 to 300 MHz, which includes the 6-meter, 2-meter, and 1.25-meter bands. See VHF.
Via: In QSL information, "via" names the route for confirmations, such as a QSL manager or the bureau; see QSL cards and logging.
VNA (vector network analyzer): An instrument that measures both magnitude and phase of reflected and transmitted signals, used to test antennas, filters, and feed lines. It goes beyond a basic Antenna analyzer.
VOACAP: Free HF propagation prediction software based on work done for the Voice of America, available online and as a download; see Propagation prediction.
Volt (V): The unit of electrical potential difference, or voltage. A typical mobile ham radio runs on 13.8 volts DC; see Ohm's law.
Voltage: The electrical pressure that pushes current through a circuit, measured in volts. It is the E in Ohm's law.
Voltage divider: Two or more resistors in series that produce a fraction of the input voltage at their junction. It is common for biasing and setting levels; see Resistors.
Voltage drop: The voltage lost across a wire, connector, or component as current flows. Long, thin DC leads can drop enough voltage to make a radio misbehave on transmit; see Power supplies.
Voltage rating (Working voltage): The highest voltage a component, such as a capacitor, can safely handle. Exceeding it can cause sudden failure; see Capacitors.
Voltage regulator: A circuit that keeps output voltage steady despite changes in input voltage or load, found in nearly all Power supplies.
Voltmeter: A meter that measures voltage, connected in parallel with the part being measured. Most hams use the voltage function of a Multimeter.
Volunteer Monitor (VM): A volunteer in the ARRL-run program that watches the bands for rule violations and helps hams correct problems before FCC action. See Volunteer Monitor program.
VOX: Voice-operated transmit, which keys the transmitter automatically when you speak into the microphone. See VOX and PTT.

W

W1AW: The ARRL headquarters station in Newington, Connecticut, a memorial to Hiram Percy Maxim. It transmits code practice and bulletins on a published schedule.
WAC (Worked All Continents): An IARU award for confirming contacts with all six inhabited continents, one of the oldest Amateur radio awards.
Walkie-talkie: A common name for a handheld two-way radio, especially consumer FRS radios; hams usually say HT. See Handheld transceiver.
Wallpaper: Slang for award certificates and QSL cards hung on the shack wall; see Amateur radio awards.
WARC bands: The 30, 17, and 12 meter bands, allocated at the 1979 World Administrative Radio Conference. By long agreement, contests stay off them; see Amateur radio bands.
WAS: Worked All States, the ARRL award for confirming contacts with all 50 US states; see Amateur radio awards.
Waterfall display (Waterfall): A scrolling display of signal strength versus frequency over time, with signals appearing as colored streaks. It is often shown beneath a Panadapter.
Watt (W): The unit of power, one joule per second. Transmitter output and power limits are measured in watts; see PEP and power measurement.
Watt-hour (Wh): A unit of energy, one watt for one hour. Multiply amp-hours by voltage to find a battery's watt-hours; see Batteries.
Wattmeter (Power meter): An instrument that measures RF power, often both forward and reflected; see PEP and power measurement.
Wavelength: The distance one cycle of a wave travels, linked to frequency by the speed of light. Bands are often named by wavelength. See Wavelength and frequency.
WAZ (Worked All Zones): The award, created by CQ magazine, for confirming contacts with all 40 CQ zones; see Amateur radio awards.
Weak signal: VHF and UHF operation using SSB, CW, and digital modes, often for long-distance contacts under marginal conditions, including Moonbounce.
WebSDR (Online SDR, KiwiSDR): A receiver connected to the internet that you can tune from a web browser, letting you hear how your signal sounds far away. See WebSDR.
Wheatstone bridge: A circuit of four resistors used to measure an unknown resistance by balancing the bridge. The same idea underlies some SWR meter designs.
Window line (450-ohm line): Ladder line with plastic insulation and windows cut out, used for low-loss feeding of multiband antennas with a tuner; see Feed line.
Winlink: A global radio email system for hams, used for emergency communication and by sailors at sea. See Winlink.
Winter Field Day: An annual January event in which hams set up emergency-style stations, testing their ability to operate in cold weather. See Winter Field Day.
Wire gauge: A system for sizing wires by diameter, where lower numbers are thicker. Use heavy enough wire for DC power to avoid voltage drop; see Power supplies.
Wires-X: Yaesu's internet linking system that connects System Fusion repeaters and nodes worldwide.
WPM (words per minute): The standard measure of Morse code speed, based on the word "PARIS"; see Learning Morse code.
Wrist strap (ESD strap): A conductive strap worn on the wrist and grounded through a resistor, protecting sensitive parts from static discharge while you work on them.
WSJT-X: Free software for weak-signal digital modes such as FT8, FT4, and WSPR. See WSJT-X.
WSPR: Weak Signal Propagation Reporter, a beacon mode for testing propagation with very low power. See WSPR.
WWFF (World Wide Flora and Fauna): An awards program for operating from parks and nature reserves worldwide. See World Wide Flora and Fauna.

X

Xastir: An open-source APRS program for Linux and other systems that shows stations, weather, and objects on maps.
XIT: Transmitter incremental tuning: shifts your transmit frequency slightly without changing your receive frequency. See RIT and XIT.
XOR gate (exclusive OR gate): A Digital logic gate whose output is high only when its inputs differ. It is useful for comparing signals and in parity checks.
XYL: Ham radio slang for a wife, from "ex-young lady." The term is used affectionately.

Y

Yagi: A directional beam antenna with a driven element, a reflector, and one or more directors. See Yagi antenna.
YL (young lady): Ham radio slang for any female operator, regardless of age. YL nets and clubs welcome women in the hobby.

Z

Zener diode: A diode designed to conduct in reverse at a specific voltage, used for voltage regulation and overvoltage protection; see Diodes.
Zero beat: Tuning so your signal is exactly on another station's frequency. On CW, you match the received tone to your sidetone pitch; see Morse code.

0–9

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

X

Y

Z

See also