Ham Dictionary – OneShack

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1.25 meters also 222 MHz: 222 to 225 MHz in the US. A quieter VHF band with repeaters and weak-signal work. More on Band Plans →
10 meters: 28.000 to 29.700 MHz. Wide open worldwide near the solar maximum, quiet near the minimum. Technicians have CW, data and some SSB privileges here. More on Band Plans →
12 meters: 24.890 to 24.990 MHz. A small WARC band that opens well when the Sun is active. More on Band Plans →
15 meters: 21.000 to 21.450 MHz. A daytime DX band that comes alive near the peak of the solar cycle. More on Band Plans →
160 meters also Top band: The lowest HF band, 1.8 to 2.0 MHz. Best at night and in winter, with big antennas and lots of noise. More on Band Plans →
17 meters: 18.068 to 18.168 MHz. A WARC band with long-distance openings and no contests by custom. More on Band Plans →
1×1 call sign also Special event call sign: A short call with one letter, one digit and one letter, issued for a few days to a special event station through volunteer coordinators.
2 meters: 144 to 148 MHz. The busiest VHF band: FM repeaters, simplex, APRS, and weak-signal SSB and CW at the bottom. More on Band Plans →
20 meters: 14.000 to 14.350 MHz. The classic long-distance band, open somewhere in the world most of the day. More on Band Plans →
2200 meters: The lowest US amateur band, near 137 kHz, used mostly for weak-signal experiments.
23 centimeters also 1296 MHz: 1240 to 1300 MHz. The lowest microwave band most hams use, for weak-signal work, ATV and some repeaters. More on Band Plans →
30 meters: 10.100 to 10.150 MHz. A narrow WARC band for CW and data only, with a 200-watt limit in the US and no contests by custom. More on Band Plans →
33 centimeters also 902 MHz: 902 to 928 MHz. A UHF band shared with many unlicensed devices. More on Band Plans →
40 meters: 7.0 to 7.3 MHz. A workhorse band: regional by day, long distance at night. More on Band Plans →
5 by 9: A signal report meaning perfectly readable and strong. On phone it is given so routinely that it has lost most of its meaning. More on Signal Reports →
5/8-wave: A vertical about five-eighths of a wavelength tall, giving a lower radiation angle and a little more gain than a quarter-wave. Common on VHF mobiles.
60 meters: A US band of fixed channels near 5.3 MHz, with power and bandwidth limits.
630 meters: A narrow amateur band near 475 kHz, with strict power limits and a requirement to notify utilities before use.
70 centimeters also 440: 420 to 450 MHz. The main UHF band for repeaters, satellites, digital voice and ATV. More on Band Plans →
73: Best regards, from the Phillips telegraph code of the 1800s. Said at the end of almost every contact. Never “73s” — it is already plural.
80 meters also 75 meters: 3.5 to 4.0 MHz. A night-time band for regional contacts and nets. The upper, phone part is often called 75 meters. More on Band Plans →
88: Love and kisses. Traditionally sent to or from a female operator, and easy to send by mistake.
8JK also 8JK beam, W8JK beam: A two-element wire beam with the elements fed out of phase, named for John Kraus, W8JK, who designed it. Bidirectional, broad lobes, a few decibels of gain, and it fits in an attic because nothing has to rotate.

A

A index: A daily average of geomagnetic activity. Under about 10 is quiet and good for HF.
Absorption wavemeter: A tuned circuit with a meter that shows when it is near a signal at its frequency. A simple check for harmonics and oscillators.
AC (alternating current): Current that reverses direction many times a second, as from a wall outlet or a radio signal.
Access tone: A tone a repeater needs to hear before it will relay you, such as CTCSS or a short tone burst.
Activator: The operator who goes to a park or summit to put it on the air for POTA or SOTA.
ADC (analog-to-digital converter): A circuit that measures a changing voltage many times a second and turns it into numbers. The heart of an SDR and of a sound card.
ADIF: The standard file format for moving log data between programs and uploading it to services such as LoTW.
Admittance: The reciprocal of impedance: conductance and susceptance combined. It makes parallel circuits easier to add up than impedance does.
AFSK (audio frequency-shift keying): Producing data tones through a radio’s microphone audio path, the way most sound card digital modes work.
AGC: Automatic gain control, which evens out the volume of strong and weak signals.
Air core: A coil wound with nothing magnetic inside it. It cannot saturate and adds no core loss, so it suits high-power tank circuits.
ALC: Automatic level control, which limits drive to the transmitter or an amplifier to prevent distortion.
ALE (automatic link establishment): A system that automatically finds and connects to another station on the best available HF frequency.
Aliasing: A signal sampled too slowly reappearing as a different, lower frequency. An anti-aliasing filter ahead of the converter prevents it.
Alligator: A station with a big transmitter and a poor receiver: all mouth, no ears.
AllStarLink: An internet linking system for repeaters and nodes, built on open-source telephone software.
AM (amplitude modulation): The oldest voice mode, kept alive by enthusiasts with vintage gear. More on AM →
Amateur Extra also Extra: The highest US license class, with every amateur privilege. More on Learn →
Amateur radio: Licensed, non-commercial two-way radio, used for experimenting, emergency communication and making contact around the world.
Amateur satellite also Bird: A satellite that relays signals between hams. Several can be worked with a handheld and a small hand-held beam.
AMBE: The proprietary voice codec used by DMR, D-STAR and Fusion.
Ammeter: An instrument that measures current, wired in series so the current passes through it.
Amp-hour also Ah: A battery’s capacity: how many amps it can deliver for how many hours. A 100 Ah battery could in theory supply 10 amps for 10 hours. More on A Guide to Portable Amateur Radio Power →
Ampere also Amp, A: The unit of current: one coulomb of charge passing a point each second. A 100-watt radio draws about 20 amps on transmit.
Amplifier: A circuit that makes a signal stronger. In ham talk, “an amplifier” or “a linear” usually means a separate box that boosts a transceiver’s output.
Amplifier classes also Class A, AB, B, C, D: Ways of running an amplifier that trade purity for efficiency. Class A is cleanest but wasteful; AB is the usual choice for SSB; C is efficient but only suits FM and CW; D and E switch on and off and are the most efficient.
AMSAT: The organization that builds and supports amateur satellites.
Anderson Powerpole also Powerpole: A genderless DC connector that has become the ham standard for 12-volt power. ARES and many clubs use a standard layout, red for positive and black for negative, so any radio plugs into any supply.
Antenna analyzer: A test instrument that measures how well an antenna is matched across a range of frequencies. The fastest way to find out whether an antenna is any good.
Antenna efficiency: The share of the power fed to an antenna that is actually radiated rather than lost as heat.
Antenna farm: A property with many antennas. Said with envy.
Antenna gain: How much an antenna concentrates signal in one direction compared with a reference antenna. Gain in one direction always means less in another.
Antenna modeling also NEC, EZNEC: Simulating an antenna’s pattern, gain and impedance in software before building it.
Anti-VOX: A VOX control that stops the speaker’s sound from keying the transmitter.
Antipode: The point exactly opposite you on the globe. Signals to your antipode can arrive from every direction at once. More on Propagation →
Apogee: The point in an orbit farthest from the Earth.
Apparent power: Volts times amps with no regard for phase, measured in volt-amperes. It matches true power only in a purely resistive circuit.
Appliance operator: Someone who buys and operates equipment without building or understanding it. Said teasingly.
APRS: A packet radio system for broadcasting position, weather and short messages, mostly on 144.390 MHz in North America. More on APRS →
APRS-IS (APRS Internet System): The internet network that collects APRS packets from iGates worldwide, feeding map sites and messaging. More on APRS →
ARDF (Amateur Radio Direction Finding): A sport combining orienteering and radio: competitors run a course to find hidden transmitters with handheld receivers and maps.
ARDOP (Amateur Radio Digital Open Protocol): An open HF data protocol used mainly to connect to Winlink stations with a sound card interface. More on Winlink →
Arduino: A family of low-cost microcontroller boards that are easy to program. Popular for keyers, antenna switches and rotator controllers.
AREDN (Amateur Radio Emergency Data Network): Modified Wi-Fi gear on amateur frequencies, used to build high-speed data networks.
ARES: Amateur Radio Emergency Service, the ARRL’s volunteer emergency communications program.
ARISS: Amateur Radio on the International Space Station, which arranges school contacts with astronauts.
ARL numbered radiogram also ARL texts: A standard message identified by ARL and a number written out, such as a greeting or a welfare report, which saves words on the air. More on Radiograms →
Armchair copy: A signal so strong and clear that no effort is needed to understand it.
ARQ (automatic repeat request): A data method in which the receiver asks for any damaged block to be sent again. Used by PACTOR and VARA.
ARRL (American Radio Relay League): The national association for amateur radio in the US, founded in 1914.
ASCII: A standard code that represents letters, numbers and symbols as numbers, used by many data modes.
Assisted: A contest category in which the operator may use spotting networks, skimmers and other outside help to find stations. More on Contests →
Astable multivibrator also Astable: An oscillator that flips back and forth on its own, used for tone generators and flashers.
Atom: The smallest piece of an element: a nucleus of protons and neutrons with electrons around it. How easily an atom gives up its outer electrons decides whether a material conducts.
Attenuation: Loss of signal strength, whether deliberate (an attenuator) or not (coax loss). Measured in decibels.
Attenuator: A control that deliberately reduces incoming signal strength. It helps when strong nearby signals overload the receiver.
Attic antenna: An antenna mounted in the attic to get around outdoor restrictions. It works, but roofing absorbs some signal, more at UHF than VHF.
Aurora: The northern and southern lights. VHF signals bounced off an aurora sound raspy and can travel hundreds of miles.
Auroral E: VHF propagation by ionization in the E region near the auroral zone during geomagnetic storms.
Auroral oval: The ring around each magnetic pole where aurora occurs. It grows toward the equator during storms.
Auroral propagation: VHF signals reflected off an aurora, with a distinctive raspy sound.
Automatic control: Operation with no control operator present, such as a repeater or beacon, allowed only on certain frequencies.
Autotransformer: A transformer with one tapped winding instead of two separate ones.
Autotuner: A tuner that finds a match on its own using relays, often built into the radio. Built-in ones handle only modest mismatches.
AUXCOMM (Auxiliary Communications): Volunteer radio operators, many of them hams, trained to work alongside public-safety staff for emergency management agencies.
Auxiliary station: A station that relays signals between parts of a system, such as a link to a remote repeater site.
Average power: The power a transmitter produces averaged over time, which depends on the mode and the duty cycle. FT8 runs at close to full power throughout; SSB speech averages far less.
Average value: The mathematical average of an AC wave over time. For a full sine wave it is zero; over one half cycle it is about 0.637 of the peak.
AWG (American Wire Gauge): The US wire size scale; smaller numbers mean thicker wire.
AX.25: The data protocol behind packet radio and APRS. More on Packet Radio →
Az-el rotator: A rotator that turns an antenna both around the compass (azimuth) and up and down (elevation), used to track satellites.
Azimuth plot: A top-down view of an antenna’s radiation pattern, showing strength in each compass direction.
Azimuthal equidistant map also Great-circle map: A map centered on your location that shows the true direction and distance to anywhere. The way to aim a beam. Try Grid Square & Distance →

B

Backscatter: Signal scattered back from an ionized region, letting two stations inside each other’s skip zone hear one another faintly.
Balun: A transformer between a balanced antenna and an unbalanced feedline. Without one, the outside of your coax becomes part of the antenna.
Band: A range of frequencies amateurs are allowed to use, named by approximate wavelength — 20 m, 40 m and so on. More on Band Plans →
Band edge: The upper or lower limit of a band or of your license privileges. Your whole signal has to stay inside it, not just the number on the dial. More on Band Plans →
Band map: A list in logging software of the stations spotted or worked on a band, sorted by frequency.
Band opening: A period when a band suddenly carries signals to a region it normally does not reach.
Band plan: An agreed layout of which part of a band is used for what. Partly law and partly gentleman’s agreement. More on Band Plans →
Band-pass filter: A filter that passes only one range of frequencies. Used at Field Day and other multi-station events so stations do not interfere.
Band-stop filter also Band-reject filter: A filter that blocks one range of frequencies and passes everything else, such as one that keeps a nearby broadcast station out of your receiver.
Bandwidth: How much spectrum a signal occupies. A CW signal needs a fraction of what a voice signal does.
Barefoot: Running a radio at its own output, with no amplifier.
Base station: A radio set up permanently at home, as opposed to mobile or portable.
Battery: Cells joined together to store energy chemically and deliver it as DC. For radio, what matters is voltage, capacity in amp-hours and how much current it can deliver. More on A Guide to Portable Amateur Radio Power →
Battery management system also BMS: The electronics inside a lithium battery that keeps the cells balanced and disconnects the pack on over-charge, over-discharge or over-current.
Baud: The number of symbol changes per second on a data signal. Not always the same as bits per second.
Baudot code also ITA2: The five-bit code used by amateur RTTY. More on RTTY →
BBS (bulletin board system): On packet radio, a mailbox station that stores and forwards messages. More on Packet Radio →
Beacon: A station that transmits continuously or on a schedule so others can check propagation.
Beacon station: An amateur station transmitting for observation of propagation or reception. Automatic beacons are limited to specific frequencies.
Beam: A directional antenna that concentrates transmit and receive in one direction. Usually a Yagi.
Beamwidth: The angle over which a directional antenna delivers most of its gain, usually measured between the points 3 dB down.
Beta also hFE: A bipolar transistor’s current gain: how many times more collector current flows than base current.
Beverage: A very long, low, receive-only wire used on the low bands to pull weak signals out of noise.
BFO (beat frequency oscillator): An oscillator in a receiver that mixes with a CW or SSB signal to make it audible.
Bias: The steady DC voltage that sets where a transistor or tube idles before any signal arrives. Wrong bias means distortion, or no output at all.
Big gun: A station with big antennas and full power, especially in contests.
Bipolar junction transistor also BJT: The common transistor with an emitter, base and collector, in NPN or PNP form. A small base current controls a larger collector current.
Birdie: A false signal generated inside a receiver, heard on the same frequency every time.
Bit depth also Resolution: How many bits each sample uses. Every extra bit adds about 6 dB of usable range, which is why 16-bit and 24-bit converters hear so much more than 8-bit ones.
BK: Break, in Morse: a quick hand-over without sending full callsigns.
Bleeder resistor: A resistor across a power supply’s filter capacitors that drains their charge when the power is off, so they are safe to touch.
Blocking: Loss of receiver sensitivity caused by a strong signal nearby in frequency.
Blocking dynamic range also BDR: How strong a nearby signal can be before it begins to reduce the receiver’s sensitivity to a weak one, given in dB. More on Receiver Numbers →
BNC: A bayonet connector that locks with a quarter turn. Common on test equipment, older handhelds and QRP gear.
Boat anchor: Old, heavy tube equipment, named with affection.
Bonding: Connecting all of a station’s grounds together so no dangerous voltage can build up between them.
Boost converter: A switching circuit that steps a DC voltage up, for example to hold a radio at 13.8 volts as a battery runs down.
BPL (Broadband over power line): Data carried over electric power wiring. It can spread interference across HF. Wide-area systems are rare in the US now, but in-home powerline network adapters are still common. More on RFI →
BPQ32 also LinBPQ: Software for running a packet radio node, bulletin board or mailbox, on Windows and Linux respectively. More on Packet Radio →
BrandMeister: The largest worldwide network linking DMR repeaters and hotspots. More on DMR →
Brass pounder: Old slang for a telegraph or CW operator, from the brass straight key.
Breadboard: A plastic board full of spring contacts for trying out a circuit without soldering.
Break: Said to interrupt a contact, usually to join in. “Break break break” means an emergency, and everyone else should stand by.
Brick: A linear amplifier, especially a solid brick-shaped one. Also, unkindly, a radio that has stopped working.
Bridge rectifier: Four diodes arranged to turn AC into DC using both halves of each cycle.
Broadband-Hamnet: A mesh network that runs on modified Wi-Fi gear on amateur frequencies.
Buck converter: A switching circuit that steps a DC voltage down efficiently, such as from a solar panel to battery voltage.
Bug: A semi-automatic mechanical Morse key that makes dits automatically and dahs by hand. More on CW keys →
Busted call also Bust: A callsign logged wrongly. In a contest it costs the contact and usually a penalty.
Bypass capacitor also Decoupling capacitor: A small capacitor that shunts stray RF or noise to ground, keeping it off a power line or out of a circuit.

C

C rate: Charge or discharge current expressed as a multiple of a battery’s capacity. For a 20 Ah battery, 0.5C is 10 amps.
Cabrillo: The standard file format for submitting contest logs.
Call area also Call district: The region a US callsign’s digit stands for: 1 is New England, 6 is California, 0 the plains. The FCC assigned it where the license was first issued, and operators keep their call when they move, so the digit is history, not an address. Not a zone: CQ zones and ITU zones are different maps.
Callbook: A directory of licensed amateurs, now online. HamQTH, QRZCQ and QRZ.com are well-known examples. More on Callsign Lookup →
Calling frequency: A frequency where operators listen for contacts, then move elsewhere to talk. Do not settle in on one.
Callsign: Your license identifier, issued by your national authority and unique worldwide. More on Callsign Lookup →
Callsign-SSID also SSID: A number added to a callsign in packet and APRS, such as -9 for a mobile, so one ham can run several stations. More on APRS →
Cans: Headphones.
Cantenna: A homemade dummy load built into a paint can filled with oil. The name is also used for can-shaped Wi-Fi antennas.
Capacitance: The ability to store energy in an electric field, measured in farads.
Capacitive reactance: A capacitor’s opposition to AC, which falls as frequency rises.
Capacitor: A component that stores energy in an electric field. It blocks DC and passes AC more easily as frequency rises.
Capacity hat: Wires or rods spread out near the top of a vertical to add capacitance, making a short antenna act longer and radiate better.
Carrier: The steady signal a transmitter produces, which modulation then shapes. SSB removes it; AM and FM keep it.
CAT control: A link that lets a computer read and set the radio’s frequency and mode. Needed for most logging and digital-mode setups. More on Interfaces →
Catenary: The curve a wire takes when it hangs between two supports under its own weight. An antenna wire always sags into one; the sag shortens its horizontal span a little and lowers its average height.
CB (Citizens Band): The license-free 11 m service just below the 10 m amateur band. Not amateur radio, though many hams started there.
CC&Rs (covenants, conditions and restrictions): Private rules written into property deeds, often enforced by an HOA. Many limit outdoor antennas. More on Antenna Limits →
Cell: One unit of a battery. A lithium iron phosphate cell is about 3.2 volts and a lead-acid cell about 2 volts, so four or six make a “12-volt” battery.
CEPT: A European agreement that lets licensed amateurs from member countries, and the US, operate in each other’s countries on short visits.
Ceramic capacitor: A small, cheap, non-polarized capacitor suitable for RF bypassing. Some types change value noticeably with voltage and temperature.
CERT (Community Emergency Response Team): Neighborhood volunteers trained for disaster response. Some teams include hams to handle communications.
Characteristic impedance: The impedance a feedline presents along its length, set by its construction. Most amateur coax is 50 ohms.
Charge controller: The box between a solar panel and a battery that charges it safely and stops it overcharging. More on A Guide to Portable Amateur Radio Power →
Cheat sheet: Any crib of frequencies, codes or procedures kept by the radio. No shame attached.
Check-in: Reporting to a net control station that you are present and available.
Chirp also CHIRP: A Morse signal that shifts in pitch as each character starts, a sign of an unstable transmitter. In capitals, CHIRP is also free software for programming radios.
Choke also RF choke: An inductor used to block AC or RF while letting DC through. A common-mode choke on coax keeps RF off the outside of the shield.
Choke balun also Common-mode choke, current balun: Coax wound through ferrite, or coiled up, to stop current flowing on the outside of the shield. Cures many cases of RF in the shack.
Chordal hop: A long-distance path where the signal skips along inside the ionosphere without touching the ground between hops.
CHU: Canada’s time station near Ottawa, sending time signals on 3330, 7850 and 14670 kHz.
Circuit: A complete path that current can flow around, from a source through a load and back. Break the path anywhere and the current stops.
Circuit breaker: A resettable switch that opens automatically when too much current flows.
Circular polarization: A signal whose polarization rotates as it travels. Used for satellites, where the incoming orientation is unknown and keeps changing.
Claimed score: The score an entrant reports before the sponsor checks the logs.
Clear: Said when ending a contact and leaving the frequency, after your callsign.
Clock sync also NTP, time sync: FT8 and FT4 only work if your computer’s clock is within about a second of true time. A small time-sync program keeps it there. More on FT8 →
Club callsign also Club station license: A callsign held by a club, with a trustee responsible for it. Members can operate under it, often at club events.
Club Log: A free online service that matches your log against DXpedition logs, tracks your DXCC progress and handles many QSL requests. More on QSLs →
CME (coronal mass ejection): A huge burst of material from the Sun that can trigger geomagnetic storms a day or more later.
CMOS (complementary metal-oxide semiconductor): The logic family in almost everything modern: very low power when idle, but sensitive to static.
CMS (Common Message Server): Winlink’s internet servers, which hold mail until a radio station collects it. More on Winlink →
Coax also Coaxial cable: Cable with a center conductor inside a shield: the usual feedline between radio and antenna. Most amateur coax is 50 ohms.
Code plug: The configuration file for a DMR radio, listing every channel, talkgroup and repeater. Usually inherited from someone local and then edited.
Code practice oscillator also CPO: A small tone generator you key for Morse practice without transmitting. Try the Morse Code Trainer →
Code Proficiency Certificate: An ARRL certificate earned by copying a W1AW qualifying run correctly at a given speed.
Code test: A Morse exam once required for HF privileges. The US dropped it in 2007.
Codec 2: A free, open-source speech codec that squeezes voice into very low bit rates. It is the voice engine of FreeDV and M17. More on M17 →
Coil loading: Adding inductance to an antenna that is too short, so it resonates as if it were longer. The coil costs some efficiency and bandwidth, which is why a full-size antenna is preferred where there is room.
Cold solder joint: A dull, lumpy joint where the solder did not flow properly. It may work at first and then fail intermittently.
Collinear: Several vertical elements stacked end to end and fed in phase, for more gain. Common on repeater antennas.
Color code: A DMR setting that works like a tone: it must match the repeater’s before you can use it. More on DMR →
Colpitts oscillator: An oscillator that uses a coil and a pair of capacitors as a divider for its feedback.
Common-mode current: Current flowing on the outside of a coax shield instead of inside. It makes the feedline radiate and causes RF in the shack and extra receive noise.
Comparator: A circuit that compares two voltages and switches its output depending on which is higher.
Complex impedance: Impedance written as resistance plus reactance, such as 50 + j25 ohms. The j part is reactive: positive is inductive, negative capacitive.
Conductance also Siemens: How easily a circuit passes current: the reciprocal of resistance, measured in siemens. Ten ohms is 0.1 siemens.
Conductor: A material that lets current flow easily, such as copper.
Connected mode: Packet operation in which two stations set up a link and acknowledge every frame, resending anything lost. More on Packet →
Contest: An organized event where stations make as many short contacts as possible within a set time.
Contestia: A keyboard mode derived from Olivia: faster, with a little less robustness. More on Olivia →
Continuity: An unbroken electrical path. A multimeter’s continuity setting beeps when a wire or fuse is good.
Control operator: The licensed person responsible for a station’s transmissions at any given moment. Their license class sets which privileges can be used.
Control point: The place from which a station’s transmitter is controlled, whether at the radio or remotely.
Controlled environment: An area where people know about RF exposure and can take steps to limit it, such as the operator’s own shack.
Cootie: Another name for a sideswiper: a side-to-side key where both directions key the transmitter and the operator times every element. More on CW keys →
Copy: To receive and understand. “Solid copy” means you got all of it.
Core loss also Copper loss: Power lost as heat in a transformer’s or coil’s core. Copper loss is the heat lost in the wire itself.
Core saturation also Saturation: The point where a magnetic core cannot carry any more flux, so inductance collapses and distortion appears. Too much power through too small a toroid does it.
Coronal hole: A dark, open region in the Sun’s outer atmosphere that sends out fast solar wind, often bringing unsettled conditions a few days after it faces Earth. More on Space Weather →
Coulomb: The unit of electric charge, equal to the charge of 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 acts as the other half of an antenna when a real ground is not available. Essential for most end-fed antennas.
County hunter: An operator working toward contacts with every county in the US. Mobile stations often drive from county to county to give them out.
Courtesy tone: The beep a repeater sends when someone stops talking. Wait for it before you transmit.
CQ: A general call to anyone listening. “CQ CQ CQ, this is…”
CQ DX Marathon: A year-long competition from CQ magazine: count the countries and zones you work each calendar year, then start again in January.
CQ zone: One of the 40 zones CQ magazine divides the world into for its Worked All Zones award and the CQ contests. The lower 48 states fall in zones 3, 4 and 5. Not the same thing as an ITU zone or a US call area.
Crest factor: Peak divided by RMS. It is 1.414 for a sine wave and much higher for speech, which is why an SSB signal’s average power is far below its peak.
Crimp: Joining a connector to a wire by squeezing it with a crimping tool. Done with the right tool it is as reliable as solder.
Critical angle: The steepest angle at which a signal can leave the Earth and still be returned by the ionosphere.
Critical frequency: The highest frequency that reflects straight back down from the ionosphere when sent straight up.
Cross-modulation: A strong unwanted signal’s modulation appearing on the signal you are listening to.
Cross-polarization: Transmitting and receiving antennas at right angles, such as vertical and horizontal. Costs a great deal of signal on VHF line of sight, very little on HF skywave.
Crowbar: Protection that shorts a power supply’s output on purpose, blowing a fuse, if the voltage rises too high.
Crystal: A quartz element that sets a precise frequency. Older radios needed one per channel.
Crystal lattice filter: A filter built from matched quartz crystals, giving steep skirts at one fixed frequency. The traditional way to shape an SSB or CW passband.
Crystal radio: The simplest receiver: a coil, a capacitor, a diode and earphones, powered only by the signal.
CSCE: Certificate of Successful Completion of Examination: the paper you get after passing, proof of your new privileges until the license is issued.
CTCSS also PL tone, tone: A low tone sent under your voice that many repeaters need before they will respond. “PL” is Motorola’s old name for it.
CUL: See you later.
Current: The flow of electric charge, measured in amperes (amps).
Current clamp: A meter jaw that reads current by sensing the magnetic field around a wire, with no need to break the circuit.
Cut numbers: Morse shorthand in which letters stand in for numbers, such as T for 0 and N for 9. Common in contests.
CW: Continuous wave — Morse code. More on CW →
CWops also CW Academy, CWT: A club of CW operators. It runs CW Academy, free online classes for learning and improving Morse, and the CWT, a weekly one-hour mini-contest. More on CW →
Cycle life: How many charge and discharge cycles a battery gives before its capacity drops to a set fraction, usually 80 percent. LiFePO4 manages thousands where lead-acid manages hundreds.

D

D layer: The lowest ionospheric layer, present by day. It absorbs low-band signals, which is why 80 m and 160 m open up after dark.
D-STAR: A digital voice and data standard from the Japan Amateur Radio League, used mostly on Icom radios. More on D-STAR →
DAC (digital-to-analog converter): The reverse of an ADC: it turns a stream of numbers back into a changing voltage, such as audio.
DATV (Digital amateur television): Amateur television sent digitally, usually with broadcast standards such as DVB-S, needing less power and bandwidth than analog ATV. More on ATV →
dBd: Antenna gain compared with a half-wave dipole. The same antenna reads 2.15 higher in dBi, so check which one an advert quotes.
dBi: Antenna gain compared with an imaginary antenna that radiates equally in every direction.
dBm: Power in decibels compared with one milliwatt. Zero dBm is 1 mW, +30 dBm is 1 watt, and a weak HF signal might be -120 dBm.
dBW: Power in decibels compared with one watt. A 100-watt transmitter is +20 dBW.
DC (direct current): Current that flows in one direction only, as from a battery.
DCS (digital-coded squelch): A digital alternative to CTCSS that some repeaters require.
DDS (direct digital synthesis): Making a signal digitally, number by number, and turning it into a sine wave. It allows very fine, fast and clean tuning.
Dead band: A band with no propagation at the moment. Often it is only that nobody is calling CQ.
Decade: A tenfold change in frequency. Used with octave to describe how steeply a filter or response curve falls.
Decibel also dB: A ratio on a logarithmic scale, used for gain and loss. 3 dB doubles or halves power; 10 dB is ten times.
Decimation: Throwing away a fixed share of the samples after filtering, to lower the data rate once the wanted slice of spectrum is all that is left.
Delta loop: A full-wavelength loop of wire in a triangle. Quieter on receive than a dipole, with a little gain.
Depletion region: The thin zone at a diode junction with no free charge carriers. Its width changes with voltage, which is how a varactor works.
Depth of discharge also DoD: How much of a battery’s capacity is used before recharging. Lead-acid lasts longest when used only lightly; LiFePO4 handles deep discharges well.
Derating: Deliberately running a part well below its maximum rating so it lasts. Half the rated power and half the rated voltage is a good habit.
Desense: A receiver losing sensitivity because a strong nearby signal is overloading it.
Desoldering braid also Solder wick: Fine copper braid that soaks up melted solder when heated, to remove a part or clean up a joint.
Deviation: How far an FM signal swings from its center frequency. Too much makes you sound loud and distorted on a repeater.
DG-ID (Digital Group ID): A number from 00 to 99 used in System Fusion to sort users into groups and to reach linked rooms. More on System Fusion →
Dielectric: An insulating material between two conductors, such as the plastic inside coax or between a capacitor’s plates. It affects capacitance and, in coax, the velocity factor.
Digipeater: A packet station that retransmits packets to extend their range. The backbone of APRS. More on APRS →
Digirig: A small, low-cost sound card and CAT interface for digital modes. More on Interfaces →
Digital electronics: Circuits that work with just two states, on and off, standing for 1 and 0. Computers, and most of a modern radio, are digital.
Digital mode: Any mode where a computer or chip encodes the signal, such as FT8, RTTY or DMR. More on Modes →
Digital Radio Mondiale also DRM: A digital broadcasting system used by some shortwave stations, giving FM-like audio from an HF signal.
Diode: A component that lets current flow in one direction only.
Dip meter also Grid dip meter: An older instrument for finding the resonant frequency of a circuit or antenna without connecting to it.
Diplexer: A filter that lets two bands share one feedline or antenna.
Dipole: The simplest practical antenna: a wire about half a wavelength long, fed in the middle. Often a new ham’s first HF antenna, and still one of the best.
Direct sampling: Digitizing the antenna signal itself, with no mixing down first. The approach behind most modern SDRs, and the reason they have so few analog stages.
Direct-conversion receiver also Zero-IF: A receiver that mixes the signal straight down to audio in one step. Simple, and the basis of many SDRs and QRP kits.
Directed net: A net run by a net control station who decides who talks when.
Directional coupler: The part inside an SWR or power meter that separates forward from reflected power by sampling the line.
Directional wattmeter: A power meter that reads forward and reflected power separately.
Directivity: How much an antenna concentrates its signal in one direction compared with spreading it evenly. Gain is directivity minus the antenna’s losses. More on Antenna Gain →
Director: An element in front of the driven element of a beam, slightly shorter, which draws signal forward.
Direwolf: Free software that replaces a hardware TNC using a computer sound card. The usual choice for new packet and APRS stations. More on Packet Radio →
Discone: A wideband VHF/UHF antenna shaped like a disk above a cone. Popular for scanning many frequencies with one antenna.
Dit and dah: The short and long elements of Morse code. More on CW →
Division also ARRL division: A group of ARRL sections. Each division elects a Director who sits on the ARRL Board.
DMR (Digital Mobile Radio): A digital voice standard borrowed from commercial radio, organized into talkgroups and time slots. More on DMR →
DMR ID: A number tied to your callsign that identifies you on DMR. Hams get one free from RadioID. More on DMR →
DominoEX: A keyboard mode that copes well with drifting signals and poor conditions, available in fldigi.
Doppler shift: The change in frequency as a satellite moves toward or away from you, which you correct for during a pass.
Double-balanced mixer also DBM: A mixer that cancels both input signals at its output, leaving mostly the sum and difference. Often a ring of four diodes and two transformers.
Double-conversion: A receiver that uses two intermediate frequencies in turn, for better image rejection and selectivity.
Doublet: A center-fed wire of any convenient length, fed with ladder line and matched with a tuner. Works on many bands with low loss.
Doubling: Two stations transmitting at the same moment so neither is heard properly. Leaving a short gap before you answer prevents most of it.
Driven element: The element of a beam that is connected to the feedline. The others are parasitic.
Dropout voltage: How much higher than its output a linear regulator’s input must stay before it loses control. It is why a 12-volt regulator cannot run from exactly 12 volts.
DSP (digital signal processing): Filtering and processing signals in software rather than with components. Behind most modern noise reduction and filters.
DTMF also Touch-tone: The dual-tone signals a phone keypad makes, used to send commands to repeaters and remote stations.
Dual-lever paddle also Single-lever paddle: A Morse paddle with two separate levers, needed for iambic keying. A single-lever paddle has one lever that swings either way. More on CW Keys →
Ducting also Tropospheric ducting: VHF and UHF signals trapped between layers of air of different temperature and travelling hundreds of miles. Often set up by a summer high-pressure system.
Dummy load: A resistor that absorbs your transmitter’s output instead of radiating it, for testing without annoying anyone.
Dupe: A contact with a station already worked in the same contest, which normally counts for nothing.
Duplex: Transmitting and receiving on different frequencies, as when using a repeater.
Duplexer: A filter set that lets a repeater transmit and receive on one antenna at the same time.
Duty cycle: How much of the time a mode keeps the transmitter keyed. FT8 and RTTY run near 100%, so many radios need turning down for them.
DX: Distance, or a distant station. On HF it usually means another continent.
DX cluster: A network where hams post spots of stations they have heard, viewable online or in logging software.
DX window: A small part of a band set aside by agreement for long-distance contacts. Local chat there is frowned on.
DXCC: The ARRL’s award for contacting 100 or more recognized entities, and by extension the list of those entities itself.
DXpedition: A trip to somewhere rare specifically to put it on the air for everyone else.
Dynamic range: How well a receiver copes with very strong and very weak signals at once without overloading.

E

E layer: The middle layer of the ionosphere, mainly a daytime feature, and home of sporadic E.
Ears: A receiver’s ability to hear weak signals. “Good ears” is a compliment to the station, or to the operator.
Earth station: An amateur station on or near the ground that communicates with space stations.
EchoLink: A system that links repeaters and stations over the internet, so you can reach a distant repeater through a local one or a computer. Signing up requires proof of license.
Eddy current: Current that circulates inside a metal core or chassis because a changing magnetic field induces it. It wastes power as heat, which is why cores are laminated or powdered.
Effective aperture also Capture area: The area from which an antenna collects a passing signal. It grows with gain and with wavelength.
EFHW (end-fed half-wave): A half-wave wire fed at one end through a matching transformer, usually 49:1 or 64:1. Popular for portable use because it needs only one support near the radio.
Eggbeater: An omnidirectional satellite antenna of two crossed loops, giving circular polarization without a rotator.
EIRP (effective isotropic radiated power): Transmitter power adjusted for losses and antenna gain, compared with an isotropic antenna.
Electric charge also Charge: The property that makes particles push or pull on each other: like charges repel, opposite charges attract. Electrons carry negative charge and protons positive.
Electric field: The region around a charge or a voltage where another charge feels a push or pull. It is measured in volts per meter.
Electricity: The effects of electric charge, whether sitting still (static) or moving (current).
Electrolytic capacitor: A capacitor with large capacitance in a small size, used for smoothing power supplies. It has a positive and negative lead, and wired backward it can burst.
Electromagnet: A coil of wire, often around an iron core, that becomes a magnet while current flows. Relays and speaker drivers use them.
Electromagnetic spectrum: The whole range of electromagnetic waves, from low-frequency radio through microwaves, infrared, visible light and ultraviolet to X-rays and gamma rays. Amateur bands are small slices of the radio end.
Electromagnetic wave: Linked electric and magnetic fields that travel through space at the speed of light. Radio, light and X-rays are all electromagnetic waves, differing only in frequency. More on Wavelength →
Electron: A tiny particle with a negative charge that moves around the nucleus of an atom. Electric current is electrons drifting through a conductor, and radio waves are made by electrons moving back and forth in an antenna.
Electronic keyer: A circuit or radio feature that makes perfectly timed dits and dahs from a paddle. More on CW Keys →
Electronics: Using components such as transistors, diodes and tubes to control the flow of electrons, for example to amplify, switch or generate signals. Every radio is an electronic device.
Electrostatic discharge also ESD: A sudden spark of static electricity. Too small to feel, it can still ruin transistors and chips, so touch a grounded surface or wear a wrist strap before handling circuit boards.
Element: One conducting part of an antenna, such as each rod on a Yagi. In US licensing, also one of the three written exams: Element 2 for Technician, 3 for General and 4 for Extra. More on Question Pools →
Element credit: Credit for an exam element already passed, shown on a CSCE and valid for 365 days.
Elevation plot: A side view of an antenna’s radiation pattern, showing strength at each angle above the horizon.
Elliptical polarization: A signal whose polarization rotates as it travels, between linear and circular. Signals bounced off the ionosphere usually end up this way.
Elmer: An experienced operator who mentors a newcomer. Being someone’s Elmer is both a duty of the hobby and an honor.
EmComm also Emergency communications: Amateur radio supporting communication when normal systems fail, usually organized through ARES or RACES.
EME also Moonbounce: Bouncing signals off the Moon to make contacts. Demanding, but possible with modest stations using digital modes.
Emergency Coordinator also EC: The ARES leader for a county or local area, who recruits members, works with served agencies and organizes drills. More on ARES →
Emission type: The kind of signal a station transmits, such as CW, phone, data or image. Band plans and rules are written in these terms.
Enforcement Bureau: The FCC bureau that investigates interference and rule violations, including in the amateur bands.
eQSL: An online service for exchanging electronic QSL cards.
Equatorial anomaly: Two bands of extra-dense ionization either side of the magnetic equator, which make trans-equatorial propagation possible.
ERP (effective radiated power): Transmitter power adjusted for feedline loss and antenna gain.
Error correction: Ways of detecting and repairing errors in received data, such as forward error correction and automatic repeat requests.
ES: “And”, in Morse shorthand.
Exchange: The information swapped in a contest contact, such as a signal report and serial number or location.
Extended double Zepp also EDZ: A center-fed wire about 1.25 wavelengths long, giving a little more gain broadside than a half-wave dipole.

F

F layer: The highest layer and the one that carries most long-distance HF. By day it splits into F1 and F2.
F region: The highest part of the ionosphere, responsible for most long-distance HF. By day it splits into F1 and F2 layers.
F2 layer: The upper and most important part of the ionosphere’s F region, which carries most long-distance HF signals.
Fan dipole also Parallel dipole: Several dipoles for different bands joined at one feedpoint and spread apart like a fan, all on one coax.
Far field: The region several wavelengths from an antenna, where its radiation pattern has settled into its final shape. Pattern measurements belong there.
Farad also F: The unit of capacitance. One farad is huge, so radio circuits use microfarads (µF), nanofarads (nF) and picofarads (pF).
Faraday rotation: The twisting of a signal’s polarization as it passes through the ionosphere. One reason antenna polarization matters little on HF.
Farnsworth: A way of learning Morse where characters are sent at full speed with longer gaps between them. More on Morse Trainer →
Fast-scan television also ATV: Amateur television with full-motion video, usually on 70 cm and higher bands.
FB (fine business): Excellent.
FCC (Federal Communications Commission): The US government agency that issues amateur licenses and makes the rules in Part 97.
FEC (forward error correction): Extra information sent with data so the receiver can fix errors on its own. A big part of why FT8 decodes signals you cannot hear.
Feedback: Feeding part of a circuit’s output back to its input. Negative feedback steadies an amplifier; positive feedback makes an oscillator, or a howl when a microphone hears its own speaker.
Feedline: The cable between radio and antenna, usually coax or ladder line.
Feedline loss also Line loss: Signal lost as heat in the feedline, rising with length and frequency. A lossy line can make a poor antenna look well matched.
Feedpoint impedance: The impedance an antenna presents where the feedline connects. A dipole is roughly 50 to 75 ohms; most radios expect 50.
FEMA: The US Federal Emergency Management Agency, which sponsors RACES.
Ferrite: Magnetic material used in chokes and snap-on beads to stop unwanted RF on cables.
Ferrite bead: A small ferrite cylinder slipped over a wire to add impedance at RF and choke off common-mode current. A row of them cures many interference problems.
Ferrite mix: The material grade of a ferrite core, which sets the frequencies it works best on. Mix 31 is a common choice for HF chokes.
FET (field-effect transistor): A transistor controlled by voltage rather than current, common in receiver front ends and power amplifiers.
FFT (fast Fourier transform): The calculation that turns a block of samples into a list of frequencies. It draws every panadapter and waterfall display.
Field Day: An annual exercise where clubs operate portable on emergency power, part contest and part practice, part picnic.
Field strength meter: A simple meter that shows the relative strength of a nearby transmitted signal. Handy for checking an antenna and easy to build.
Film capacitor: A capacitor using a plastic film dielectric. Stable and non-polarized, common in audio and timing circuits.
Filter: A circuit that passes some frequencies and blocks others. Radios use them to pick out one signal and to keep transmitters clean.
Firmware: The built-in software that runs a radio or other device. Makers release updates that fix bugs and add features.
Fist: An operator’s recognizable Morse sending style.
Flat-topping: Distortion when a transmitter or amplifier is driven past its limit and the peaks of the waveform are flattened. It causes splatter.
fldigi: Free software covering a wide range of HF digital modes including PSK31, RTTY and Olivia.
Flip-flop: A circuit that remembers one bit until it is told to change. The building block of counters, dividers and registers.
Float charge: A steady low voltage that holds a lead-acid battery full without overcharging it, the normal state for a standby battery.
Flutter: Rapid fading that makes a signal warble, typical of aurora, meteor and some polar paths.
Flux: A chemical that cleans metal as it is soldered so the solder flows and bonds. Rosin flux is the kind for electronics.
FM (frequency modulation): The standard voice mode on VHF and UHF repeaters. More on FM →
Foldback current limiting: Power supply protection that cuts the output current right back when there is a short circuit.
Folded dipole: A dipole made from a loop of wire or rod, with a higher feed impedance, about 300 ohms.
Footswitch: A foot pedal for push-to-talk, leaving both hands free.
Forward bias also Reverse bias: Voltage applied to a diode in the direction that lets it conduct. Reverse bias is the opposite, which blocks current.
Foxoring: A short-range form of ARDF in which tiny transmitters sit near points marked on a map.
Free-space path loss: The weakening of a signal as it spreads out with distance. Doubling the distance costs 6 dB.
FreeDV: Free, open-source digital voice for HF, run from a computer and a sound card interface. More on FreeDV →
Frequency: How many times per second a radio wave cycles, measured in hertz. The number on your dial.
Frequency coordination: The volunteer process that assigns repeater frequencies in an area to keep them from interfering. A coordinated repeater has priority in a dispute.
Frequency coordinator also Coordination: The local body that assigns repeater frequencies so repeaters do not interfere with each other.
Frequency counter: An instrument that measures and displays the frequency of a signal.
Frequency Measuring Test also FMT: An ARRL event in which operators try to measure the exact frequency of special test transmissions.
Frequency multiplier: A circuit that produces a whole-number multiple of its input frequency, used in older VHF transmitters.
Frequency response: How evenly a circuit passes signals across a range of frequencies, such as the audio range of a microphone or a transmitter’s filter.
FRN (FCC Registration Number): The ID you need before taking a US exam. Get one free online beforehand. More on Learn →
Front-to-back ratio: How much stronger a directional antenna is to the front than to the rear, in dB.
FRS (Family Radio Service): License-free, short-range UHF handhelds.
FSK (frequency-shift keying): Sending data by switching between two or more tones. RTTY is the classic example.
FST4: A WSJT mode for weak signals on the low bands, including the 2200 and 630 m bands.
FST4W: A WSPR-like beacon mode in WSJT-X with longer transmissions, aimed mainly at the low bands such as 630 and 2200 meters. More on WSPR →
FT4: A faster cousin of FT8 designed for contests, with 7.5-second cycles. More on FT4 →
FT8: A very sensitive digital mode using short automated exchanges, now among the most used modes on HF. More on FT8 →
Full break-in also QSK: CW operation in which the receiver comes back between every dit and dah, so you can hear the other station while you send. More on CW →
Full gallon also Full legal limit: Running the maximum power the license allows, 1,500 watts PEP in the US.
Full quieting: An FM signal strong enough to silence the receiver’s background hiss completely.
Full-wave rectifier also Half-wave rectifier: A rectifier that uses both halves of the AC cycle, giving smoother DC that is easier to filter. A half-wave rectifier uses only one half.
Fuse: A protective part that melts and breaks the circuit when too much current flows.

G

G5RV: A multiband dipole about 102 feet long, fed with a section of ladder line and then coax. Named for its designer’s callsign; it needs a tuner on most bands.
Gain: How much a circuit increases a signal, usually given in decibels. Antenna gain is a different idea: it concentrates power in one direction rather than adding any.
Gain-bandwidth product also GBW: For an amplifier such as an op-amp, the gain multiplied by the bandwidth stays about constant: more gain means less bandwidth.
Gate time: How long a frequency counter counts cycles for each reading. Longer gates give more digits.
General: The middle US license class, which opens most of the HF bands. More on Learn →
Geomagnetic storm: A disturbance of the Earth’s magnetic field caused by solar activity. It degrades HF and can bring aurora.
GFCI: A ground-fault circuit interrupter, an outlet or breaker that cuts power when current leaks to ground. Important around water and outdoors.
Gilbert cell: A transistor circuit that multiplies two signals, the basis of many mixer chips.
GMRS (General Mobile Radio Service): A US UHF service that needs a license but no exam. Not amateur radio, but popular with families.
Go-kit also Go-box: A packed, ready-to-use station for emergency deployment, with radio, power, cables and tools kept together.
GPSDO: A GPS-disciplined oscillator, the standard for frequency accuracy in microwave and precision digital work.
Grace period: The two years after a US license expires during which it can still be renewed, though you may not transmit until it is.
Gray line also Grey line, terminator: The band of twilight circling the Earth at sunrise and sunset. Signals traveling along it often go unusually far on the low bands. More on Gray Line →
Great circle: The shortest route between two points on a globe. A beam pointed at a distant station follows it, which is why headings look odd on a flat map.
Green stamp: A US dollar bill sent with a QSL request to cover return postage.
Grid square also Maidenhead locator: A short code such as FN31pr identifying a location, used for reporting and for awards. More on Grid Square & Distance →
GridTracker: Free software that maps FT8 and other digital-mode activity live, alongside WSJT-X or JS8Call. More on Software →
Ground: A common reference point in a circuit, usually the negative side or the chassis, and also a connection to the earth itself. Station, safety and RF grounds do different jobs. More on Single-point ground →
Ground conductivity: How well the soil under an antenna conducts electricity. Moist or salty ground helps verticals a great deal; dry rock and sand hurt them.
Ground loop: Two or more paths to ground carrying stray current between pieces of equipment, heard as hum or buzz. Bonding everything to one point cures it.
Ground plane: The conducting surface a vertical antenna works against, whether radials, a car roof or the earth.
Ground radial also Radial system: One of the wires laid on or just under the ground around a vertical antenna to carry its return current. The more of them, the better the efficiency: a handful raised above ground does what dozens do on the soil.
Ground rod: A copper-clad rod driven into the earth as part of a station’s safety ground. Electrical codes usually require it to be bonded to the house ground.
Ground wave: A signal that follows the Earth’s surface. Useful on the lowest bands; short-range on HF.
Grounded-grid: A tube amplifier circuit in which the grid is at RF ground and the drive goes to the cathode. Common in HF linear amplifiers.
Gutter antenna: A rain gutter and downspout pressed into service as an HF radiator, usually loaded with a tuner. A real option under antenna restrictions, though results depend on the joints being electrically sound.

H

HAARP: An ionospheric research facility in Alaska, run by the University of Alaska Fairbanks, that sometimes invites hams to report hearing its experiments.
Half-power point also 3 dB point: The frequency where a filter or tuned circuit has dropped to half its peak power output. The span between the two half-power points is its bandwidth.
Half-sloper: A quarter-wave wire sloping down from a tower, fed against the tower. A simple low-band antenna for a tower owner.
Half-wave: An antenna or element about half a wavelength long at its working frequency. For a wire dipole, length in feet is roughly 468 divided by the frequency in MHz.
Hall effect device: A sensor that produces a voltage when a magnetic field crosses a current-carrying chip. Used in DC current clamps and contactless switches.
Ham: A licensed amateur radio operator. Nobody agrees where the word came from.
Ham cram: A one-day class that packs in exam study and ends with the exam itself. More on Learn →
Hamfest: A gathering combining a flea market, talks and a chance to meet people you have only heard.
HamSCI (Ham Radio Science Citizen Investigation): A collaboration between hams and university researchers that uses amateur stations and data to study the ionosphere and space weather. More on Citizen Science →
Hamshack Hotline: A free internet phone network for hams, using desk VoIP phones.
Hamstick: A popular style of mobile HF whip, one band per whip, with a loading coil built into a fiberglass rod.
Hamvention: The largest hamfest in the US, held each May near Dayton, Ohio.
Handheld also HT, handie-talkie: A portable VHF/UHF transceiver small enough to hold in one hand, and most operators’ first radio. HT comes from Handie-Talkie, an early Motorola product name.
Handiham: A program that helps people with disabilities get licensed and on the air, with study help and adapted equipment.
Handling instructions also HX: Codes in a radiogram’s preamble that tell stations how to handle the message, such as asking for a reply or a report of delivery. More on Radiograms →
Hang AGC: An AGC setting that holds the gain steady for a moment after a signal stops, then recovers quickly. It suits SSB and CW.
Hardline: Coax with a solid outer shield and very low loss, used for long runs and at repeater sites.
HAREC: A CEPT certificate showing that a ham passed an exam to the shared European standard, recognized by many countries for licensing visitors. More on Operating Abroad →
Harmonic distortion: Distortion that adds whole multiples of the original frequency. In a transmitter it puts energy on other bands, which is why a low-pass filter follows the final stage.
Harmonics: Unwanted multiples of your transmit frequency. Also, jokingly, an operator’s children.
Hartley oscillator: An oscillator that uses a tapped coil for its feedback.
Head copy: Reading Morse in your head as it arrives, without writing it down. More on CW →
Heat shrink: Plastic tubing that shrinks tight when heated, used to insulate and protect joints.
Heat sink: A metal block, usually finned, that draws heat away from transistors and regulators. The back of most radios is one.
Helical antenna: A coil of wire wound around a boom, giving circular polarization. Used at UHF and microwave for satellites. A rubber duck is a small, different kind of helical.
Hellschreiber also Feld Hell, Hell: A mode that sends each character as a small picture, painted on screen like a fax strip. Invented by Rudolf Hell in the 1920s.
Henry also H: The unit of inductance. Radio coils are usually measured in microhenries (µH).
Hertz also Hz, kHz, MHz: Cycles per second. 1 kHz is a thousand, 1 MHz a million.
Heterodyne: A whistle heard when two carriers are close in frequency.
Hex beam: A lightweight multiband directional antenna with wire elements on a frame like an upturned umbrella. A popular choice for smaller lots.
HF: High frequency, 3–30 MHz. Where worldwide contacts happen.
Hi hi also Hihi: Laughter, sent in CW. HI HI in Morse sounds like a chuckle, and the habit carried over into voice.
High bands: 20 m up to 10 m, which depend most on the solar cycle.
High-altitude balloon also Ham balloon, pico balloon: A balloon carrying a small amateur transmitter, often APRS or WSPR, that climbs into the stratosphere and sends back position and telemetry. A favorite school and club project, tracked by anyone with a receiver.
High-pass filter: A filter that passes frequencies above a cutoff. Often used to keep HF signals out of TVs and VHF receivers.
HOA (homeowners association): Many restrict outdoor antennas, which is why stealth antennas exist.
Homebrew: Equipment you built yourself.
Horizontal loop also Skywire: A full-wavelength or longer loop of wire strung horizontally. Works on its design band and its harmonics and is known for low noise.
Hot switching: Switching a relay while RF is flowing through it, which burns the contacts. A sequencer prevents it.
Hotspot: A small box that links a digital-voice radio to the internet, giving access to worldwide networks without a nearby repeater.
Hunter also Chaser: An operator who contacts POTA or SOTA activators, usually from home.
Hurricane Watch Net: A net that activates on HF when a hurricane threatens, passing surface reports from the affected area to the National Hurricane Center. More on Emergency Groups →
Hydrogen line: Radio emission from hydrogen gas in our galaxy near 1420 MHz. Hams detect it with a small dish and an SDR. More on Radio Astronomy →
Hysteresis: A magnetic core’s reluctance to follow a changing field exactly, which loses a little energy on every cycle. It sets a limit on how high a core material can usefully work.

I

Iambic: A keying style using a dual-lever paddle, where squeezing both levers sends alternating dits and dahs. More on CW keys →
IARU (International Amateur Radio Union): The federation of national societies that represents amateurs internationally and coordinates band plans by region.
IC (integrated circuit): Many transistors and other parts built together on one piece of silicon.
ICS (Incident Command System): The standard structure US agencies use to manage emergencies. Many EmComm groups ask members to take the free online courses.
IF (intermediate frequency): A fixed frequency inside a superheterodyne receiver, to which every incoming signal is converted for filtering and amplification.
IF filter: A filter at the intermediate frequency that sets how wide a slice of band a receiver hears.
iGate also Internet gateway: An APRS station that passes packets heard on the air to the internet (APRS-IS), and sometimes messages back the other way. More on APRS →
Image rejection: How well a receiver ignores signals on its image frequency, a false response created by its mixing process.
Image response also Image: A signal appearing at the wrong dial setting because it is as far above the local oscillator as the wanted signal is below it. Good filtering ahead of the mixer prevents it.
IMBE: The voice codec used by P25 Phase 1 radios.
Impedance: Opposition to alternating current, in ohms, combining resistance and reactance. Amateur gear is built around 50 ohms.
Incident action plan also IAP: The written plan for an operating period of an emergency response, including the communications plan.
Incident Commander: The person in overall charge of an emergency response under the Incident Command System. More on ICS →
Incidental radiator: A device that gives off radio energy as a by-product, such as a motor or a light dimmer. More on RFI →
Inductance: The ability to store energy in a magnetic field, measured in henrys.
Inductive reactance: A coil’s opposition to AC, which rises with frequency.
Inductor also Coil: A component that stores energy in a magnetic field. It passes DC and resists AC more as frequency rises.
Insertion loss: The signal a filter or switch swallows just by being in the path, in decibels. A good coax relay loses a few hundredths of a dB; a cheap filter can cost a dB or more.
Insulator: A material that blocks current flow, such as glass, plastic or ceramic.
Interlock: A switch that cuts power when an equipment cover is opened, protecting against dangerous voltages inside.
Intermodulation also IMD, intermod: Unwanted mixing of two or more signals inside a receiver or amplifier, producing sums and differences that were never transmitted. On a repeater it makes phantom signals appear.
Intruder Watch also Band intruders, IARU Monitoring System: Volunteers who log non-amateur signals intruding in the amateur bands and report them to their national society.
Inverted L: A vertical wire that bends over at the top to run horizontally. Common on 160 and 80 m, where a full-height vertical would be too tall.
Inverted V: A dipole with its center at the top of a single support and the two legs sloping down. Needs only one tall support and works nearly as well as a flat dipole.
Inverter: A device that turns DC from a battery into AC like a wall outlet. Many are electrically noisy on HF.
Ionosonde also Ionogram: A radar that sweeps up through HF and times the echoes from the ionosphere. Its chart, the ionogram, shows the critical frequency overhead. More on Forecasts →
Ionosphere: Layers of charged gas roughly 40 to 600 miles up that bend HF signals back to Earth, making long-distance contacts possible.
IOTA (Islands on the Air): An awards program for contacting islands around the world.
IRLP (Internet Radio Linking Project): An older system for linking repeaters over the internet.
IS-100 also ICS-100: FEMA’s free online introduction to the Incident Command System. Many ARES groups ask members to take it, with IS-200 and IS-700. More on ICS →
ISED (Innovation, Science and Economic Development Canada): The Canadian government department that issues amateur radio certificates.
Isotropic antenna: An imaginary antenna radiating equally in every direction, used as a reference for gain.
ISS (International Space Station): The crewed station that carries an amateur radio station. Hams work its repeater and packet system on VHF and UHF, and schools talk to the crew through the ARISS program.
ITU (International Telecommunication Union): The UN agency that allocates radio spectrum worldwide, including the amateur bands.
ITU region: The world is split into three regions with slightly different band allocations. North and South America are Region 2.
ITU zone: One of the 90 zones the International Telecommunication Union divides the world into, used by the IARU HF Championship and some awards. A different map from the 40 CQ zones, and nothing to do with the digit in a US callsign.

J

J-pole: A half-wave vertical fed through a quarter-wave matching section, shaped like the letter J. A cheap, easy antenna to build for 2 m and 70 cm.
JFET (Junction field-effect transistor): A field-effect transistor controlled by a reverse-biased junction at its gate. Quiet, and common in receiver front ends and VFOs.
JOTA (Jamboree on the Air): The Scouting weekend each October when clubs put Scouts on the air to talk to other Scouts worldwide. One of the biggest youth events in the hobby.
JS8Call: A keyboard-to-keyboard mode built on FT8’s technology, able to relay messages through other stations. More on JS8Call →
JT65: An older weak-signal mode, largely replaced by FT8 on HF but still used for moonbounce.
JT9: A very narrow weak-signal mode from the WSJT family, used mostly on the low bands.
JTAlert: A companion program for WSJT-X that sounds alerts for stations you need and passes contacts to your log. More on Software →
JTDX: An alternative to WSJT-X for FT8 and related modes, preferred by some for its decoding. More on Software →
Junk box: The collection of salvaged parts every builder keeps. The measure of a well-stocked shack.

K

K and KN: K: go ahead, anyone. KN: go ahead, only the station I am working.
K index: A three-hour measure of disturbance in the Earth’s magnetic field, from 0 to 9. Low is good; 5 and above means a storm and poor HF.
Keplerian elements also Keps, TLE: The set of numbers describing a satellite’s orbit, fed to tracking software so it can predict passes.
Kerchunk: Keying a repeater briefly without identifying, just to hear it respond. Technically illegal and mildly annoying.
Key: The device used to send Morse — straight key, paddle or bug.
Key click also Key clicks: Hard, square edges on a CW signal that make clicks and thumps up and down the band. Shaped keying, which every modern radio has, removes them.
Keyboard-to-keyboard: A digital mode for live typed conversation, such as PSK31 or RTTY.
Keyer: Electronics that form properly timed dits and dahs from a paddle. More on CW keys →
Kids Day: An ARRL event in which licensed hams help young people get on the air and talk to other kids.
Kirchhoff’s laws: Two rules for any circuit: the currents flowing into a point equal the currents flowing out, and the voltages around any closed loop add up to zero.
KISS also KISS TNC, KISS mode: A simple protocol between a computer and a TNC: the TNC only sends and receives packets, and the computer program does the rest. More on TNCs →
Kit: A radio or accessory sold as parts to assemble yourself.
Knife-edge diffraction: Signal bending over a sharp ridge, so a station in the shadow of a hill can still be worked on VHF.
Koch method: Learning Morse by starting with two characters at full speed and adding one at a time. More on Morse Trainer →
Kp index also Ap index: Planetary versions of the K and A indices, combining readings from stations around the world. A high Kp means a stormy magnetic field. More on Space Weather →

L

L-network: The simplest matching circuit: one coil and one capacitor.
Ladder line: Open-wire feedline with very low loss, especially when the match is poor.
LDMOS: A type of power transistor used in modern solid-state amplifiers, rugged and able to run at high power.
Leap second: An extra second occasionally added to UTC to keep it in step with the Earth’s slowing spin. Timekeepers have agreed to stop adding them by 2035.
Learning net: A regular on-air session where a club teaches a topic and newer operators can ask questions.
LED (light-emitting diode): A diode that gives off light when current flows through it.
Legal limit: The maximum power allowed. In the US it is 1,500 watts PEP output on most bands.
LEO (Low Earth orbit): An orbit a few hundred miles up. LEO satellites pass overhead in about ten minutes and are easy to work with simple gear.
License term: A US amateur license lasts ten years and can be renewed.
Lid: A poor or discourteous operator. Old slang, still in use.
LiFePO4 also Lithium iron phosphate: The battery chemistry most portable operators now use. Lighter than lead-acid and safer than other lithium types.
Lightning arrester also Surge arrester, lightning arrestor: A device in the feedline that shunts a surge to ground before it reaches the radio. It belongs on a grounded entry panel and helps with nearby strikes, not direct hits; disconnecting the antenna in a storm is safer.
Line of sight: A straight-line path, which limits VHF and UHF to about the horizon without help from the weather or a repeater.
Linear: An amplifier that increases transmit power without distorting the signal.
Linear power supply: A heavy supply with a large transformer and a regulator. It wastes more power as heat but makes almost no radio noise.
Linear transponder: A satellite repeater that relays a whole slice of band at once, so SSB and CW contacts can share it. More on Satellites →
Linearity: How faithfully an amplifier’s output follows its input. SSB needs a linear amplifier; CW and FM do not.
Link budget: An accounting of every gain and loss between transmitter and receiver, used to work out whether a path will work.
Link layer: In networking, the part that handles getting data reliably across one radio link.
Link margin: How much stronger the received signal is than the minimum needed. Extra margin covers fading.
Linked repeaters: Repeaters connected by radio or internet, so a signal into one comes out of all of them.
Listening also Monitoring: Said on a repeater with your callsign to let others know you are there, without calling anyone in particular.
Lithium-ion also Li-ion: A light, compact battery type used in handhelds and laptops. A four-cell pack reaches about 16.8 volts when full, above what most 12-volt radios accept. More on A Guide to Portable Amateur Radio Power →
Little pistol: A modest station, the opposite of a big gun.
LMR-400: Low-loss 50-ohm coax popular for VHF and UHF runs. Stiffer than RG-8X and needs connectors made for it.
LO (local oscillator): The oscillator in a receiver or transmitter that the mixer uses to shift signals to a new frequency.
Load: Whatever a circuit delivers power to, such as a radio on a power supply or an antenna on a transmitter.
Loaded Q: A tuned circuit’s Q once the load is connected. It is always lower than the unloaded Q, and it is what sets the real bandwidth.
Loading coil: A coil placed partway along an antenna to make it electrically longer, so a short antenna works on a lower band.
Local control: Operating a station with the control operator at the radio itself.
Log: The record of your contacts. No longer legally required in the US, but needed for every award and contest.
Log periodic also LPDA: A directional antenna with many elements of graded lengths, covering a wide frequency range with steady performance.
Logic gate: A basic digital circuit that gives an output from one or more on/off inputs, such as AND, OR and NOT.
Logic level: The voltage ranges a digital circuit reads as 0 and 1. Mixing 5-volt and 3.3-volt parts without a converter is a common way to destroy a microcontroller.
Long path: Reaching a station the long way round the Earth, opposite the direct route. Sometimes stronger than the short path.
Long wire: Strictly, a wire antenna at least one wavelength long. Commonly and loosely used for any end-fed wire.
LoRa: A long-range, low-power radio technique used by Meshtastic and many sensors.
LoTW also Logbook of the World: The ARRL’s online system for confirming contacts electronically, accepted for DXCC and other awards.
Low bands: 160, 80 and 40 m. Best at night, and demanding on antennas because of their long wavelengths.
Low-pass filter: A filter that passes frequencies below a cutoff and blocks those above. Used after a transmitter to suppress harmonics.
LUF (lowest usable frequency): The lowest frequency that gets through between two points; below it, absorption swallows the signal.

M

M17: An open-source digital voice mode built by hams, free of proprietary voice codecs. More on M17 →
Machine: Slang for a repeater.
Mag mount also Magnet mount: A vehicle antenna base held on by a magnet. No holes needed, and at VHF and UHF it performs almost as well as a through-hole mount.
Magic band: Nickname for 6 m, known for sudden, unpredictable openings.
Magnetic field: The region around a magnet or a current-carrying wire where magnetic force acts. Every current makes one, which is how inductors, transformers and motors work.
Magnetic loop also Mag loop, small transmitting loop: A small loop, often about three feet across, tuned by a variable capacitor. Very narrow bandwidth and handy where space is tight; the capacitor carries high voltage.
Maidenhead: The locator system behind grid squares, named for the English town where it was agreed.
Malicious interference: Deliberate jamming or disruption. Prohibited everywhere, and the usual advice is not to react on the air.
Maritime mobile: Operating from a boat or ship at sea, signed with /MM after the callsign.
Maritime Mobile Service Network: An HF net that keeps contact with boats at sea, helping with traffic, weather and emergencies.
MARS (Military Auxiliary Radio System): Licensed amateurs who train to provide backup communications for the US military.
Mast: A pole, often telescoping, for raising an antenna. Lighter and simpler than a tower.
MDS (minimum discernible signal): The weakest signal a receiver can detect above its own noise.
Mechanical filter: An IF filter that uses tiny vibrating metal disks to pass a narrow band of frequencies, found in many older and some newer radios.
Memory channel: A stored frequency and its settings, recalled with one button.
Meshtastic: Open-source software for small, low-cost LoRa radios that pass text messages across a mesh. It can run license-free, so it is not strictly ham radio, but many hams use it.
Metal film resistor also Carbon film, wirewound: Common resistor types. Metal film is precise and quiet; carbon film is cheap; wirewound handles power but acts like a coil at RF.
Meteor scatter: Brief VHF contacts made by reflecting signals off the ionized trails of meteors.
Method of moments: The math behind NEC and most antenna modeling programs: the antenna is cut into short segments and the current on each is calculated.
Metric prefixes: Short forms for multiples: pico (p) is one trillionth, nano (n) one billionth, micro (µ) one millionth, milli (m) one thousandth, kilo (k) a thousand, mega (M) a million and giga (G) a billion. So 14,250 kHz is 14.25 MHz.
MF (medium frequency): 300 kHz to 3 MHz, including AM broadcast and the 160 m band.
MFSK (multiple frequency-shift keying): Sending data with many tones at once, which helps it survive poor conditions. FT8 and Olivia work this way.
Mic gain: How much the radio amplifies your microphone. Too much makes you sound distorted and splatters onto your neighbors.
Mica capacitor: A very stable capacitor that holds up under high RF voltage, traditional in transmitter tank circuits and antenna tuners.
Microcontroller: A small computer on one chip, with memory and inputs and outputs, used to run keyers, controllers and radio front panels.
Microvolt: One millionth of a volt, the usual way of quoting receiver sensitivity. S9 on HF is defined as 50 microvolts at the antenna socket.
Microwave: Frequencies above about 1 GHz. Amateurs have several bands there, from 23 cm upward.
Mixer: A circuit that combines two signals to produce new frequencies at their sum and difference.
MMDVM (Multi-Mode Digital Voice Modem): The board and firmware inside most hotspots and many repeaters, handling DMR, D-STAR, System Fusion and other modes. More on Hotspots →
Mobile: A station installed in a vehicle, or operating from one.
Mobile whip: A vertical antenna mounted on a vehicle. HF whips use a loading coil to work on bands their length would not otherwise reach.
Mode: The kind of signal you transmit: CW, SSB, FM, FT8 and so on. More on Modes →
Mode (satellite): The pair of bands a satellite listens and transmits on, such as U/V for a 70 cm uplink and 2 m downlink.
Mode V/U also Mode J: A satellite that listens on 2 meters and transmits on 70 centimeters. Mode U/V is the other way round.
Modulation: Changing a carrier to carry information, by varying its strength, frequency or phase.
Monopole: A single vertical element working against a ground plane, like a quarter-wave vertical.
Monostable multivibrator also One-shot: A circuit that produces one pulse of a set length each time it is triggered.
MOSFET: A type of field-effect transistor widely used in RF power amplifiers and switching power supplies.
Moxon: A compact two-element beam with its element ends folded toward each other. Good front-to-back ratio for its size.
MPE (maximum permissible exposure): The FCC’s limits on RF exposure, which vary with frequency and whether the area is controlled or uncontrolled.
MPPT (maximum power point tracking): A charge controller that constantly adjusts to get the most power a solar panel can give, typically 10 to 30 percent more than a simple controller. More on A Guide to Portable Amateur Radio Power →
MSHV: Free software for FT8 and related modes that can send several signals at once, a feature DXpeditions use. More on Software →
MSK144: A WSJT mode for meteor scatter on 6 and 2 m.
MT63: A very robust keyboard mode that spreads text over 64 tones with heavy error correction. Popular on VHF emergency nets.
MUF (maximum usable frequency): The highest frequency that will come back to Earth between two points at a given time.
Multi-hop: A signal that bounces between the ionosphere and the ground several times to cover a great distance.
Multimeter: A meter for voltage, current and resistance. The first test instrument most hams own.
Multipath: A signal arriving by two or more routes at slightly different times, causing fading, flutter or distortion.
Multiplexer also Mux: A switch that picks one of several inputs and passes it on, under digital control.
Multiplier: In a contest, a bonus for each new state, country or zone worked, multiplied into your score.
Mutual inductance: The coupling between two coils, which lets a changing current in one make a voltage in the other. It is how transformers work.

N

N connector also N-type: A weatherproof connector that holds its impedance well into the gigahertz range. Preferred for VHF and UHF feedlines.
N1MM Logger+: Free contest logging software for Windows, the most widely used by contesters. More on Software →
NAND gate: A logic gate whose output is low only when all inputs are high: an AND gate followed by an inverter. Any other gate can be built from NANDs.
NanoVNA: An inexpensive pocket vector network analyzer. It shows SWR, impedance and cable faults far more clearly than an SWR meter.
Narrowband: FM with reduced deviation, on 12.5 kHz channels. A wideband radio on a narrowband repeater sounds loud and distorted.
National Radio Quiet Zone also NRQZ: About 13,000 square miles of West Virginia, Virginia and a corner of Maryland, set up in 1958 to protect the radio telescopes at Green Bank and the Navy site at Sugar Grove. Fixed stations there may need coordination. More on the Quiet Zone →
NBEMS (Narrow Band Emergency Messaging System): A set of free programs, fldigi and flmsg among them, for sending forms and messages by radio without the internet. More on Software →
NCVEC: The National Conference of Volunteer Examiner Coordinators, whose committee writes the exam question pools. More on Question Pools →
Near field: The region close to an antenna, within about a wavelength, where its fields behave irregularly and nearby objects strongly affect it.
Negative feedback also Positive feedback: Feeding part of an amplifier’s output back to its input to cancel errors, giving steady, predictable gain. Positive feedback adds to the input and makes oscillators.
Net: A scheduled on-air meeting run by a net control station, for traffic, training or conversation.
Net control: The operator who runs a net, calling for check-ins and directing who transmits.
Net script also Preamble: The standard text a net control reads to open and run a net.
Neutralization: Feeding back a small, opposite signal in a tube amplifier to cancel unwanted feedback that would make it oscillate.
Neutron: A particle in the nucleus of an atom with no electric charge. It adds weight but plays no part in electric current.
NMO mount: A standard vehicle antenna mount, usually fitted through a hole in the roof. The usual permanent choice for VHF and UHF mobiles.
Node: A station on a packet or mesh network that passes traffic on for others. More on Packet Radio →
Noise blanker: A circuit that removes short, sharp pulses of noise, such as ignition or electric-fence clicks.
Noise figure: How much noise a receiver or amplifier adds to the signal, in dB. Lower is better.
Noise floor: The background noise your receiver hears with no signal present. Lowering it often matters more than running more power.
Non-inductive resistor: A resistor made to have almost no inductance, needed for dummy loads and RF work.
Non-resonant antenna also Non-resonant dipole: A wire that is not cut to a quarter or half wavelength on the band in use, matched with a tuner instead. Fed with ladder line it works on many bands with little loss, which is why attic and stealth antennas are often built this way.
NOR gate: A logic gate whose output is high only when all inputs are low.
Notch filter: A filter that removes one narrow frequency, such as a carrier or a whistle.
Novice and Advanced: Older US license classes no longer issued. Holders can still renew them.
NR (noise reduction): Digital processing that softens steady hiss. Too much makes voices sound watery.
NTS (National Traffic System): The ARRL’s network of nets for relaying formal messages across the country.
NTSC: The old North American analog television standard, still used for some amateur fast-scan TV.
NVIS: Near vertical incidence skywave — aiming signals almost straight up to cover a region out to a few hundred miles with no skip zone.
NXDN: A commercial narrow digital voice standard used by a small number of amateur repeaters.
Nyquist rate: Twice the highest frequency in a signal: the slowest sampling that can still capture it. Sample slower and the signal comes back as a false lower frequency.

O

Occupied bandwidth: The width of spectrum your signal actually takes up. The whole of it must stay inside the band.
Octave: A doubling of frequency. A filter that falls 6 dB per octave halves its output each time frequency doubles.
OCXO (Oven-controlled crystal oscillator): A crystal oscillator kept at a constant temperature in a tiny oven, for very stable frequency.
Ofcom: The UK communications regulator, which issues British amateur licences.
OFDM: A data method that sends many closely spaced carriers at once. Used by VARA and some other HF modems.
Off-center-fed dipole also OCF, Windom: A dipole fed about a third of the way along rather than in the middle, which lets it work several bands through a 4:1 balun.
Official Emergency Station also OES: An ARRL appointment for an ARES member who takes on extra emergency duties for the Emergency Coordinator.
Official Observer also OO: A former ARRL volunteer appointment that monitored the bands and sent friendly advisory notices. It was replaced by the Volunteer Monitor program.
Official Relay Station also ORS: An ARRL appointment for an operator who regularly handles message traffic on traffic nets.
Offset also Repeater offset, shift: The difference between a repeater’s input and output frequencies. Standard is 600 kHz on 2 m and 5 MHz on 70 cm.
Ohm also Ω: The unit of resistance and impedance. Most ham radios and coax are built around 50 ohms.
Ohm’s law: Voltage equals current times resistance. The first formula on the exam and the most useful in the shack.
Old timer also OT: A long-licensed operator. Worn as a badge of honor.
Olivia: A slow, very robust digital mode that works through conditions which defeat almost everything else. More on Olivia →
OM (old man): Any male operator, whatever his age.
Op-amp also Operational amplifier: A general-purpose amplifier chip whose behavior is set by a few outside parts. Common in audio filters and control circuits.
Open circuit: A break in a circuit, such as a broken wire or a blown fuse, so no current flows.
Open collector also Open drain: An output that can only pull down, never up, so several can share one line. Needs a pull-up resistor to work.
Open net: A net run loosely, where stations talk to one another without a net control directing every exchange. More on Nets →
Open-loop gain: An amplifier’s gain with no feedback applied.
Optocoupler also Optoisolator: An LED and a photodetector in one package, passing a signal across a gap with no electrical connection. It keeps a computer safely apart from a transmitter’s keying line.
OQRS (Online QSL Request Service): A web form for asking a station, often a DXpedition, to send its QSL card, usually by the bureau or for a small fee by direct mail. More on QSLs →
Orbital period: How long a satellite takes to go once around the Earth.
OSCAR (Orbiting Satellite Carrying Amateur Radio): The series name given to amateur satellites once they work in orbit. OSCAR 1 was launched in 1961. More on Satellites →
Oscillator: A circuit that generates a steady signal at a set frequency.
Oscilloscope also Scope: An instrument that draws a signal’s voltage over time on a screen.
Out: The contact is finished. “Over and out” is a contradiction, and old hands will say so.
Out-of-band emission: Signal energy just outside your operating bandwidth, caused by the modulation itself. Distinct from spurious emissions further away.
Over: I have finished; your turn.
Overdrive: Feeding too much signal into an amplifier, causing distortion.
Overmodulation: Driving a transmitter’s modulation too hard, causing distortion and splatter onto nearby frequencies.

P

P25: A digital voice standard used by US public-safety agencies. A few hams use it on VHF and UHF.
Packet: Digital networking over radio using AX.25 frames, supporting bulletin boards, mail and multi-hop paths. More on Packet Radio →
PACTOR: A family of HF data modes used for Winlink and marine email, needing a dedicated modem. More on Winlink →
Paddle: A two-lever Morse key used with an electronic keyer. More on CW keys →
Panadapter also Spectrum scope: A live display of signals across a stretch of band, so you can see activity instead of tuning for it.
Parallel circuit: Components connected across each other, so each gets the same voltage.
Parasitic element: An element not connected to the feedline that shapes a beam’s pattern by re-radiating energy.
Parasitic oscillation: An unwanted oscillation in an amplifier, often far from the operating frequency.
Part 15: The FCC rules for unlicensed devices such as Wi-Fi, chargers and computers. They may not cause harmful interference and must accept any they receive. More on RFI →
Part 97: The section of US federal rules that governs amateur radio.
Passband: The range of frequencies a filter lets through. Narrowing the passband on CW cuts noise and nearby signals.
Passband ripple also Ripple: Small ups and downs in a filter’s response inside its own passband. Too much makes audio sound uneven or hollow.
Patch lead also Jumper, patch cable: A short length of coax with connectors, used between pieces of equipment in the shack.
Payload: Whatever a balloon, rocket or satellite carries: for hams, usually a transmitter, a GPS receiver and some sensors. Weight and battery life decide what fits.
PCB (printed circuit board): A board with copper tracks that connect the parts mounted on it.
Peak inverse voltage also PIV: The highest reverse voltage a diode can take without breaking down.
Peak value also Peak voltage: The highest voltage or current an AC wave reaches in one direction. For a sine wave it is about 1.414 times the RMS value.
Peak-to-peak: The voltage from the highest to the lowest point of a waveform.
PEP (peak envelope power): A transmitter’s power at the peak of its signal. US power limits are stated in PEP.
Perfboard also Protoboard: A board drilled with a grid of holes, for building a one-off circuit by soldering parts and wires to it.
Perigee: The point in an orbit closest to the Earth.
Permeability: How readily a core material carries magnetic flux. High-permeability ferrite gives far more inductance per turn than an air core.
Phase: Where a wave is in its cycle at a given moment, measured in degrees. Two signals in phase add up; 180 degrees out of phase, they cancel.
Phase noise: Random jitter in an oscillator’s signal that can let strong nearby signals mask weak ones.
Phased array: Two or more antennas fed with controlled timing so their signals add in some directions and cancel in others.
Phasor: An arrow that shows a voltage or current’s size and its phase angle at the same time. Adding phasors is how AC circuits with reactance are solved.
Phillips Code: A telegraph shorthand from the 1800s, and the source of 73.
Phone: Any voice mode — SSB, FM or AM. Not a telephone.
Phonetic alphabet: The standard words for letters, such as Alpha, Bravo and Charlie, used to spell callsigns clearly. More on Learn →
Photodiode: A diode that turns light into current. Used in optocouplers, light sensors and fiber links.
Photon: The smallest packet of electromagnetic energy. A radio photon carries so little energy that radio waves are treated as smooth waves rather than particles.
Pi network: A matching circuit shaped like the Greek letter pi: two capacitors and a coil. The classic output network of tube transmitters and amplifiers.
Pi-Star: Popular free software for running a digital voice hotspot on a Raspberry Pi. More on Hotspots →
Picket fencing: The rapid flutter of a VHF or UHF signal from a moving vehicle as it passes through reflections.
Picofarad also pF, nanofarad, microfarad: Small units of capacitance: 1,000 picofarads make a nanofarad, and 1,000 nanofarads make a microfarad.
Pierce oscillator: A simple crystal oscillator circuit, found in most digital clocks and microcontrollers.
Pileup also Pile-up: The crowd of stations all calling one rare station at once. How you get through it is a skill in itself.
PIN diode: A diode that acts as an RF switch or variable resistor depending on its DC current. Used to switch antennas and transmit paths without relays.
PL-259: The standard male connector on most HF coax. Despite belonging to the “UHF” family, it performs poorly above about 300 MHz.
Plate also Anode: The electrode in a vacuum tube that collects the electrons. In power tubes it runs at high voltage.
PLL (phase-locked loop): A circuit that locks an oscillator to a stable reference so it can be tuned in exact steps. Most synthesized radios use one.
Polar cap absorption also PCA: Heavy HF absorption over the polar regions caused by energetic protons after a big solar event. It can last for days. More on Space Weather →
Polarity: Which side is positive and which is negative. Reversing the polarity on a radio’s power leads can destroy it in an instant, which is why red is positive and black negative.
Polarization: The orientation of a radio wave, usually horizontal or vertical. On VHF and UHF, mismatched polarization can cost a great deal of signal.
Portable: Operating away from home with gear you carry, such as for POTA, SOTA or Field Day.
Portable designator: An addition to a callsign such as /P, /M or /QRP. When operating abroad, the local prefix usually goes in front of your call.
POTA: Parks on the Air. Operating portable from a park and logging contacts with people chasing you. Very beginner-friendly.
Potentiometer: A variable resistor, such as a volume control.
Powdered iron core: A core of iron particles in a binder, used in tuned circuits where a steady, predictable inductance matters more than maximum inductance.
Power: The rate at which energy is used or delivered, measured in watts. Volts times amps.
Power factor: True power divided by apparent power. A power factor of 1 means voltage and current are in step; anything less means some of the current is doing no work.
Power supply: Converts household AC to the 13.8 volts DC most amateur radios run on. Size it for the radio’s full transmit current.
PRB-1: The FCC ruling, now in Part 97, that state and local rules must reasonably accommodate amateur antennas. It does not cover private deed restrictions. More on Antenna Limits →
Preamp: An amplifier that boosts weak signals before the receiver. Useful on VHF and above; on HF it often just amplifies noise.
Precedence: The priority label on a radiogram, such as Routine, Welfare, Priority or Emergency. It tells every station how fast to pass the message on. More on Radiograms →
Predistortion: Adding a deliberate, opposite distortion to a signal before the amplifier, so the output comes out cleaner. Used in some modern amplifiers and SDR transmitters.
Prefix: The first letters and number of a callsign, which identify the country and sometimes the region. More on Prefixes & DXCC →
Prescaler: A circuit that divides a high frequency down so a counter can measure it.
Preselector: A tunable filter ahead of a receiver that rejects strong signals outside the band you want.
Primary allocation: A band where a service has first call on the spectrum. Services with secondary status must not interfere with it.
Privileges: The bands, modes and power your license class allows. More on Band Plans →
Product detector: The receiver stage that combines an SSB or CW signal with the BFO to recover the audio.
Programming cable: The cable that connects a radio to a computer for loading channels and settings.
Propagation: How and where radio signals travel, which changes hour by hour with the ionosphere. More on Reference →
Prosign: A Morse character sent as one unbroken symbol with a special meaning, such as AR for end of message or SK for end of contact. More on CW →
Proton: A particle in the nucleus of an atom with a positive charge equal and opposite to an electron’s. Protons stay put; in circuits it is the electrons that move.
PSK (phase-shift keying): Sending data by shifting the phase of a tone. The basis of PSK31. More on PSK31 →
PSK Reporter: A website that maps reception reports from digital-mode software in real time.
PSK31: A narrow digital mode designed around typing speed, giving real keyboard-to-keyboard conversation. More on PSK31 →
PTT (push to talk): The button that switches the radio to transmit.
Public Information Officer also PIO: The person who speaks for an organization to the media and public. Many ham clubs and ARRL sections appoint one.
Pull-up resistor: A resistor that holds a logic input at the supply voltage until something pulls it down. Without one, an unconnected input floats and reads randomly.

Q

Q factor also Q: A measure of how sharply a resonant circuit responds. High Q means narrow and selective.
Q-code: Three-letter codes starting with Q, used as shorthand for common questions and statements. More on Q-codes →
Q65: A WSJT mode for very weak signals, used for moonbounce and other difficult paths.
QAM (quadrature amplitude modulation): A way of packing more data into a signal by varying both amplitude and phase.
QCWA (Quarter Century Wireless Association): A club, founded in 1947, for hams who hold a current license and were first licensed at least 25 years ago.
QO-100 (Qatar-OSCAR 100): An amateur transponder on a geostationary satellite, always in the same spot over Africa. Its coverage runs roughly from Brazil to Thailand, so it cannot be reached from North America.
QRO: High power operating. The opposite of QRP.
QRP: Low power operating, conventionally 5 watts or less on CW and 10 watts on SSB.
QRS: Please send more slowly. Sent by an operator who needs a slower Morse speed. More on Q-Codes →
QRSS: Morse sent extremely slowly, with dots seconds long, and read by eye on a computer screen. Used for very low power beacons.
QSL bureau also Buro: A service run by national societies that bundles QSL cards together to save postage.
QSL card: A postcard confirming a contact. Still collected, still mailed, increasingly also electronic.
QSL manager: Someone who handles QSL cards on behalf of a DX station or expedition.
QSO party: A contest centered on one state or province, in which everyone else tries to work as many of its counties as possible.
Quad: A directional antenna made of square wire loops instead of straight elements.
Quagi: A VHF/UHF beam with quad loops for the reflector and driven element and Yagi rods for the directors. More on Beams →
Quantization: Rounding each sample to the nearest step a converter can represent. The rounding error appears as a faint hiss called quantization noise.
Quarter-wave matching section also Q-section: A quarter-wavelength of line of a chosen impedance used to transform one impedance to another.
Quarter-wave vertical: A vertical element a quarter wavelength tall, working against a ground plane or radials. The standard VHF mobile antenna.
Question pool: The published bank of questions every exam is drawn from. Each US pool is revised every four years. More on Learn →
Question pool committee also QPC: The NCVEC committee that writes and revises the amateur exam question pools every four years. More on Question Pools →

R

RAC (Radio Amateurs of Canada): Canada’s national amateur radio society.
RACES: Radio Amateur Civil Emergency Service, a US government-sponsored emergency service run through local emergency management.
Radial: A wire laid out at the base of a vertical antenna to act as part of its ground system. More is better.
Radiation pattern: A plot of how strongly an antenna radiates in each direction.
Radiation resistance: The part of an antenna’s feed impedance that represents power actually radiated.
Radio blackout: Sudden loss of HF on the sunlit side of the Earth after a solar flare.
Radio direction finding also RDF, fox hunting: Locating a transmitter by taking bearings on its signal. Hidden-transmitter hunts are a popular club activity.
Radio horizon: How far a VHF or UHF signal reaches before the curve of the Earth blocks it. A little beyond the visible horizon, because the atmosphere bends signals slightly.
Radio JOVE: An education project, started with NASA support, in which people build simple receivers to hear radio storms from Jupiter and the Sun. More on Radio Astronomy →
Radiogram: A formal message with a standard header and word count, passed through the National Traffic System.
Rag chew: A long, unhurried conversation, as opposed to a quick contest exchange.
Random wire: A wire of no particular length, fed at one end through a tuner or unun. Simple and forgiving, but it needs a good counterpoise.
Raspberry Pi: A credit-card-size Linux computer, often used as a hotspot controller, packet node or remote-station computer.
RBN (Reverse Beacon Network): A worldwide network of receivers that automatically decodes CW and digital signals and reports who heard whom. A quick way to see where you are being heard.
REACT: A volunteer emergency communications group that started with CB radio and now includes hams.
Reactance: The part of impedance caused by capacitance or inductance. It stores energy rather than radiating it, and a tuner cancels it out.
Reactive power: Power that flows back and forth between the source and a capacitor or inductor without being used up. Measured in volt-amperes reactive, not watts.
Reception report: A note from a listener telling a station how it was heard, often in exchange for a QSL card.
Reciprocal agreement: An agreement that lets a licensed ham from one country operate while visiting another. More on Operating Abroad →
Reciprocal counter: A frequency counter that measures the time of one cycle and works out the frequency, giving high resolution quickly on audio and low frequencies.
Reciprocal mixing: Noise created when a strong nearby signal mixes with a receiver’s own oscillator noise.
Reciprocal operating: Operating in another country under your own license, allowed where the two countries have an agreement.
Rectifier: A diode or group of diodes that converts AC into DC.
Reflected power: Power bounced back toward the transmitter by a mismatch.
Reflection coefficient: How much of a signal is reflected at a mismatch, from 0 (none) to 1 (all). SWR and return loss are other ways of saying the same thing.
Reflector: On a beam antenna, the element behind the driven element, slightly longer, which sends signal forward. In digital voice, an internet server that links repeaters and hotspots into shared rooms, mainly for D-STAR.
Regenerative receiver also Regen: A simple receiver that feeds part of its output back to its input for big gain and selectivity from one tube or transistor.
Relay: A switch operated by an electromagnet, letting a small signal switch a larger current.
Remote control: Operating a station from a distance over a link such as the internet, with the control operator still responsible for it.
Remote tuner also Remote auto tuner: An automatic antenna tuner mounted at the antenna feedpoint rather than in the shack, so the coax between them runs at a low SWR and the loss stays small.
Repeater: A station that receives on one frequency and retransmits on another, greatly extending the range of handhelds.
Report and Order also R&O: The FCC document that adopts new rules after public comment.
Resistance: Opposition to current flow, measured in ohms.
Resistor: A component that opposes current by a fixed amount, measured in ohms.
Resolution bandwidth also RBW: The filter width a spectrum analyzer uses for each point of its display. Narrower shows more detail but sweeps more slowly. More on Test Gear →
Resonance: The frequency at which an antenna’s impedance is purely resistive, with no reactance. Resonant is convenient, but it is not the same as efficient.
Resonant circuit also Tuned circuit: A combination of inductance and capacitance that responds strongly at one frequency. The heart of every filter and oscillator.
Return loss: How much of the power sent into an antenna or cable comes back, in dB. Higher is better; 20 dB is about 1.2:1 SWR.
Reverse split: A repeater whose input and output are swapped compared with the usual pairing. Also, listening on a repeater’s input to check whether you can work a station directly.
RF burn: A sting from touching something carrying radio frequency energy while transmitting. A sign something is wrong.
RF clipping: Speech processing done on the RF signal, with filtering afterward, to raise average power with less distortion than clipping the audio.
RF exposure: Rules and safe distances for being near transmitting antennas. The FCC requires every station to evaluate it.
RF in the shack: Stray radio energy where it should not be: tingling metal, distorted audio or a computer that crashes on transmit. Usually a feedline or grounding problem.
RF power meter: A meter placed in the feedline to measure transmitter output power.
RF safety: Keeping people a safe distance from antennas and within exposure limits. The FCC requires every station to be evaluated.
RFI (radio frequency interference): Your transmitter upsetting nearby electronics, or local devices making noise in your receiver.
RG-213: Thick 50-ohm coax with lower loss than RG-8X, used for longer HF runs.
RG-58: Thin, flexible 50-ohm coax. Fine for short runs and patch leads on HF; lossy on long runs and at VHF and above.
RG-8X: Mid-size 50-ohm coax, a common compromise between flexibility and loss for HF.
Rig: Your radio.
RIT also Clarifier: Receiver incremental tuning: shifts the receive frequency slightly without moving the transmit frequency.
RMS (root mean square): The effective value of an AC voltage. For a sine wave it is about 0.707 times the peak.
Roger: Message received and understood. It does not mean yes.
Roller inductor: A coil with a wheel that rolls along its turns, giving smoothly variable inductance in tuners and amplifiers.
Roofing filter: A filter early in the receiver that keeps strong signals near your frequency from overloading later stages.
Rotator also Rotor: A motor that turns a directional antenna from inside the shack.
Roundtable: An informal conversation among several stations taking turns, usually passing the microphone in a set order.
Rover: A station that moves between grid squares during a VHF contest to give out new ones.
RR73: In FT8, the message that says “report received, 73” and closes the exchange. More on FT8 →
RSGB (Radio Society of Great Britain): The UK’s national amateur radio society.
RST: The signal report format: readability, strength and, on CW, tone. More on Signal Reports →
RTL-SDR: A low-cost USB receiver, first made from a TV tuner stick, that works as a software-defined radio for listening.
RTTY: Radioteletype, a long-established digital mode that remains a contest mainstay. More on RTTY →
Rubber duck: The short, flexible antenna that comes with a handheld. Convenient but a poor performer; a better antenna is often the cheapest upgrade a handheld can get.
Rubber-stamp contact: A minimal contact of callsign, report, name and location, then 73.
Run: Holding a frequency and calling CQ while stations come to you, especially in a contest.

S

S unit also S point, S-unit: One step on a receiver’s signal meter (S-meter), defined as 6 dB, so S7 is 6 dB stronger than S6. Above S9, readings are given as S9 plus so many dB. Real meters rarely follow the standard closely. More on Signal Reports →
Safety ground: The connection that keeps equipment cases at ground potential so a fault cannot make them live.
Sampling rate: How many times a second an analog-to-digital converter measures a signal. It must be more than twice the highest frequency of interest.
SASE: Self-addressed stamped envelope, sent with a QSL request.
Satellite pass also Pass: One transit of a satellite across the sky, from rise to set. A low-orbit pass lasts about ten to fifteen minutes.
SATERN: The Salvation Army Team Emergency Radio Network, whose hams support the Salvation Army’s disaster work.
Scatter: Weak, fluttery propagation from signals bouncing off irregularities in the ionosphere or atmosphere. It can fill in the skip zone.
Schematic: A circuit drawing that uses standard symbols to show how components connect.
Schmitt trigger: A switching circuit with two thresholds, which turns a slow or noisy input into a clean on-off signal.
School Club Roundup: An on-the-air event for school and youth radio clubs, encouraging contacts between students and the wider ham community.
Schottky diode: A diode with a low forward voltage drop and fast switching, used in power circuits and RF detectors.
SCR (silicon-controlled rectifier): A switch that stays on once triggered until the current through it stops. Used in power control and crowbar protection circuits.
Screen grid: The second grid in a tetrode or pentode, which shields the control grid from the plate.
Screwdriver antenna: A motorized HF mobile antenna whose loading coil slides in and out to retune across bands.
SDR (software-defined radio): A radio in which most signal processing is done in software rather than in dedicated circuits. Most new radios now use it in some form.
Search and pounce also S&P: Tuning across the band to find and answer stations rather than calling CQ yourself.
Secondary allocation: A band shared on the condition that you do not interfere with primary users and accept interference from them. Amateurs are secondary on several bands.
Section also ARRL section: One of the areas the ARRL divides the US into, each led by an elected Section Manager who appoints volunteers for emergency, traffic and technical work.
Section Manager: The elected ARRL volunteer who leads a section and appoints its field officials.
Selectivity: How well a receiver separates the signal you want from others close by.
Self-resonant frequency: The frequency at which a coil or capacitor resonates on its own, because of its stray capacitance or inductance. Above it, the part no longer behaves as labeled.
Semi break-in: CW operation in which the transmitter keys up with the first character and returns to receive after a short pause in your sending. More on CW →
Semiconductor: A material, usually silicon, whose conductivity can be controlled. The basis of diodes, transistors and chips.
Sense antenna: A small extra antenna on a direction-finding receiver that tells you which of two opposite directions the signal comes from.
Sensitivity: How weak a signal a receiver can hear.
Sequencer: A device that switches station equipment on and off in a set order, for example so a preamp is out of the line before the amplifier transmits.
Sequential callsign: A callsign issued automatically, in order, when a license is first granted.
Series circuit: Components connected end to end, so the same current flows through all of them.
Served agency: An organization such as a county emergency management office, the Red Cross or a hospital that hams support with communications. More on ARES →
Service monitor: A combined test instrument for aligning and checking radios and repeaters, including frequency, deviation and power.
Session fee: A fee some volunteer examiner teams charge to cover their costs. It is separate from the FCC’s application fee. More on Your License →
Shack: Wherever your station lives, be it a room, a desk or a corner of the garage.
Shack in a box: A single radio covering HF, VHF and UHF.
Shape factor: How steep a filter’s sides are: the width at 60 dB down divided by the width at 6 dB down. Closer to 1 is sharper. More on Receiver Numbers →
Shielding: A metal enclosure or covering that keeps RF in or out.
Shift register: A chain of flip-flops that passes bits along one step at a time. It turns a few microcontroller pins into many outputs.
Short circuit also Short: An accidental low-resistance path that lets far too much current flow, usually between the two sides of a supply. Fuses exist to stop shorts from causing fires.
Short path: The direct, shorter route between two stations around the globe.
Shortwave broadcast bands: The HF segments set aside for international broadcasting, between the amateur bands.
Shunt: A precise low-value resistor placed in the current path so a voltmeter can read the current across it. How most high-current meters work.
Sidescatter: A signal reaching you after scattering from a point off to the side of the direct path, often heard when the direct path is closed.
Sideswiper also Cootie: A Morse key that moves side to side, sending with either direction. More on CW keys →
Sidetone: The tone the radio plays so you can hear the Morse you are sending.
Signal generator: An instrument that produces a test signal at a chosen frequency and level.
Signal tracer: A simple amplifier and speaker used to follow a signal stage by stage through a receiver to find where it stops.
SignaLink: A widely used sound card interface connecting a computer to a radio for digital modes.
Simplex: Transmitting and receiving on the same frequency, radio to radio, with no repeater in between.
Simulated Emergency Test also SET: An ARRL exercise in which ARES groups, nets and served agencies practice handling an emergency together. More on Emergency Groups →
Sine wave: The smooth, pure wave shape of a single frequency. A clean transmitter’s carrier is a sine wave; anything else carries harmonics.
Single-op also Single operator: A contest entry category for one person doing all the operating and logging, as opposed to multi-operator stations. Usually split further by power level and by whether spotting assistance is used.
Single-point ground: Bringing every cable and ground connection to one entry point, so lightning surges have one path to earth and no loops.
SINPO: A listener’s report code for broadcasts: Signal, Interference, Noise, Propagation and Overall, each from 1 to 5. More on Signal Reports →
Situational awareness: Knowing what is happening around you during an incident. Ham reports often add to an agency’s picture.
SK (Silent Key): A ham who has died. From the Morse prosign for the end of a contact.
SKCC (Straight Key Century Club): A club for operators who use mechanical keys: straight keys, bugs and sideswipers. Members swap membership numbers on the air. More on CW Keys →
Sked also Schedule: A planned contact at an agreed time and frequency.
Skewed path: A signal arriving well off the great-circle direction, bent around storms or the auroral zone.
Skimmer also CW Skimmer: Software that decodes many CW or digital signals at once from a wide receiver and reports the callsigns. Skimmers feed the Reverse Beacon Network.
Skin effect: At radio frequencies, current flows mostly near the surface of a conductor. That is why thick or hollow conductors and wide straps have lower RF loss.
Skip: Signals refracted by the ionosphere back to earth far away, leaving a zone in between where nothing is heard.
Skip zone: The gap between where the ground wave fades and the first sky-wave signal lands, where a station cannot be heard.
Sky wave: A signal returned to Earth by the ionosphere: the basis of long-distance HF.
SKYWARN: The US National Weather Service’s volunteer storm-spotter program. Many spotters report by amateur radio.
SKYWARN Recognition Day: An event each December when hams make contacts with National Weather Service offices to thank storm spotters.
SLA (sealed lead-acid): A sealed, maintenance-free lead-acid battery. Cheap and tough, but heavy, and it should not be drained much below half. More on A Guide to Portable Amateur Radio Power →
Slim Jim: A folded version of the J-pole, popular for VHF and UHF base and portable use.
Sloper: A wire antenna run at a slant from a high point down toward the ground.
SMA: A small threaded connector used on most modern handhelds. Radios differ on whether the male or female half is on the radio.
SmartBeaconing: An APRS tracker setting that beacons more often when you move fast or turn, and less often when you are parked. More on APRS →
Smith chart: A circular chart for plotting impedance, used to design and see matching. Many analyzers display one.
SNR (signal-to-noise ratio): How far a signal stands above the noise, in dB. FT8 reports it in place of an RST.
SO-239: The female socket a PL-259 screws onto, found on the back of most HF radios and on many antennas.
Solar cycle: The roughly 11-year rise and fall of sunspot activity, which drives how good the higher HF bands are.
Solar flare: A sudden burst of solar radiation that can wipe out HF on the daylight side of the Earth for minutes to hours.
Solar flux also SFI, solar flux index: A daily measure of the Sun’s radio output. Higher numbers generally mean better conditions on the upper HF bands.
Solar maximum also Solar minimum: The peak of the roughly 11-year solar cycle, when sunspots are most numerous and the higher HF bands open widely. Solar minimum is the quiet low point. More on Space Weather →
Solar panel: A panel of photovoltaic cells that turns sunlight into DC power. Folding panels are popular for portable operating. More on A Guide to Portable Amateur Radio Power →
Solar wind: The stream of charged particles flowing out from the Sun. Gusts of it stir up the Earth’s magnetic field. More on Space Weather →
Solder: A soft metal alloy melted to join wires and parts. Electronics solder has a core of flux; never use plumbing solder with acid flux.
Soldering iron: The tool that melts solder. A temperature-controlled station with a fine tip suits most radio work; big connectors like PL-259s need more heat.
Solid state: Equipment built with transistors instead of tubes.
SOTA: Summits on the Air. Like POTA, but you carry the station up a hill first.
Sound card interface: A box between radio and computer that carries audio and keying for digital modes. SignaLink and Digirig are common examples. More on Interfaces →
Soundmodem: Free software that turns a computer sound card into a packet TNC, used with a simple radio interface. More on Packet →
Space station: In FCC rules, an amateur station more than 50 km above the Earth’s surface, such as a satellite.
Space wave: At VHF and above, the combination of the direct signal and the one reflected off the ground between two stations in line of sight.
Space weather: Conditions on the Sun and in near-Earth space that affect the ionosphere and radio propagation.
Span: The range of frequencies shown across a spectrum analyzer’s screen.
Spark-gap transmitter: The earliest kind of transmitter, which made broad, noisy signals from sparks. Long banned for amateur use. More on History →
Special event station: A station with a short, distinctive callsign set up for an event or anniversary. Contacts usually earn a commemorative QSL card.
Spectrum analyzer: An instrument that shows signal strength across a range of frequencies, revealing harmonics and other unwanted signals.
Speech processor also Compression: A circuit that raises the average level of your voice for more punch on SSB. A little helps; too much sounds harsh.
Spin fading: Regular fading on a satellite’s signal as it rotates.
Splatter: Distortion that spreads a signal wider than it should be, interfering with nearby frequencies. Usually caused by overdriving.
Split: Transmitting on one frequency and listening on another. Standard practice for rare DX working a pile-up.
Split operation also Working split: Listening on one frequency and transmitting on another. DX stations work split so callers do not sit on top of them.
Sporadic E also Es: Patches of dense ionization in the E layer that open 6 m and 10 m for sudden, strong contacts. Most common in early summer.
Spot also Spotting: A report posted to a DX cluster or spotting site saying which station is on which frequency, so others can find it. Posting one is called spotting.
Spread spectrum: Transmitting a signal spread across a much wider band than it needs, which makes it resistant to interference.
Sprint: A short contest, usually a few hours, that rewards fast, accurate operating. More on Contests →
Spurious emission: Any unwanted signal a transmitter puts out away from its intended frequency.
Squelch: A control that mutes the receiver until a strong enough signal arrives. Mostly used on FM.
SSB: Single sideband, the standard voice mode on HF. More on SSB →
SSTV: Slow-scan television — sending still images as audio over a voice-bandwidth channel. More on SSTV →
STA (special temporary authority): A short-term permit the FCC grants for operation not normally allowed.
Standing wave: The pattern of voltage and current along a feedline when some power is reflected back from a mismatch.
State of charge also SoC: How much charge a battery has left, as a percentage. Resting voltage gives a rough idea; a lithium battery’s flat curve makes it a poor guide.
Static electricity also Static: Charge that builds up on a surface and stays there until it finds a path to discharge, such as the spark from a doorknob. On an antenna it can build up from wind and rain and should be drained to ground.
Station identification also ID: Giving your callsign as required. In the US, at least every ten minutes during a contact and at the end of it.
Stealth antenna: An antenna designed to go unnoticed, such as thin wire in a tree or a flagpole vertical.
STEM (science, technology, engineering and mathematics): The school subjects amateur radio is often used to teach, because a balloon flight or a satellite contact wraps physics, electronics and geography into one project.
Stopband: The range of frequencies a filter is meant to reject, and how far down it pushes them.
Store and forward: Holding a message and passing it on later, as a mailbox, a Winlink server or a satellite does.
Storm spotter: A trained volunteer who reports severe weather to the National Weather Service. Many spotters are hams working through SKYWARN. More on Emergency Groups →
Straight key: The simplest Morse key: press to send, release to stop. More on CW keys →
Straight Key Night also SKN: An ARRL event on New Year’s Day (UTC) when operators dust off straight keys and older gear for relaxed CW contacts. More on CW Keys →
Stub: A cut length of feedline used as a tuned circuit, to match an antenna or filter out a frequency.
Subelement: A section of a question pool covering one topic. Each exam takes one question from every group within it. More on Question Pools →
Sudden ionospheric disturbance also SID: A sudden fade-out of HF on the daylit side of the Earth caused by X-rays from a solar flare. See also radio blackout. More on Space Weather →
Suffix: The letters after the number in a callsign.
Sunspot number: A daily count of sunspots and sunspot groups, the long-running measure of the solar cycle. More on Space Weather →
Sunspots: Dark regions on the Sun linked to strong solar activity. More sunspots mean a stronger ionosphere and better high-band conditions.
Superheterodyne also Superhet: The classic receiver design, which mixes incoming signals down to a fixed IF. Most radios before SDR worked this way.
Surface-mount also SMD, SMT: Tiny parts soldered directly to the surface of a board rather than pushed through holes. Nearly all modern radios use them.
Susceptance: The reciprocal of reactance, the easy-flow counterpart for capacitors and inductors. Used with conductance when circuits are worked in parallel.
Swapfest: Another name for a hamfest, especially one that is mostly buying and selling gear.
Sweepstakes: The ARRL’s November contest across the US and Canada, with a long exchange that includes the year you were first licensed.
Switching power supply also Switcher: A light, efficient supply that chops the input at high speed. Good ones are quiet; cheap ones can spray noise across the HF bands.
SWL (shortwave listener): Someone who listens to HF without transmitting. Many hams start as SWLs.
SWR: Standing wave ratio, a measure of how well your antenna matches your feedline. High SWR means power reflected back rather than radiated.
SWR meter: A meter in the feedline showing forward and reflected power. A low reading means a good match at that point, not necessarily a good antenna or good coax.
System Fusion also C4FM, YSF: Yaesu’s digital voice system, using the C4FM modulation. More on Fusion →

T

T-network: A matching circuit of two capacitors and a coil arranged like a letter T. Used in many manual antenna tuners.
Tactical call: A role name such as “Shelter One” used on an emergency net in place of a callsign. You still identify with your own callsign as required.
Tail-ending: Calling a station right as it finishes a contact, so you are next in line.
Tailgating: Selling gear from the back of a car at a hamfest.
Takeoff angle also Radiation angle: The angle above the horizon at which an antenna sends most of its signal. Low angles favor DX; high angles favor short-range and NVIS.
Talkgroup: A virtual channel on a digital voice network such as DMR, shared across many repeaters worldwide.
Tank circuit: The tuned circuit at a transmitter’s output that stores energy and smooths the output into a clean sine wave.
TCXO: Temperature-compensated crystal oscillator, which keeps a radio’s frequency steady as it warms up. Important for FT8 and other narrow digital modes.
TDMA: Time-division multiple access: sharing one channel by taking turns in short time slices. How DMR fits two conversations on one repeater. More on DMR →
TDR (time-domain reflectometry): Finding a fault in a cable by timing reflections. A NanoVNA can do it and estimate the distance to a short, open or bad connector.
Technician: The entry-level US license, with full VHF and UHF privileges and limited HF. More on Learn →
Telecommand: Signals sent to control a space station or other remote amateur station.
Telemetry: Measurements sent back automatically from a remote station, such as a satellite reporting its temperature and battery voltage.
Temperature coefficient: How much a component’s value drifts as it warms up, often given in parts per million per degree. It decides whether an oscillator stays on frequency.
Temperature inversion: Warm air sitting above cooler air, the condition that forms a tropospheric duct.
Temporary identifier: The “/AG” or “/AE” added to a callsign after passing an upgrade exam, used until the new license class appears in the FCC database.
Thermal resistance: How many degrees a device heats up per watt it must dissipate. Adding a heat sink lowers it.
Thermal runaway: A rising-temperature loop that feeds itself: a hot semiconductor passes more current, which makes it hotter still. Proper bias and a heat sink prevent it.
Thermistor: A resistor whose value changes with temperature, used to sense heat, for example to start a cooling fan.
Third party: A person who is not the control operator, often unlicensed, on whose behalf a message is sent or who speaks at the microphone.
Third-order intercept also IP3: A measure of how well a receiver resists intermodulation from strong signals. Higher is better.
Third-party agreement: An agreement between two countries that lets hams pass messages for people who are not licensed. More on Part 97 →
Third-party traffic: Passing a message for someone who is not licensed, or letting them speak on the air. Allowed only with countries that have an agreement with yours.
THOR: A keyboard mode built on incremental frequency keying with error correction, available in fldigi.
Through-hole: Parts with wire leads that go through holes in a board and are soldered on the other side. Easier to handle, so most kits use them.
Tiger tail also Rat tail: A quarter-wave wire clipped to the ground side of a handheld’s antenna connector, giving the rubber duck a proper counterpoise. A cheap way to get noticeably more range, once it is trimmed to length.
Time constant: How quickly a capacitor or inductor charges through a resistor. After one time constant it reaches about 63 percent.
Time slot: DMR splits each channel into two alternating slots, so one repeater carries two conversations at once. More on DMR →
Time-out timer: A limit on how long a repeater, or your radio, will transmit in one go. Talk too long and it cuts you off.
tinySA: A small, low-cost handheld spectrum analyzer popular with hams. More on Test Gear →
TNC: Terminal node controller — the modem for packet radio. Increasingly replaced by software such as Direwolf.
TNX also TU: Thanks, and thank you.
Tolerance: How far a component may legitimately differ from its marked value, such as 5 percent for a common resistor.
Tone squelch also TSQL: Setting your radio to stay silent unless the incoming signal carries the right tone.
Top band: Nickname for 160 m, the lowest amateur HF band.
Top loading also Center loading, base loading: Adding capacitance or inductance to make a short vertical act longer. Loading near the top is most efficient, near the base least.
Toroid: A doughnut-shaped core of ferrite or powdered iron, used to wind chokes, baluns and coils.
Tower: A structure for mounting antennas high. Climbing one is dangerous and calls for training and proper fall protection.
Trace: A copper track on a circuit board that takes the place of a wire.
Traffic: Formal messages passed between stations on behalf of others, with a defined format and handling procedure.
Traffic net: A net that meets to pass formal written messages (radiograms) from station to station toward their destination. More on Nets →
Trans-equatorial propagation also TEP, transequatorial propagation: A VHF path between stations roughly the same distance either side of the magnetic equator, best in the late afternoon and evening.
Transceiver: A combined transmitter and receiver, which is what almost every modern radio is.
Transconductance: How much a field-effect transistor’s or tube’s output current changes for a given change in input voltage. The gain figure for voltage-controlled devices.
Transformer: Two or more coils on a shared core that step AC voltage up or down, or match impedances.
Transistor: A semiconductor device that amplifies or switches signals.
Transmatch: Another name for an antenna tuner.
Transverter: A converter that lets a radio on one band transmit and receive on another, usually higher, band.
Trap: A coil and capacitor tuned to one frequency, placed in an antenna so it works on more than one band. A wet or mistuned trap is a common fault.
Trap dipole: A dipole with tuned traps along each leg that electrically shorten it on the higher bands, so one wire resonates on several bands without a tuner. Narrower bandwidth and a little loss are the price.
Triac: A thyristor that conducts both ways, used to control AC power such as a lamp dimmer. A common source of buzzing RF interference.
Triangulation: Finding a transmitter by taking bearings from two or more places and seeing where the lines cross.
Trickle charge: A small continuous charging current to make up for a battery’s self-discharge. It suits lead-acid and is wrong for lithium.
Triode also Tetrode, pentode: A vacuum tube with three electrodes: cathode, grid and plate. Tetrodes add a screen grid and pentodes add a suppressor grid as well.
Tropospheric ducting also Tropo, ducting: Weather conditions that trap VHF and UHF signals and carry them far beyond the horizon, often along coasts and over water.
Tropospheric scatter also Troposcatter: Weak but steady VHF and UHF signals scattered by the lower atmosphere to stations a few hundred miles beyond the horizon.
True power also Real power: The power a circuit actually turns into heat or radiation, measured in watts. Only the resistive part of a load consumes it.
True RMS: A meter that measures the real RMS value of any waveform, not just a sine wave. More on Test Gear →
Trustee: The licensed ham responsible for a club or repeater callsign and for how the station is operated.
Truth table: A table listing what a logic circuit outputs for every possible combination of inputs. The clearest way to describe a gate.
TTL (transistor-transistor logic): An older 5-volt logic family. Its voltage levels are still the reference when people say a signal is “TTL level”.
Tube also Valve: A vacuum tube. Still found in older radios and some amplifiers.
Tuner also ATU, antenna tuner, matcher: A matching unit between radio and feedline that makes the system look like 50 ohms to the radio. It protects the radio but does not make the antenna itself any better, which is why “matcher” is the more honest name.
Tuning up: Adjusting a tuner or amplifier on the air. Do it briefly, on a clear frequency, or into a dummy load.
Tunnel diode: A diode with a negative-resistance region that can oscillate or amplify on its own. Once important at microwave frequencies, now a curiosity.
Twin-lead: Flat two-wire feedline, typically 300 ohms, like old TV antenna cable.
Two-tone test: Feeding two audio tones into an SSB transmitter to check its linearity and peak power with a scope or spectrum analyzer.

U

Ugly balun: A choke made by winding a few turns of coax into a coil at the feedpoint. More on Chokes →
UHF: Ultra high frequency, 300 MHz–3 GHz. In amateur terms usually the 70 cm band.
UHF connector: The family name for the PL-259 and SO-239. The name dates from the 1930s, when anything above about 30 MHz counted as UHF.
ULS (Universal Licensing System): The FCC’s database where US licenses are issued and renewed, and the source behind most callsign lookups. More on Callsign Lookup →
Uncontrolled environment: An area where the public may be exposed without knowing it, such as a neighbor’s yard. Limits are stricter.
Unintentional radiator: A device that makes radio-frequency signals inside it but is not meant to send them out, such as a computer or a switching power supply. More on RFI →
Unity of command: The ICS principle that each person reports to one supervisor.
Universal gate: A logic gate, NAND or NOR, from which any other logic function can be built.
Unloaded Q: A tuned circuit’s Q on its own, with nothing drawing power from it. It shows the best the components can do.
Unun: A transformer between an unbalanced antenna, such as an end-fed wire, and unbalanced coax. 9:1 and 49:1 are the common types.
Up: In a pileup, “up” or “up 5” means the DX station is listening above its own frequency, so call there.
Up-conversion: Mixing a signal to a higher intermediate frequency, often above the whole HF range, to keep images far away.
Upgrade: Moving to a higher license class. More on Learn →
Uplink also Downlink: The frequency you send to a satellite on; the downlink is the one it sends back on.
UR: “Your” or “you are”, in Morse shorthand.
USB and LSB also Upper and lower sideband: The two halves of an SSB signal. By convention, voice uses LSB below 10 MHz and USB above, except 60 m, which is USB. Digital modes use USB on every band. More on SSB →
UTC also Zulu: Coordinated Universal Time, the single clock hams use for logs and schedules. “Zulu” is the military name for it.
Utility station: A non-broadcast station heard on shortwave, such as aviation, maritime, military or weather services.

V

Vacuum variable capacitor: A variable capacitor sealed in a vacuum so it can handle high voltage in a small space.
Vanity callsign: A callsign you choose, within the rules for your license class, instead of one issued in sequence. The FCC charges a fee.
VARA: A commercial HF and VHF modem program, popular with Winlink users, with a free slower version. More on Winlink →
VarAC: Keyboard chat and file transfer software built on the VARA modem. More on Software →
Varactor also Varicap: A diode whose capacitance changes with the voltage across it, used to tune circuits electronically.
Varicode: The character code used by PSK31, in which common letters get the shortest codes, much as in Morse. More on PSK31 →
VE (Volunteer Examiner): A licensed amateur accredited to administer license exams. More on Learn →
VE team: At least three accredited volunteer examiners who hold exam sessions together, often through a local club. More on Learn →
VEC (Volunteer Examiner Coordinator): An organization that accredits VE teams and sends exam results to the FCC, such as the ARRL VEC or Laurel VEC. More on Learn →
Velocity factor: How fast a signal travels in a cable compared with free space, as a fraction. It matters when cutting coax to an exact electrical length.
Vertical: An antenna mounted upright, usually needing a ground plane or radials. Popular where there is no room for wire.
Vestigial sideband also VSB: A way of sending analog TV that keeps one full sideband and a trace of the other, saving bandwidth. More on ATV →
VFO: Variable frequency oscillator, and by extension the main tuning knob. Most radios have two, A and B, which is how split operation works.
VHF: Very high frequency, 30–300 MHz. In amateur terms usually 2 m and 6 m.
Via: A plated hole carrying a connection from one side of a circuit board to the other.
VNA (vector network analyzer): A test instrument that measures how an antenna, cable or circuit responds across a range of frequencies, including phase.
VOACAP: Free propagation prediction software, originally developed for US government use, that estimates which bands will reach where and when.
Volt also V: The unit of voltage, the electrical pressure that pushes current around a circuit. Most mobile radios run on about 13.8 volts.
Voltage: The electrical pressure that pushes current through a circuit, measured in volts.
Voltage divider: Two resistors in series used to tap a smaller voltage from a larger one. The tapped voltage falls as soon as the tap draws current.
Voltage drop: Voltage lost along a wire or across a component. Thin or long power leads can drop enough voltage on transmit to make a radio misbehave. More on A Guide to Portable Amateur Radio Power →
Voltage rating also Working voltage: The most voltage a part can safely stand. In an antenna tuner or amplifier, RF voltages run far higher than the DC supply, so ratings must be generous.
Voltage regulator: A circuit that keeps an output voltage steady despite changes in load or input.
Voltmeter: An instrument that measures voltage across two points. It must have a high input resistance so it does not change what it is measuring.
Volunteer Monitor also VM: A program of volunteer hams who watch the bands and send friendly advice notices, working with the ARRL and the FCC.
VOX: Voice-operated transmit: the radio switches to transmit by itself when you speak.
VOX delay: How long the transmitter stays on after you stop talking before VOX drops back to receive.
VUCC (VHF/UHF Century Club): An ARRL award for confirming contacts with different grid squares: 100 on 6 meters, 2 meters or via satellite, fewer on the higher bands. More on Awards →

W

W1AW: The ARRL’s headquarters station in Newington, Connecticut, which sends code practice and bulletins on a published schedule.
WAC (Worked All Continents): An award for contacting all six inhabited continents.
Walkie-talkie: A handheld two-way radio. The first practical one is generally credited to Canadian Donald Hings in 1937.
Wallpaper: QSL cards and award certificates on the shack wall.
WARC bands: The 30, 17 and 12 m bands, added at the 1979 World Administrative Radio Conference. By agreement, no contests are held on them.
WAS: Worked All States, an award for contacting all fifty US states.
Waterfall also Waterfall display: A scrolling picture of the band with time running down the screen and frequency across it, brightness showing signal strength. Reading a waterfall is how FT8 operators find activity.
Watt also W: The unit of power: volts times amps for a simple DC circuit. A 13.8-volt supply delivering 10 amps provides 138 watts.
Watt-hour also Wh: Stored energy: watts times hours. Amp-hours times the battery’s voltage gives watt-hours, which makes batteries of different voltages easy to compare. More on A Guide to Portable Amateur Radio Power →
Wattmeter also Power meter: A meter that measures transmitter output, often combined with an SWR meter.
Wavelength: The distance a radio wave travels in one cycle. In meters it is about 300 divided by the frequency in MHz, which is where band names come from. More on Band Plans →
WAZ (Worked All Zones): An award for contacting all 40 CQ zones.
Weak signal: Operating aimed at contacts with signals too faint to hear, using modes such as FT8 and WSPR.
WebSDR also Online SDR, KiwiSDR: A receiver on the internet that anyone can tune from a web browser. A handy way to hear how your own signal is getting out.
Wheatstone bridge: Four resistances in a diamond, balanced so a meter across the middle reads zero. An SWR bridge is the same idea at RF.
WIDEn-N: The APRS path setting that tells digipeaters how many hops to repeat a packet. WIDE1-1,WIDE2-1 is the usual choice for mobiles. More on APRS →
Window line also 450-ohm line: Two-wire feedline with the insulation cut into windows. Very low loss, and the usual feed for a doublet.
Winlink: A worldwide network for sending and receiving email over radio. More on Winlink →
Winlink Express: The free Windows program most hams use to send and receive Winlink email by radio. More on Winlink →
Winter Field Day: A Field Day-style event in late January that tests portable operating in cold weather.
Wire gauge: The thickness of a wire. In the US it is given in AWG, where a smaller number means a thicker wire; a 100-watt radio usually needs 10 or 12 AWG power leads. More on A Guide to Portable Amateur Radio Power →
Wireless Telecommunications Bureau also WTB: The FCC bureau that runs amateur licensing and the Universal Licensing System.
Wires-X: Yaesu’s internet linking system for Fusion repeaters and nodes, organized into rooms. More on Fusion →
World Amateur Radio Day: April 18, the anniversary of the founding of the International Amateur Radio Union in Paris in 1925.
WPM (words per minute): The measure of Morse speed.
WPX (Worked All Prefixes): CQ magazine’s award for confirming contacts with different callsign prefixes. CQ also runs the WPX contests, where each new prefix is a multiplier. More on Awards →
Wrist strap also ESD strap: A strap worn on the wrist and connected to ground through a resistor, so static drains away before it can damage parts.
WRTC (World Radiosport Team Championship): An international contest held about every four years in which two-person teams operate identical stations, so skill decides the result.
WSJT-X: The software behind FT8, FT4 and WSPR among others.
WSPR: A beacon mode for measuring where your signal actually reaches, rather than for making contacts. More on WSPR →
WWFF (World Wide Flora and Fauna): An international program for operating from nature reserves, similar to POTA.
WWV also WWVH: The US time and frequency stations run by NIST: WWV near Fort Collins, Colorado, and WWVH on Kauai, Hawaii. Their HF signals are a handy check of propagation.

X

Xastir: Free APRS software for Linux. More on APRS →
XIT: Transmitter incremental tuning: the transmit counterpart to RIT.
XOR gate (exclusive OR gate): A logic gate whose output is high when its inputs differ. Used in parity, comparison and some modulators.
XYL: A ham’s wife, from “ex-young lady”.

Y

Yagi: The classic directional antenna with a driven element, a reflector and one or more directors.
YASME Foundation: A nonprofit that supports amateur radio with grants for clubs, youth projects, DXpeditions and research. It takes its name from Danny Weil’s DXpedition yacht.
YL (young lady): Any female operator, whatever her age.
YOTA (Youth on the Air): Camps, events and special stations that bring young hams together, first in Europe and now in the Americas too.

Z

Zener diode: A diode designed to hold a steady voltage, used in simple voltage regulators.
Zero beat: Tuning to exactly the same frequency as another station.