Alternating current (ac) -- Electrical current that flows first in one direction in a wire and then in the other. The applied voltage is also changing polarity. This direction reversal continues at a rate that depends on the frequency of the ac.
Amateur operator -- A person holding a written authorization to be the control operator of an amateur station.
Amateur service -- A radiocommunication service for the purpose of self-training, intercommunication and technical investigations carried out by amateurs, that is, duly authorized persons interested in radio technique solely with a personal aim and without pecuniary interest.
Amateur station -- A station licensed in the amateur service, including necessary equipment, used for amateur communication.
Ammeter -- A test instrument that measures current.
Ampere (A) -- The basic unit of electrical current. Current is a measure of the electron flow through a circuit. If we could count electrons, we would find that if there are 6.24 × 1018 electrons moving past a point in one second, we have a current of one ampere. We abbreviate amperes as amps. (Numbers written as a multiple of some power are expressed in exponential notation, as shown here.)
Amplitude modulation (AM) -- A method of combining an information signal and an RF (radio-frequency) carrier. In double-sideband voice AM transmission, we use the voice information to vary (modulate) the amplitude of an RF carrier. Shortwave broadcast stations use this type of AM, as do stations in the Standard Broadcast Band (535-1710 kHz). Few amateurs use double-sideband voice AM, but a variation, known as single sideband, is very popular.
Antenna -- A device that picks up or sends out radio frequency energy.
Antenna switch -- A switch used to connect one transmitter, receiver or transceiver to several different antennas.
Antenna tuner -- A device that matches the antenna system input impedance to the transmitter, receiver or transceiver output impedance. Also called an antenna-matching network, impedance-matching network or Transmatch.
Autopatch -- A device that allows repeater users to make telephone calls through a repeater.
Balun -- Contraction for balanced to unbalanced. A device to couple a balanced load to an unbalanced source, or vice versa.
Band spread -- A receiver quality used to describe how far apart stations on different nearby frequencies will seem to be. We usually express band spread as the number of kilohertz that the frequency changes per tuning-knob rotation. Band spread and frequency resolution are related. The amount of band spread determines how easily signals can be tuned.
Band-pass filter -- A circuit that allows signals to go through it only if they are within a certain range of frequencies. It attenuates signals above and below this range.
Bandwidth -- The width of a frequency band outside of which the mean power is attenuated at least 26 dB below the mean power of the total emission, including allowances for transmitter drift or Doppler shift. Bandwidth describes the range of frequencies that a radio transmission occupies.
Battery -- A device that converts chemical energy into electrical energy.
Beacon station -- An amateur station transmitting communications for the purposes of observation of propagation and reception or other related experimental activities.
Beam antenna -- A directional antenna. A beam antenna must be rotated to provide coverage in different directions.
Beat-frequency oscillator (BFO) -- A receiver circuit that provides a signal to the detector. The BFO signal mixes with the incoming signal to produce an audio tone for CW reception. A BFO is needed to copy CW and SSB signals.
Block diagram -- A drawing using boxes to represent sections of a complicated device or process. The block diagram shows the connections between sections.
Broadcasting -- Transmissions intended to be received by the general public, either direct or relayed.
Capacitance -- A measure of the ability of a capacitor to store energy in an electric field.
Capacitor -- An electrical component usually formed by separating two conductive plates with an insulating material. A capacitor stores energy in an electric field.
Centi -- The metric prefix for 10--2, or divide by 100.
Chassis ground -- The common connection for all parts of a circuit that connect to the negative side of the power supply.
Chirp -- A slight shift in transmitter frequency each time you key the transmitter.
Closed repeater -- A repeater that restricts access to those who know a special code.
Closed, or complete circuit -- An electrical circuit with an uninterrupted path for the current to follow. Turning a switch on, for example, closes or completes the circuit, allowing current to flow.
Coaxial cable -- Coax (pronounced kó-aks). A type of feed line with one conductor inside the other.
Color code -- A system in which numerical values are assigned to various colors. Colored stripes are painted on the body of resistors and sometimes other components to show their value.
Conductor -- A material that has a loose grip on its electrons, so an electrical current can pass through it.
Connected -- The condition in which two packet-radio stations are sending information to each other. Each is acknowledging when the data has been received correctly.
Continuous wave (CW) -- Morse code telegraphy.
Control operator -- An amateur operator designated by the licensee of a station to be responsible for the transmissions of an amateur station.
Control point -- The locations at which the control operator function is performed.
Controlled environment -- Any area in which an RF signal may cause radiation exposure to people who are aware of the radiated electric and magnetic fields and who can exercise some control over their exposure to these fields. The FCC generally considers amateur operators and their families to be in a controlled RF exposure environment to determine the maximum permissible exposure levels.
Core -- The material used in the center of an inductor coil, where the magnetic field is concentrated.
Courtesy tone -- A tone or beep transmitted by a repeater to indicate that it is okay for the next station to begin transmitting. The courtesy tone is designed to allow a pause between transmissions on a repeater, so other stations can call. It also indicates that the time-out timer has been reset.
CQ -- "Calling any station": the general call when requesting a conversation with anyone.
Crystal oscillator -- A device that uses a quartz crystal to keep the frequency of a transmitter constant.
Crystal-controlled transmitter -- A simple type of transmitter that consists of a crystal oscillator followed by driver and power amplifier stages.
CTCSS -- Continuous tone coded squelch system. A sub-audible tone system used on some repeaters. When added to a carrier, a CTCSS tone allows a receiver to accept a signal. Also called PL.
Cubical quad antenna -- An antenna built with its elements in the shape of four-sided loops.
Current -- A flow of electrons in an electrical circuit.
CW (Morse code) -- A communications mode transmitted by on/off keying of a radio-frequency signal. Another name for international Morse code.
D region -- The lowest region of the ionosphere. The D region contributes very little to short-wave radio propagation. It acts mainly to absorb energy from radio waves as they pass through it. This absorption has a significant effect on signals below about 7.5 MHz during daylight.
Data -- Computer-based communications modes, such as packet radio, which can be used to transmit and receive computer files, or digital information.
DE -- The Morse code abbreviation for "from" or "this is."
Deci -- The metric prefix for 10--1, or divide by 10.
Delta loop antenna -- A variation of the cubical quad with triangular elements.
Detector -- The stage in a receiver in which the modulation (voice or other information) is recovered from the RF signal.
Digipeater -- A packet-radio station used to retransmit signals that are specifically addressed to be retransmitted by that station.
Digital communications -- Computer-based communications modes. This can include data modes like packet radio and text-only modes like radioteletype (RTTY).
Dipole antenna -- See Half-wave dipole. A dipole need not be ½ wavelength long.
Direct current (dc) -- Electrical current that flows in one direction only.
Directional wattmeter (see Wattmeter)
Director -- An element in front of the driven element in a Yagi and some other directional antennas.
Double-pole, double-throw (DPDT) switch -- A switch that has six contacts. The DPDT switch has two center contacts. The two center contacts can each be connected to one of two other contacts.
Double-pole, single-throw (DPST) switch -- A switch that connects two contacts to another set of contacts. A DPST switch turns two circuits on or off at the same time.
Driven element -- The part of an antenna that connects directly to the feed line.
Dual-band antenna -- An antenna designed for use on two different Amateur Radio bands.
Dummy antenna -- A station accessory that allows you to test or adjust transmitting equipment without sending a signal out over the air. Also called dummy load.
Dummy load -- A station accessory that allows you to test or adjust transmitting equipment without sending a signal out over the air. Also called dummy antenna.
Duplexer -- A device that allows a dual-band radio to use a single dual-band antenna.
Duty cycle -- A measure of the amount of time a transmitter is operating at full output power during a single transmission. A lower duty cycle means less RF radiation exposure for the same PEP output.
DX -- Distance, foreign countries.
E region -- The second lowest ionospheric region, the E region exists only during the day. Under certain conditions, it may refract radio waves enough to return them to Earth.
Earth ground -- A circuit connection to a ground rod driven into the Earth or to a cold-water pipe made of copper that goes into the ground.
Earth station -- An amateur station located on, or within 50 km of, the Earth's surface intended for communications with space stations or with other Earth stations by means of one or more other objects in space.
Earth-Moon-Earth (EME) or Moonbounce -- A method of communicating with other stations by reflecting radio signals off the Moon's surface.
Electric field -- An invisible force of nature. An electric field exists in a region of space if an electrically charged object placed in the region is subjected to an electrical force.
Electromotive force (EMF) -- The force or pressure that pushes a current through a circuit.
Electron -- A tiny, negatively charged particle, normally found in an area surrounding the nucleus of an atom. Moving electrons make up an electrical current.
Emergency -- A situation where there is a danger to lives or property.
Emergency traffic -- Messages with life and death urgency or requests for medical help and supplies that leave an area shortly after an emergency.
Emission -- The transmitted signal from an amateur station.
Emission privilege -- Permission to use a particular emission type (such as Morse code or voice).
Emission types -- Term for the different modes authorized for use on the Amateur Radio bands. Examples are CW, SSB, RTTY and FM.
Energy -- The ability to do work; the ability to exert a force to move some object.
F region -- A combination of the two highest ionospheric regions, the F1 and F2 regions. The F region refracts radio waves and returns them to Earth. Its height varies greatly depending on the time of day, season of the year and amount of sunspot activity.
False or deceptive signals -- Transmissions that are intended to mislead or confuse those who may receive the transmissions. For example, distress calls transmitted when there is no actual emergency are false or deceptive signals.
Feed line -- The wires or cable used to connect a transmitter, receiver or transceiver to an antenna. See Transmission line.
Filter -- A circuit that will allow some signals to pass through it but will greatly reduce the strength of others.
Frequency -- The number of complete cycles of an alternating current that occur per second.
Frequency bands -- A group of frequencies where amateur communications are authorized.
Frequency coordination -- Allocating repeater input and output frequencies to minimize interference between repeaters and to other users of the band.
Frequency coordinator -- An individual or group that recommends repeater frequencies to reduce or eliminate interference between repeaters operating on or near the same frequency in the same geographical area.
Frequency discriminator -- A type of detector used in some FM receivers.
Frequency modulated (FM) phone -- The type of signals used to communicate by voice (phone) over most repeaters. FM is a method of combining an RF carrier with an information signal, such as voice. The voice information (or data) changes the RF carrier frequency in the modulation process. (see Amplitude modulation). As you might suspect, we use voice or data to vary the frequency of the transmitted signal. FM broadcast stations and most professional communications (police, fire, taxi) use FM. VHF/UHF FM voice is the most popular amateur mode.
Frequency privilege -- Permission to use a particular group of frequencies.
Front-end overload -- Interference to a receiver caused by a strong signal that overpowers the receiver RF amplifier ("front end"). See also receiver overload.
Fuse -- A thin metal strip mounted in a holder. When too much current passes through the fuse, the metal strip melts and opens the circuit.
General-coverage receiver--A receiver used to listen to a wide range of frequencies. Most general-coverage receivers tune from frequencies below the standard-broadcast band to at least 30 MHz. These frequencies include the shortwave-broadcast bands and the amateur bands from 160 to 10 meters.
Giga -- The metric prefix for 109, or times 1,000,000,000.
Grace period -- The time FCC allows following the expiration of an amateur license to renew that license without having to retake an examination. Those who hold an expired license may not operate an amateur station until the license is reinstated.
Ground connection -- A connection made to the earth for electrical safety. This connection can be made inside (to a metal cold-water pipe) or outside (to a ground rod).
Ground rod -- A copper or copper-clad steel rod that is driven into the earth. A heavy copper wire from the ham shack connects all station equipment to the ground rod.
Ground-wave propagation -- The method by which radio waves travel along the Earth's surface.
Half-wave dipole -- A basic antenna used by radio amateurs. It consists of a length of wire or tubing, opened and fed at the center. The entire antenna is ½ wavelength long at the desired operating frequency.
Ham-bands-only receiver -- A receiver designed to cover only the bands used by amateurs. Usually refers to the bands from 80 to 10 meters, sometimes including 160 meters.
Harmonics -- Signals from a transmitter or oscillator occurring on whole-number multiples (2×, 3×, 4×, etc) of the desired operating frequency.
Health and Welfare traffic -- Messages about the well being of individuals in a disaster area. Such messages must wait for Emergency and Priority traffic to clear, and results is advisories to those outside the disaster area awaiting news from family and friends.
Hertz (Hz) -- An alternating-current frequency of one cycle per second. The basic unit of frequency.
High-pass filter -- A filter designed to pass high-frequency signals, while blocking lower-frequency signals.
Impedance -- The opposition to electric current in a circuit. Impedance includes factors other than resistance, and applies to alternating currents. Ideally, the characteristic impedance of a feed line is the same as the transmitter output impedance and the antenna input impedance.
Impedance-matching device -- A device that matches one impedance level to another. For example, it may match the impedance of an antenna system to the impedance of a transmitter or receiver. Amateurs also call such devices a Transmatch, impedance-matching network or antenna tuner.
Inductance -- A measure of the ability of a coil to store energy in a magnetic field.
Inductor -- An electrical component usually composed of a coil of wire wound on a central core. An inductor stores energy in a magnetic field.
Input frequency -- A repeater's receiving frequency. To use a repeater, transmit on the input frequency and receive on the output frequency.
Insulator -- A material that maintains a tight grip on its electrons, so that an electric current cannot pass through it (within voltage limits).
Intermediate frequency (IF) -- The output frequency of a mixing stage in a superheterodyne receiver. The subsequent stages in the receiver are tuned for maximum efficiency at the IF.
Ionizing radiation -- Electromagnetic radiation that has sufficient energy to knock electrons free from their atoms, producing positive and negative ions. X-rays, gamma rays and ultraviolet radiation are examples of ionizing radiation.
Ionosphere -- A region of electrically charged (ionized) gases high in the atmosphere. The ionosphere bends radio waves as they travel through it, returning them to Earth. Also see sky-wave propagation.
K -- The Morse code abbreviation for "any station respond."
Kilo -- The metric prefix for 103, or times 1000.
Lightning protection -- There are several ways to help prevent lightning damage to your equipment (and your house), among them unplugging equipment, disconnecting antenna feed lines and using a lightning arrestor.
Limiter -- A stage of an FM receiver that makes the receiver less sensitive to amplitude variations and pulse noise.
Line-of-sight propagation -- The term used to describe VHF and UHF propagation in a straight line directly from one station to another.
Lower sideband (LSB) --The common single-sideband operating mode on the 40, 80 and 160-meter amateur bands.
Low-pass filter -- A filter that allows signals below the cutoff frequency to pass through and attenuates signals above the cutoff frequency.
Malicious (harmful) interference -- Intentional, deliberate obstruction of radio transmissions.
Maximum useable frequency (MUF) --- The highest-frequency radio signal that will reach a particular destination using sky-wave propagation, or skip. The MUF may vary for radio signals sent to different destinations.
MAYDAY -- From the French m'aidez (help me), MAYDAY is used when calling for emergency assistance in voice modes.
Mega -- The metric prefix for 106, or times 1,000,000.
Metric prefixes -- A series of terms used in the metric system of measurement. We use metric prefixes to describe a quantity as compared to a basic unit. The metric prefixes indicate multiples of 10.
Metric system -- A system of measurement developed by scientists and used in most countries of the world. This system uses a set of prefixes that are multiples of 10 to indicate quantities larger or smaller than the basic unit.
Micro -- The metric prefix for 10--6, or divide by 1,000,000.
Microphone -- A device that converts sound waves into electrical energy.
Milli -- The metric prefix for 10--3, or divide by 1000.
Mobile device -- A radio transmitting device designed to be mounted in a vehicle. A push-to-talk (PTT) switch activates the transmitter.
Modem -- Short for modulator/demodulator. A modem modulates a radio signal to transmit data and demodulates a received signal to recover transmitted data.
Modulate -- To vary the amplitude, frequency, or phase of a radio-frequency signal.
Modulation -- The process of varying an RF carrier in some way (the amplitude or the frequency, for example) to add an information signal to be transmitted.
Monitor mode -- One type of packet radio receiving mode. In monitor mode, everything transmitted on a packet frequency is displayed by the monitoring TNC. This occurs whether or not the transmissions are addressed to the monitoring station.
Morse code (see CW).
Multimeter -- An electronic test instrument used to measure current, voltage and resistance in a circuit. Describes all meters capable of making these measurements, such as the volt-ohm-milliammeter (VOM), vacuum-tube voltmeter (VTVM) and field-effect transistor VOM (FET VOM).
Multimode transceiver--Transceiver capable of SSB, CW and FM operation.
National Electrical Code -- A set of guidelines governing electrical safety, including antennas.
Network -- A term used to describe several packet stations linked together to transmit data over long distances.
Nonionizing radiation -- Electromagnetic radiation that does not have sufficient energy to knock electrons free from their atoms. Radio frequency (RF) radiation is nonionizing.
NPN transistor -- A transistor that has a layer of P-type semiconductor material sandwiched between layers of N-type semiconductor material.
Offset--The 300 to 1000-Hz difference in CW transmitting and receiving frequencies in a transceiver. For a repeater, offset refers to the difference between its transmitting and receiving frequencies.
Ohm -- The basic unit of electrical resistance, used to describe the amount of opposition to current.
Ohm's Law -- A basic law of electronics. Ohm's Law gives a relationship between voltage (E), current (I) and resistance (R). The voltage applied to a circuit is equal to the current through the circuit times the resistance of the circuit (E = IR).
One-way communications -- Transmissions that are not intended to be answered. The FCC strictly limits the types of one-way communications allowed on the amateur bands.
Open circuit -- An electrical circuit that does not have a complete path, so current can't flow through the circuit.
Open repeater -- A repeater that can be used by all hams who have a license that authorizes operation on the repeater frequencies.
Operator/primary station license -- An amateur license actually includes two licenses in one. The operator license is that portion of an Amateur Radio license that gives permission to operate an amateur station. The primary station license is that portion of an Amateur Radio license that authorizes an amateur station at a specific location. The station license also lists the call sign of that station.
Output frequency -- A repeater's transmitting frequency. To use a repeater, transmit on the input frequency and receive on the output frequency.
Packet radio -- A system of digital communication whereby information is broken into short bursts. The bursts ("packets") also contain addressing and error-detection information.
Parallel circuit -- An electrical circuit in which the electrons follow more than one path in going from the negative supply terminal to the positive terminal.
Parasitic beam antenna -- Another name for the beam antenna.
Parasitic element -- Part of a directive antenna that derives energy from mutual coupling with the driven element. Parasitic elements are not connected directly to the feed line.
Peak envelope power (PEP) -- The average power of a signal at its largest amplitude peak.
Pecuniary -- Payment of any type, whether money or other goods. Amateurs may not operate their stations in return for any type of payment.
Phone -- Another name for voice communications.
Phone emission -- The FCC name for voice or other sound transmissions.
Phonetic alphabet -- Standard words used on voice modes to make it easier to understand letters of the alphabet, such as those in call signs. The call sign KA6LMN stated phonetically is Kilo Alfa Six Lima Mike November.
Pico -- The metric prefix for 10--12, or divide by 1,000,000,000,000.
PL (see CTCSS)
PNP transistor -- A transistor that has a layer of N-type semiconductor material sandwiched between layers of P-type semiconductor material.
Polarization -- The electrical-field characteristic of a radio wave. An antenna that is parallel to the surface of the earth, such as a dipole, produces horizontally polarized waves. One that is perpendicular to the earth's surface, such as a quarter-wave vertical, produces vertically polarized waves. An antenna that has both horizontal and vertical polarization is said to be circularly polarized.
Portable device -- A radio transmitting device designed to have a transmitting antenna that is generally within 20 centimeters of a human body.
Potentiometer -- Another name for a variable resistor. The value of a potentiometer can be changed over a range of values without removing it from a circuit.
Power -- The rate of energy consumption. We calculate power in an electrical circuit by multiplying the voltage applied to the circuit times the current through the circuit (P = IE).
Power supply -- A circuit that provides a direct-current output at some desired voltage from an ac input voltage.
Priority traffic -- Emergency-related messages, but not as important as Emergency traffic.
Procedural signal (prosign) -- One or two letters sent as a single character. Amateurs use prosigns in CW contacts as a short way to indicate the operator's intention. Some examples are K for "Go Ahead," or AR<OVERSCORE> for "End of Message." (The bar over the letters indicates that we send the prosign as one character.)
Product detector -- A device that allows a receiver to process CW and SSB signals.
Propagation -- The study of how radio waves travel.
Q signals -- Three-letter symbols beginning with Q. Used on CW to save time and to improve communication. Some examples are QRS (send slower), QTH (location), QSO (ham conversation) and QSL (acknowledgment of receipt).
QRL? -- Ham radio Q signal meaning "Is this frequency in use?"
QSL card -- A postcard that serves as a confirmation of communication between two hams.
QSO -- A conversation between two radio amateurs.
Quarter-wavelength vertical antenna -- An antenna constructed of a quarter-wavelength long radiating element placed perpendicular to the earth.
Radio Amateur Civil Emergency Service (RACES) -- A part of the Amateur Service that provides radio communications for civil preparedness organizations during local, regional or national civil emergencies.
Radio-frequency interference (RFI) -- Disturbance to electronic equipment caused by radio-frequency signals.
Radioteletype (RTTY) -- Radio signals sent from one teleprinter machine to another machine. Anything that one operator types on his teleprinter will be printed on the other machine. Also known as narrow-band direct-printing telegraphy.
Receiver--A device that converts radio waves into signals we can hear or see.
Receiver incremental tuning (RIT)--A transceiver control that allows for a slight change in the receiver frequency without changing the transmitter frequency. Some manufacturers call this a clarifier (CLAR) control.
Receiver overload -- Interference to a receiver caused by a strong RF signal that forces its way into the equipment. A signal that overloads the receiver RF amplifier (front end) causes front-end overload. Receiver overload is sometimes called RF overload.
Reflection -- Signals that travel by line-of-sight propagation are reflected by large objects like buildings.
Reflector -- An element behind the driven element in a Yagi and some other directional antennas.
Repeater station -- An amateur station that automatically retransmits the signals of other stations.
Resistance -- The ability to oppose an electric current.
Resistor -- Any material that opposes a current in an electrical circuit. An electronic component specifically designed to oppose or control current through a circuit.
Resonant frequency -- The desired operating frequency of a tuned circuit. In an antenna, the resonant frequency is one where the feed-point impedance contains only resistance.
RF burn -- A burn produced by coming in contact with exposed RF voltages.
RF carrier -- A steady radio frequency signal that is modulated to add an information signal to be transmitted. For example, a voice signal is added to the RF carrier to produce a phone emission signal.
RF overload -- Another term for receiver overload.
RF radiation -- Waves of electric and magnetic energy. Such electromagnetic radiation with frequencies as low as 3 kHz and as high as 300 GHz are considered to be part of the RF region.
RF safety -- Preventing injury or illness to humans from the effects of radio-frequency energy.
Rig --The radio amateur's term for a transmitter, receiver or transceiver.
RST -- A system of numbers used for signal reports: R is readability, S is strength and T is tone. (On single-sideband phone, only R and S reports are used.)
Safety interlock -- A switch that automatically turns off ac power to a piece of equipment when the top cover is removed.
Schematic symbol -- A drawing used to represent a circuit component on a wiring diagram.
Selectivity --The ability of a receiver to separate two closely spaced signals.
Sensitivity --The ability of a receiver to detect weak signals. Shack--The room where an Amateur Radio operator keeps his or her station equipment.
Series circuit -- An electrical circuit in which all the electrons must flow through every part of the circuit. There is only one path for the electrons to follow.
Shack -- The room where an Amateur Radio operator keeps his or her station equipment.
Short circuit -- An electrical circuit in which the current does not take the desired path, but finds a shortcut instead. Often the current goes directly from the negative power-supply terminal to the positive one, bypassing the rest of the circuit.
Sidebands -- The sum or difference frequencies generated when an RF carrier is mixed with an audio signal. Single-sideband phone (SSB) signals have an upper sideband (USB -- that part of the signal above the carrier) and a lower sideband (LSB -- the part of the signal below the carrier). SSB transceivers allow operation on either USB or LSB.
Simplex operation -- Receiving and transmitting on the same frequency. See duplex operation.
Single Sideband (SSB) phone -- A common mode of voice operation on the amateur bands. SSB is a form of amplitude modulation.The amplitude of the transmitted signal varies with the voice signal variations.
Single-pole, double-throw (SPDT) switch -- A switch that connects one center contact to one of two other contacts.
Single-pole, single-throw (SPST) switch -- A switch that only connects one center contact to another contact.
Skip zone -- An area of poor radio communication, too distant for ground waves and too close for sky waves.
Sky-wave propagation -- The method by which radio waves travel through the ionosphere and back to Earth. Sometimes called skip, sky-wave propagation has a far greater range than line-of-sight and ground-wave propagation.
SOS<OVERSCORE> -- A Morse code call for emergency assistance.
Space station -- An amateur station located more than 50 km above the Earth's surface.
Specific absorption rate (SAR) -- A term that describes the rate at which RF energy is absorbed into the human body. Maximum permissible exposure (MPE) limits are based on whole-body SAR values.
Splatter -- A type of interference to stations on nearby frequencies. Splatter occurs when a transmitter is overmodulated.
Spurious emissions -- Signals from a transmitter on frequencies other than the operating frequency.
Standing-wave ratio (SWR) -- Sometimes called voltage standing-wave ratio (VSWR). A measure of the impedance match between the feed line and the antenna. Also, with a Transmatch in use, a measure of the match between the feed line from the transmitter and the antenna system. The system includes the Transmatch and the line to the antenna. VSWR is the ratio of maximum voltage to minimum voltage along the feed line. Also the ratio of antenna impedance to feed-line impedance when the antenna is a purely resistive load.
Station grounding -- Connecting all station equipment to a good earth ground improves both safety and station performance.
Sunspot cycle -- The number of sunspots increases and decreases in a predictable cycle that lasts about 11 years.
Sunspots -- Dark spots on the surface of the sun. When there are few sunspots, long-distance radio propagation is poor on the higher-frequency bands. When there are many sunspots, long-distance HF propagation improves.
Switch -- A device used to connect or disconnect electrical contacts.
SWR meter -- A measuring instrument that can indicate when an antenna system is working well. A device used to measure SWR.
Tactical call signs -- Names used to identify a location or function during local emergency communications.
Teleprinter -- A machine that can convert keystrokes (typing) into electrical impulses. The teleprinter can also convert the proper electrical impulses back into text. Computers have largely replaced teleprinters for amateur radioteletype work.
Television interference (TVI) -- Interruption of television reception caused by another signal.
Temperature inversion -- A condition in the atmosphere in which a region of cool air is trapped beneath warmer air.
Temporary state of communications emergency -- When a disaster disrupts normal communications in a particular area, the FCC can declare this type of emergency. Certain rules may apply for the duration of the emergency.
Terminal -- An inexpensive piece of equipment that can be used in place of a computer in a packet radio station.
Third-party communications -- Messages passed from one amateur to another on behalf of a third person.
Third-party communications agreement -- An official understanding between the United States and another country that allows amateurs in both countries to participate in third-party communications.
Third-party participation -- The way an unlicensed person can participate in amateur communications. A control operator must ensure compliance with FCC rules.
Ticket--A common name for an Amateur Radio license.
Time-out timer -- A device that limits the amount of time any one person can talk through a repeater.
Transceiver -- A radio transmitter and receiver combined in one unit.
Transistor -- A solid-state device made of three layers of semiconductor material. See NPN transistor and PNP transistor.
Transmission line -- The wires or cable used to connect a transmitter or receiver to an antenna. Also called feed line.
Transmitter -- A device that produces radio-frequency signals.
Troposphere -- The region in Earth's atmosphere just above the Earth's surface and below the ionosphere.
Tropospheric bending -- When radio waves are bent in the troposphere, they return to Earth farther away than the visible horizon.
Tropospheric ducting -- A type of VHF propagation that can occur when warm air overruns cold air (a temperature inversion).
Unbalanced line -- Feed line with one conductor at ground potential, such as coaxial cable.
Uncontrolled environment -- Any area in which an RF signal may cause radiation exposure to people who may not be aware of the radiated electric and magnetic fields. The FCC generally considers members of the general public and an amateur's neighbors to be in an uncontrolled RF radiation exposure environment to determine the maximum permissible exposure levels.
Unidentified communications or signals -- Signals or radio communications in which the transmitting station's call sign is not transmitted.
Upper sideband (USB)--The common single-sideband operating mode on the 20, 17, 15, 12 and 10-meter HF amateur bands, and all the VHF and UHF bands.
Variable capacitor -- A capacitor that can have its value changed within a certain range.
Variable resistor -- A resistor whose value can be adjusted over a certain range, without removing it from a circuit.
Variable-frequency oscillator (VFO) -- An oscillator used in receivers and transmitters. The frequency is set by a tuned circuit using capacitors and inductors. The frequency can be changed by adjusting the components in the tuned circuit.
Vertical antenna -- A common amateur antenna, often made of metal tubing. The radiating element is vertical. There are usually four or more radial elements parallel to or on the ground.
Visible horizon -- The most distant point one can see by line of sight.
Voice -- Any of the several methods used by amateurs to transmit speech.
Voice communications -- Hams can use several voice modes, including FM and SSB.
Volt (V) -- The basic unit of electrical pressure or EMF.
Voltage -- The EMF or pressure that causes electrons to move through an electrical circuit.
Voltmeter -- A test instrument used to measure voltage.
Watt (W) -- The unit of power in the metric system. The watt describes how fast a circuit uses electrical energy.
Wattmeter -- Also called a power meter, a test instrument used to measure the power output (in watts) of a transmitter. A directional wattmeter measures both forward and reflected power.
Wavelength -- Often abbreviated l. The distance a radio wave travels in one RF cycle. The wavelength relates to frequency. Higher frequencies have shorter wavelengths.
Yagi antenna -- The most popular type of amateur directional (beam) antenna. It has one driven element and one or more additional elements.