For A
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.

for B
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.

for C
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.