Foundation Amateur Radio Exam key terms

A radio communication service for self-training, intercommunication, and technical investigation, carried out by licensed individuals without payment. Its operators must hold a valid authorization from their national administration.

The official authorization granted to a person after passing required examinations, permitting that person to operate amateur stations under stated privileges and conditions set by the licensing authority.

A unique identifier assigned to a licensed amateur station, used to identify the operator and station during transmissions. It usually contains a national prefix, a district numeral, and a suffix of letters.

The required practice of announcing your assigned call sign at specified times during and at the end of a communication, so stations can tell who is transmitting on the frequency.

The specific operating rights granted by a license class, such as which frequency bands, transmission modes, and power levels the holder may use. Higher classes generally receive broader access.

Defined ranges of radio spectrum, usually named by approximate wavelength, that amateurs are allocated for use. Each band has its own propagation traits and sharing rules with other services.

Messages passed on behalf of someone other than the licensed control operator. Rules restrict when such messages may be sent internationally or for business purposes, and the operator remains responsible for content.

The licensed person responsible for the proper operation of a station at any given moment. This person must be present or reachable by remote control and ensures all rules are followed.

A written or electronic record of transmissions, often listing date, time, frequency, mode, and stations contacted. Keeping one is sometimes required and is always useful for proving compliance.

The physical distance a radio wave travels during one complete cycle, equal to the speed of light divided by frequency. It is often used to name bands and to size antennas.

The number of complete cycles of a radio wave occurring each second, measured in hertz (Hz). Higher frequency means shorter wavelength and generally different propagation behavior.

A logarithmic unit used to compare two power or signal levels. A 3 dB increase roughly doubles power, while a 3 dB decrease halves it, making it convenient for expressing gain and loss.

The rate at which electrical energy is delivered or radiated, measured in watts. In radio work it usually refers to transmitter output or effective radiated power from the antenna system.

The electrical potential difference that drives current through a circuit, measured in volts. It is one of the basic quantities relating current, resistance, and power in Ohm's law.

The flow of electric charge through a conductor, measured in amperes. It is proportional to voltage and inversely proportional to resistance in a simple circuit.

The opposition to current flow in a circuit, measured in ohms. It converts electrical energy into heat and determines how much current flows for a given applied voltage.

The relationship stating that voltage equals current multiplied by resistance. Knowing any two of these quantities lets you calculate the third in a circuit.

The total opposition a circuit presents to alternating current, combining resistance and reactance. Matching impedances between a transmitter, feed line, and antenna minimizes loss and reflection.

The ability of a component to store electric charge, measured in farads. Capacitors oppose changes in voltage and are used in filters, tuning circuits, and coupling networks.

The property of a coil or conductor that opposes changes in current by storing magnetic energy, measured in henries. Inductors are used with capacitors to form tuned circuits.

The condition in which a tuned circuit's inductive and capacitive reactances cancel, producing a peak response at one frequency. It is central to tuning antennas, filters, and oscillators.

The fraction of time a transmitter actually emits energy during a period of operation. Modes with high duty cycle stress components and reduce safe power limits more than intermittent modes.

The process of varying a carrier wave to carry information, such as changing its amplitude, frequency, or phase. The chosen method affects bandwidth, clarity, and equipment complexity.

One of the two bands of frequencies created above and below the carrier when a signal is amplitude modulated. Single sideband transmits only one, saving power and bandwidth.

A method in which the carrier's frequency shifts to convey audio information. It is resistant to amplitude noise but occupies more bandwidth than amplitude modulation.

The range of frequencies a signal occupies or a receiver can pass. Narrower bandwidth reduces noise but limits the information that can be carried or heard clearly.

A circuit that passes desired frequencies while blocking others. In receivers it selects the wanted signal and rejects interference; in transmitters it suppresses unwanted emissions.

A signal at an integer multiple of a fundamental frequency. Harmonics can interfere with other services and are suppressed by filtering and good transmitter design.

Any unwanted radio energy emitted outside the intended signal's necessary bandwidth, including harmonics and mixing products. Regulations set limits on how strong these emissions may be.

A measure of the weakest signal a receiver can detect and reproduce usefully. Better sensitivity lets you hear distant or low-power stations otherwise lost in noise.

A receiver's ability to separate a desired signal from strong signals on nearby frequencies. Good selectivity prevents adjacent stations from masking the one you want.

The level of background noise present in a receiver or at an antenna, setting the weakest signal that can be heard. Atmospheric, man-made, and thermal sources all raise it.

The comparison of desired signal strength to background noise level, usually expressed in decibels. A higher ratio means clearer, more reliable reception.

The physical size of an antenna, normally chosen in relation to the operating wavelength. A half-wavelength dipole or quarter-wavelength vertical are common starting designs.

A simple antenna made of two straight conducting sections fed at the center. Its length is typically about a half wavelength, and it radiates most strongly broadside to its axis.

The transmission line connecting a transmitter or receiver to its antenna, such as coaxial cable or ladder line. Proper choice and installation minimize loss and unwanted radiation.

A measure of impedance mismatch in a feed line, expressed as a ratio. A value near 1:1 means a good match; higher values indicate reflected power and possible equipment stress.

A network of adjustable inductors and capacitors placed between a transmitter and feed line. It transforms impedance so the transmitter sees a good match across a range of frequencies.

The power a station appears to radiate in its strongest direction, accounting for transmitter output, feed line loss, and antenna gain. Rules often limit this value rather than raw transmitter power.

The increase in radiated signal strength in a preferred direction compared with a reference antenna. Gain is achieved by concentrating energy rather than creating it, so other directions suffer.

A ratio describing how much a device or antenna increases signal level, often stated in decibels. Positive gain means amplification or focusing; negative gain means loss.

The way radio waves travel from a transmitting antenna to a receiving antenna. It depends on frequency, time of day, weather, and ionospheric conditions, and determines reliable range.

Layers of electrically charged particles high in the atmosphere that can refract radio waves back toward Earth. Its changing density strongly affects long-distance communication on lower bands.

The shortest ground distance at which a sky wave refracted by the ionosphere returns to Earth. Inside that gap, reception may be possible only by ground wave.