Ham Radio General key terms

The average power supplied to the antenna transmission line by a transmitter during one radio frequency cycle at the crest of the modulation envelope, measured under normal operating conditions.

A volunteer recognized by the FCC who recommends channels and frequencies to local repeater and auxiliary station owners to minimize interference among stations in the same area.

The licensed amateur designated by the station licensee to be responsible for the proper operation of a station at all times it is transmitting, including remote and automatic operation.

The person or entity holding the FCC amateur license for a station; the licensee is ultimately accountable for that station's transmissions regardless of who is operating it.

Messages passed on behalf of a person who is not the control operator and not a licensed amateur, permitted only when the amateur service rules of the foreign country involved allow it.

Operating an amateur station in a foreign country under the authority of that country's government, typically because a treaty or agreement recognizes the visitor's home license.

One of three geographic zones defined by the International Telecommunication Union for allocating radio frequencies; amateur privileges and band edges differ between regions.

A voluntary or coordinated arrangement that maps modes and activities to segments of an amateur band, helping operators avoid interference and find like-minded contacts.

A frequency widely understood to be used for initiating contacts, such as calling CQ or requesting a contact, before both stations move elsewhere to continue.

Transmitting on one frequency while listening on a different frequency, commonly used for DX contacts or repeaters so callers do not transmit on the station's listening channel.

The fixed frequency difference between a repeater's input and output frequencies, set by convention for each band so that a user's transmit frequency lands on the repeater's receiver.

Continuous Tone-Coded Squelch System; a subaudible tone transmitted with a signal that a repeater or receiver uses to open its squelch only for signals carrying the correct tone.

A receiver circuit that mutes audio output unless the received signal exceeds a chosen strength threshold, suppressing background noise between transmissions.

A postcard-style written confirmation of a two-way radio contact, exchanged directly or through a bureau, often used to obtain awards for contacting distant stations.

A distant station, generally one far enough away to be a desirable or challenging contact, or the activity of pursuing such contacts on the amateur bands.

The region of the upper atmosphere, roughly 60 to 600 km up, where solar radiation ionizes gases and enables long-distance radio communication by refracting signals back toward Earth.

The highest and most important ionospheric layer for HF communication; it can refract signals over very long distances and changes dramatically between day and night.

Irregular, short-lived patches of intense ionization in the E region that can refract VHF signals over unexpectedly long distances, especially in summer.

The highest frequency that can be refracted by the ionosphere back to a given receiving point along a path at a particular time and angle.

The highest frequency that a radio wave sent straight up will be reflected back to Earth by a given ionospheric layer at a given moment.

Refraction of VHF and UHF signals within layers of the lower atmosphere, allowing contacts well beyond the normal horizon, often associated with temperature inversions.

The direct, unobstructed path between two antennas; VHF and UHF communication is primarily limited to this path plus some diffraction and refraction beyond the horizon.

A prediction of band conditions based on solar activity, sunspot numbers, and geomagnetic indices, used to anticipate which frequencies will support long-distance contacts.

The ratio of maximum to minimum voltage or current along a feed line, indicating how well the load impedance matches the line; 1:1 means a perfect match.

The intrinsic impedance of a transmission line, determined by conductor spacing and dielectric material, that governs how signals travel and reflect along the line.

A feed line with a center conductor surrounded by insulation, a braided shield, and an outer jacket; its shield confines the signal and reduces unwanted radiation and pickup.

A device that converts between a balanced feed line or antenna and an unbalanced line such as coax, helping prevent RF current from flowing on the outside of the coax shield.

An adjustable matching network placed between transmitter and feed line that transforms the antenna system impedance to present a low SWR to the transmitter.

The increase in signal strength in a preferred direction compared with a reference antenna, achieved by concentrating radiated power rather than adding total power.

The property of an antenna by which it radiates or receives more effectively in some directions than others, usually described along with gain and front-to-back ratio.

A directional antenna made of a driven element plus parasitic elements, typically a reflector and one or more directors, mounted on a boom to focus radiation forward.

The fraction of time a transmitter is actually emitting power during a period of operation, important for comparing average power with peak envelope power.

The RF power delivered by a transmitter to its antenna system, measured as peak envelope power for SSB or average power for continuous modes like FM and CW.

Radiocommunication using voice, as opposed to telegraphy or data; on the amateur bands, phone subbands are reserved for voice modes such as SSB and FM.

An amplitude modulation form in which the carrier and one sideband are removed, concentrating power in a single sideband and improving efficiency over full-carrier AM.

A modulation method in which the carrier's frequency shifts in step with the modulating signal while amplitude stays constant, giving good noise immunity for local voice work.

The maximum amount a frequency-modulated carrier shifts above or below its resting frequency, commonly limited to about 5 kHz on amateur VHF and UHF FM channels.

The relationship stating that voltage equals current multiplied by resistance, used to calculate any one of the three quantities when the other two are known.

The relationship that electrical power equals voltage multiplied by current, or current squared times resistance, used to compute dissipation and required ratings in circuits.

The opposition to alternating current offered by a capacitor or inductor, which depends on frequency and stores energy rather than dissipating it as heat.

The total opposition to alternating current in a circuit, combining resistance with reactance and including any phase difference between voltage and current.

The condition in a circuit containing inductance and capacitance where their reactances cancel, leaving only resistance and allowing maximum or minimum response at one frequency.

A circuit that passes signals in selected frequency ranges while attenuating others, built from resistors, capacitors, and inductors arranged as low-pass, high-pass, or band-pass networks.

An unintended path for current from a live conductor to earth; proper grounding and a ground-fault circuit interrupter reduce the risk of electric shock.

Bonding equipment chassis and antenna system grounds to a common earth point to reduce shock hazard, RF interference, and stray RF in the shack.

Tissue injury caused by radio frequency current flowing through the body, which can occur on contact with an energized antenna or feed line even at modest power.