GROL key terms

A commercial FCC license held by an individual that authorizes operation and internal adjustment of radiotelephone transmitters at specified ship and aircraft stations; it is earned by passing written examination elements covering rules, fundamentals, and practical equipment.

An FCC authorization issued to the vessel itself that permits the ship station to transmit on marine frequencies, naming the vessel and the frequencies and equipment authorized; it must be kept aboard for inspection.

A limited FCC permit that allows a person to operate certain ship or aircraft radiotelephone stations; it requires no examination, but it does not authorize internal repair or adjustment of transmitters.

The formal assignment of bands of frequencies to particular radio services, made nationally by the FCC and internationally through the ITU, so that different services share the spectrum without causing harmful interference.

The international treaty text maintained by the International Telecommunication Union that governs use of the radio spectrum, including distress frequencies, calling procedures, and obligations binding on member administrations and their licensees.

The spoken radiotelephone distress signal, sent three times in succession, announcing that a vessel, aircraft, or person is in grave and imminent danger and needs immediate assistance.

The spoken urgency signal, repeated three times, used when a station has an urgent message about the safety of a vessel or person but is not yet in immediate danger requiring distress traffic.

The spoken safety signal, repeated three times, announcing that an important navigational or meteorological warning, such as a storm warning or hazard to navigation, will follow on the working frequency.

A digitally encoded calling system used on VHF, MF, and HF marine bands that transmits formatted alert messages, including distress alerts with position data, when the operator keys a dedicated controller instead of speaking.

An emergency position-indicating radio beacon that, once activated in the water, transmits a coded distress alert on 406 MHz to satellites so search and rescue authorities can locate the vessel.

The relationship stating that current through a resistance equals the voltage across it divided by the resistance; written as I equals V over R, it underlies nearly all circuit analysis.

The opposition a capacitor offers to alternating current, equal to one divided by two pi times frequency times capacitance; it decreases as frequency or capacitance rises and is measured in ohms.

The opposition an inductor offers to alternating current, equal to two pi times frequency times inductance; it increases with frequency and is measured in ohms.

The total opposition to alternating current in a circuit, combining resistance with capacitive and inductive reactance into a complex quantity expressed in ohms, having both magnitude and phase.

A two-terminal junction device that conducts readily in one direction and blocks current in the other, used for rectification, protection, and signal detection in radio power and receiving circuits.

The steady direct voltages and currents set at a transistor's terminals to fix its operating point, keeping the device in the desired region of its characteristic curves for linear amplification.

The condition in which a coil and capacitor exchange energy so their reactances cancel at one particular frequency, producing maximum or minimum response and setting oscillator frequency or receiver selectivity.

The residual alternating variation remaining on a power supply's direct output after rectification and smoothing; excessive ripple causes hum and can disturb sensitive radio frequency circuits.

An amplifier biased so that output current flows for less than half of each cycle, giving high efficiency and power output; its output must be filtered because it generates many harmonics.

The process in which a portion of an amplifier's output is returned to its input in the correct phase and with sufficient amplitude to sustain continuous oscillation at a frequency set by the resonant tank.

The ratio of maximum to minimum voltage along a transmission line, showing how well the line and its load are matched; a value close to one to one indicates a good match.

The impedance a transmission line presents to a traveling wave, fixed by conductor spacing and insulation, typically 50 or 75 ohms, and independent of the line's length.

A cable having a center conductor surrounded by insulation, a braided shield, and an outer jacket; it carries radio frequency energy from transmitter to antenna with little radiation and predictable loss.

A balanced antenna whose total length is about half a wavelength at the operating frequency, fed at its center, presenting roughly 73 ohms and a broad doughnut-shaped radiation pattern.

The increase in radiated field strength in a stated direction compared with a reference antenna, expressed in decibels; it comes from concentrating energy, not from creating additional power.

A modulation method in which the instantaneous amplitude of a radio frequency carrier is varied in step with an audio or data signal, while carrier frequency and phase remain constant.

The amount a carrier's frequency shifts above or below its assigned center value under frequency modulation; greater deviation generally yields louder recovered audio and wider occupied bandwidth.

A standardized code of letters and digits describing a transmission's necessary bandwidth, modulation class, and the nature of its modulating signal, recorded in FCC and international licensing records.

An amplitude modulation mode in which the carrier and one sideband are removed before transmission, concentrating transmitter power in the remaining sideband for more efficient voice communication.

The average power delivered to the antenna during one radio frequency cycle at the crest of the modulation envelope; it is the usual power limit applied to single sideband and other modulated transmitters.

A signal at an integer multiple of a transmitter's fundamental frequency, produced by nonlinear stages and requiring filtering so it does not interfere with stations in other services.

Radio transmission in which signals travel upward, are refracted by ionized layers of the upper atmosphere, and return to Earth, allowing long-distance HF communication well beyond the horizon.

The highest frequency that a given ionospheric layer will refract back to Earth along a specified path at a given time; signals above it pass into space instead of returning.

A radio wave that travels along the Earth's surface, bending with its curvature and losing more energy at higher frequencies; it provides dependable short and medium distance communication at MF and lower HF.

A combination of filters that lets one antenna serve a transmitter and a receiver at the same time, protecting the sensitive receiver from transmitter power while passing each signal to the antenna.

A vacuum tube oscillator in which electrons spiral through crossed electric and magnetic fields, producing high pulsed power at microwave frequencies for marine and other radar transmitters.

The duration of each transmitted radar pulse; short pulses give finer range resolution, while long pulses place more energy on a target and extend detection range.

The weakest input signal a receiver can convert into usable output at a specified signal-to-noise ratio; it depends mainly on front-end noise figure, bandwidth, and gain.

The generation of unwanted signals at sum and difference frequencies when two or more strong signals pass through a nonlinear stage, causing interference on frequencies that were never transmitted.

A receiver circuit that senses output level and adjusts front-end or intermediate frequency gain so strong and weak signals give similar audio volume, preventing overload and fading distortion.