Frequency
From DictionGloss
For a periodic function, the number of cycles or events per unit time.
The rate of a repetitive event. If T is the period of a repetitive event, then the frequency f is its reciprocal, 1/T. Conversely, the period is the reciprocal of the frequency, T = 1/f. Since the period is a time interval expressed in seconds (s), it is easy to see the close relationship between time interval and frequency. The standard unit for frequency is the hertz (Hz), defined as the number of events or cycles per second. The frequency of electrical signals is often measured in multiples of hertz, including kilohertz (kHz), megahertz (MHz), or gigahertz (GHz).
frequency accuracy - The degree of conformity to a specified value of a frequency.
frequency aging - Of an oscillator, the change in frequency, over time, caused by internal changes in oscillator parameters even when external factors, such as environment and power supply characteristics, are constant.
frequency-analysis compaction - Data compaction accomplished by using an expression composed of a number of different frequencies of different magnitudes to represent a particular curve.
frequency assignment - Authorization, given by an Administration, for a radio station to use a radio frequency or radio frequency channel under specified conditions The process of authorizing a specific frequency, group of frequencies, or frequency band to be used at a certain location under specified conditions, such as bandwidth, power, azimuth, duty cycle, or modulation.
frequency assignment authority - The power granted an Administration, or its designated or delegated leader or agency via treaty or law, to specify frequencies, or frequency bands, in the electromagnetic spectrum for use in systems or equipment.
frequency averaging - The process by which the relative phases of precision clocks are compared for the purpose of defining a single time standard. A process in which network synchronization is achieved by use, at all nodes, of oscillators that adjust their frequencies to the average frequency of the digital bit streams received from connected nodes.
frequency band - A particular range of frequencies in a region of the electromagnetic spectrum.
frequency-change signaling - A signaling method in which one or more discrete frequencies correspond to each desired significant condition of a code.
frequency compatibility - Of an electronic device, the extent to which it will operate at its designed performance level in its intended operational environment (including the presence of interference) without causing interference to other devices. The degree to which an electrical or electronic device or devices operating on or responding to a specified frequency or frequencies is capable of functioning with other such devices.
frequency departure - An unintentional deviation from the nominal frequency value.
frequency-derived channel - A channel derived by dividing an allocated or available bandwidth over a medium into two or more portions, each usable separately.
frequency deviation - The amount by which a frequency differs from a prescribed value, such as the amount an oscillator frequency drifts from its nominal frequency. In frequency modulation, the absolute difference between the maximum permissible instantaneous frequency of the modulated wave or the minimum permissible instantaneous frequency of the modulated wave and the carrier frequency. In frequency modulation, the maximum absolute difference, during a specified period, between the instantaneous frequency of the modulated wave and the carrier frequency.
frequency dispersal - An electronic counter-countermeasure (ECCM) in which communications nets= operating frequencies are widely separated from each other, causing a requirement to spread jamming power over wider frequency bands and thus compelling a reduction of available jamming power on any single channel or frequency, or causing a requirement for more jamming power or more jamming equipment.
frequency displacement - The end-to-end shift in frequency that may result from independent frequency translation errors in a circuit.
frequency diversity - Transmission and reception in which the same information signal is transmitted and received simultaneously on two or more independently fading carrier frequencies.
frequency-division multiple access - The use of frequency division to provide multiple and simultaneous transmissions to a single transponder.
frequency-division multiplexing - The deriving of two or more simultaneous, continuous channels from a transmission medium by assigning a separate portion of the available frequency spectrum to each of the individual channels.
frequency drift - An undesired progressive change in frequency with time.
frequency-exchange signaling - Frequency-change signaling in which the change from one significant condition to another is accompanied by decay in amplitude of one or more frequencies and by buildup in amplitude of one or more other frequencies.
frequency frogging - The interchanging of the frequencies of carrier channels to accomplish specific purposes, such as to prevent feedback and oscillation, to reduce crosstalk, and to correct for a high frequency-response slope in the transmission line.
frequency guard band - A frequency band deliberately left vacant between two channels to provide a margin of safety against mutual interference.
frequency hopping - repeated switching of frequencies during radio transmission according to a specified algorithm, to minimize unauthorized interception or jamming of telecommunications.
frequency-hopping spread spectrum - A signal structuring technique employing automatic switching of the transmitted frequency. Selection of the frequency to be transmitted is typically made in a pseudo-random manner from a set of frequencies covering a band wider than the information bandwidth. The intended receiver would frequency-hop in synchronization with the code of the transmitter in order to retrieve the desired information.
frequency hour - One frequency used for one hour regardless of the number of transmitters over which it is simultaneously broadcast by a station during that hour.
frequency lock - The condition in which a frequency-correcting feedback loop maintains control of an oscillator within the limits of one cycle.
frequency modulation - Modulation in which the instantaneous frequency of a sine wave carrier is caused to depart from the center frequency by an amount proportional to the instantaneous value of the modulating signal.
frequency offset - The difference between the frequency of a source and a reference frequency.
frequency prediction - A prediction of the maximum usable frequency (MUF), the optimum traffic frequency, and the lowest usable frequency (LUF) for transmission between two specific locations or geographical areas during various times throughout a 24-hour period.
frequency range - A continuous range or spectrum of frequencies that extends from one limiting frequency to another.
frequency response curve - A plot of the gain or attenuation of a device, such as an amplifier or a filter, as a function of frequency.
frequency scanning - Conducting a search for signals over a band or range of frequencies by means of a manually or automatically tuned receiver.
frequency sharing - The assignment to or use of the same radio frequency by two or more stations that are separated geographically or that use the frequency at different times.
frequency shift - Any change in frequency. Any change in the frequency of a radio transmitter or oscillator. In facsimile, a frequency modulation system where one frequency represents picture black and another frequency represents picture white. Frequencies between these two limits may represent shades of gray. An intentional frequency change used for modulation purposes.
frequency-shift keying - Frequency modulation in which the modulating signal shifts the output frequency between predetermined values.
frequency-shift telegraphy - Telegraphy by frequency modulation in which the telegraph signal shifts the frequency of the carriers between predetermined values.
frequency spectrum - The distribution of signal amplitudes as a function of frequency of the constituent signal waves.
frequency spectrum congestion - The situation that occurs when many stations transmit simultaneously using frequencies that are close together, i.e., with insufficient width of frequency guard bands or channel spacing.
frequency stability - The degree to which variations of the frequency of an oscillator deviate from the mean frequency over a specified period of time.
frequency standard - A stable oscillator used for frequency calibration or reference.
frequency synthesizer - A device that produces frequencies that are phase coherent with a reference frequency.
frequency tolerance - The maximum permissible departure by the center frequency of the frequency band occupied by an emission from the assigned frequency, or by the characteristic frequency of an emission from the reference frequency. Frequency tolerance is expressed in parts per 106 or in hertz.
frequency translation - The transfer of signals occupying a specified frequency band, such as a channel or group of channels, from one portion of the frequency spectrum to another, in such a way that the arithmetic frequency difference of signals within the band is unaltered.