frequency guard band
A frequency band deliberately left vacant between two channels to provide a margin of safety against mutual interference.
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frequency hopping
[The] repeated switching of frequencies during radio transmission according to a specified algorithm, to minimize unauthorized interception or jamming of telecommunications. [NIS] [INFOSEC-99]
Note: The overall bandwidth required for frequency hopping is much wider than that required to transmit the same information using only one carrier frequency.
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. [47CFR]
frequency instability
See frequency stability.
frequency lock
The condition in which a frequency-correcting feedback loop maintains control of an oscillator within the limits of one cycle.
Note: Frequency lock does not imply phase lock, but phase lock does imply frequency lock.
frequency modulation (FM)
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.
Note 1: In FM, the carrier frequency is called the center frequency.
Note 2: FM is a form of angle modulation.
Note 3: In optical communications, even if the… (Read More →)
Frequency of Optimum Traffic (FOT)
Synonym FOT.
Frequency of Optimum Transmission (FOT)
See FOT.
In the transmission of radio waves via ionospheric reflection, the highest effective, i.e., working, frequency that is predicted to be usable for a specified path and time for 90% of the days of the month.
Note 1: The FOT is normally just below the value of the maximum usable frequency (MUF). In the prediction of usable frequencies, the… (Read More →)
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.
Note: The prediction is usually indicated by means of a graph for each frequency plotted as a function of time. [From Weik '89]
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