Frequency is one of the characteristics of oscillationsamplitude of a certain physical quantity with respect to its mean value. In physics, there are many kinds of oscillations of a different nature, for example, oscillations of the electromagnetic field. In addition to spontaneous electromagnetic oscillations of a natural nature, there are also oscillations, the emergence of which is set by the will of man to solve certain problems arising from the needs of human activity. Most often, with the help of oscillatory processes, the issues of energy and / or information transfer are solved, i.e. communication, broadcasting, television work, etc. are carried out.
The process of communication includes trainingthe corresponding energy field and its modulation by a useful signal and consists in the generation by the transmitter of a carrier frequency with certain values of the parameters - amplitude and frequency. The first parameter is proportional to the field energy and determines the transmission range, and the second parameter is the destination. At this stage, we have only a carrier signal, which acts as a "carrier" of information.
Information content of the energy fieldis introduced into the signal by a corresponding change in some of its parameters. In practice, various variants of changing the field parameters are used - this process is called carrier frequency modulation. In this case, a change in carrier amplitude or carrier frequency deviation is applied. At the stage of the formation of radio communication, amplitude modulation was most often used when the information is contained in the amplitude of the carrier signal. In this case, changes in the carrier amplitude in accuracy
repeat the information analog signal. The consumer receives a signal by
the carrier frequency, and then selects the demodulator contained in it
information. At low frequencies, up to the short-wave range, only amplitude modulation is used. Its main disadvantage is the change in the amplitude of the carrier frequency, because of which the signal-to-noise ratio, a very important indicator of the quality of the communication channel, is reduced.
In addition to amplitude modulation, frequency information is used to transmit information, in which frequency deviation is applied. The advantage of frequency
modulation - higher noise immunity, therefore in professional
communication systems use only frequency-modulated signals. An example of the use of such signals is VHF broadcasting, television, and special communication.
Deviation is the maximum change in the carrierfrequency relative to its mean value. In this case, the spectrum of the frequency-modulated carrier wave oscillation depends on the value of the amplitude of the useful signal, and its amplitude does not change, due to which the stability of the coupling is initially much higher.
Devices for modulating the carrier frequency by a signalFrequency modulators. Their role in the process of transmitting a radio signal is to control the generators of the carrier frequency of the transmitter. Frequency deviation determines
requirements for the bandwidth of both the transmitter and the receiver.
Since the basic requirement for a communication channel isthe transmission of the original signal is possible, then the bandwidth of the input-output circuits of the receiver and the transmitter must be at least twice the bandwidth of the original signal. However, here we have to look for the "golden mean", because causes of deviation on the side of the transmitter can be associated with parasitic oscillations caused by both interference of external emissions and the creation of targeted jamming, and one way to combat such signal distortions is to narrow the bandwidth. Usually talk about the relationship of the main
characteristics of deviation - the sweep band and the width of the spectrum of the transmitted signal.
If the modulation indexes are large, then both parameters
the frequency deviation is characterized by approximately the same values. Deviation is measured in units of Hz.