Frequency deviation

The frequency is one of the characteristics of the amplitude oscillations 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 information transfer includes the preparation of an appropriate 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.

The information content of the energy field is 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 carrier frequency relative to its average value. In this case, the spectrum of the frequency-modulated carrier wave oscillation depends on the amplitude of the useful signal, and its amplitude does not change, due to which the stability of the coupling is initially much higher.

The devices for modulating the carrier frequency by a signal are called frequency modulators. Their role in the process of transmitting the 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 main requirement for the communication channel is that the original signal can be more accurately transmitted, 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 it is necessary to search for the "golden mean", because The causes of deviation on the transmitter side can be related to parasitic oscillations caused both by interference of external emissions and the creation of targeted interference, and one way to combat such signal distortions is to narrow the bandwidth. Usually speak about a parity of the basic
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.