rate - is one of the characteristics of the amplitude of the oscillations of a physical quantity with respect to its mean value.In physics, there are many kinds of vibrations of different nature, for example, fluctuations in the electromagnetic field.In addition to spontaneous natural character of electromagnetic waves, there are fluctuations, the occurrence of which is given by the will of man to solve specific problems arising from the needs of human activity.Frequently using oscillatory processes questions are resolved energy transfer and / or information, i.e.It is in communication, radio, television, etc. work
information transmission process includes the preparation of the corresponding energy field and its modulation of the useful signal and is generating a transmitter carrier frequency to determine the value of - amplitude and frequency.The first parameter is proportional to the energy field, and determines the transmission range, and the second - the addressee.At this stage we have only the carrier signal, performing the role of "carrier" of information.
information content of the energy field is brought into a signal corresponding change any of its parameters.In practice, use a variety of options for changing the parameters of the field - this process is called modulation carrier frequency.This change applies amplitude of the carrier or carrier frequency deviation.On the stage of the Radio frequently used amplitude modulation, when the information is contained in the amplitude of the carrier signal.The changes in carrier amplitude accuracy
repeated analog signal information.The consumer receives the signal on the basis
carrier frequency and then selects a demodulator contained therein
information.At low frequencies, up to the short wavelength, using only amplitude modulation.Its main drawback is the change in the amplitude of the carrier frequency, which is why the signal - noise ratio, very important indicator of the quality of the communication channel is reduced.
Besides amplitude modulation is used for transmission of information and the frequency at which the applied frequency deviation.The advantage of frequency modulation
- higher noise immunity, so in professional communication systems used
exclusively chastotnomodulirovannye signals.An example of the use of such signals - VHF radio, television, special communication.
deviation - is the maximum carrier frequency change relative to the average of its value.The spectrum of the frequency-modulated carrier oscillation is dependent on the amplitude of the useful signal and its amplitude does not vary, whereby connection stability is much higher than initially.
devices for modulating the carrier frequency signal is called frequency modulators.Their role in the transmission of radio - control transmitter carrier frequency generators.The frequency deviation
defines requirements for the bandwidth of both the transmitter and receiver.
Since the main requirement for the communication channel - perhaps more accurate transmission of the original signal, the bandwidth of the input-output circuits of the transmitter and receiver should be at least double the value of the original baseband signal.However, here we have to look for the "golden mean" becausereasons for the deviation on the side of the transmitter can be associated with parasitic oscillations caused by interferences as a flame simulation, and the creation of targeted interference, and one way to deal with such distortion of the signal - the restriction of bandwidth.It is usually said of the relationship between the major characteristics
deviation - swing band and width of the spectrum of the transmitted signal.
If the modulation index have great value, both parameters that characterized
frequency deviation, have approximately the same magnitude.The deviation is measured in units of Hz frequency.
