Frequency Shift Keying (FSK)Frequency shift keying means the carrier frequency of the radio wave undergoes a discrete change which allows to transmit the digital data. In case of FSK two specified frequencies of the sinusoidal signal of invariable amplitude corresponds to binary "0" and "1". Frequency shift keying is very jam-resistant because the noise of a telephone channel affects generally the amplitude of the signal, not its frequency.However, the frequency shift keying wastes the bandwidth resource of the telephone channel.Therefore this type of modulation is used in low-speed protocols, which allow to use the channels with high noise-to-signal ratio to connect.Just two different frequencies are used for FSK. "1", as a rule, corresponds to the low frequency, and "0" corresponds to the high frequency. Frequency minimal shift keying is a method of modulation characterized by continuous phase of the signal. Frequency changes occur in the moment of zero value of the carrier signal.Frequency minimal shift keying is unique, because the deference between the frequency of the logical "0" and "1" is equal to half of the data transfer rate. In other words, the modulation index is 0.5.For example, when data transfer rate is 1200 bps, the signal will be formed by the oscillations of two frequencies - 1200 Hz and 1800 Hz - corresponding to logical "0" and "1".FSK was especially used in telegraph data transmission.
Keywords: data transfer, frequency, signal
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