The modulation method that makes the carrier frequency change according to the modulation signal is called frequency modulation. The frequency variation amplitude of the modulated wave is determined by the amplitude of the modulated signal, and the variation period is determined by the frequency of the modulated signal. The amplitude of the modulated wave remains unchanged. The waveform of FM wave is like a spring that is unevenly compressed. FM waves are represented by the English letter FM. FM radio is a radio that uses FM carrier to transmit radio signals. Because of the short wavelength, the transmitted signal is much better than that of AM-wavelength radio, but because it is short wave, the transmission distance is relatively short.