Frequency offset is the amplitude of frequency swing of FM wave, generally speaking, it is the maximum frequency offset, which affects the spectrum bandwidth of FM wave.

However, it does not mean that the larger the maximum frequency offset, the wider the spectrum bandwidth, and there is still a modulation index problem.

Modulation index m= maximum frequency offset/frequency of modulated low frequency, which directly affects the shape and bandwidth of frequency-shifted spectrum.

Generally speaking, the larger the modulation index, the wider the bandwidth of frequency shift spectrum. The maximum frequency offset is a decisive factor of modulation index, so the frequency bandwidth frequency offset that affects FM wave refers to the fixed frequency of FM wave shifting to both sides. First of all, FM wave is a form of electromagnetic wave and a tool to transmit useful signals such as images and sounds. Sound can be spread by FM waves, such as FM broadcasting; You can also transmit images, such as TV and so on. Modulating FM waves with sound signals (technical terms are audio signals) can shift the fixed FM wave frequency to both sides, and of course, using image signals (technical terms are video signals) can also shift the fixed FM wave frequency to both sides. This shifts the frequency of FM waves.

The frequency offset amplitude is stipulated by the International Radio Management Committee: the maximum modulation frequency offset of audio to FM wave is 200KHz, and the maximum modulation frequency offset of video to FM wave is 6.5MHz, which is determined in order to obtain the best transmission effect and save frequency resources as much as possible.