The frequency modulation can be classified into wideband frequency modulation (WBFM) and narrowband frequency modulation (NBFM) according to the magnitude of the phase offset of the carrier after signal modulation. There is no strict limit between the wideband and the narrowband. However, it is generally considered that the maximum instantaneous phase shift caused by frequency modulation is much smaller than 30°, which is called narrowband frequency modulation. Otherwise, it is called wideband frequency modulation.
Wideband is suitable for applications with high sound quality requirements, while narrowband sound quality is not as good as wideband, but the number of wave stations is greater than that of wideband FM.
The wideband standard is that the modulation frequency offset of the high-frequency carrier is 75KHZ. The wireless microphone we use is also like this. It has good sound quality and is suitable for transmitting audio signals from 40HZ to 18KHZ.
The narrowband is mainly used for transmission with wireless voice, and the frequency offset is usually 3 to 5KHZ. Suitable for mid-range audio signals from 800 to 3KHZ. Narrowband is widely used in Two-way radio.
There was no narrow bandwidth band in the early radio technology, and later there was a narrower and wider technology than the radio channel bandwidth, so there was a narrowband and wideband.
For digital communications, narrowband channels and spread spectrum wideband channels are mainstream, but the width is still relative here. Because the varactor does not distinguish between wideband and narrowband, the bandwidth of the channel is mainly determined by the circuit structure.