1. When the amplitude of the input signal changes, it will cause the capacitance of the varactor diode to change, thus changing the frequency of the resonant circuit. This change is proportional to the amplitude of the input signal, so the frequency of the output FM wave will change with the amplitude of the input signal.
2. Frequency modulation circuit usually consists of input loop, output loop, modulator and power supply. The input loop is responsible for receiving the input signal and transmitting it to the modulator, and the modulator converts the amplitude change of the input signal into frequency change to generate frequency modulated waves. The output loop filters and amplifies FM waves to meet the output requirements.
The application of FM circuit in life is as follows:
1, radio broadcasting: Frequency modulation circuits are commonly used in radio broadcasting to modulate audio signals onto high-frequency carriers to realize the transmission of sound signals. Listeners can receive FM signals through the radio and restore the original sound signals.
2. TV signal transmission: TV signal transmission also adopts frequency modulation technology, which modulates image and sound signals onto high-frequency carriers and sends them out through the transmitting equipment of TV stations. Viewers can receive signals through TV receivers and restore clear images and sounds.
3. Mobile communication: In the field of mobile communication, FM technology has also been widely used. For example, mobile devices, such as mobile phones and tablet computers, communicate through FM wireless signals to realize voice, data and video transmission.
4. Radar velocimeter: FM circuit can also be used in radar velocimeter to calculate the speed by transmitting FM signal to the target and measuring the time difference of echo. This speedometer is widely used in traffic law enforcement and vehicle speed monitoring.
5. Induction heating: In industrial production, frequency modulation circuit can be used for induction heating, and eddy current effect is generated by high-frequency alternating magnetic field, so that metal materials can be heated quickly, which is often used in metal melting, welding and other fields.
6. Electronic tag: FM circuit can also be used for electronic tag, which can realize functions such as identity recognition and item tracking through wireless communication with readers. This kind of electronic tag has been widely used in logistics, inventory management, identity authentication and other fields.