A phase-locked loop (PLL) and a voltage-controlled oscillator (VCO) generate a transmitting RF carrier signal, which is buffered, amplified and amplified to generate rated RF power, and harmonic components are suppressed by an antenna low-pass filter, and then transmitted by an antenna.

2. Receiving part:

The receiving part adopts the second frequency conversion superheterodyne mode. The signal input from the antenna is amplified by radio frequency after passing through the transceiver conversion circuit and bandpass filter, and then enters the mixer. An amplified signal from a radio frequency is mixed with a first local oscillator signal from a PLL frequency synthesizer circuit at a first mixer to generate a first intermediate frequency signal. The first intermediate frequency signal further eliminates the clutter signals of adjacent channels through a crystal filter. The filtered first intermediate frequency signal enters the intermediate frequency processing chip and is mixed with the second local oscillator signal again to generate the second intermediate frequency signal. The second IF signal is filtered, amplified and frequency-discriminated by a ceramic filter to generate an audio signal. After amplification, band-pass filtering, de-emphasis and other circuits, the audio signal enters the volume control circuit and power amplifier for amplification, driving the speaker and getting the information people need.

3, modulation signal and modulation circuit:

The human voice is converted into an audio signal through a microphone, and the audio signal enters a voltage-controlled oscillator through an amplifier circuit, a pre-emphasis circuit and a band-pass filter for direct modulation.

4, signaling processing:

The CTCSS/DTCSS signal generated by CPU is amplified and adjusted, and then enters the voltage controlled oscillator for modulation. A part of low-frequency signals obtained after receiving frequency discrimination are amplified, filtered and shaped by a sub-audio band-pass filter, and then enter the CPU, where they are compared with preset values, and the results control the output of the audio power amplifier and speakers. That is, if it is the same as the preset value, turn on the speaker; If not, please turn off the speakers.