How does walkie-talkie communication equipment work?

1. Launch part:

The phase-locked loop and voltage-controlled oscillator (VCO) generate the transmitted RF carrier signal. After buffer amplification, excitation amplification and power amplifier, the rated RF power is generated, which passes through the antenna low-pass filter to suppress the harmonic components, and then is transmitted through the antenna. .

2. Receiving part:

The receiving part mixes the amplified signal from the radio frequency with the first local oscillator signal from the phase-locked loop frequency synthesizer circuit at the first mixer and generates a first intermediate frequency signal. The first IF signal passes through a crystal filter to further eliminate clutter signals in adjacent channels. The filtered first IF signal enters the IF processing chip and is mixed again with the second local oscillator signal to generate a second IF signal. The second IF signal passes through a ceramic filter to filter out useless spurious signals, and is amplified and frequency-identified. Generate audio signals. The audio signal passes through amplification, bandpass filter, de-emphasis and other circuits, enters the volume control circuit and power amplifier for amplification, drives the speaker, and obtains the information people need.

3. Modulation signal and modulation circuit:

Human speech is converted into audio electrical signals through a microphone

4. Signaling processing:

The CTCSS/CDCSS signal generated by the CPU is amplified and adjusted, and then enters the voltage controlled oscillator for modulation. After receiving the low-frequency signal obtained after frequency identification, part of it is filtered and shaped by amplification and sub-audio bandpass filters, enters the CPU, and is compared with the preset value, and the result controls the output of the audio power amplifier and speaker. That is, if it is the same as the preset value, the speaker will be turned on, if it is different, the speaker will be turned off.