What is the working principle of the walkie-talkie?

- Sep 21, 2018 -

The walkie-talkie works as follows:

1. Launch part:

The phase-locked loop and the voltage-controlled oscillator (VCO) generate the transmitted RF carrier signal, which is buffer amplified, stimulates the amplification, and the power amplifier generates the rated RF power. The antenna low-pass filter suppresses the harmonic components and then transmits them through the antenna. .

2. Receiving part:

The receiving portion 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 intermediate frequency signal further cancels the adjacent channel clutter signal through the crystal filter. The filtered first intermediate frequency signal enters the intermediate frequency processing chip, and the second local oscillation signal is mixed again to generate a second intermediate frequency signal, and the second intermediate frequency signal is filtered and removed by a ceramic filter to filter out unwanted spurious signals. Generate an audio signal. The audio signal is amplified by amplifying, bandpass filter, de-emphasis, etc., into the volume control circuit and the power amplifier to amplify, drive the speaker, and get the information people need.

3. Modulation signal and modulation circuit:

The voice of a person is converted into an electrical signal of audio through a microphone

4. Signaling processing:

The CPU generates a CTCSS/CDCSS signal that is amplified and adjusted to enter the voltage controlled oscillator for modulation. The low frequency signal obtained after receiving the frequency discrimination is filtered and shaped by the bandpass filter of the amplification and sub-audio, enters the CPU, compares with the preset value, and controls the output of the audio power amplifier and the speaker. That is, if it is the same as the preset value, the speaker is turned on, and if it is different, the speaker is turned off.

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