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What is the working principle of hand-held walkie talkie?

Jun 17, 2020

What is the working principle of hand-held walkie talkie?


Working principle of walkie talkie:


1. Launch part:


The radio frequency carrier signal is generated by the phase-locked loop and voltage controlled oscillator (VCO) of the interphone accessories. After buffer amplification, excitation amplification and power amplifier, the rated radio frequency power is generated. Through the antenna low-pass filter, the harmonic component is suppressed, and then transmitted through the antenna.


2. Receiving part:


The receiving part is a secondary frequency conversion superheterodyne mode. The signal input from the antenna is amplified by RF after passing through the transceiver conversion circuit and band-pass filter. After passing through the band-pass filter, it enters into the first mixing. The amplified signal from RF and the first local oscillator signal from the PLL frequency synthesizer circuit are mixed at the first mixer and the first IF signal is generated. The first intermediate frequency signal is further eliminated by the crystal filter. The filtered first IF signal enters the if processing chip and mixes with the second local oscillator signal again to generate the second IF signal. The second IF signal is amplified and discriminated to generate the audio signal after filtering the useless stray signal through a ceramic filter. Through amplifying, band-pass filter, de weighting and other circuits, the audio signal enters the volume control circuit and power amplifier to amplify and drive the loudspeaker to get the information people need.


3. Signaling processing:


After amplifying and adjusting the CTCSS / dtcss signal generated by CPU, it enters the VCO for modulation. After receiving the low-frequency signal from frequency discrimination, part of it is filtered and shaped by band-pass filter of amplification and sub audio, and then enters CPU, compares with the preset value, and controls the output of audio power amplifier and loudspeaker. That is, if it is the same as the preset value, turn on the loudspeaker; if it is different, turn off the loudspeaker.


4. Modulation signal and modulation circuit:


Human voice is converted into audio signal through microphone, and audio signal is directly modulated by amplifying circuit, pre weighting circuit and band-pass filter into VCO.

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