Description of the working principle of the main function module based on the analog walkie-talkie
First, the general analog walkie-talkie mainly includes several functional modules:
Transmitting module, receiving module, modem module, signaling module and power control module.
Second, their basic working principles are described as follows:
1. Transmitting part: the phase-locked loop and the voltage-controlled oscillator (VCO) generate the transmitted RF carrier signal, and after buffer amplification, excitation amplification, and power amplifier, generate the rated RF power, and pass the low-pass filter in the antenna to suppress the harmonics. The composition is then emitted through the antenna.
2. Receiving part: The receiving part is a double-conversion super-heterodyne mode. The signal input from the antenna is amplified by the transceiver through the transceiving conversion circuit and the low-pass filter, and then passed through the band pass filter to enter the first mixing, and the amplified signal from the radio frequency and the first phase from the phase-locked loop frequency synthesizer circuit The local oscillator signal is mixed at the first mixer and generates an intermediate frequency signal. The first intermediate frequency signal first eliminates the adjacent channel clutter signal through the crystal filter, and then enters the intermediate frequency processing chip, and the second local oscillator signal is again mixed to generate the second intermediate frequency signal, and the second intermediate frequency signal is filtered by a ceramic filter. After the unwanted spurious signals are amplified and frequency-converted, an audio signal is generated. 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. Signaling processing: The original walkie-talkie does not need signaling, only needs to be tuned to the corresponding channel and can press PTT to speak, and receive the information sent by other walkie-talkies at any time. In order to suppress the useless voice or unwanted signaling from mobile stations outside the system or other users in the system, most of the walkie-talkies on the market today adopt the cTcss (continuous Tone Coded Squelch System) continuous tone coding squelch system. The CTCSS signal generated by the MCU or the dedicated chip is amplified and adjusted to enter the voltage controlled oscillator for modulation. The low frequency signal obtained after receiving the frequency discrimination is subjected to band-pass filtering shaping of the amplification and sub-audio, enters the MCU, 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, turn on the speaker, otherwise turn off the speaker.
4. Modulation signal and modulation circuit: The human voice is converted into an audio electrical signal through a microphone. After the audio signal passes through the amplifying circuit, the pre-emphasis circuit and the band pass filter, it is sent to the voltage controlled oscillator for direct modulation.
5, power control: CPU control in different states, send a different power supply to achieve as much power as possible.
(1) Receiving power: Normally in intermittent operation mode to ensure power saving:
(2) Transmit power: only when there is power;
(3) cpu power supply: stable power supply.
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