Walkie-talkie works as follows:
1, the transmission part:
Phase-locked loop and voltage-controlled oscillator (VCO) generates a radio frequency carrier signal transmitted through the buffer amplifier, driver amplification, amplifier, produces rated RF power through the antenna low pass filter to suppress harmonic components, and then sent through the antenna .
2, the receiving section:
Receiving the amplified signal from the RF section and the first local signal from the PLL frequency synthesizer and a mixer circuit to generate a first intermediate frequency signal at the first mixer. The first intermediate frequency signal through the crystal filter to further eliminate clutter adjacent channel. After a first IF signal is filtered into the intermediate frequency processing chip, and a second local oscillation signal to generate a second intermediate frequency signal is again mixed, the second intermediate frequency signal reject unwanted spurious signals by a ceramic filter, is amplified and frequency discriminator, generating an audio signal. By amplifying the audio signal, band pass filter, de-emphasis circuit, volume control circuit and power amplifier into the amplified speaker driver to give people the information they need.
3, the modulation signal and the modulation circuit:
Human voice through a microphone is converted into audio signals
4, signaling processing:
CPU generates CTCSS / CDCSS signal after amplification adjustment, enter VCO modulation. After receiving the low frequency signal obtained by frequency discriminator, and a portion of the amplified audio sub-band-pass filter for filtering shaping into the CPU, with a preset value, the result will be to control the output audio amplifier and speakers. That is, if the preset values are the same, then turn on the speaker, if different, off the speaker.
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