Shanxi intercom telling - talkie works as follows: 1, the transmitter section: PLL and voltage controlled oscillator (VCO) generating a radio frequency carrier signal transmitted through the buffer amplifier, incentive amplification, amplifier, rated RF power generated through antenna low pass filter to suppress harmonic components, and then sent through an antenna. 2, the receiving section: receiving the amplified signal from the RF section and the first local oscillator signal from the PLL frequency synthesizer and a mixer circuit generates 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 the first intermediate frequency signal into the filtered IF processing chip, and the second local oscillator signal to generate a second intermediate frequency signal is again mixed, the second intermediate frequency signal is filtered out unwanted spurious signals by a ceramic filter, is amplified and frequency discriminator, generating an audio signal. Audio signal amplification, band-pass filter, de-emphasis and other circuits, to enter volume control circuit and power amplifier amplifies, drive the speaker to give people the information they need. 3, the modulation signal and modulation circuit: the human voice through a microphone is converted into audio signals 4, signaling processing: CPU generate CTCSS / CDCSS signal after amplification adjustment, enter the VCO modulation. After receiving the low frequency signal obtained by frequency discriminator part amplified and sub audio band-pass filter for filtering the plastic into the CPU, with a preset value, the result will 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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