How the intercom equipment works
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. .
Receiving part
The receiving part is a double-conversion super-heterodyne mode, and the signal input from the antenna is subjected to radio frequency amplification after being subjected to a transceiving conversion circuit and a band-pass filter, and after passing through a band-pass filter, enters a mixing frequency, and the amplified signal from the radio frequency is derived from The first local oscillator signal of the phase-locked loop frequency synthesizer circuit is in the first mixer
Mixing and generating 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 passes through a circuit such as amplification, band pass filter, de-emphasis, etc.
The quantity control circuit and the power amplifier amplify and drive the speaker to get the information people need.
The voice of the signaling processor is converted into an electrical signal of the audio through a microphone, and the audio signal is directly modulated by entering the voltage controlled oscillator through an amplifying circuit, a pre-emphasis circuit, and a band pass filter.
The CPU generates a CTCSS/DTCSS 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.
power control
When the CPU is controlled in different states, different power supplies are sent.
Receiving power: Normally in intermittent mode to ensure power saving
Transmit power: only when there is a launch
CPU power: stable power supply
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