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2)Transmitter System
1.Microphone Amplifier
The input signal from built-in or external microphone is led to the microphone mute
circuit Q15,pre-emphasis circuit ,IDC circuit IC4,the signal is input to the maximum
deviation adjustment volume VR2.Then mixed at the add VR2 with the CTCSS tone
signal which is generated by CPU,Then it is input to VCO as the modulation signal.
2.Power Amplifier
The signal from VCO is amplified by IC1 and then passed through the low-pass filter,
the antenna switch circuit and the output low-pass filter.
The unwanted harmonics frequency signal is eliminated by the low-pass filter and
input to the antenna.
3)PLL,VCO Circuit
Output frequency of PLL circuit is set by the serial data from microprocessor.
PLL circuit consists of VCO Q2,buffer amplifier Q6.
The pulse wave output of chage pump is converted to DC voltage by PLL loop filter
circuit,snd supplied to D2,D15 of varicap diode in VCO unit.
The frequency modulation is executed when audio signal voltage is supplied to the
varicap D3.
When PLL is unlocked,pin10 of IC2 goes to “High”.
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