8. PLL
PLL-IC102 is used to control the oscillating frequency of the VCO.
IC102 is controlled by the serial control signal sent from the microprocessor
IC2. The 21.25MHz reference frequency of IC102 oscillates the crystal
oscillator X101 at the inside circuit.
IC102 compares the frequency gained by dividing the signal added to pin 14
of IC2 by the control signal from IC2 with the frequency gained by dividing
the reference frequency of 21.25MHz inside IC102.
When the phase difference is found as a result of phase comparison, the pulse
signal is output from the charge pump output of pin 16 of IC102, then the
signal is converted into the DC voltage at the passive filter and added to the
cathode side of the VCO vari-cap D103 and D105 to make the phases equal.
In result the stabilized oscillation can be done at the desired frequency.
2) Transmission
1. Microphone Amplifier
The microphone amplifier IC4 has 2 operational amplifiers. The voice is
converted into the electric signal through the microphone, then supplied to
IC4.
The input signal is amplified and pre-emphasized to be output.
The signal output from microphone amplifier is adjusted the maximum
frequency deviation at VR102. The adjusted signal is added to the cathode of
the VCO vari-cap D104 for deviation to change the capacity of the oscillation
circuit resulting the FM deviation.
2. Power Amplifier
The oscillated signal of the VCO is supplied to the power amplifier Q104,
passing through buffer amplifier Q107, pre-driver amplifier IC101, driver
amplifier Q105. The power-amplified signal is supplied to the antenna
through the duplexer after the harmonics are attenuated enough.
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