Alinco DJ-C1, Service Manual

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7. PLL Circuit The PLL circuit (IC204) is used to control the frequency oscillated by the VCO.
Control uses the serial control signal from the microcomputer (IC101). The
reference frequency that IC204 uses is oscillated to 21.25 MHz by IC202 in the
crystal oscillator (X201) and input to pin 1 of the IC204. The IC204 divides the
control signal sent to pin 6 from IC101 and the 21.25 MHz reference signal
internally, and compares phases between the two. If a difference is detected in
the comparison, the charge pump in pin 9 outputs a pulse signal. The pulse is
converted to DC voltage by the PLL loop filter and input to the cathode of the
VCO varicaps (D203 and D205) in order to eliminate the difference. This
enables stable oscillation at the desired frequency.
2) Transmission
1. Microphone Amplifier
The microphone amplifier (IC205) has two operating amplifiers. Sound is
converted to an electric signal and input to IC205. The input signal is amplified
for pre-emphasis and then output. The output signal is regulated for maximum
frequency deviation by VR202 and input to the cathode of the demodulation
varicap (D206) of the VCO, thereby generating an FM signal by capacitance
change.
2. Power Amplifier
The signal oscillated by the VCO is passed through two buffer amplifiers
(Q205 and Q222) and an exciter (Q204), and is then input to a power amplifier
(Q206). The signal from the power amplifier is passed through a low-pass filter
to attenuate harmonic components and is then supplied to the matching circuit
and antenna.
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