Alinco DJ-C1, Service Manual

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5. Audio Audio output is switched between AM and FM by IC209. Volume is controlled
by Q222 and Q223. The signal is input to pin 2 of the audio power amplifier
(IC208) and output from pin 6, thus producing sound from the earphones, etc.
6. VCO The VCO is built on a Colpits oscillator. Frequency is determined by D203,
D207 and L214, and the signal is oscillated by a transistor (Q203). The
oscillated signal is passed through a buffer amplifier (Q204) and input to pin 6
of a PLL circuit (IC204).
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 bin 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 D207) 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 modulation
varicap (D206) of the VCO, thereby generating an FM signal by capicitance
change.
2. Power Amplifier The signal oscillated by the VCO is passed through two buffer amplifiers
(Q204 and Q218) and an exciter (Q206), and is then input to a power amplifier
(Q205). 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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