Pll Vco Circuit; Transmitter System - Alinco DJ-180 Service Manual

2) PLL, VCO Circuit

3) Transmitter System

1. Microphone
Amplifier
2. Power Amplifier The signal from VCO is amplified by buffer amplifiers Q4 and Q5, and input
3. Automatic Power
Control Circuit
Output frequency of PLL circuit is set by the serial data (pin9: clock, pin10:
data, pin11 : toad enable) from microprocessor.
PLL circuit consists of VCO Q201, buffer amplifier Q202 and Q17.
When PLL is locked, pin7 of IC2 goesto "high" and UNLOCK SW Q19
becomes OFF, then T.MUTE signal goes to "low".
The pulse wave output of charge pump is converted to DC voltage by PLL
loop filter circuit, and supplied to D201 , D202 of varicap diode in VCO unit.
The VCO tune voltage is applied to the varicaps D3, D4, D5 and D6 in the
frontend.
The frequency modulation is executed when the audio signal voltage is
supplied to the varicaps D201, D202 and D203.
The voice from the internal or external microphone is led to the pre-empha-
sis circuit, and then input to the microphone amplifier IC4, which consists of
two operational amplifiers.
The amplified signal is input to the low.pass filter lC4.
The output from the microphone amplifier is passed through variable resis-
tors VR2 tor modulation adjustment to varicap diode of the VCO, contromng
the VCO frequency.
to the buffer amplifiers Q6 and input to the power amplifier Q7. The amplified
signal is output from Q7, and then passed through the low-pass filter, the an-
tenna switch circuit and the output low-pass tilter. The unwanted harmonies
frequency signal is eliminated by the low-pass fitter and input to the antenna.
The LC matching circuits located between amplifiers of the transmitting
circuit make the transmission smooth.
The automatic power control(APC) circuit is used to obtain a stable transmis-
sion power. This circuit detects the transmission power by D8 in the low-
pass filter consisting of L18, L19, C59, and C64. The detected DC voltage is
supplied to APC circuit. When the detected voltage goes higher than the
settled voltage, the bias voltage of APC amplifier Q9 goes to low. The
collector voltage of APC amplifier Q10 goes to low and the power supply
voltage of Q5 goes to low, and output power becomes small to prevent from
the over power.
At low power the Power Control Switch Q8 lets the base voltage of APC
DET Q11 and the collector voltage of APC AMP Q10 down, also switches
between high power and low power, and inhibits the transmission.
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