Alinco DJ-G1T Service Manual page 5

6. Audio Power
Amplifier Circuit
7. Signal Meter
Circuit
2) Transmitter System
1. Microphone Amplifier
Modulator Circuit
2. Power Amplifier
Circuit
3. APC Circuit
"High" (squelch circuit does not work). This signal "SD" is led to the CPU
Pin of IC401, and then processed by CPU. When the squelch circuit is
active, Q311 and Q304 are off. When the squelch circuit does not work,
Q311 and Q304 are on. In this way the audio output signal is controlled.
When the squelch circuit does not work, Q323 goes on, the squelch indicator
LED (D303B) light turns on. When the squelch circuit is active, Q323 goes
off, the squelch indicator LED (D303B) light turns off.
When the power supply voltage of radio becomes above 6.3V in the voltage
stabilizer circuit (Q302, Q303, D301 and D304). The power supply voltage of
audio power amplifier IC (IC305) is controlled below 6.3V.
The voltage of audio power amplifier IC (IC305) is controlled by the Q304.
The Q304 is ON when the squelch is OFF, BEEP sound is outputting, and
DTMF monitor (TX) is ON, then IC305 works.
The IC301 has S meter function. When the signal strength is low, voltage of
Pin 16 becomes lower, and when the signal strength is high, voltage of Pin
16 becomes higher. The S meter voltage of Pin 16 is led to the variable
resistor (VR310) and input to the Pin of IC401 (CPU). It is converted by A/D
converter built-in CPU, and S is appeared in the LCD.
After the voice is converted into the electric signal through the internal or
external microphone, the signal is led to the microphone amplifier IC304.
IC304 consists of two operational amplifiers. One operational amplifier (Pin5,
6 and 7) uses pre-emphasis circuit and IDC circuit, and the other operational
amplifier (Pin1, 2 and 3) uses splatter filter. The output from the microphone
amplifier is passed through variable resistors VR305 for maximum deviation
adjustment to cathode of varicap (D206) diode of the VCO, controlling the
VCO frequency and so producing a frequency-modulation.
The signal from VCO is amplified by RF amplifier Q4 and drives amplifier
Q3, and input to the power module Pin 1 of IC1. The signal is amplified by
power module IC1, and output from Pin5 of IC1, and then led to the low-
pass filter (L6, C15, C16), the antenna switch circuit D1 and the low-pass
filter (L1, L2, C3, C4 and C5). The unwanted harmonics frequency signal is
eliminated by the low-pass filter and input to the antenna.
Part of the transmission power is passed through the C17, C11 and detected
by D3. The detected DC voltage is amplified by Q2 and drives the Q1. This
voltage is controlled by the bias voltage of Pin3 of IC1 and collector voltage
of RF amplifier Q3 to stabilize the transmission power. When the transmis­
sion power goes higher than the settled power, detected voltage by D3 goes
higher, collector voltage of Q1 goes to low. When the transmission power
goes lower than the settled power, detected voltage by D3 goes lower,
collector voltage of Q1 goes to high. The high power setting variable resistor