Icom IC-M36 Service Manual - Page 21

4-3 FREQUENCY SYNTHESIZER CIRCUITS VCO While transmitting, the VCO (Q21, 22, D20-23) oscillating frequency is determined by the value of D22, D23, L22, C26 and C27, and the frequency modulation is carried out by adding modulation signals to D20. While receiving, D21 is turned ON and C28 is connected to the GND to shift the oscillation frequency lower. The oscillated signals are output via the buffers (Q23, 24). • FREQUENCY SYNTHESIZER CIRCUITS PLL IC1 is a PLL IC which contains prescaler, programmable counter, phase comparator and charge pump in its package. The 21.25 MHz reference frequency signal is fed from X1. The loop filter for the VCO is composed by R8, R10, R22, C11, C13 and C24. IC1 PLL IC LOOP FIL PLL control signal X1 21.25MHz PLLO 2ND LO CPU IC170 IF IC IC360 Q 21,Q22 D22,D23 Q23 BUFF Q25 BUFF Q24 BUFF D 50,D51 LO SW VCO BPF Q150 1st mixer TX AMPs 4-4 VOLTAGE BLOCK DIAGRAM Voltage from the power supply is routed to the whole of the transceiver via regulators and switches. CHASSIS Battery Q353 HV POWER CTRL IC220 5V regulator Q224 Q225 VCC 5V regulator CPU5V : To CPU and EEPROM MAIN UNIT S5V : To TX/RX common circuits Q221 R5V SW R5V : To RX circuits Q220 V5V SW Q222 T5V SW V5V : To VCO T5V : To TX circuits 4 - 3