Icom ic-f5021 Service Manual

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Icom ic-f5021 Service Manual Manual pdf 14 page image

5 - 45-3 FREQUENCY SYNTHSIZER CIRCUITSVCOsThe TX VCO which generates TX signal is composedby Q13, D16, D31, L25, L38, etc., and the frequencymodulation is carried out by applying modulation signals toD18.The RX VCO which generates 1st LO signals is composedby Q14, D33, D34, L26, L39, etc.These two VCOs are switched by the VCO SW (Q15, 16)using “RXC” signal.The output signals from each VCO are amplified by thebuffer AMP (Q11) and LO AMP (Q10), then applied to theTX or RX circuits.A portion of oscllated signals is applied to the PLL IC (IC4)via buffer AMP (Q12).PLLThe applied VCO output is divided according to the serialdata including divide ratio from the CPU, at the prescalerand programmable divider. In the same way, the referencefrequency signal from the reference frequency signaloscillator is applied to the PLL IC and divide so that theseare the same frequency.The frequency-matched signals are applied to the phasecomparator and phase-compared. The resulted phasedifference is detected as a phase-type signal, and level-adjusted at the charge pump then output. The output pulsetype signal is passed through the loop filter to be convertedinto the DC voltage (=Lock Voltage).Applying the lock voltage to the variable capacitors(VD) which composes a part of the resonator of VCO,the capacitance of VDs changes corresponding to theapplied lock voltage. This causes the change of resonationfrequency that determines the VCO oscillating frequency tokeep the VCO frequency constant.When the oscillation frequency drifts, its phase changesfrom that of the reference frequency, causing a lock voltagechange to compensate for the drift in the VCO oscillatingfrequency.• FREQUENCY SYNTHESIZER CIRCUITS5-4 VOLTAGE DIAGRAMVoltage from the power supply is routed to the whole of the transceiver via regulators and switches.LPFREFX2CR-794TX/RXSWD14,D15Q14,D33,34Q13,D16,31FILRIPPLEQ17VCOSWQ15,16FILLOOPPLLICIC4MB15A02X3Q34FMMODD18BPFBUFFQ10BUFFQ11LPFIC19AMPX2Q12BPFD54,55TLVAD JD53RLVAD JD52IF IC8VRXCRX VCOTX VCOIC1:TA31136FNREF 15.3MHzClock,Data,Strobe45.9MHz182.35 MHz-220.35 MHz136/146 MHz-1740 MHzTXCT8VRLVATLVALVLVSWPOWERQ23 Q24+55VREGQ27 Q28+8REGIC9T8REGQ25 Q29D23W2Power supply cableREGCPU5IC10Q26 Q30R8REGDriver(Q9), APC AMP(IC2), etc.IF IC (IC1), PLL IC(IC4), etc.RF AMP(Q2), 1st IF AMP(Q4), 1st mixer(Q3), etc.External output(from J6)VCOs, FRONT UNITT8VR8V8VVCCTMUTRXCPWONHVCPU5CPU5VCC8V8V8VHPA module(IC3) HV