Icom IC-F43GT Service Manual

Also see for IC-F43GS: Instruction manual Instruction manual Instruction manual Instruction manaul Service manual

Contents

Icom IC-F43GT Service Manual Manual pdf 11 page image

4 - 54-5 OTHER CIRCUITS4-5-1 COMPANDER CIRCUIT (MAIN UNIT)IC-F43GT/GS/F44GT/GS have compander circuit which canimprove S/N ratio and become wide dynamic range. The cir-cuit is composed in the base band IC (IC14).(1) IN CASE OF TRANSMITTINGThe audio signals from the microphone are applied to thebase band IC (IC14, pin 3) via microphone amplifier (IC23).The signals are amplified at the amplifier section, and arethen applied to the compressor circuit to compress the audiosignals. The signals pass through (or bypass) scramblersection, and are then applied to the limiter section afterbeing passed through the high-pass filter. The filtered sig-nals pass through the splatter filter section, and are thenapplied to the modulation circuit (D12) via the FM/PM switch(IC13), low-pass filter (IC6) and D/A converter (IC12).(2) IN CASE OF RECEIVINGThe demodulated AF signals from the IF IC are applied tothe amplifier section in base band IC (IC14, pin 23), andthen pass through the low-pass and high-pass filter sectionto suppress unwanted signals. The filtered signals passthrough (or bypass) scrambler section, and are then appliedto the expander circuit to expand AF signals. The signals areapplied to the base band IC’s amplifier section (IC14, pins19, 20), and are then applied to the AF amplifier circuit.Scrambler/De-scramblerTX/RXHPFPre-emphasis Limiter Splatter VR2Expander VR4RXA2SMFDe-emphasisCom-pressorVR1(HPF)RXLPFVR3(HPF)4TXINO7 MOD181920 SIGNAL3TXIN22RXINO23RXIN21SDEC1014MDIR9MTDTMTCK13MSCK11MDIO12MRDFMSKModulatorMSKDemodulatorMSKBPFControlRegisterTXA1RXA1• BASE BAND IC BLOCK DIAGRAM4-6 PORT ALLOCATIONS4-6-1 D/A CONVERTOR IC (IC12)1014152223BALTLVARLVAT1T2Outputs the modulation balance levelcontrol signal. The signal is applied tothe buffer amplifier (IC24, pin 1).Outputs the TX VCO lock voltage con-trol signal.Outputs the RX VCO lock voltage con-trol signal.Outputs the bandpass filter tuning sig-nal. The output signal is applied to thebandpass filters (D19, D20, D24,D25).• Outputs the bandpass filter tuningsignal. The output signal is applied tothe bandpass filters (D14, D15).• Outputs the TX power control signal.The output signal is applied to theAPC amplifier (IC16, pin 1).Pin Port Descriptionnumber name