Icom IC-F33GT Service Manual

Also see for IC-F33GS: Instruction manual Instruction manual Instruction manual Service manual Service manual

Contents

Icom IC-F33GT Service Manual Manual pdf 13 page image

4 - 54-5 OTHER CIRCUITS4-5-1 COMPANDER CIRCUIT (MAIN UNIT)IC-F33GT/GS/F34GT/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) scrambler sec-tion, and are then applied to the limiter section after beingpassed through the high-pass filter. The filtered signals passthrough the splatter filter section, and are then applied to themodulation 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 sec-tion to 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.PinNumberPortname Description10 BALOutputs the modulation balance levelcontrol signal. The signal is applied tothe buffer amplifi er (IC24, pin 1).14 TLVA Outputs the TX VCO lock voltagecontrol signal.15 RLVA Outputs the RX VCO lock voltagecontrol signal.22 T1Outputs the bandpass filter tuningcontrol signal . The output signal isapplied to the bandpass filters (D19,D240).23 T2• Outputs the bandpass filter tuningcontrol signal . The output signal isapplied to the bandpass fi lters (D14,D15).• Outputs the TX control signal . Theoutput signal is applied to the APCamplifi er (IC2, pin 1).Scrambler/De-scramblerTX/RXHPFPre-emphasis Limiter Splatter VR2Expander VR4RXA2SMFDe-emphasisCom-pressorVR1(HPF)RXLPFVR3(HPF)7 MOD181920 SIGNAL3TXIN23RXIN21SDEC1014MDIR9MTDTMTCK13MSCK11MDIO12MRDFMSKModulatorMSKDemodulatorMSKBPFControlRegisterTXA1RXA14-6 PORT ALLOCATIONS4-6-1 D/A CONVERTOR IC (IC12)• BASE BAND IC BLOCK DIAGRAM