Icom IC-F50 Service Manual Addendum

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Icom IC-F50 Service Manual Addendum Manual pdf 30 page image

4 - 54-5 OTHER CIRCUITS4-5-1 COMPOUNDER CIRCUIT (MAIN UNIT)IC-F50/F51 have compounder circuit which can improveS/N ratio and become wide dynamic range to suppressthe transmitting signal and to extend receiving signal. Thecircuit is composed of the base band IC (MAIN unit; IC10).(1) IN CASE OF TRANSMITTINGThe audio signals from the microphone are applied to thebase band IC (IC10, pin 3) via microphone mute circuit(FRONT unit; IC406), microphone amplifier (IC407), etc.The signals are amplified at the amplifier section, andare then applied to the compressor circuit to compressthe audio signals. The signals pass through (or bypass)scrambler section, and are then amplified at limiter amplifiersection after being passed through the high-pass filter. Theamplified signals pass through the low-pass filter section,and are then applied to the modulation circuit (Q13, D16–D18) via the FM/PM switch (IC11), low-pass filter (IC5) andD/A converter (IC6).(2) IN CASE OF RECEIVINGThe demodulated AF signals from the IF IC are appliedto the amplifier section of base band IC (IC10, pin 23),and then pass through the low-pass and high-pass filtersection to suppress unwanted signals. The filtered signalspass through (or bypass) scrambler section, and are thenapplied to the expander circuit to expand AF signals. Thesignals pass through (or bypass) scrambler IC (IC14), andare then applied to the analog switch (IC13, pins 8, 11).The signals are applied to the base band IC’s amplifiersection (IC10, pins 19, 20), and are then applied to the AFamplifier circuit.456711121314LEDRLEDTLIGTAFONDUSEMCONCSFTSPONOutputs RX LED control signal.Low: Lights ON.Outputs TX LED control signal.Low: Lights ON.Outputs back light LED control signal.Low: Back light is ON.Outputs audio control signal.Low: Outputs audio signals fromspeaker.• Outputs CTCSS/DTCS switchingsignal when transmitting.High: Selected DTCS.• Outputs Min. VR switching signalwhen receiving.Low: Select Min VR.NOTE: Audio signals are prior totransmitting.Outputs microphone select signal.High: While the internal microphoneis used.Outputs shift signal for referenceoscillator’s frequency.Outputs the internal speaker controlsignal.High: The internal speaker isselected.Pin Port Descriptionnumber nameScrambler/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 EXPANDER IC (FRONT UNIT; IC410)