Icom IC-F5121D Service Manual

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Icom IC-F5121D Service Manual Manual pdf 12 page image

5 - 2RX AF CIRCUITSThe demodulated AF signal from the linear codec (IC2006)is amplified by the AF AMP (IC1007), and then adjusted inlevel by the electronic volume (IC1006). The level-adjustedAF signal is then amplified by the pre-AMP (IC1004) and AFpower AMP (IC1009).The amplified AF signal is passed through the externalspeaker jack, and then applied to the internal speaker.• RX AF CIRCUITSSQUELCH CIRCUITS (Analog mode only)The squelch circuit cuts off the AF output signals when noRF signals are received. Detecting noise components in thedemodulated AF signals, the squelch circuit stops audio sig-nals being emitted.A portion of demodulated AF signal from the IF IC (IC4)is passed through the D/A converter (IC1006) for level(=threshold) adjustment. The level-adjusted AF signals arepassed through the noise filter (IC4, pins 7, 8 and Q9, R42,R44–R45, C68–C70) to filter the noise components (approx.30 kHz signals) only. The noise components are rectified,resulting in DC voltage corresponding to the noise level.If the noise level is higher than the preset one, the internalcomparator set the “NOISE” signal to the CPU to “High”,then the CPU turns the “AFON” signal which controlls the AFmute SW (Q1008, Q1012, D1007) to “Low,” to stop the AFoutput.• SQUELCH CIRCUITSAFAMPAFAMPIC1009 J1002SP1Int.speakerExt.speakerFrom the linear codecIC1004AFODAFOElectronicvolumeFRONT UNITIC1006AMPIC1007DAC NoiseAMPNoise filterFrom IF IC(IC4, Pin16)To RX AF circuitsNoisedetectorCom-paratorNOISE SQUELCH DIAGRAM“NOIS”IC1006IC414871315J1FRONT UNIT[Option connector][MICJACK]J1003MICGAINSWIC53AMPIC7ALCAMPIC1005BHPFIC1005ALIMITAMPIC1007AMICLINEIC1008SWDMIDSPLINEARCODECIC2006 IC2007LPFIC1007BMOD DMOD/AIC10065-2 TRANSMITTER CIRCUITSTX AF CIRCUITSThe audio signal from the microphone (MIC signal) is passedthrough the MIC gain SW (IC53), and then applied to the MICAMP (IC7).• WHILE OPERATING IN THE ANALOG MODEThe amplified MIC signal is passed through the HPF(IC1005A), which attenuates frequencies 300 Hz and below,and then applied to the limiter AMP (IC1007). The amplitude-limited MIC signal is applied to the linear codec (IC2006)through the MIC line SW (IC1008).The MIC signal is converted into a digital audio signal by thelinear codec (IC2006), processed by the DSP (IC2007), andthen converted into an analog baseband signal (modulationsignal).• WHILE OPERATING IN THE DIGITAL MODEThe amplified MIC signal is applied to the ALC (IC1005B)which keeps the signal level fi xed.The level-adjusted MIC signal is applied to the linear codec(IC2006) through the MIC line SW (IC1008).The MIC signal is converted into a digital audio signal by thelinear codec (IC2006), processed by the DSP (IC2007), andthen converted into the digital baseband signal (modulationsignal).The signal from the linear codec (IC2006) is passed throughthe LPF (IC1007), and then applied to the D/A converter(IC1006) which adjusts its level (=deviation).The level-adjusted modulation signal is applied to the modu-lation circuit.• TX AF CIRCUITS