Icom IC-F4001 Service Manual

Contents

Icom IC-F4001 Service Manual Manual pdf 10 page image

4 - 2• RX AF CIRCUITSAFAM PIC55 TPA0211DGN J52IC62RXMUTESP1HPFIC58AFAM PIC12TA7368FHPFIC58J53Int.speakerExt.speaker12LPFIC58LPFIC59the demodulatorcircuitsIC56AF line SWCD4066AFONAFORMUT 1D/AconverterIC57R2A20178RX AF CIRCUITSThe demodulated AF signal from the IF demodulatorIC is passed through the LPF, HPF which attenuatesfrequencies 300 Hz and below. The filtered AF signal ispassed through the AF line SW, HPF which additionallyattenuates frequencies 300 Hz and below, de-emphasiscircuit which provides –6 dB/oct of frequency response.The de-emphasized AF signal is passed through the AFSW, LPF which attenuates frequencies 3 kHz and above, isadjusted in level by the D/A converter. The level-adjusted AFsignal is then applied to the AF power AMP via the AF lineSW.The amplified AF signal is applied to the internal or externalspeaker.4-2 TRANSMITTER CIRCUITSTX AF CIRCUITSThe audio signal from the internal or external microphone(MIC signal) is passed through the MIC gain SW and appliedto the MIC AMP. The amplified MIC signal is passed throughthe MIC mute SW, HPF which attenuates frequencies300 Hz and below. The filtered MIC signal is passed throughthe pre-emphasis circuit which provides +6 dB/oct offrequency response, then they applied to the limiter AMP.The amplitude-limited MIC signal is passed through theMIC line SW, and applied to the splatter filter, whichattenuate harmonics in the MIC signal to prevent exceedingpermissible deviation.The filtered MIC signal is applied to the D/A converter whichadjusts its level (=deviation). The level-adjusted MIC signalis applied to the TX VCO as the modulation signal.• TX AF CIRCUITSAMlimitPIC58MICMUTEIC62MICGAINSWIC62HPFIC58MC51AMMICPIC60LPFIC58SplatterJ51Ext.MICInt.MICD/AMOD To the modulation circuitsIC56MIClineSWCD4066IC57MODULATION CIRCUITThe modulation signal from the TX AF circuits is applied toD15 of the TX VCO to frequency-modulate it. The frequency-modulated signal from the TX VCO is buffer-amplified bytwo buffers, and applied to the TX AMP circuits via the TX/RX SW (D5).• MODULATION CIRCUITSLOSWD5,D6Q14,D16FREQUENCYMODULATIOND15BUFFQ8BUFFQ10TX VCOFrom the TX AF circuitsTo the TX AMP circuits