Icom IC-A210 Service Manual
Also see for IC-A210: Price listInstruction manualInstruction manualInstallation guideInstruction manual
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3 - 33-2 TRANSMITTER CIRCUITSTX AF CIRCUITSThe TX AF circuit consists of microphone amplifier (MICAMP), ALC and AF fi lters. ALC (Automatic Level Control) isan amplifier which reduces its gain automatically to preventover deviation.The audio signals from the connected headset's microphone(MIC signals) are passed through the electric volume to beadjusted MIC gain, and amplified by ALC (Automatic LevelControl) AMP and MIC AMP. The amplified MIC signals arepassed through the MOD/AF SW and the switched capacitorfilter (IC7) which removes unwanted signals. The filtered AFsignals are passed through the HPF, and amplified by buffer,then applied to the AM modulation cicuits as the modulationsignals, via the DAC for deviation adjustment.AFAMP HPFLPFMC1/2ALCAMP BUFFSWMOD/AFIC26IC2 IC13 IC22 IC8DACIC78IC7IC9AM_DEPTHIC 8Electricvolume2187 43 16 84 5 9 10 912 1TX AMPLIFIERSThe TX amplifers consist several RF amplifier (predriver,driver, power, etc.), and amplify the VCO output to thetransmit output level.The TX VCO output is applied to the RF amplifier via buffers(Q33 and Q35) and TX/RX switch (D36), and amplified tothe level need for PA UNIT. The TX signal is amplified bypre-drive and drive AMPs. The amplified TX signal is thenpower-amplified by power AMP where the AM modulation isaccomplished.The power-amplified TX signal is passed through the TXpower detector, ANT SW and LPF (as a harmonic filter),then applied to the antenna via the K-CONNECT UNIT orMB-113.AM MODULATION CIRCUITSThe AM modulation circuits mudulate the carrier with theMIC signals (=modulation signals).The level-adjusted modulation signals are applied to thePWM modulation circuit via the AF SW (IC71, pins 1, 2),then converted into the triangle wave form by being mixedwith the triangle wave which is generated by the IC16, atIC25.The triangle wave form modulation signals applied to theFET driver to drive the AF power AMP (FETs; Q15, Q16).The power-amplified modulation signals are applied to thedrain terminal of the TX power AMP, then the currectorcurrent of the TX amplifier changes corresponding to theamplitude of the modulation signals. Thus the gain of theTX amplifier changes corresponding to the amplitude of themodulation signals, and it causes change of the TX outputpower to obtain an Amplitude Modulation.PWRAMPDRIVEPRE DRIVEPREPREAMPPWRDETAPCAMPAPCCTRLTX/RXSWLINEFILTERAFPOWERAMPFE TDRIVERPWMMODTRIANGLEOSCQ500 Q501 Q504I C500I C500D36 D500 D501Q41IC25IC17 Q15 Q16IC16WAVEPCONLP FANTSWANTD502 D503 D504PA UNITMAIN UNITIC71IC80AM DEPTH 52018127 53L521 L523C572 575 577 578 582APC CIRCUITThe APC (Automatic Power Control) circuit stabilizestransmit output power to prevent transmit output power levelchange, which is caused by load mismatching or heat effect,etc.The power detector rectifies a portion of the TX signal andconverts it into DC voltage which is in proportion to thetransmit output power level. The detected voltage is appliedto the input terminal (pin 3) of dual operational AMP (IC500;as a comparator). The TX power setting is applied to anotherinput terminal as the reference voltage.The comparator compares the detected voltage and refer-ence voltage, and the difference of voltage is output fromoutput terminal.The output voltage is amplified by APC AMP, and controlsthe bias of the pre-driver and driver amplifiers to reduce/increase the gain of these amplifiers for stable TX outputpower.• TX AF CIRCUITS• AM MODULATION AND TX AMPLIFIER CIRCUITS |
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