Icom IC-F50V Service Manual

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Icom IC-F50V Service Manual Manual pdf 9 page image

4 - 34-2 TRANSMITTER CIRCUITSTX AF CIRCUITSThe TX AF circuits consist of microphone amplifier (MICAMP) and AF filters. The AF filter cuts off the signals exceptvoice signals (300 Hz or lower and 3 kHz or higher).The audio signals from the internal microphone (MICsignals) are passed through MIC mute SW and amplified bytwo MIC AMPs (#1 and #2).The MIC signals from the external microphone "EXMIC” areapplied to the FRONT UNIT via [SP MIC] jack, and amplifiedby MIC AMP (#2).The amplified MIC signals "MIC” are applied to the MAINUNIT via J401(FRONT UNIT) and J1 (MAIN UNIT).The MIC signals from the FRONT UNIT are applied to thebaseband IC (IC10, pin 3) and processed.SQUELCH CIRCUITS• NOISE SQUELCHThe noise squelch cuts off the AF output signals whenno RF signals are received. Extracting noise components(approx. 30 kHz signals) in the demodulated AF signals,the squelch circuit turns the AF power amplifier and AFswitches ON and OFF.A portion of FM-demodulated AF signal from the IF IC isadjusted its level (=squelch threshold level) by DAC (D/Aconverter; IC6, pins 1, 2), then passed through the noisefilter (M: IC1, pins 7, 8 and R42, 44–46, C68–70) to extractthe noise components (approx. 30 kHz signals) only. Thenoise components are rectified to be converted into thepulse-type signal by noise detector to produce DC voltagecorresponding to the noise level "NOIS". Then the DCvoltage is applied to the CPU (IC401, pin 41) and comparedwith the reference level preset in the CPU.If the CPU interpretes that the noise level is higher thanpreset one, the CPU sets the "AFON" signal to "High" toturn the AF power AMP controller OFF, and the AF muteSW is turned OFF simultaneously. Thus closing the squelchis accomplished.• TONE SQUELCHThe tone squelch connects the RX AF line and activatesthe AF power amplifier to emit the AF signals only whenreceiving a signal which contains the tone frequencymatched with preset in the CPU. Detecting signal in thedemodulated AF signals, the tone squelch circuit turns theAF power amplifier and AF switches ON and OFF.A portion of FM-demodulated AF signals from the FM IFIC are passed through the tone filter (M: Q6, pins 5, 6) toremove unwanted voice siganls. The filtered tone signalsare applied to the CPU (IC401, pin 44).<2/5 TONE, DTMF>A portion of FM-demodulated AF signals are output fromthe baseband IC (M: IC10, pin 21), and passed throughthe tone filter (M: R136, C220) to remove unwanted voicesiganls. The filtered tone signals are applied to the CPU(IC401, pin 43).The CPU compars the tone frequency/code preset in theCPU, and if the applied tone frequency/code is matched topreset one, the CPU controls the AF power AMP and AFmute SW as same as "NOISE SQUELCH."C512R524C405R522C437C497Q406Q401, Q402C510R525C513R446C404W401C421R518R407R408SP401Q415R511R426R519R405R513W402C496C502C481C407R401R428IC403131214R539C426R520C498IC4061234 5678MC401C503C482C435R537R433R541J402123456C425R523C401Q413IC407231C406R402R445R521R538R517C423R406R430R434IC407657R432R535R512R429IC4051GND1 2NC 3OUT1 + 4MODE 5SVRR 6SELECT 7NC 8OUT2 + 9NC 10GND211 VCC212 NC13 OUT2-14 IN2-15 IN2+16 IN1+17 IN1-18 OUT1-19 NC20 VCC1SIGNALAFONVCCBEEPDUSEMICEXMICSPONAFONBPMAXPWONAFOVR UNITW6011234MIC/AFMUTE SWMIC AMP#1 MIC AMP#2LPFAF POWER AMPCONTROLLERAF POWER AMPAUDIOLEVELADJUSTDAC1 2 NoiseAMPFc=30 kHzActive filterFrom IF IC (Pin16)To RX AF circuitsNoise detectorRectify“NOIS”NOISE SQUELCH DIAGRAM• TX AF CIRCUITS