Icom IC-F43GT Service Manual

Also see for IC-F43GS: Instruction manual Instruction manual Instruction manual Instruction manaul Service manual

Contents

Icom IC-F43GT Service Manual Manual pdf 9 page image

4 - 3posed of microphone amplifier, compressor, scrambler, lim-iter, splatter filter, MSK modulator, etc. at the microphoneamplifier section.The AF signals (MIC) from the microphone (MC1) areapplied to the amplifier (IC23, pins 6, 7). The amplified sig-nals are applied to the microphone amplifier section of thebase band IC (IC14, pins 3, 4). The amplified signals arepassed through or bypass the compressor, scrambler sec-tions of IC14, and are then passed through the high-pass,limiter amplifier, splatter filter sections of IC14.The filtered AF signals are applied to the FM/PM switch(IC13, pin 6), and pass through the low-pass filter (IC6, pin2).The filtered signals are applied to the D/A converter (IC12,pin 4). The output signals from the D/A converter (IC12, pin3) are applied to the modulation circuit (D12).4-2-2 MODULATION CIRCUIT (MAIN UNIT)The modulation circuit modulates the VCO oscillating signal(RF signal) using the microphone audio signals.The AF signals from the D/A converter (IC12, pin 3) changethe reactance of varactor diode (D12) to modulate the oscil-lated signal at the TX VCO circuit (Q16, D10). The modulat-ed VCO signal is amplified at the buffer amplifiers (Q15,Q29) and is then applied to the drive amplifier circuit via theT/R switch (D16).The CTCSS/DTCS signals (“CENC0”, “CENC1”, ”CENC2”from the CPU (IC22, pins 13, 15, 16) pass through the low-pass filter (IC6, pins 12, 14), and are then applied to the D/Aconverter via the “TONC” line (IC12, pin 12). The output sig-nal from the D/A converter (IC12, pin 11) are mixed with“MOD” signal after pass through the low-pass filter (IC6).The mixed siganls are applied to the D/A converter (IC12,pin 3, 4), and are then applied to the D12 in the VCO circuit.4-2-3 DRIVE/POWER AMPLIFIER CIRCUITS(PA UNIT)The drive/power amplifier circuits amplify the VCO oscillat-ing signal to an output power level.The signal from the VCO circuit passes through the T/Rswitch (MAIN unit; D16), and is amplified at the YGR (Q703,Q704), drive (Q702), power (Q701) amplifiers to obtain 4 Wof RF power (at 7.2 V DC).The amplified signal is passed through the low-pass filter(L704, C711, C712, C713, C755), power detector (D702,D703), antenna switching circuit (D701) and another low-pass filters (PA unit; L709, C744, C745), (ANT unit; L801,L802, C802, C803, C804, C805), and is then applied to theantenna connector (CHASSIS unit; J1).The bias current of the drive (Q702) and power (Q701)amplifiers are controlled by the APC circuit.4-2-4 APC CIRCUIT (PA AND MAIN UNITS)The APC circuit protects the drive and power amplifiers fromexcessive current drive, and selects output power of HIGHor LOW.The power detector circuit (PA unit; D702, D703) detects thetransmit power output level and converts it into DC voltage.The output voltage is at a minimum level when the antennaimpedance is matched with 50 Ω and is increased when it ismismatched.The detected voltage is applied to the differential amplifierPoweramp.APCamp.Driveramp.+–YGRamp.VCCto ANT unitPA unitT2TMUTD29RF signalfrom PLL circuitT5VAPC control circuitD703D702YGRamp.ANTSW LPFLPFQ702Q704IC16Q703 Q701D701• APC CIRCUIT