Icom IC-A110EURO Service Manual Addendum

Also see for IC-A110: Price list Specification sheet Instruction manual Service manual Instruction manual

Contents

Icom IC-A110EURO Service Manual Addendum Manual pdf 45 page image

3 - 33-2 TRANSMITTER CIRCUITS3-2-1 MICROPHONE AMPLIFIER CIRCUIT(MAIN UNIT)The microphone amplifier circuit amplifies audio signalsfrom the microphone, within +6 dB/octave pre-emphasischaracteristics (300 Hz–3 kHz), to a level needed for themodulation circuit.The AF signals from the microphone are applied to theIN/EXT MIC switch (IC16, pin 7) via the “MIC” signal. Whenusing a headset, “EXTMIC” signal are applied to the exter-nal switch (IC16, pin 6) via R336 to adjust the externalmicrophone level. The output signal from IC16 (pin 1) areapplied to the ALC amplifier (IC4, pin 9) via R110 to adjustthe microphone sensitivity.The output signal from IC4 (pin 7) are amplified at the AFamplifier (IC5), and then applied to the MOD/AF switch viathe high-pass filter (IC51) and low-pass filter (IC19) to filterout RF components. The filtered signals are applied to themodulation circuit.3-2-2 MODULATION CIRCUIT (MAIN UNIT)The modulation circuit modulates the VCO oscillating signal(RF signal) using the microphone AF signal.The audio signals are passed through the MOD/AF switch(IC48, pin 6) via the modulation depth adjustment pot R121.The signals are converted to the PWM (Pulse-Width-Modulation) wave form at the PWM IC (IC44, pin 3), andpower amplified at the FET driver (IC47, pin 5) and powerMOS FET (Q92, Q93). The power-amplified signals arepassed through the line filter (L62–L64, L81, C456, C457,C462, C463, C468), and then applied to the drain of poweramplifier (Q51) for the last stage modulation.3-2-3 DRIVE/POWER AMPLIFIER CIRCUITS(MAIN UNIT)The amplifier circuit amplifies the VCO oscillating signal tothe output power level.The signal from the buffer amplifiers (Q14, Q15) is passedthrough the TX/RX switch (D11), and is amplified at the pre-amplifier (Q42), pre-drivers (Q20, Q21) and the poweramplifier (Q51) to obtain 9 W of RF power.The amplified signal is passed through the antenna swtich-ing circuit (D3) and low-pass filter, and is then applied to theantenna connector.3-2-4 APC CIRCUIT (MAIN UNIT)The APC (Automatic Power Control) circuit protects thedrive and power amplifiers from mismatched output loads.The APC detector circuit (D4, D5) detects forward andrefrected signals respectively. The combined voltage is at aminimum level when the antenna is matched at 50 Ω and isincreased when it is mismatched.The detected voltage is applied to one of the APC controllerinputs (IC50, pin 3) and a power setting voltage is applied tothe other input (pin 1). When the antenna impedance is mis-matched, the detected voltage exceeds the reference volt-age. Thus the bias voltage of the pre-drivers is decreased.PWRAMPAPCCNTQ51Q21Q98 Q11Q20"MOD V" signal from the AF power amplifiers(MAIN unit; Q92, Q93)Pre-amplified signal(from MAIN unit; Q42)IC50Q99"TMUT" signal from theexpander IC(Front unit; IC5; pin 14)to the AntennaPower detector circuitL75R153(Power adjustment)R2R3R150R148R151T8R149C14 C13L6C17 C16C18 C19C139D4D5APCAMPPWRCNTPREDRIVEPREDRIVE• APC CONTROL CIRCUIT