Icom IC-2200H Service Manual

Also see for IC-2200H: Instruction manual Addendum Instruction manual Service manual Instruction manual

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Icom IC-2200H Service Manual Manual pdf 11 page image

4 - 34-2 TRANSMITTER CIRCUITS4-2-1 MICROPHONE AMPLIFIER CIRCUIT(LOGIC unit)The microphone amplifier circuit amplifies audio signals with+6 dB/octave pre-emphasis characteristics from the micro-phone to a level needed for the modulation circuit.The AF signals from the microphone pass through themicrophone switch (IC2, D4), and are then amplified at themicrophone amplifier (IC3a ,pin 2). The amplified signalspass through (or bypass) the ALC circuit.4-2-2 ALC CIRCUIT (LOGIC UNIT)The ALC (Automatic Level Control) circuit reduces the gainof IF amplifiers in order for the transceiver to output a con-stant RF power set by the RF power setting even when thesupplied voltage shifts, etc.• IN CASE OF PASSING THROUGH THE ALC CIRCUITThe amplified signals are applied to the ALC switch (IC520,pin 3), and are then output from pin 4. The signals areapplied to the ALC amplifier (IC514, pin 3), and are thenreapplied to the ALC switch (IC520, pin 8). The signals passthrough the high-pass filter (IC3d, pins 12, 14), and are thenapplied to the analog switch (IC6, pin 4).• IN CASE OF BYPASSING THE ALC CIRCUITThe amplified signals are applied to the ALC switch (IC520,pin 2), and are then output from pin 1. The signals areapplied to the ALC switch (IC520, pin 9) again, and thenpass through the high-pass filter (IC3d, pins 12, 14) via theIC520, pin 10. The signals are applied to the analog switch(IC6, pin 4).4-2-3 DIGITAL SWITCH CIRCUIT (LOGIC UNIT)The signals from the analog switch (IC6, pin 3) pass throughthe high-pass filter (IC3, pins 6, 7), and are then reapplied tothe analog switch (IC6, pin 9). The signals are applied to theDI/AN switch via the “MOD_I” line.• IN CASE OF DIGITAL AF SIGNALSThe AF signals are applied to the DI/AN switch (IC522, pin10), and are then applied to the optional digital voice unitafter being passed through the J4 (pin 4) via the “ANA-LOGUE_MOD_IN” line. The A/D converted AF signals areapplied to the DI/AN switch (IC522, pin 1) from the J4 (pin 3)via the “DIGITAL_MOD_OUT” line. The digital AF signalsfrom DI/AN switch (IC522, pin 2) are applied to the modula-tion circuit after being passed through the J3 via the“MODIN” line.• IN CASE OF ANALOG AF SIGNALSThe AF signals are applied to the DI/AN switch (IC522, pin9), and are then reapplied to the switch (pin 4) from pin8.The signals output from the switch (pin 3) as analog AFsignals , and are then applied to the modulation circuit afterbeing passed through the J3 via the “MODIN” line.4-2-4 MODULATION CIRCUIT (MAIN UNIT)The modulation circuit modulates the VCO oscillating signal(RF signal) using the microphone audio signals.The digital or analog audio signals (MODIN) change thereactance of D2 and D4 to modulate the oscillated signal atthe TX-VCO circuit (Q6). The modulated signal is amplifiedat the LO amplifier (Q9) and buffer amplifier (Q11), thenapplied to the drive amplifiers.4-2-5 DRIVE AMPLIFIER CIRCUIT (MAIN UNIT)The drive amplifier circuit amplifies the VCO oscillating sig-nal to the level needed at the power amplifier.The RF signal from the buffer amplifier (Q11) passesthrough the T/R switch (D6) and is amplified at the pre-drive(Q17) and drive (Q35) amplifiers. The amplified signal isapplied to the power amplifier circuit.4-2-6 POWER AMPLIFIER CIRCUIT (MAIN UNIT)The power amplifier circuit amplifies the driver signal to anoutput power level.The RF signal from the drive amplifier (Q35) is applied to thepower module (IC10) to obtain 65 W (50 W for Korea ver-sion, 25 W for Taiwan version) of RF power.The amplified signals is passed through the antenna switch-ing circuit (D12), APC detector circuit (D14, D17, L39), andlow-pass filter (L47, L48, C208, C210, C217) and is thenapplied to the antenna connector.Control voltage for the power amplifier (IC10, pin 2) are con-trolled by the APC circuit to protect the power module froma mismatched condition as well as to stabilize the outputpower.MicrophoneMICswitch"THROUGH" from the CPU(MAIN unit; IC1, pin 80)"ALC" from the CPU(MAIN unit; IC1, pin 81)"THROUGH" from the CPU(MAIN unit; IC1, pin 80)IC3AIC2, D4ThroughswitchSwitchALCswitchALCswitchMIC IC514IC520 IC520IC520Q524IC525to the modulator circuitALCPowersupply• ALC CIRCUIT