3-2 TRANSMITTER CIRCUITS3-2-1 MICROPHONE AMPLIFIER CIRCUIT(MAIN UNIT)The microphone amplifier circuit amplifies microphone audiosignals to a level needed for the DSP.Audio signals from the [MIC] connector (MIC board; J1, pin1) are amplified at the audio amplifier section in IC451 (pins21–23) via the analog switch (IC3002, pins 12, 14), thenapplied to the buffer amplifier section (IC451, pin 5) andVCA section. The gain controlled signals are output from(IC451, pin 9) and passed through the analog switch(IC3005, pins 14, 12) and then applied to the DSP circuit asthe DTAF signal.The VCA section in IC451 (pins 7–9) controls microphoneinput gain according to the [MIC GAIN] control level usingthe MIGV signal coming from the main CPU via the I/Oexpander (IC3751, pin 4).3-2-2 VOX CIRCUIT (MAIN UNIT)The VOX (Voice-Operated Transmission) circuit sets transmittingconditions according to voice input.A portion of the amplified audio signals from the AF amplifiersection in IC451 are again amplified at the VOX amplifiersection IC451 (pin 9), also gain contolloed signals at theVCA section (pin 9) are amplified at the AF amplifier(IC3004b, pins 6, 7), and then applied to the main CPU(IC3501, pin 106) after passing through the analog switch(IC362, pins 6, 1) as the VOXL signal.The VOGV signal is applied to the VCA section in IC3003(pin 7–9) from the main CPU via the I/O expander (IC3751,pin 9) to adjust VOX actionable sensitivity. This is controlledby the VOX gain set in the VOX SET mode.3-2-3 DSP TRANSMITTER CIRCUIT (DSP BOARD)The microphone audio signals from the MAIN unit via theDTAF line are passed through the analog switch (IC2201,pins 4 and 3 or 5) and applied to the each modulation circuits.(1) When SSB modeThe audio signals from the analog switch (IC2201, pin 5) areamplified at the limitter amplifier (IC2281b) and applied tothe low-pass filter (IC2281d/c) to limit the transmit passbandwidth.