Icom IC-F43TR Service Manual

Also see for IC-F43TR: Instruction manual Instruction manual Instruction manual

Contents

4 - 24-1-5 AF AMPLIFIER CIRCUIT (MAIN UNIT)The AF amplifier circuit amplifies the demodulated AF sig-nals to drive a speaker. This transceiver employs the baseband IC which is composed of pre-amplifier, expander,scrambler, MSK de-modulator, etc. at the AF amplifier sec-tion.The AF signals from the FM IF IC (IC9, pin 9) are amplifiedat the AF amplifier section of the base band IC (IC14, pin 23)and are then applied to the low-pass filter section of it.The filtered signals passes through the high-pass filter tosuppress unwanted harmonic components. The signalspass through (or bypass) scrambler and expander sections.The signals are amplified at the amplifier section of the baseband IC (IC14).The amplified signals pass through the AF volume (R315),and are then applied to the AF power amplifier (IC15) todrive the speaker.4-1-6 RECEIVE MUTE CIRCUITS (MAIN UNIT)• NOISE SQUELCHA squelch circuit cuts out AF signals when no RF signals arereceived. By detecting noise components in the AF signals,the squelch circuit switches the AF mute switch.Some noise components in the AF signals from the FM IF IC(IC9, pin 9) are passed through the D/A converter (IC12, pin1). The signals are applied to the active filter section in theFM IF IC (IC9, pin 8). The active filter section filters andamplifies noise components. The amplified signals are con-verted into the pulse-type signals at the noise detector sec-tion. The detected signals output from pin 13 (NOIS) via thenoise comparator section.The “NOIS” signal from the FM IF IC is applied to the CPU(IC22, pin 75). Then the CPU analyzes the noise conditionand outputs the AF mute signal as “AFON” from the pin 70to the AF power controller (Q41, Q42).• CTCSS AND DTCSThe tone squelch circuit detects AF signals and opens thesquelch only when receiving a signal containing a matchingsubaudible tone (CTCSS or DTCS). When tone squelch is inuse, and a signal with a mismatched or no subaudible toneis received, the tone squelch circuit mutes the AF signalseven when noise squelch is open.A portion of the “DET” AF signals from the FM IF IC (IC9, pin9) passes through the low-pass filter (IC19, pin 5) to removeAF (voice) signals, and are then applied to the amplifier(IC19, pin 3). The amplified signals are applied to theCTCSS or DTCS decoder inside of the CPU (IC22, pin 46)via the “CDEC” line. The CPU outputs AF mute control sig-nal and AF power supply circuits (Q41, Q42) control signalsvia the “AFON” line.4-2 TRANSMITTER CIRCUITS4-2-1 MICROPHONE AMPLIFIER CIRCUIT(MAIN UNIT)The microphone amplifier circuit amplifies audio signalswithin +6 dB/octave pre-emphasis characteristics from themicrophone to a level needed for the modulation circuit.This transceiver employs the base band IC which is com-posed 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).Base band IC(IC14)"DET" AF signalfrom FM IF IC (IC9, pin 9) 23 20 LPFAFvolumeAFAMPIC15SpeakerIC23IC23IC13IC6 IC12 D12MicrophoneAMP374FM/PM switchD/A converter FM mod.LPF"CTCSS/DTCS" signal fromD/A conveter IC (IC12, pin 11)"TONE" signal from CPU via low-passfilter (IC22, pin 43)to TX VCO circuit(Q16, D13)3• AF AND MIC AMPLIFIER CIRCUIT