Icom IC-F610 Service Manual

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Icom IC-F610 Service Manual Manual pdf 11 page image

4 - 54-5 OTHER CIRCUITS4-5-1 COMPANDER CIRCUIT (MAIN UNIT)IC-F610 series have compander circuit which can improve S/N ratio and become wide dynamic range. The circuit is com-posed in the compander IC (IC14).(1) IN CASE OF RECEIVINGThe demodulated AF signals from the FM IF IC (IC1, pin9) are applied to the amplifier section in the compander IC(IC14, pin 3), and then pass through the low-pass filter andhigh-pass filter sections to suppress unwanted signals. Thefiltered signals are applied to the expander circuit to expandAF signals.The output signals from the compander IC (IC14, pin 38) isapplied to the AF amplifier circuit after amplified at the ampli-fi er section.(2) IN CASE OF TRANSMITTINGThe audio signals from the microphone amplifier (FRONTUNIT; IC2) are applied to the compander IC (IC14, pin 12)via the D/A converter (IC6, pins 9, 10). The signals are am-plified at the amplifier section, and are then applied to thecompressor circuit to compress the audio signals. The sig-nals are pass through the low-pass filter and high-pass filtersections and are then applied to the limiter amplifier sectionafter being passed through the high-pass fi lter section.The filtered signals pass through the splatter filter section,and are then applied to the modulation circuit (D18) via thePM/FM switch (IC15, pins 1, 6, 7) and D/A converter (IC6,pins 21, 22).• COMPANDER IC BLOCK DIAGRAM4-6 PORT ALLOCATIONS4-6-1 OUTPUT EXPANDER (FRONT UNIT; IC1)PinnumberPortname Description1–3 KS0–KS2Output ports for the programmablefunction keys (P0–P4, , , , ).4, 5 DIM1,DIM2Output LCD backlight control signals.7 HORNOutputs external device control signal.High: When matched 2/5 tone sig-nals are received.DIM1 DIM2 LIGHTHIGH HIGH ONHIGH LOW OFFLOW HIGH DIMLOW LOW OFF4-6-2 D/A CONVERTER (MAIN UNIT; IC7)PinnumberPortname Description1–3 T1–T3 Output the bandpass filters (D4, D8,D9) tuning signals.4 T4• Outputs the bandpass filter (D10)tuning signal while receiving.• O u t p u t s t h e T X p owe r c o n t r o lsignal which selects High, Low1,Low2 of TX power while trans-mitting. The output signal is ap-plied to the APC amplifier (IC2,pin 1).EXPANDERDEMODMSKAMP LPFLPFHPF AMP AMPLPFTX OUTRX OUTLIMITAMPAMPHPFHPFAMPBPF MODMSKCOM-PRESSOR3TX INMSK INRX IN512 638