Icom IC-R3 Service Manual

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Icom IC-R3 Service Manual Manual pdf 8 page image

4 - 2The 65 MHz–107.995 MHz signals pass through the bandswitching diode (D503) and bandpass filter (D501), and arethen amplified at the RF amplifier (Q501). The amplified sig-nals pass through the bandpass filter (D502) and bandswitching diode (D504).The 108 MHz–173.995 MHz signals pass through the bandswitching diode (D603) and bandpass filter (D601), and arethen amplified at the RF amplifier (Q601). The amplified sig-nals pass through the bandpass filter (D602) and bandswitching diode (D604).The 174 MHz–224.995 MHz signals pass through the bandswitching diode (D703) and bandpass filter (D701), and arethen amplified at the RF amplifier (Q701). The amplified sig-nal pass through the bandpass filter (D702) and bandswitching diode (D704).(3) 330 MHz–469.995 MHzRF signals (330 MHz–469.995 MHz) from the RF switchingcircuit pass through the band switching diode (D21) and abandpass filter (C19–C27, L2–L5, L39). The filtered signalsare amplified at an RF amplifier (Q7), and then passedthrough the bandpass filter (D22, D23). The filtered signalsare then applied to the 1st mixer circuit (IC1) via the bandswitching diode (D24).(4) 470 MHz–799.995 MHzRF signals (470 MHz–799.995 MHz) from the RF switchingcircuit pass through the band switching diode (D805) and alow-pass filter (C321–C325, L81, L82). The filtered signalsare passed through each bandpass filter and RF amplifierdepending on the receiving frequency. The amplified signalsare then applied to the 1st mixer circuit (IC1) via the bandswitching diode (D804 or D854) respectively.The 470 MHz–599.995 MHz signals pass through the bandswitching diode (D803) and bandpass filter (D801), and arethen amplified at the RF amplifier (Q801). The amplified sig-nals pass through the bandpass filter (D802) and bandswitching diode (D804).The 600 MHz–799.995 MHz signals pass through the bandswitching diode (D853) and bandpass filter (D851), and arethen amplified at the RF amplifier (Q851). The amplified sig-nals pass through the bandpass filter (D852) and bandswitching diode (D854).(5) 225 MHz–329.995 MHz AND 800 MHz–1149.995 MHzRF signals (225 MHz–329.995 MHz and 800 MHz–1149.995MHz) from the RF switching circuit pass through the bandswitching diode (D33). The signals are passed through eachbandpass filter and RF amplifier depending on the receivingfrequency. The amplified signals are then applied to the 1stmixer circuit (IC1) via the band switching diodes (D35 orD36) respectively.The 225 MHz–329.995 MHz signals pass through the band-pass filter (C40–C43, C395, C396, L58, L59), and are thenamplified at the RF amplifier (Q9). The amplified signalspass through the band switching diode (D35).The 800 MHz–1149.995 MHz signals pass through thebandpass filter (C46–C49, C51–C54, L11–L14), and arethen amplified at the RF amplifier (Q8). The amplified sig-nals pass through the band switching diode (D36).4-1-3 1ST MIXER CIRCUIT (RF UNIT)The 1st mixer circuit converts the received RF signals to afixed frequency of the 1st IF signal with a PLL output fre-quency. By changing the PLL frequency, only the desiredfrequency will pass through the bandpass filters at the nextstage of the 1st mixer.The filtered or amplified RF signals from each RF circuit aremixed with 1st LO signal at the 1st mixer circuit (IC1) to pro-duce each 1st IF signal depending on the receiving fre-quency. The 1st IF signal is output from pin 6, and passedthrough the bandpass filter (FI904) to suppress unwantedharmonic components. The filtered 1st IF signal is applied tothe 2nd mixer circuit.*1 30–799.995 MHz and 1321–2099.995 MHz range*2 800–1320.995 MHz and 2100–2450.095 MHz rangeThe 1st LO signals are generated at the 1st VCO (VCO unit;Q22, Q23, D62) and are applied to the 1st mixer (IC1, pin 3)directly or passed through the doubler circuit (Q26) afterbeing amplified at the buffer amplifier (VCO unit; IC4).1ST IFFM, AM, WFM240.1 MHzC3F (TV)241.85*1, 238.35*2MHz1ST MIXER CIRCUIT (RF UNIT)"RFO" signals fromthe each front-end circuit"1st VCO" signal fromthe 1st VCO circuit (VCO unit)"R3V" signal fromthe LOGIC unit"1st IF" signal tothe 2nd mixer circuit"1st IF" signal tothe FM-TV unit1st mixer IC (IC1)C153R255 R256 R257123654C152 C70C234