Icom IC-R3 Service Manual

Also see for COMMUNICATIONS RECEIVER IC-R3: Instruction manual Brochure & specs Service manual

Contents

Icom IC-R3 Service Manual Manual pdf 7 page image

SECTION 4 CIRCUIT DESCRIPTION4 - 14-1 RECEIVER CIRCUITS4-1-1 RF SWITCHING CIRCUIT (RF UNIT)(1) Below 1150 MHzThe RF signals from the antenna connector pass throughthe band switching diode (D2) and an attenuator (D12, D13).The signals are then applied to the RF circuit which sup-press out-of-band signals via the band switching diode(D911).(2) Above 1150 MHzThe RF signals from the antenna connector pass throughthe limitter (D1), band switching diode (D909) and high-passfilter (C932–C936, C963, C964, L911, L912, L914). The fil-tered signals are applied to the AF amplifier (IC14, pin 1),and are then applied to the convertor circuit (IC13, pin 1).Above 1150 MHz RF signals are mixed with “CONLO” signalfrom CONV VCO circuit for convertion into below 1150 MHzRF signals at the converter circuit (IC13). The converted sig-nals are output from IC13 (pin 6), and are then applied to theRF circuit which suppress out-of-band signals.4-1-2 RF CIRCUIT (RF AND RF-B UNITS)The RF circuit amplifies the received signals within therange of frequency coverage and filters out-of-band signals.(1) 0.495 MHz–29.995 MHzRF signals (0.495 MHz–29.995 MHz) from the RF switchingcircuit pass through a low-pass filter (C321–C325, L81,L82). The filtered signals are amplified at an RF amplifier(Q3) passing through each low-pass, bandpass, high-passfilter depending on the receiving frequency. The amplifiedsignals are then applied to the 1st mixer circuit (IC1) via theband switching diode (D10).The signals below 1.9 MHz pass through a low-pass filter(C344–C347, L89, L90) between the band switching diode(D4, D7), and are then applied to the RF amplifier circuit(Q3).The 1.9 MHz–14.995 MHz signals pass through the bandswitching diode (D5) and bandpass filter (C332–C341,L85–L88), and are then applied to the RF amplifier circuit(Q3) via the band switching diode (D8).The 15 MHz–29.995 MHz signals pass through the bandswitching diode (D6) and high-pass filter (C326–C330, L83,L84) and are then applied to the RF amplifier circuit (Q3) viathe band switching diode (D9).(2) 30 MHz–224.995 MHz (RF-B UNIT)RF signals (30 MHz–64.995 MHz, 65 MHz–107.995 MHz,108 MHz–173.995 MHz, 174 MHz–224.995 MHz) from theRF switching diode (RF unit; D11) are passed through thelow-pass filter (RF unit; C12–C17, L57–L59). The filteredsignals pass through the each bandpass filters and RFamplifier depending on the receiving frequency. The signalsare then applied to the 1st mixer circuit (RF unit; IC1).The 30 MHz–64.995 MHz signals pass through the bandswitching diode (D403) and bandpass filter (D401), and arethen amplified at the RF amplifier (Q401). The amplified sig-nals pass through the bandpass filter (D402) and bandswitching diode (D404).RF CIRCUIT ANTANTSWD909, D912"CONLO" signal fromthe CONV VCO circuitANTSWD2, D911IC13Below 1150 MHz RF signalsAbove 1150 MHz RF signalsLPFLPF ANTSWBPFRFD4—D9ANTSWD3, D100.495 30 MHz30 225 MHz330 470 MHz470 800 MHz225 330 MHz,800 1150 MHzQ3LPFANTSWBPF BPFRFD403, D404D503, D504D603, D604D703, D704ANTSWD11Q401, Q501,Q601, Q701BPF BPFRF ANTSWD21, D24Q7BPF BPFRF ANTSWANTSWD803, D804D853, D854 D805Q801, Q851LPFBPFRF ANTSWD33, D35, D36Q8, Q91st LOIC1D902D1to the FM-TV circuitto the 2nd mixer circuitFM-TV UNITRF-B UNITDisplayed frequencyCONVERTED RF FREQUENCY LISTRF frequency1150.000—1176.0001176.005—1229.9951230.000—1255.0001255.005—1286.0001286.005—1320.9951321.000—1349.9951350.000—1384.9951385.000—1394.9951395.000—1427.9951428.000—1515.9951516.000—1569.9951570.000—1579.9951580.000—1739.9951740.000—1789.9951790.000—1809.9951810.000—1849.9951850.000—2039.9952040.000—2109.9952110.000—2204.9952205.000—2250.9952251.000—2450.095141.000—115.000143.995—90.00561.000—36.00064.995—34.00064.995—30.00530.000—58.99530.000—64.99594.000—103.99575.000—107.995137.000—224.995196.000—249.995250.000—259.995289.000—448.995420.000—469.995499.000—518.995490.000—529.995559.000—748.995720.000—789.995819.000—913.995885.000—930.995960.000—1159.095