Icom ID-880H Service Manual

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Icom ID-880H Service Manual Manual pdf 8 page image

4 - 1• RF CIRCUITSSECTION 4. CIRCUIT DESCRIPTIONLPFHPFBPFRFAM PLPFTX/RXSWBPFBPFHPFRFAM PTX/RXSWRFAM PRXSWBPFBPFRXSWRXSWRFAM PRFAM PRXSWBPFBPFD59,68,75,77From VHF TX circuitFrom UHF TX circuitTo the 1st IF mixer (Q124)To the 1st IF mixer (Q125)<- To the 1st IF mixer (IC64)<- To the 1st IF mixer (IC64)D30,53,61,62,177LIMITERD78,D79D41,D44,D60Q19Q33<- 810-999 MHzQ28<- 420-550 MHz<- 230-420 MHzQ35VHFLPFUHFLPFD16D 13D12,14,23D56D57,58D45,D51Q34D36D18,D20D9<- 118-174 MHzBPF1,2,3BPF1,2,3BPF2,3BPF2,3BPF1BPF14-1 RECEIVE CIRCUITSRF CIRCUITS144 MHz BAND (118–174 MHz)The RX signals (118–174 MHz) from the antenna arepassed through two LPFs and TX/RX SW for VHF band (D59,68, 75, 77), and applied to the RF circuit.The RX signals are passed through the limiter (D78, 79) andBPF, and amplified by the RF AMP (Q33). The amplified RXsignals are filtered by tuned BPF (D41, 44, 60) to removeunwanted signals, then applied to the 1st mixer (Q124).The passband frequency of the tuned BPF (D41, 44, 60) istuned by the tuning voltage from the D/A converter controlledby the CPU (IC25).300 MHz BAND (230–420 MHz)The RX signals (230–420 MHz) from the antenna arepassed through the LPF, HPF and TX/RX SW for UHF band(D30, 53, 61, 62, 177), and applied to the RF circuit.The RX signals are passed through the RX SW (D56) andfiltered by the tuned BPF (D57, 58) to remove unwantedsignals, then applied to the RF AMP (Q35).The amplified RX signals are filtered by another tuned BPF(D45, 51) to remove unwanted signals, and amplified byanother RF AMP (Q34). The RF AMP (Q34) improves theisolation between the 1st mixer (IC64) and the tuned BPF.The amplifi ed RX signals are applied to the 1st mixer (IC64).The pass-band frequencies of the tuned BPFs (D57, 58:D45, 51) are tuned by the tuning voltage from the D/Aconverter controlled by the CPU (IC25).440 MHz BAND (420–550 MHz)The RX signals (420–550 MHz) from the antenna arepassed through the LPF, HPF and TX/RX SW for UHF band(D30, 53, 61, 62, 177), and applied to the RF circuit.The RX signals are passed through the RX SW (D16) andtuned BPF (D13) to remove unwanted signals, and appliedto the RF AMP (Q19). The amplified RX signals are filteredby another tuned BPF (D12, 14, 23) to remove unwantedsignals, then applied to the 1st mixer (Q125).The pass-band frequencies of tuned BPFs (D13: D12,14, 23) are controlled by the tuning voltage from the D/Aconverter controlled by the CPU (IC25).800 M Hz BAND (810–999 MHz)The RX signals (810–999 MHz) from the antenna arepassed through the HPF, and applied to the RF AMP (Q28).The amplified RX signals are filtered by the tuned BPF (D18,20) to remove unwanted signals, then applied to the 1stmixer (IC64) via the RX SW (D9).The pass-band frequency of tuned BPF (D18, 20) is tunedby the tuning voltage from the D/A converter controlled bythe CPU (IC25).