ID-880H/E880 SERVICE MANUAL

SECTION 4.CIRCUIT DESCRIPTION4-1 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 amplifi ed by the RF AMP (Q33). The amplifi ed 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).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 amplifi ed RX signals are fi ltered 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).• RF CIRCUITSD59,68,75,77300 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.From VHF TX circuitFrom UHF TX circuitTX/RXSWD30,53,61,62,177TX/RXSWLPFHPFUHFLPFVHFLPFLPFThe 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).D41,D44,D60To the 1st IF mixer (Q124)BPFQ33RFAM PBPFD78,D79LIMITER