Icom ID-1 Service Manual

Also see for ID-1: Addendum Instruction manual Instruction manual

Contents

Icom ID-1 Service Manual Manual pdf 7 page image

4 - 1SECTION 4 CIRCUIT DESCRIPTION4-1 RECEIVER CIRCUITS4-1-1 ANTENNA SWITCHING CIRCUIT (MAIN UNIT)The antenna switching circuit functions as a low-pass filterwhile receiving and a resonator circuit while transmitting.This circuit does not allow transmit signals to enter thereceiver circuits.Received signals from the antenna connector (CHASSIS;J1) are passed through the low-pass filter which containsstrip-line and C1198, and are then applied to the λ⁄4 typeantenna switching circuit (D1160–D1162, L1162).While receiving, no voltage is applied to D1160–D1162.Thus, the receive line and ground are disconnected andreceived signals are applied to the RF circuit.4-1-2 RF CIRCUIT (MAIN UNIT)The RF circuit amplifies signals within the range of frequen-cy coverage and filters out-of-band signals.The signals from the antenna switching circuit pass throughthe high-pass filter (L1–L4, C2–C5) and then applied to theRF amplifier (Q1). The amplified signals are passed throughthe bandpass filter (FI1) and then applied to the another RFamplifier (Q2). The amplified signals are passed through theanother bandpass filter (FI2) to suppress unwanted signals.The filtered signal is applied to the 1st mixer circuit.4-1-3 1ST MIXER AND 1ST IF CIRCUITS (MAIN UNIT)The 1st mixer circuit converts the received signals intofixed frequency of the 1st IF signal with the 1st LO signal.By changing the 1st LO signal, only the desired frequencypasses through the bandpass filter at the next stage of the1st mixer circuit.The RF signals from the bandpass filter (FI2) are mixedwith the 1st LO signal, where come from the 1st VCO cir-cuit, at the 1st mixer circuit (IC71) to produce a 243.95MHz 1st IF signal. The 1st IF signal is passed through thebandpass filter (FI71) to suppress unwanted signals andpass only the desired signals.The filtered signal is applied to the 2nd IF circuit.4-1-4 2ND MIXER AND 2ND IF CIRCUITS(MAIN UNIT)The 2nd mixer circuit converts the 1st IF signal into the 2ndIF signal with the 2nd LO signal.• DV/FM MODEThe filtered 1st IF signal from the bandpass filter (FI71) ismixed with the 2nd LO signal (275.00 MHz), where comefrom 2nd VCO circuit, at the 2nd mixer circuit (Q131) toproduce the 2nd IF signal (31.05 MHz). The 2nd IF signalis passed through the MCF (FI191) via the DV/FM switch(D131). The filtered signal is applied to the IF amplifier(Q191) and then applied to the 3rd mixer circuit in thedemodulator IC (IC191).• DD MODEThe filtered 1st IF signal from the bandpass filter (FI71) ismixed with the 2nd LO signal (233.25 MHz), where comefrom the 2nd VCO circuit, at the 2nd mixer circuit (Q131)to produce the 2nd IF signal (10.7 MHz). The 2nd IF signalis passed through the bandpass filter (FI272) to removeunwanted heterodyned frequencies via the DD switch(D273). The filtered signal is amplified at the IF amplifier(Q270) and then passed through the another bandpassfilter (FI273). The filtered signal is applied to the another IFamplifier (Q271) and then applied to the MSK receiver IC(IC271).FI2FI1Q1 Q21240–1300 MHz1st mixerIC711st LO:3rd LO: 30.6 MHzAF amplifiercircuitLOGIC-1 unit1056.05–1016.05 MHz2nd IF: 31.05 MHz2nd IF: 10.7 MHzFl71BPFAMPAMP1st IF:243.95 MHz2nd mixerQ1312nd LO:DV, FM: 275.00 MHzDD: 233.25 MHzHPF BPFBPFFI272FI273Q271 Q270AMPAMP BPFBPFFI191D131D273 DD modeDV, FM modeIC191IC271Q191AMP BPFDemodulatorICMSKreceiver• RF AND IF CIRCUITS