Icom IC-2720H Service Manual

Also see for IC-2720H: Step-by-Step Programming Guide Instruction manual Service manual Operating guide

Contents

4 - 1SECTION 4 CIRCUIT DESCRIPTION4-1 RECEIVER CIRCUITS4-1-1 TRIPLEXER AND RX BAND SWITCHINGCIRCUITS (MAIN UNIT)The transceiver has a triplexer (low-pass and high-pass fil-ters) on the first stage from the antenna connector to sepa-rate the signals into VHF and UHF signals. The RF signalsfrom the antenna connector are applied to the tripler or RXband swtich circuits.• RF SIGNALS V-V (118 MHz–180 MHz), U-V (136MHz–174 MHz)The V-V and U-V RF signals from the antenna connectorpass through the low-pass filter (L76, L77, L80, C205, C209,C242, C243, C264), and then applied to the TX/RX switchingcircuit (D42, D46, D52, D67, D2049). The filtered signals areamplified at the pre-amplifier (Q33), and are applied to theleft side or right side displayed RX circuits.• RF SIGNALS U-U, V-U2 (375 MHz–550 MHz)The U-U and V-U2 RF signals from the antenna connectorpass through the high-pass filter (L78, L81, C206, C210,C213, C265), and then applied to the TX/RX switching circuit(D55, D64, D65, D2050) via the SWR detector (D50, D58).The filtered signals are amplified at the pre-amplifier (Q24),and are applied to the left side or right side displayed RX cir-cuits.• RF SIGNALS U-U3 (810 MHz–1000 MHz)The U-U3 RF signals from the antenna connector passthrough the two low-pass filters (L76, L77, L80, C205, C209,C242, C243, C264, L87, L88, C266–C268), and are thenapplied to the RX band swtiching circuit (D2061). The filteredsignals are amplified at the RF amplifier (Q18), and areapplied to the right side displayed RX circuits.• RF SIGNALS V220 (174 MHz–260 MHz), V-U1 (225MHz–375 MHz)The V220 and V-U1 RF signals from the antenna connectorare applied to the RX band swtiching circuit (Q34, D66, RL1),and are applied to the left side displayed RX circuit.4-1-2 RF CIRCUIT FOR LEFT SIDE DISPLAY(MAIN UNIT)• RF SIGNALS V-V (118 MHz–180 MHz)The amplified signals are applied to the RF amplifier (Q29)after being passed through the attenuator (D59) and band-pass filter (D47, D53). The signals are applied to the RXband switching circuit (D28) via the another bandpass filter(D32, D39) to supress the unwanted signals.• RF SIGNALS V220 (174 MHz–260 MHz)The signals are applied to the RF amplifier (Q31) after beingpassed through the RX band switching circuit (D62) andbandpass filter (D51). The amplified signals are applied tothe RX band switching circuit (D28) via the another bandpassfilter (D34) to supress the unwanted signals and attenuator(R195–R197).• RF SIGNALS V-U1 (225 MHz–375 MHz)The signals are applied to the RF amplifier (Q32) after beingpassed through the RX band switching circuit (D63) andbandpass filter (D49). The amplified signals are applied tothe RX band switching circuit (D31) via the attenuator(R198–R200) and another bandpass filter (D35) to supressthe unwanted signals.• RF SIGNALS V-U2 (375 MHz–550 MHz)The amplified signals are applied to the RF amplifier (Q20)after being passed through the attenuator (D25) and band-pass filter (D23, D73). The signals are applied to the RXband switching circuit (D9) via the another bandpass filter(D13, D17) to supress the unwanted signals.BPF BPFANTENNA1st mixer(IC1005)1st LOto 2nd mixercircuitATTRXSW RF PREBPF BPF ATTRXSW RF PREBPF BPFATTRXSW RXSWRXSWRFBPF BPFATTRXSW RXSWRFD59Q29V-V (118 MHz—174 MHz)V220 (174 MHz—260 MHz)V-U1 (225 MHz—375 MHz)V-U2 (375 MHz—550 MHz)D28 D32, D39 D47, D53D62Q31D30 D34 D51D63Q32D31 D35 D49Q33Q34, D66,RL1D25Q20D9 D13, D17 D23, D73 Q24• RF CIRCUIT FOR LEFT SIDE DISPLAY