Icom ID-51A Service Manual - Page 10

SECTION 4. CIRCUIT DESCRIPTION 4-1 RECEIVE CIRCUITS RF CIRCUITS VHF BAND (108-174 MHz) The RF signal from the antenna is passed through two LPFs (L513, L515, L516, C547, C549, C553, C555 and C556), ANT SW (D506, D903) and BPF (L705, L706, L909, C724 and C976), and then applied to the RF AMP (Q702). • Band A (137-174 MHz) The amplified signal is passed through the BPF (D705, L703 and C715) and AGC circuit (Q49, Q50, D34, D704), and then applied to the RF AMP (Q701). The amplified signal is applied to the 1st IF circuit, through the BPF (D702, D703, L701, C703 to C705). • Band B (108-174 MHz) The amplified signal is passed through the ATT (D745), BPF (D744, L742 and C753) and AGC circuit (Q903, D743), and then applied to the RF AMP (Q740). The amplified signal is applied to the 1st IF circuit, through the BPF (D741, D742, L740, C741 to C743). UHF BAND (380-479 MHz) The RF signal from the antenna is passed through the HPF (L512, L514, C545, C548, C550, C551 and C554), two LPFs (L511, C536, C539 and L507, C524, C526, C529), ANT SW (D508 and D510) and BPF (L608, L610, L612, C630, C631 and C634), and then applied to the RF AMP (Q602). • Band A The amplified signal is passed through the two BPFs (D605, L605, C615 and D606, L606, C619) and AGC circuit (Q49, Q50, D34, D604), and then applied to the RF AMP (Q601). The amplified signal is applied to the 1st IF circuit, through the BPF (D602, D603, L602, L603, C603 to C605, C607, C907). • Band B The amplified signal is passed through the BPF (D645, D646, L644, L645, C654, C655, C658) and AGC circuit (Q903, D644), and then applied to the RF AMP (Q641). The amplified signal is applied to the 1st IF circuit, through the BPF (D642, D643. L641, L642, C642 to C644, C646 and C972). • RF CIRCUITS To the 1st IF circuit (Band A). BPF D702,D703 RF AMP Q701 To the 1st IF circuit (Band B). BPF D741,D742 RF AMP Q740 -Band A:137M-174MHz- AGC BPF Q49,Q50,D34 D705 D704 -Band B:108M-174MHz- 108M-174MHz AGC Q903,D743 BPF D744 ATT D745 Q702 RF AMP To the 1st IF circuit (Band A). BPF D602,D603 RF AMP Q601 To the 1st IF circuit (Band B). BPF D642,D643 RF AMP Q641 -Band A:380M~479MHz- AGC BPF Q49,Q50,D34 D605,D606 D604 -Band B:380M~479MHz- AGC Q903,D644 BPF D645,D646 380M-479MHz Q602 RF AMP D503,D504 D506,D903 ANT SW TX:136.000M~174.000MHz RX:108.000M~174.000MHz LPF LPF From the TX circuit D501 D508 D510 ANT SW LPF From the TX circuit TX:400.000M~479.000MHz RX:380.000M~479.000MHz LPF HPF 4 - 1