Icom IC-F50V Service Manual

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Icom IC-F50V Service Manual Manual pdf 7 page image

4 - 1SECTION 4 CIRCUIT DESCRIPTIONWhile transmitting, serial-connected PIN diodes are ON,thus the TX line is connected to the antenna, and the RXline is connected to the GND simultaneously to prevent TXsignal entering.The limitter protects RX line from over-level RF inputs, andthe BEF (=trap) damps unwanted signals to GND.The tuned-BPF is adjusted so that it responds to receivingfrequency and rejects all others, by the variable capacitorwhose capacitance is varied by added voltage "T1" and "T2."The RF AMP amplifies RX signals to a level suited to the 1stmixer.4-1 RECEIVER CIRCUITSRF CIRCUITSRF circuits consist of RF filters, antenna switch (ANT SW),RF amplifi er (RF AMP), etc., and extracts and amplifi es thesignals of frequency which desired to receive.The received signals (RX signals) from the antenna are passedthrough the LPF, ANT SW (as an LPF in RX), limitter , BEF(Band Eliminate Filter) and the two-staged tuned BPF. Thefiltered RX signals are amplified by the RF AMP, and passedthrough another two-staged tuned BPF. The filtered RX signalsare then applied to the 1st IF circuits.The ANT SW toggles RX line and TX line. While receiving,the TX line and the antenna is disconnected to prevent RXsignals entering. The RX line is disconnected from the GNDsimultaneously, and an LPF which guides received signalsto the RX circuits is composed.1ST IF CIRCUITSThe 1st IF circuits consist of 1st mixer, 1st IF filter and 1st IFamplifier (IF AMP). And it converts the RX signals into the1st IF signal, then filters to remove unwanted signals andamplifies.The filtered RX signals are applied to the 1st mixer to beconverted into the 1st IF signal, by being mixed with the 1stLocal Oscillator (LO) signals “1stLO” from the RX VCO viathe LPF.C55D10L13C60FL-335FI11IN2 OU T 3GND4 GND56R30R481stIFR25Q3L142C54Q4C322D9R2 2R34C56C5 8 C4 1C5 11R31R20C39C53C324C36C44C52R3 33 R23L11R29R21C48C35L11stLO2C183C321C323R26R35R32C57C50 R28C59C329R2 7C45C38C40D26C49R5V R5V R5VLPFLIMITTER1st IFAMP1stMIXERTwo-stagedTUNED BPF1st IFFILETRC14D10C26C186R11L14R12R172C426PC25R15 R18R13C322D9R2 2C28C27C4 1L5C2 2R20C39D23C324C36C44L6D6L31C19C23C43C17Q2R23C37L11D8R21R171Q1L7C20R19R174L9C29C35L11stLO2C183R173C24C184C32R213C323C16R14C18C33R175D5L8R16C31R17D4C30C45C38D7C40C49T2T1RSSIR5VBEFLPFLPF (ANT SW)LPFLIMITTERRFAMPAGC LINEDRIVERTwo-stagedTUNED BPFTwo-stagedTUNED BPFC2To ANTL2 L1C6C5C1R51C4C3To TX AMPThe converted 1st IF signal is passed through the 1st IF filterto be removed unwanted signals. The filtered 1st IF signal isapplied to the 1st IF AMP via the limitter. The amplified 1stIF signal is then applied to the 2nd IF circuits.• RF CIRCUITS• 1ST IF CIRCUITS