Icom IC-F4160 Service Manual

Contents

Icom IC-F4160 Service Manual Manual pdf 165 page image

5 - 1SECTION 5 CIRCUIT DESCRIPTION5-1 RECEIVER CIRCUITS5-1-1 ANTENNA SWITCH (MAIN and RF UNITS)The received signals from the antenna connector are passedthrough the antenna switch which toggles the receive (RX) lineand transmit (TX) line.The received signals from the antenna connector are passedthrough the low-pass filter (LPF; L601−L603, C601−C607), andthe antenna switch (D601, D602 and D603 are OFF).While transmitting, the voltage on the T5V line is applied toD601, D602 and D603, and these are ON. Thus the TX lineis connected to the antenna. Simultaneously, the RX line isconnected to the GND to prevent transmit signal entering.While receiving, no voltage is applied to the D601, D602and D603, and these are OFF. Thus the TX line and theantenna is disconnected to prevent received signals entering.Simultaneously, the RX line is disconnected from the GND andthe received signals are passed through the LPF (RF UNIT; L604,C610, C611).The filtered signals from the LPF (RF UNIT; L604, C610, C611)are then applied to the RF circuit via the two staged tunablebandpass filter (BPF; D21−D24, L31, L32, C120−C122, C125−C127).5-1-2 RF CIRCUIT (MAIN UNIT)The received signals are filtered and amplified at the RFcircuit.The filtered signals are applied to the RF amplifier (Q10). Theamplified signals are applied to the 1st mixer (Q9) via another two-staged BPF (D28, D29, L33, L34, C141−C144, C147, C148).5-1-3 1st IF CIRCUITSThe received signals are converted into the 1st IF signal, andamplified at the 1st IF circuits.The filtered signals from the RF circuit are converted into the46.35 MHz 1st IF signal by being mixed with the 1st LocalOscillator (LO) signals from the VCO at the 1st mixer (Q9).The LO signals for 435/485 MHz (Low band/High band) and lowerfrequencies are generated by the RX1 VCO (Q2, D5, D6, D8), andthe LO signals for 435/485 MHz (Low band/High band) and higherfrequencies are generated by the RX2 VCO (Q1, D1, D2).The converted 1st IF signal is passed through the 1st IF filter(in wide mode; FI1, in narrow mode; FI4) via the bandwidthswitch (D34), to remove adjacent signals. The filtered signalis applied to the 1st IF amplifier (Q25) via another bandwidthswitch (D35). The amplified 1st IF signal is then applied to theFM IF IC (IC3, pin 16).5-1-4 2nd IF AND DEMODULATOR CIRCUITS (MAIN UNIT)The 1st IF signal is converted into the 2nd IF signal, and de-modulated.The 1st IF signal from the 1st IF amplifier (Q25) is applied tothe 2nd IF mixer in the FM IF IC (IC3, pin 16). And the 1st IFsignal is converted into the 450 kHz 2nd IF signal by beingmixed with the 2nd LO signal from the reference frequencyoscillator (X1) via the tripler (Q18).The converted 2nd IF signal is output from pin 3, and passedthrough the 2nd IF filter (FI2) to suppress sideband noise. Innarrow mode, the 2nd IF signal is also passed through another2nd IF fi lter (FI3) via bandwidth switches (D32, D33).The filtered 2nd IF signal is applied to the limiter amplifier inthe FM IF IC (IC3, pin 5). The amplified 2nd IF signal is FM-demodulated at the quadrature detector (X5, IC3, pins 10, 11)and output from pin 9. The demodulated AF signals are thenapplied to the AF circuits.5-1-5 AF CIRCUITS (FRONT and MAIN UNITS)The demodulated AF signals from the FM IF IC are amplifiedand filtered at AF circuits. This transceiver employs thebase band IC for audio signal processing for both transmitand receive. The base band IC is an audio processor andcomposed of pre-amplifier, compressor, expander, scrambler,etc. in its package.The demodulated AF signals from the FM IF IC (IC3, pin 9) areapplied to the base band IC (IC5, pin 23) via the Digital/Analogswitch (IC14, pins 2, 15).The applied AF signals are amplified at the amplifier (RXA1)and level adjusted at the volume controller (VR3), thensuppressed unwanted 3 kHz and higher audio signals at LPF.The filtered AF signals are applied or bypassed the TX/RXHPF, scrambler, de-emphasis sections in sequence.D/A converter(IC4)MixerRSSIQuadraturedetector211st IF signal from the IF amplifier (Q25)16Noisedetector+5VX51110FM IF IC (IC3)Filteramp.Limiteramp.Demodulated signalsto the AF circuits• 2nd IF AND DEMODULATOR CIRCUITS9“NOIS” signal to the CPU (IC18: pin 37)“RSSI” signal to the CPU (IC18: pin 50)1312Q18X115.3 MHz45.9 MHz BPF238 7 35FI2FI3N/WSW N/WSWD33 D32