Icom IC-F5121D Service Manual

Also see for IC-F5121D: Instruction manual Price list Instruction manual

Contents

Icom IC-F5121D Service Manual Manual pdf 11 page image

5 - 1SECTION 5. CIRCUIT DESCRIPTION5-1 RECEIVER CIRCUITSRF CIRCUITSThe RX signal from the antenna is passed through the LPFand antenna SW (D24–D26, D28, D32), then fi ltered by the2-staged tuned BPFs (D31 and D37) to eliminate unwantedout-of-band signals. The filtered RX signal is amplified by theRF AMP (Q20), and filtered by another tuned BPF (D21) toobtain a good image response, then applied to the 1st IF cir-cuits.The BPFs are tuned to the RX frequency by applying ad-equate tuning voltages: “T1” and “T2” to the variable capaci-tors.• RF CIRCUITS1ST IF CIRCUITSThe RX signal from the RF circuits is applied to the 1st IFmixer (Q19) and mixed with the 1st LO signal from the RXVCO, resulting in the 46.35 MHz 1st IF signal. The 1st IFsignal is passed through the IF SWs (D13, D14, D17, D18)and the crystal filter (FI4: analog mode, FI5: digital mode) tobe filtered, amplified by the 1st IF AMP (Q14), then appliedto the 2nd IF circuits.• 1ST IF CIRCUITS2ND IF AND DEMODULATOR CIRCUITSThe signal from the 1st IF circuits is applied to the IF demod-ulator IC (IC4) which contains the 2nd IF mixer, 2nd IF AMP,FM detector, squelch circuit and AF AMP in its package.The 1st IF signal is applied to the 2nd IF mixer and mixedwith the 2nd LO signal resulting in the 450 kHz 2nd IF signal.The 2nd LO signal is generated by tripling the 15.3 MHzreference frequency signal generated by the reference fre-quency oscillator (TCXO; X2).• WHILE OPERATING IN THE ANALOG MODEThe 2nd IF signal is filtered by the 2nd IF filter (FI2: wide/middle mode) or filters (FI1 and FI2: narrow) to eliminate un-wanted signals. It is amplified by the 2nd IF AMP, and thendemodulated by the detector circuit, which employs the dis-criminator (X1) as the phase shifter.The demodulated AF signal is amplified by the AF AMP(IC6), and then applied to the linear codec (IC2006). The AFsignal is converted into a digital audio signal by the linearcodec (IC2006), processed by the DSP (IC2007), and thendecoded into an analog audio signal.• WHILE OPERATING IN THE DIGITAL MODEThe 2nd IF signal is filtered by the 2nd IF filters (FI1 and FI2)to eliminate unwanted signals, and applied to the IF AMP(IC5) through the buffer (Q5). The amplified 2nd IF signal ispassed through the ceramic filter (FI3), and then applied tothe A/D converter (IC2002) to be encoded into a digital sig-nal. The digital signal is demodulated by the DSP (IC2007),and then applied to the linear codec (IC2006) to be decodedinto an analog audio signal.The AF signal is applied to the RX AF circuits.• 2ND IF AND DEMODULATOR CIRCUITSLPFANTSWD24-D26,D28,D32RFAMPQ20BPFD21 D37BPFT2 T1D31BPFT1From the TX circuitsTo the 1st IF circuitsANTLOSWD5,D6D17,D18D13,D14Q19BPFXTALFI4IFAMPQ14BUFFQ8BUFFQ10ATTIF SWIF SWRX VCOTo the TX circuitsFrom the RF circuitse 2nd IF circuits46.35MHzBPFXTALFI546.35MHz 1st IF mixerX3Q4BPFX2TCXOW/NSWD2,D3X1DiscriminatorBPFCERAMICFI2BPFCERAMICFI1W/NSWD8,D9D/AconverterIF IC From the 1st IFcircuits(Analog path)To the RX AF circuit(Digitalpath)IC415.3MHz45.9MHzDISCSQINIC57450kHz450kHzNOISCERAMICBPFFI3DIFBUFFIC5BUFFQ5AMPIC6A/DIC2002DSPLINEARDISCCODECIC2006IC2007DAFO