Icom IC-F3001 Service Manual

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Contents

Icom IC-F3001 Service Manual Manual pdf 25 page image

4 - 1SECTION 4. CIRCUIT DESCRIPTION• RF CIRCUITS• 1ST IF CIRCUITS• 2ND IF CIRCUITS4-1 RECEIVER CIRCUITSRF CIRCUITSThe RX signal from the antenna is passed through the LPFand antenna SW, then filtered by the 2-staged tuned BPFto eliminate unwanted out-of-band signal. The filtered RXsignal is amplified by the RF AMP, and filtered by another2-staged tuned BPF to obtain a good image response, thenapplied to the 1st IF circuits.The tuned BPFs are tuned to the RX frequency by applyingadequate tuning voltages; “T1” and “T2” to the variablecapacitors.1ST IF CIRCUITSThe RX signal from the RF circuits is applied to the 1st IFmixer and mixed with the 1st LO signal from the RX VCO,resulting in the 46.35 MHz 1st IF signal. The 1st IF signal isfiltered by the crystal filter, amplified by the 1st IF AMP, thenapplied to the 2nd IF circuits.2ND IF CIRCUITS AND DEMODULATORThe signal from the 1st IF circuits is applied to the IFdemodulator IC which contains the 2nd IF mixer, 2nd IFAMP, FM detector, etc. 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 IFsignal.The 2nd LO signal is generated by tripling the 15.3 MHzreference frequency signal oscillated by the referencefrequency oscillator (TCXO).The converted 2nd IF signal is filtered by the crystal filter/filters to eliminate unwanted signal, and amplified by the2nd IF AMP, then demodulated by the detector circuit whichemploys a discriminator as the phase shifter.The demodulated AF signal is applied to the RX AF circuits.LPFANTSWD1,D22RFAMPQ22BPFD28 D24,D26BPFT2 T1From the TX circuitsTo the 1st IF circuitsANTLOSWD5,D6Q23BPFXTALFI1IFAMPQ24BUFFQ8BUFFQ10ATTRX VCOTo the TX circuitsFrom the RF circuitsTo the 2nd IF&demodulator circuits 46.35MHz1st IF mixerPLLICIC2MB15A02X3Q26BPFX2TCXOW/NSW Q27,D33,D34X1DiscriminatorBPFCERAMICFI2BPFCERAMICFI3W/NSWD31,D32D/AconverterIF IC From the 1st IFcircuitsTo the RX AF circuitsIC3:NJM259115.3MHz45.9MHzDISCSQINIC57R2A20178450kHz450kHzNWCNOIS