Kenwood FM Transceiver TK-481 Service Manual

Also see for FM Transceiver TK-481: User manual Instruction manual Specifications Instruction manual Service manual

14TK-480/4811. OverviewThis transceiver is an 800/900MHz band EFJ LTR™trunked system compatible FM portable transceiver that canbe programmed to operate on both LTR and conventionalsystems.2. Circuit Configuration by FrequencyThe receiver is a double-conversion superheterodynewith a first intermediate frequency (IF) of 44.85MHz and asecond IF of 455kHz. Incoming signals from the antenna aremixed with the local signal from the PLL to produce the firstIF of 44.85MHz.This is then mixed with the 44.395MHz second local os-cillator output to produce the 455kHz second IF. This is de-tected to give the demodulated signal.The transmit signal frequency is generated by the PLLVCO, and modulated by the signal from the microphone. Itis then amplified and sent to the antenna.Fig. 1 Frequency configurationANTANTSWRFAMP1st MIX MCFCF455kHzIF SYSTEMTK-480TX 806~825MHz851~870MHzRX 851~870MHzTK-481TX 896~902MHz935~941MHzRX 935~941MHzAFAMP44.395MHzPAAMPTXAMPMICAMP44.85MHzTK-480 :806.15~825.15MHzTK-481 :890.15~896.15MHzTK-480806~825MHz851~870MHzTK-481896~902MHz935~941MHzPLLVCOSPMIC3. Receiver System3-1. RF unitAn incoming RF signal from the antenna terminal ispassed through the antenna switch (D7, D9, and D10 areoff) and then the bandpass filter (L11). The signal is ampli-fied by RF amplifier Q9, and passed through the bandpassfilter (L20) to remove the spurious signal again. The result-ing signal is applied to the first mixer (Q6), where it is mixedwith the first local oscillator signal output from the fre-quency synthesizer to produce the first IF (44.85MHz).3-2. IF unitThe first IF signal is passed through a four-pole mono-lithic crystal filter (XF1) to remove a adjacent channel signal.The filtered first IF signal is amplified by the first IF amplifier(Q5) and then applied to the IF system IC (IC9). The IF sys-tem IC provides a second mixer, second local oscillator, lim-iting amplifier, quadrature detector and RSSI (Received Sig-nal Strength Indicator). The second mixer mixes the first IFsignal with the 44.395MHz of second local oscillator output(crystal unit X1) and produces the second IF signal of455kHz.The second IF signal is passed through the ceramic filter(CF1,2) to more remove the adjacent channel signal. Thefiltered second IF signal is amplified by the limiting amplifierand demodulated by the quadrature detector with ceramicdiscriminator (CD1). The demodulated signal is routed tothe audio circuit.Fig. 2 Receiving systemANTSWCF1CF21st localOSC (PLL)2nd localOSCX1L30 D9,D10L11BPFQ9RF AMPL20BPFQ61st MIXXF1MCFQ51st IFIC9MIX,DET,IFIC8 (2/2)AF AMP41IC3 (2/2)AF AMP IC4VOL AF AFQ310SWSSWVC1VC2IC300AF PAINT.SPEXT.SPHPFDE-EMPLPF HPF BEF52 1IC12ANTEXP MUTECIRCUIT DESCRIPTION