Kenwood TK-260G Service Manual

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TK-260G/270G17Fig. 3 Wide/Narrow changeover circuitCIRCUIT DESCRIPTION1. Frequency configurationThe receiver utilizes double conversion. The first IF is 49.95MHz and the second IF is 450 kHz. The first local oscillatorsignal is supplied form the PLL circuit.The PLL circuit in the transmitter generates the necessaryfrequencies. Fig. 1 shows the frequencies.Fig. 1 Frequency configuration1) Front end (RF AMP)The signal coming form the antenna passes through thetransmit/receive switching diode circuit, (D3,D7) passesthrough a BPF(L307), and is amplified by the RF amplifier(Q301).The resulting signal passes through a BPF (L305 and L306)and goes to the mixer. These BPFs are adjusted by variablecapacitors (D302, 303,305). The input voltage to thevariable capacitor is regulated by voltage output from themicroprocessor (IC13)2) First mixerThe signal from the front end is mixed with the first localoscillator signal generated in the PLL circuit by Q19 toproduce a first IF frequency of 49.95 MHz.The resulting signal passes through the XF1 MCF to cutthe adjacent spurious and provide the opitimuncharacteristics, such as adjacent frequency selectivity.Fig. 2 Receiver section2. ReceiverThe frequency configuration of the receiver is shown in Fig. 2.5RQ14Q17 D14R78R75C263C265R80D13Q23R98R108C133 CD1R79W/N "H" : Wide"L" : NarrowMXOIFIMXIIFOAFO IC4FM IF SYSTEMQ225RW/NC107R74C108CF1CF2R81QADR1053) IF Amplifier circuitThe first IF signal is passed through a four-pole monolithiccrystal filter (XF1) to remove the adjacent channel signal.The filtered first IF signal is amplified by the first IF amplifier(Q22) and then applied to the lF system IC (IC4). The IFsystem IC provides a second mixer, second local oscillator,limiting amplifier, quadrature detector and RSSI (ReceivedSignal Strength Indicator). The second mixer mixes thefirst IF signal with the 50.4MHz of the second local oscillatoroutput (TCXO X3) and produces the second IF signal of450kHz.The second IF signal is passed through the ceramic filter(CF1; Wide, CF2 ; Narrow) to remove the adjacent channelsignal. The filtered second IF signal is amplified by thelimiting amplifier and demodulated by the quadraturedetector with the ceramic discriminator (CD1). Thedemodulated signal is routed to the audio circuit.4) Wide/Narrow changeover circuitNarrow and Wide settings can be made for each channelby switching the ceramic filters CF1 (Wide) and CF2(Narrow).The WIDE (high level) and NARROW (low level) data isoutput from IC5 (OUTPUT EXPANDER), pin 4.When a WIDE (high level) data is received, Q14 turn offand Q17 turn on. When a NARROW (low level) data isreceived, Q14 turn on and Q17 turn off. D14 and D13 areswitched to ceramic filters when a high/low level data isreceived.Q23 turns on/off with the Wide/Narrow data and the IC4detector output level is changed to maintain a constantoutput level during wide or narrow signals.ANT TX/RX : 150~174MHzANTSWRFAMPPAAMPTXAMPMCF49.95MHz 50.4MHzCF450kHzIFSYSTEMAFAMP SPRX : 199.95~223.95MHzRX : 399.9~447.9MHzTX : 300~348MHz16.8MHzPLLVCOX3multiply TCXOMICAMP MICTX : 150~174MHz1/2DIVIDERIC4IF, MIX, DETAF AMPIC16 (2/2)1/2DIVDERPLLVCO5DE-EMP MUTEEXPHPF LPF HPF BEFIC14 2 141SPAF AMPIC11AF AMPIC15(2/2) AF VOLANTSWRFAMPQ301L307D303BPFL306,305D302.305BPFANT MIXERQ19TUNEIC301TUNEIF AMPQ22MCFXF1CF1 : WideCF2 : Narrow1st LocalX3 multiplyQ12 TCXO2nd Local