Kenwood TK-260G Service Manual
Also see for TK-260G: Instruction manualService manualInstruction manualService manualService manual
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TK-260G/270G19CIRCUIT DESCRIPTIONFig. 7 Microphone amplifierFig. 8 Drive and final amplifier and APC circuit3) UNLOCK DETECTORIf a pulse signal appears at the LD pin of IC2, an unlockcondition occurs, and the DC voltage obtained form D1,R1, and C6 causes the voltage applied to the microprocessorto go low. When the microprocessor detects this condition,the transmitter is disabled, ignoring the push-to-talk switchinput signal.(See Fig. 6)Fig. 6 Unlock detector circuit4. Transmitter System1) Microphone amplifierThe signal from the microphone passes through the limittercircuit in D23, and through the high-pass filter, the ALCcircuit, the low-pass filter, the high-pass filter, and pre-emphasis/IDC circuit IC14. When encoding DTMF, the muteswitch (Q35) is turned OFF for muting the microphone inputsignal.The signal passes through the D/A converter (IC17) for themaximum deviation adjustment, and goes to the VCXOmodulation input.IC2LDPLL ICD1C6R15CIC13ULCPU12 HPF LPF HPF IDCPREEMPALC COMPSWLIMITD23MICIC14 15 16 18 19Q35MUTEDTMF/2 TONE9 86D/AIC13CPUIC17QT/DQTIC15(2/2)2TOTCXO20TOVCO22VCOAFAMPTCXO(RX Audio)LPF LPFLPFX1DTMF/ 2 TONE3) APC circuitThe APC circuit always monitors the current flowing throughthe RF power amplifier (IC1) and keeps a constant current.The voltage drop at R56, R57 and R58 is caused by thecurrent flowing through the RF power amplifier and thisvoltage is applied to the differential amplifier IC3(1/2).IC3(2/2) compares the output voltage of IC3(1/2) with thereference voltage from IC13, and the output of IC3(2/2)controls the VGG of the RF power amplifier to make bothvoltages the same.The change of power high/low is carried out by the changeof the reference voltage.4) Encode signaling(1) QT/DQT (Low-speed data)QT,DQT data of the TOTCXO Line is output form pin 20 ofthe CPU. The signal passes through a low-pass CR filterand goes to the TCXO(X1).The QT,DQT data of the TOVCO Line is output form pin 22of the CPU. The signal passes through a low pass CR filter,mixes with the audio signal, and goes to the VCO modulationinput. TX deviation is adjusted by the CPU. (See fig.7)(2) DTMF/2 TONE (High-speed data)High-speed data is output from pin 2 of the CPU. The signalpasses through a low-pass CR filter, and provides a TXand SP out tone, and is then applied to the audio processor(IC14). The signal is mixed with the audio signal and goesto the VCO.TX deviation is adjusted by the CPU. (See fig.7)5. Power supplyThere are five 5V power supplies for the microprocessor:5V,5M,5C,5R, and 5T. 5V is always output while the poweris on. 5M is always output, but turns off when the power isturned off to prevent malfunction of the microprocessor.5C is a common 5V and is output when SAVE is not set toOFF.5R is 5V for reception and output during reception.5T is 5V for transmission and output during transmission.2) Drive and Final amplifierThe signal from the T/R switch (D5 is on) is amplified by thedrive amplifier (Q6) to 50mW.The output of the drive amplifier is amplified by the RF poweramplifier (IC1) to 5.0W (1W when the power is low). TheRF power amplifier consists of two MOS FET stages. Theoutput of the RF power amplifier is then passed through theharmonic filter (LPF) and antenna switch (D3 is on) andapplied to the antenna terminal.FromT/R SW(D5)DRIVEAMPRFPOWER AMP LPFANTSWD3ANTVGGQ6 IC1VDDR56R57R58+BIC3(1/2)IC3(2/2)APC(IC13)Downloaded from www.Manualslib.com manuals search engine |
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