Kenwood TK-2202 Service Manual

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TK-2202/220610CIRCUIT DESCRIPTIONFig. 6 Microphone amplifierFig. 7 Drive and final amplifier and APC circuit3) APC CircuitThe APC circuit always monitors the current flowing throughthe RF power amplifier (Q106) and keeps a constant current.The voltage drop at R127, R128 and R129 is caused by thecurrent flowing through the RF power amplifier and thisvoltage is applied to the differential amplifier IC101(1/2).IC101(2/2) compares the output voltage of IC101(1/2) withthe reference voltage from IC405. The output of IC101(2/2)controls the VG of the RF power amplifier, drive amplifierand pre-drive amplifier to make both voltages the same.The change of power high/low is carried out by the changeof the reference voltage.4) Encode Signalling(1) QT/DQTQT,DQT data of the QTTCXO Line is output from pin 28 ofthe CPU. The signal passes through a low-pass CR filterand goes to the TCXO(X1).2) Drive and Final AmplifierThe signal from the T/R switch (D101 is on) is amplified bythe pre-drive (Q102) and the drive amplifier (Q103) to 50mW.The output of the drive amplifier is amplified by the RF poweramplifier (Q106) 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 throughthe harmonic filter (LPF) and antenna switch (D103 andD104) and applied to the antenna terminal.FromT/R SW(D101)DRIVEAMPRFPOWER AMP LPFANTSWD103D104ANTVGVGVDQ103 Q106Pre-DRIVEAMPQ102VDD5TR127R128R129+BIC101(2/2)IC101(1/2)PCTV(IC405)IC301IC405LPFDTMFQTTCXOQTVCOCPUAGCVCOMICX1TCXOLPFLPFAQUAThe QT,DQT data of the QTVCO Line is output from pin 24of 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.(2) DTMFHigh-speed data is output from pin 2 of the CPU. The signalpasses through a low-pass CR filter, and provides a TX andSP out tone, and is then applied to the audio processor(IC301). The signal is mixed with the audio signal and goesto the VCO.TX deviation is adjusted by the CPU.(3) MSK (Fleet Sync)Fleet Sync utilizes 1200bps and 2400bps MSK signal isoutput from pin 6 of IC301. And is routed to the VCO.When encoding MSK, the microphone input signal is muted.5. Power SupplyThere are four 5V power supplies for the microprocessor:5M,5C,5R, and 5T. 5M for microprocessor is always outputwhile the power is on. 5M is always output, but turns off whenthe power is turned off to prevent malfunction of themicroprocessor.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.6. Control CircuitThe control circuit consists of a microprocessor (IC405) andits peripheral circuits. It controls the TX-RX unit. IC405 mainlyperforms the following:(1) Switching between transmission and reception by thePTT signal input.(2) Reading system, group, frequency, and program datafrom the memory circuit.(3) Sending frequency program data to the PLL.(4) Controlling squelch on/off by the DC voltage from thesquelch circuit.(5) Controlling the audio mute circuit by the decode data input.(6) Transmitting tone and encode data.1) Frequency Shift CircuitThe microprocessor (IC405) operates at a clock of7.3728MHz. This oscillator has a circuit that shifts thefrequency by BEAT SHIFT SW (Q407,Q408).A beat sound may be able to be evaded from generation if“Beat Shift” is set to ON when it is generated in the internalspurious transmission modulated sound of a transceiver.