Kenwood TK-2107 Service Manual

Also see for TK-2107: Instruction manual Instruction manual Service manual Service manual

Contents

8TK-2107TK-260 :K, K2CIRCUIT DESCRIPTION3) VCO and RF amplifierThe transmit signal obtained from the VCO buffer amplifierQ100, is amplified by Q101. This amplified signal is passed tothe power amplifier, Q102 and Q105, which consists of a 2-stage FET amplifier and is capable of producing up to 5W ofRF power. (See Fig.7)Fig. 7 APC systemAMPQ101DRIVE AMPQ1025TBQ103, Q104B SWDETIC100APC5TQ109SWQ106SWAPC5TQ108SWRXD102,103ANT SWFINAL AMPQ105ANT SWD101LPFANT5TSWQ107TH1004) ANT switch and LPFThe RF amplifier output signal is passed through a low-pass filter network and a transmit/receive switching circuitbefore it is passed to the antenna terminal. The transmit/receive switching circuit is comprised of D101, D102 andD103. D102 and D103 turned on (conductive) in transmitmode and off (isolated) in receive mode.5) APCThe automatic power control (APC) circuit stabilizes thetransmitter output power at a predetermined level by sensingthe drain current of the final amplifier Field Effect Transistor(FET) . The voltage comparator, IC100 (2/2), compares thevoltage obtained from the above drain current with a referencevoltage which is set using the microprocessor. An APCvoltage proportional to the difference between the sensedvoltage and the reference voltage appears at the output ofIC100 (1/2). This output voltage controls the gate of the FETpower amplifier, which keeps the transmitter output powerconstant. The transmitter output power can be varied by themicroprocessor which in turn changes the reference voltageand hence, the output power.6) Terminal protection circuitWhen the thermistor (TH100) reaches about 80˚C, theprotection circuit turns on Q107 to protect transmitting finalamplifier (Q105) from the over heating.5. Power supplyA 5V reference power supply [5M] for the control circuit isderived from an internal battery. This reference is used toprovide a 5V supply in transmit mode [5T], a 5V supply inreceive mode [5R], and a 5V supply common in both modes[5C] based on the control signal sent from the microprocessor.6. Control systemThe IC403 CPU operates at 7.37MHz . This oscillator has acircuit that shifts the frequency according to the EEPROMdata.