Kenwood TK-3107 Service Manual

Also see for TK-3107: Instruction manual Instruction manual Service manual Service manual

Contents

7TK-31074. Transmitter1) Transmit audioThe modulation signal from the microphone is amplified byIC500 (1/2), passes through a preemphasis circuit, andamplified by the other IC500 (1/2) to perform IDC operation.The signal then passes through a low-pass filter (splatter fiIter)(Q501 and Q502) and cuts 3kHz and higher frequencies. Theresulting signal goes to the VCO through the VCO modulationterminal for direct FM modulation. (See Fig. 6)2) QT/DQT encoderA necessary signal for QT/DQT encoding is generated byIC403 and FM-modulated to the PLL reference signal. Sincethe reference OSC does not modulate the loop characteristicfrequency or higher, modulation is performed at the VCO sideby adjusting the balance. (See Fig. 6)CIRCUIT DESCRIPTIONFig. 6 Transmit audio QT/DQTMUTEVR501MAXDEVBALANCEX1, IC1D5, Q4VCOREFERENCEOSC(TCXO)MICIC500 (1/2)MICAMPIC500 (1/2)IDCQ503SWPREEMPHASISQ501, 502LPF(SPLATTER FILTER)IC403TO QT/DQTVR5003) VCO and RF amplifierThe transmit signal obtained from the VCO buffer amplifierQ100, is amplified by Q101 and Q102. This amplified signal ispassed to the power amplifier, Q105 and Q107, whichconsists of a 2-stage FET amplifier and is capable ofproducing up to 4W of RF power. (See Fig.7)4) 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 are turned on (conductive) in transmitmode and off (isolated) in receive mode.Fig. 7 APC systemAMPQ101,Q102DRIVE AMPQ1055TBQ103, Q104B SWDETIC100APC5TQ109SWQ106SWAPC5TQ108SWRXD102,103ANT SWFINAL AMPQ107ANT SWD101LPFANT5TSWQ110TH1025) 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 (TH102) reaches about 80˚C, theprotection circuit turns on Q110 to protect transmitting finalamplifier (Q107) 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.3) UNLOCK DETECTORIf a pulse signal appears at the LD pin of IC1, an unlockcondition occurs, and the DC voltage obtained from D7, R6,and C1 causes the voltage applied to the UL pin of themicroprocessor to go low. When the microprocessor detectsthis condition, the transmitter is disabled, ignoring the push-to-talk switch input signal. ( See Fig.5)Fig. 5 Unlock detector circuitIC1LDPLL ICD7C1R65CIC403ULMPU