Kenwood TK-7102H Service Manual

Also see for TK-7102H: Specification Instruction manual Service manual Service manual

12TK-7102HPLL Frequency SynthesizerThe PLL circuit generates the first local oscillator signalfor reception and the RF signal for transmission. PLLThe frequency step of the PLL circuit is 5 or 6.25kHz. A16.8MHz reference oscillator signal is divided at IC1 by afixed counter to produce the 5 or 6.25kHz reference fre-quency. The voltage controlled oscillator (VCO) output sig-nal is buffer amplified by Q15, then divided in IC1 by a dual-module programmable counter. The divided signal is com-pared in phase with the 5 or 6.25kHz reference signal in thephase comparator in IC1. The output signal from the phasecomparator is filtered through a low-pass filter and passedto the VCO to control the oscillator frequency. (See Fig. 6) VCOThe operating frequency is generated by Q11 in transmitmode and Q10 in receive mode. The oscillator frequency iscontrolled by applying the VCO control voltage, obtainedfrom the phase comparator, to the varactor diodes (D10 andD12 in transmit mode and D9 and D11 in receive mode).The TX/RX pin is set low in receive mode causing Q12 andQ7 to turn Q11 off, and turn Q10 on. The TX/RX pin is sethigh in transmit mode. The outputs from Q10 and Q11 areamplified by Q15 and sent to the RF amplifiers.CIRCUIT DESCRIPTIOND10,12Q11TX VCOQ15BUFFAMPD9,11Q10RX VCOQ7,12T/R SWChargepumpLPFPhasecomparator1/M1/N 5kHz/6.25kHz5kHz/6.25kHzREFOSC16.8MHzPLLDATAIC1 : PLL ICQ3AMPFig. 6 PLL circuitIC6CPUQ29SWQ31SWIC1PLLQ30SWQ33SWLD8RC8C8R 8T8TCPLL lock: LD “H”Fig. 7 Unlock circuit Unlock CircuitDuring reception, the 8RC signal goes high, the 8TC sig-nal goes low, and Q29 turns on. Q31 turns on and a voltageis applied to the collector (8R). During transmission, the8RC signal goes low, the 8TC signal goes high and Q30turns on. Q33 turns on and a voltage is applied to 8T.The CPU in the control unit monitors the PLL (IC1) LDsignal directly. When the PLL is unlocked during transmis-sion, the PLL LD signal goes low. The CPU detects thissignal and makes the 8TC signal low. When the 8TC signalgoes low, no voltage is applied to 8T, and no signal is trans-mitted.