Kenwood TS-950S Service Manual

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TS-950S/SDCIRCUIT DESCRIPTIONAT UNITX53-3240-00|Forward/reflected|,7,IN wave detectioncircuityYdifferencedetectionQ1,02,1C1D1, 2, IC6PREWSw UNIT{A)iy710}Matching circuitMi_M2 vei Vezala | =ale aaja | ed* or fe.McA Seale4 | emses a| xFES @23H 2co co 2 ScageRPREBAO| 2 PRB piaawS OsRal paa Bagre 2-|— AD”?mpZoom SFaaxri 3= &oSmomDIGITAL UNITFig. 14 Auto antenna tuner block diagram1) Auto tuning modeThe transmitter power from the final unit, via thefilter unit, passes through the current/voltage detec-tion transformers L.1 and L2, which make use of atorcidal core. The current and voltage componentsdetected here are rectified by a waveform rectificationcircuit consisting of D4, Q1, and D7, and Q2, and arethen phase-compared by IC1 (SN74S74N). The outputsignals from pins 8 and 9 of IC1 (Q and Q) passhrough the switch by IC2 (TC4066BP), and are appliedto motor drive IC (!C4). Variable capacitor VC1 isturned by motor M1 so that the phase difference ofhe voltage and current components decreases.The voltage and current components detected byL1 and L2 are rectified by germanium diodes (1N60)D1 and D2, and are applied to the voltage comparisoncircuit 1C6 (NJM2903S) as the amplitude componentof the signal. The comparator output passes throughhe switch by IC3 (TC4066BP). Motor M2 is driven byanother motor drive IC, !C5 (BA6109U2), which is usedto turn variable capacitor VC2 in the direction thatdecreases the amplitude difference of the voltage andcurrent components.Therefore, variable capacitor VC1 adjusts the ca-pacitance of the circuit so that the current and voltagephases match. Variable capacitor VC2 adjusts theresistance of the circuit so that the current and voltageamplitude difference decreases.The voltage standing wave ratio (VSWR) is calcu-lated by the digital unit from the forward wave and re-flected wave that is detected by the filter unit. TheVSWR signal, which is 0 to 5 V according to the caicu-lated results, is applied to SWR comparison circuit [C7(b/2). Voltage corresponding to an SWR of 1.2 is ap-plied to the reference voltage pin (pin 7) of this com-parison circuit via the potentiometer. When the actualSWR value is 1.2 or higher, the output pin (pin 8) ofSWR comparison circuit IC7 (b/2) goes high, Q8 turnson, and motor drive voltage control transistor Q7 turnson. Emitter Q4 has approximately 15 V. This voltage isoutput to the digital unit as a signal indicating tuning(high) which lights the AT TUNE LED.The sawtooth wave generated by IC8 (NE555C) isapplied to the inverted input pin of IC7 (a/2). TheVSWR signal that was described previously is appliedto the non-inverted input. Therefore, as the SWR de-creases, the output of IC7 (a/2) changes from a con-tinuous waveform to a continuously changing pulsewith a relatively small duty cycle. This waveform drivesQ5 and Q4 as the motor drive voltage.25