Kenwood TS-950S Service Manual

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TS-950S/SD16CIRCUITDESCRIPTION+ Noise blanker circuits1) NB1NB1 is a noise blanker circuit that has been de-signed for short-duration pulse noise, such as automo-bile ignition noise. The 8.83-MHz IF signal generatedfrom the first main IF of 73.05 MHz is amplified bynoise amplifiers Q40 (2SK210), Q41, Q42, and Q44(2SC2712), passes through buffer amplifier Q45(2$C2712), and is noise-detected by D30 (HSM88AS).This signal is used to switche Q47 (2$C2712}, turns onQ48 (DTA124EK), and switches the main IF signal lineaccording to the incoming noise pulses. The signal isalso used to turn on Q48, which turns on IF unit Q8and Q6 (2SC2712), and switches the sub IF signallineccording to the main noise.The 10.695-MHz IF signal generated from the firstsub IF of 40.055 MHz is amplified by noise amplifiersQ26 (2SK210), Q27, Q28 and Q29 (2SC2714) of the IFunit, passes through buffer amplifier Q31 (28C2714),and is noise-detected by D33_ (HSM88AS). This signalis used to switche O33 (2SC2712), turns on Q34(DTA124EK), switches Q8 and Q6, and switches thesub IF signal tine according to the incoming noise. Thesignal turns on Q34 (DTA124EK), and switches themain IF signal line ccording to the sub noise.When NB1 turns on, a DC voltage is applied to theemitter of Q47 on the AF unit from threshold variableresistor VR12 for the main reciever. A correspondingDC voltage is applied to the emitter of Q33 on the IFunit from threshold variable resistor VR12 for the subreceiver. The effect of the NB circuit can be adjustedby changing these emitter voltages.FOR SERVICEMANUALSCONTACT:MAURITRONTECHNICAL SERVICES.www.mauritron.co.ukTEL:01844-351694FAX:01844-3525542) NB2NB2 is a noise blanker circuit that is used to blanknoise pulses with a comparatively long duration and alarge pulse width, like the Russian woodpecker.For the main receiver NB2 circuit, the noise signalamplified by noise amplifiers Q40, 041, Q42, and Q44of the AF unit is noise-detected by D28 (HSM88AS) ina manner very similar to that of NB1. The threshoidvoltage of emitter Q46 (2SC2712) is varied by VR12.The output from Q46 enters the NB2 module unit(X59-3350-00) and is used to generate the pulse widthand period synchronized with the woodpecker noise.For the sub receiver NB2 circuit, the noise signalamplified by noise amplifiers Q26, Q27, Q28, and Q29is noise-detected by IF unit D382 (HSM88AS) in a man-ner very similar to that of NB1. The threshold voltageof emitter Q32 (2SC2712) is varied by VR12. Theoutput from Q32 enters the NB2 module unit (X59-3350-00) and is used to generate the pulse width andperiod synchronized with the woodpecker noise.TheNB2switchingsignaldetected bythemain!F,andtheNB2switchingsignaldetectedbythesub!Fswitchthemain and sub!FsignallinesinamannerverysimilartoNB1.IC1(TC4011BF),1/4,4/4,and2/4,3/4inthemoduleunitaresettoapulsewidthof40ms. Normally,woodpeckernoisehasapulsewidthof3to 4msandaperiodoffrom80to100ms.Somewoodpeckernoiseshaveaperiodofabout50 ms,althoughthisisrare.Therefore,evenawoodpeckernoisesignal,withalargepulsewidthcanbeblanked byswitchingthenoisein5-msintervals.However,ifanoisesignal,withaperiodof severalmslikeanignitionnoiseisblankedat a5msinterval,thesignalreceive timebe-comeszero.To preventthis,aone-shotmulti-vibratorcomposedofIC?2/4and3/4isprovidedsothatthenextpulseisnotblankedforaperiodof40msaftertheoneshotisissuedfrom1/4and4/4.