Kenwood TS-950S Service Manual

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13-9505/SDCIRCUIT DESCRIPTION3) AMThe bandwidth of the modulating signal from the A/D converter is limited by the low-pass filter, given aspecific offset, and is multiplied by the carrier to pro-duce the modulated AM signal.The low-pass filter is an Finite Impulse Response(FIR) digital filter of the 84th degree, which providesgood frequency characteristics and flat group delaycharacteristics. Additionally, since linear modulationprocessing is performed with a digital multiplier, modu-jated waves with little distortion are obtained up tolevels of 100% modulation.24.594KH2 49. 18SkHz+he+Ler7Sin wetLPFdata ROMFig. 53 AM modulation block diagram4) FSKThe mark and space frequencies are generated di-rectly by digital signal processing according to thefrequency shift data from the RTTY line (DDS).The DSP detects the leading and trailing edges ofthe shift signal. The OSP reads the data from theinternal square cosine characteristics ROM and ob-tains the shaped FSK as the DDS frequency data. Themark frequency does not greatly interfere with thespace frequency because of the square cosine wave-form shaping characteristics, as in the CW mode, andbecause FSK modulation is performed with continuousphases. There is, therefore, less character change orbit errors when demodulating the signal.Strictly speaking, the actual shift width is not170,200, 425, and 850, but 171.129, 201.152, 426.322,and 849.642 due to the frequency steps that can begenerated by the DSP. This should not prove to be ofany practical concern.49. 189KHbt i salEdgeRTTY detection/ Shift data(Shift) waveform settingshapingShift data5) AF-SLOPE TUNEinterlocked with the SSB-SLOPE TUNE control ofthe main unit, this functions as the AF-SLOPE TUNEfor the audio band.12.297 KHZFig. 54 FSK block diagrama 49. 189K Hz -|be 49.199KH2 otinterpolationfilter+|| Through |ipalpth |ce fod |ae ce 7 oeYi) ’HPF cut-off LPF cut-offFig. 55 AF SLOPE TUNE biock diagram61