Kenwood TS-950S Service Manual

Also see for TS-950S Digital: Instruction manual Instruction manual Instruction manual Instruction manual Service manual

TS-9505/SDCIRCUIT DESCRIPTIONThe modulated waveform that has been digitallyprocessed and supplied by the D/A converter IC17(PCMS56P) has a modulation spectrum rich in odd orderharmonics that are 1/4 the sampling frequency (1/4, 3/4, 5/4, etc). A frequency of 36.891 kHz, which is 3/4the sampling frequency, is taken by the bandpass filterand is mixed with a frequency of 491.891 kHz by IC21(MC74HC4053F) in order to generate a signal of 455kHz. The unwanted adjacent components of this sig-nal are eliminated by ceramic filter CF1, amplified byQ2 (2SC2412k), and output from buffer amplifier Q4(2SC2412K). In the CW and AM modes, the outputlevel is reduced in order to match the level of the mainunit.Figure 39 shows the frequency spectrum of theMIC input, A/D input, D/A output, 36.891-kHz band-pass filter output, and 455-kHz output.Item RatingNominal center frequency (fo) | 455kHz3dB bandwidth +5.0kHz or more (from 455kHz)6dB bandwidth +7.5kHz or more (from 455kHz)70dB bandwidth +12.5kHz or less (from 455kHz)Guaranteed attenuation 80dB or more at 455+ 100kHz50dB or more at 0.1 to IMHzRipple 3dB or less at 4554+5.0kHz6dB or less at 45547, 5kHzInsertion loss 6dB or lessVoltage capacity (between pins) 50V DC (1 minute)Input and output impedance | 1.5kQTable 11 Ceramic filter (L72-0375-05) (DSP unit CF1)AmplitudePNseeLahnMIC signal0D/A output + ; 7 :f Af0 1/48 4 og, 3/4 ts fs 5/4fs36.891-kHzBPF output ‘ | eet0) 1/2fs 3/4fs fsDSP-10 output : ESfs: Sampling frequency53 Fig. 39 Frequency spectrum in SSB modet455kHz2) AF-SLOPE TUNEThe audio signal supplied from the input bufferamplifier (C5/1 (NJM4558M), like the MIC signal, ispassed through the limiting amplifier in order to limitthe level of the signal applied to the A/D converter.The signal then passes through the low-pass filter.This signal is then converted into a Pulse Code Modu-lated waveform by the sample and hold amplifier cir-cuit before it is applied to the A/D converter. Thesignal is converted to a digital signal with a samplingfrequency of 49.189 kHz by the A/D converter. Furtherprocessing of the signal is accomplished in the Digitalunit. This signal is then applied to the D/A ConverterIC17 where the now processed audio is obtained.The PCM signal from the D/A converter is passedthrough low-pass filter 1C20 (NJM4558M) to eliminateundesirable harmonics and smooth the signal. Its levelis equalized with the input level, switched by analogswitch 1C3 (MC74HC4053F), and applied to the AFOUT terminal.Figure 40 shows the frequency characteristics ofthe audio input, low-pass filter output, A/D input, D/Aoutput, and resulting audio output.~Audioinput—__—{_—_$_$$$_FoldeliminationfilterT CeA/D inputT1/2fsAudio output44D/A output a4T1/2fs fsFig. 40 Frequency characteristics ofAF SLOPE TUNEFOR SERVICE MANUALSCONTACT:MAURITRON TECHNICAL SERVICESwww, mauritron.co.ukTEL: 01844 - 351694FAX: 01844 - 352554