CTC30 & Katruud 8x are using same design for 38KHz DSB generator.
DSB/Pilot generator is similar with unknown Kathrein stereo exciter.
Stereo coder module (hybrid?) used inside of professional RVR SDC100 stereo/RDS coder or Elettronika PLL-CS FM exciter. Switching performed with FETs BSR56 (BF245C) and 4015 counters.
Simulation of R&S professional stereo coder 14x oversampled. Rohde & Schwarz NU002-B exciter, similar 14X Phatom FM stereo coder MPX 38KHz generator use 8 precision resistors to obtain 16x oversampling.ĥ. Audio 15KHz elliptical LPF is same with Inovonics 705/715/718. PM1000 exciter is very interesting and I intend to build entire stereo coder type "9506". Resistors R13 and R15 are used to adjust 19KHz symmetry / null crossover.
Pilot tone and MPX are cleand by S&H at 608KHz.
Pilot tone 19KHz is composed from 16 digital steps, inverted and after combined in order to result 32 steps full "sine". DB ELETTRONICA TELECOMUNICAZIONI PM1000 SERIES Center sampling eliminates integration of switching noise that is concurrent with leading/trailing edges of the waveform steps.Ĥ. This charge 330pF capacitor to the sample voltage value, which is held by operational buffer until next center sample is taken. Switches SW1,2 are turned ON for one-half of one clock cycle at the center of each stepped pilot waveform sample. In the next image, both DSB and Pilot signals are filtered at 608KHz. After S&H circuit, a simple LC low pass filter is required. Digital noise generated during switching resistor taps can be eliminated. Sometimes, digital synthesis of 38KHz subcarrier and 19KHz pilot is succeeded by "Sample & Hold" filtering. Correct position of zero line is with one step above, at 15 and 31 level.
Update : In the next image, Zero Center is wrong. Update : David III Clone was tested with very good results! Please check my page: DAVID III Stereo Coder. If you like to build this professional Stereo Generator, i drew the PCB but wasn't yet tested. Digital block built up with 4028/4029/4051 CMOS integrated circuits, differential power supply for 40xx circuits (+/-9V ?) and interesting digital logic was implemented. DSB 38KHz multiplexer working in same mode, but with 16x oversampling and 608KHz clock.įor more details read “Inovonics David III 718 FM Stereo Processor/Generator”, can be downloaded from Internet. Entire 608KHz pulse is necessary for one sample step. Now one example of sampling technique using 608KHz clock, but in this case is generated sinusoidal 19KHz pilot tone.ģ2 samplings per period are performed for pilot tone. Input operational amplifiers were not used during simulation. Usually 4067 is supplied with +/-7,5V.Ĭlock signal necessary for 16X at 38KHz is 304KHz. This version is frequently posted over Internet. During simulation, Left and Right audio channels were connected to +5V/-5V.īelow, other 16X oversampled DSB generator with 4067. Katruud (or similar schematic) 8X stereo coderĨx oversampling DSB generator with 4051 multiplexer. Not recommended design due to wrong logic sequence, poor supression of carrier.ġ. Update 05.2020 - My old 4067 16x Stereo Coder deleted. I will try to share my experiments about some stereo coders. Unfortunately is difficult to find free information about this subject. Sampling stereo coders are frequently manufactured because offers good S/N ratio, excellent dynamic, stable operation, low harmonic level. Do not use high order filters to clean MPX channel (poor phase linearity). High sampling rate is preferred, harmonic level decrease and MPX signal is easier to be filtered. The most important parameters of digital stereo coders are sampling rate and how many bits are used to generate 38KHz L-R subcarrier. This web page contains information only for educational purpose! Below examples I hope to be useful for the amateur interested to build/experiment a good stereo coder and to learn about oversampling "modulators".