Hi Friends,
I am going to make a Hybrid 256x oversampled FM Stereo Encoder. I know only basic idea of FM stereo multiplexing (like 2x, 8x oversampled circuit) also I read in an article circuits like DAC, Sine LUT ROM etc can be used for higher sampled MPX system. But I don't know how to implement the circuit and where to begin.Please help me. I expect good design ideas and circuits. Sorry for my poor English. Have a nice day
I am going to make a Hybrid 256x oversampled FM Stereo Encoder. I know only basic idea of FM stereo multiplexing (like 2x, 8x oversampled circuit) also I read in an article circuits like DAC, Sine LUT ROM etc can be used for higher sampled MPX system. But I don't know how to implement the circuit and where to begin.Please help me. I expect good design ideas and circuits. Sorry for my poor English. Have a nice day
Yes, I know the analog design of fm stereo encoder and I implemented successfuly that by using MC1496 DSBSC ic. But now I would like to use the hybrid circuit part that is Time Division Multiplexing method rather than the Frequency Division Multiplexing.( I know complexity of TDM method is high compaired to FDM method but I would like to combine the advantages of digital method also for the circuit ). Thank you
I am afraid the link does not work on my PC.
The idea of time division mpx is new to me. So could you please explain?
Is the signal you are generating compatible to FM stereo receivers as we know them?
I.e does the signal consist of the three frequency bands: baseband (L+R) and both sidebands of 38kHz (L-R) and (R-L). + the pilot of course. That would be frequency division mpx imho.
The idea of time division mpx is new to me. So could you please explain?
Is the signal you are generating compatible to FM stereo receivers as we know them?
I.e does the signal consist of the three frequency bands: baseband (L+R) and both sidebands of 38kHz (L-R) and (R-L). + the pilot of course. That would be frequency division mpx imho.
In a simple TDM MPX (2x oversampled) method we can use an SPDT electronic switch like CD4053 (analog ES) ic. Imagine left channel is applied to N/C arm of ES and right channel is applied to N/O arm of ES the common arm is applied to a wide band signal summing amplifier(Op amp as an adder) here 19kHz is also applied to get a composite MPX signal at output of said signal summer. Later is applied to a wide band mono FM transmitter. A 38kHz square wave derived from 19kHz pilot (phase locked) is applied to the control input of ES. The out put of ES is an alternate series of left and right channel with duty cycle 50% and repeating period equal to 1/38kHz.
On the other hand in FDM MPX method , first we have to derive L+R and L-R by matrixing. The L+R and pilot is applied to a signal summing amplifier, the output of later is applied to a wide band mono FM transmitter. The L-R signal is DSBSC modulated(multiply) with 38kHz square (or sine) wave. The DSBSC wave an alternate series of L-R and R-L with 50% duty cycle and 1/38kHz period. This DSBSC wave is algebraically added to the L+R signal in the said summer where L-R overlap with L+R for +ve half cycles of 38kHz subcarrier results 2L and R-L overlap with L+R for the -ve half cycles of 38kHz subcarrier results 2R. Thus the output of summing amplifier is an alternate series of 2L and 2R with period 1/38kHz and 10% pilot is also present.
Thus the output of FDM MPX method is nearly equal to TDM MPX method except TDM MPX method generates lot of harmonics of switching frequency. This can be overcome by using oversampling methods and filtering.
One more thing is that when switching alternatively from one channel to other the average value of output contains sum (L+R) of input channel. the peak differences of inputs (L-R) re-creates troughs and crests of the suppressed switching wave (here 38kHz) or DSBSC modulated L-R signal. Again we can say that TDM MPX method is equivalent to FDM MPX method.
For more information please see this website RBS FM 92.60 MHz the Best Radio Station in Tulungagung - Digital Stereo Encoder Simulation
Thanking you
On the other hand in FDM MPX method , first we have to derive L+R and L-R by matrixing. The L+R and pilot is applied to a signal summing amplifier, the output of later is applied to a wide band mono FM transmitter. The L-R signal is DSBSC modulated(multiply) with 38kHz square (or sine) wave. The DSBSC wave an alternate series of L-R and R-L with 50% duty cycle and 1/38kHz period. This DSBSC wave is algebraically added to the L+R signal in the said summer where L-R overlap with L+R for +ve half cycles of 38kHz subcarrier results 2L and R-L overlap with L+R for the -ve half cycles of 38kHz subcarrier results 2R. Thus the output of summing amplifier is an alternate series of 2L and 2R with period 1/38kHz and 10% pilot is also present.
Thus the output of FDM MPX method is nearly equal to TDM MPX method except TDM MPX method generates lot of harmonics of switching frequency. This can be overcome by using oversampling methods and filtering.
One more thing is that when switching alternatively from one channel to other the average value of output contains sum (L+R) of input channel. the peak differences of inputs (L-R) re-creates troughs and crests of the suppressed switching wave (here 38kHz) or DSBSC modulated L-R signal. Again we can say that TDM MPX method is equivalent to FDM MPX method.
For more information please see this website RBS FM 92.60 MHz the Best Radio Station in Tulungagung - Digital Stereo Encoder Simulation
Thanking you
Plz see this linkPLL FM STEREO for DDS FM Stereo coder and different methods to generate 19kHz and 38kHz sine wave.
Hi Friends,
I am going to make a Hybrid 256x oversampled FM Stereo Encoder. I know only basic idea of FM stereo multiplexing (like 2x, 8x oversampled circuit) also I read in an article circuits like DAC, Sine LUT ROM etc can be used for higher sampled MPX system. But I don't know how to implement the circuit and where to begin.Please help me. I expect good design ideas and circuits. Sorry for my poor English. Have a nice day
Hi Syamkumar, this is a 1KHz tone in a 16x oversampling coder i am working:
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Hello folks,
Adding to an old thread instead of making a new one.
I want to build a FM stereo encoder for my RF sig generators, HP 8656B and HP 11715A.
Of course one option is to spend more money and buy yet another RF SG like a ST1000A or Panasonic unit but I want to take the cheaper route and build my own just for the fun of it.
I have copied this design.
www.inase.org/library/2014/santorini/bypaper/ROBCIRC/ROBCIRC-29.pdf
How to build an fm-stereo generator.
I have verified that the hex file is good with my MPLab s/w and ICD3 programmer. At this time I did not buy the source code.
Of course I could have paid for the layout files, but I am not sure if they are proper gerber/cnc data or just pdf of the layers. I do not want to pay and find out it is a pdf and I have to etch my own pcb, which is a PITA. Also the size would result in a much more expensive pcb, so did it myself will reduce my costs a fair bit.
So far I have taken this design and done up a small layout(100x100mm) and plan to get it made at pcbway for $10 for 10 deal, which is hard to beat. Since I did the design in smt, I have a fair bit of pcb area left for other circuitry.
I will add an additional composite driver,based on user OS pitchfork headphone amp that I have simulated using ltspice. It offers the performance that I need, so it can drive the 50 ohm input Z of the low THD 11715A AM/FM test source.
I was wondering if anyone has suggestions to add more features?
1) I still need to add the regulators on board, but they do not take up much room.
One thing I should probably add is a couple of low THD oscillators for the left/right channels, instead of having to use external oscillators. I could copy the ST1000A oscillators but their maybe better ckts to use, any suggestions?
I have attached the schematics and pcb placement so far.
Thanks
Rick
Adding to an old thread instead of making a new one.
I want to build a FM stereo encoder for my RF sig generators, HP 8656B and HP 11715A.
Of course one option is to spend more money and buy yet another RF SG like a ST1000A or Panasonic unit but I want to take the cheaper route and build my own just for the fun of it.
I have copied this design.
www.inase.org/library/2014/santorini/bypaper/ROBCIRC/ROBCIRC-29.pdf
How to build an fm-stereo generator.
I have verified that the hex file is good with my MPLab s/w and ICD3 programmer. At this time I did not buy the source code.
Of course I could have paid for the layout files, but I am not sure if they are proper gerber/cnc data or just pdf of the layers. I do not want to pay and find out it is a pdf and I have to etch my own pcb, which is a PITA. Also the size would result in a much more expensive pcb, so did it myself will reduce my costs a fair bit.
So far I have taken this design and done up a small layout(100x100mm) and plan to get it made at pcbway for $10 for 10 deal, which is hard to beat. Since I did the design in smt, I have a fair bit of pcb area left for other circuitry.
I will add an additional composite driver,based on user OS pitchfork headphone amp that I have simulated using ltspice. It offers the performance that I need, so it can drive the 50 ohm input Z of the low THD 11715A AM/FM test source.
I was wondering if anyone has suggestions to add more features?
1) I still need to add the regulators on board, but they do not take up much room.
One thing I should probably add is a couple of low THD oscillators for the left/right channels, instead of having to use external oscillators. I could copy the ST1000A oscillators but their maybe better ckts to use, any suggestions?
I have attached the schematics and pcb placement so far.
Thanks
Rick
Fm stereo encoder
For those looking at a 256khz oversampled stereo encoder, see the project at radiospurs.uk web site. The design presented is dated around the year 2000 so some of the components used are end of life. Feel free to use the same design principles with newer vesions. I would suggest the Analog Sharc series 5 or the slightly older series 4 as a replacement for the series 2 given
For those looking at a 256khz oversampled stereo encoder, see the project at radiospurs.uk web site. The design presented is dated around the year 2000 so some of the components used are end of life. Feel free to use the same design principles with newer vesions. I would suggest the Analog Sharc series 5 or the slightly older series 4 as a replacement for the series 2 given
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