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#1
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An SDR or DDS question?
Presumably those SDR rigs which do not work on the IF but
directly from antennae must have, separately from the DSP processor, some semblance of a DDS generator (but without the final DAC) to act as the equivalent of the VFO, for I cannot perceive that a fractional-Hz tuning rate could be achieved with machine code running in the DSP processor? |
#2
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An SDR or DDS question?
In message , gareth
writes Presumably those SDR rigs which do not work on the IF but directly from antennae must have, separately from the DSP processor, some semblance of a DDS generator (but without the final DAC) to act as the equivalent of the VFO, for I cannot perceive that a fractional-Hz tuning rate could be achieved with machine code running in the DSP processor? I'm not an expert ,but I think what you're asking is " how is the local oscillator generated" in a direct conversion SDR and "what determines its resolution" There is an example here, :- http://www.radioelementi.it/public/saqrx.pdf The "c" source code is here,which I can just about understand ( My software background is FORTRAN and Matlab) :- https://sites.google.com/site/sm6lkm/saqrx/ Softies shouldn't have a problem with it although I was able to mess about with it and recompile it successfully In this case the spectrum is dc to 22050Hz in 512 steps. It's not the LO precision ( it's floating point in this one) that limits it but the size of the FFT , the sample rate and thus the record length, that sets the minimum FFT bin width . This one tunes in lumps of about 43Hz HTH Brian -- Brian Howie |
#3
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An SDR or DDS question?
"Brian Howie" wrote in message
... In message , gareth writes Presumably those SDR rigs which do not work on the IF but directly from antennae must have, separately from the DSP processor, some semblance of a DDS generator (but without the final DAC) to act as the equivalent of the VFO, for I cannot perceive that a fractional-Hz tuning rate could be achieved with machine code running in the DSP processor? I'm not an expert ,but I think what you're asking is " how is the local oscillator generated" in a direct conversion SDR and "what determines its resolution" There is an example here, :- http://www.radioelementi.it/public/saqrx.pdf The "c" source code is here,which I can just about understand ( My software background is FORTRAN and Matlab) :- https://sites.google.com/site/sm6lkm/saqrx/ Softies shouldn't have a problem with it although I was able to mess about with it and recompile it successfully In this case the spectrum is dc to 22050Hz in 512 steps. It's not the LO precision ( it's floating point in this one) that limits it but the size of the FFT , the sample rate and thus the record length, that sets the minimum FFT bin width . This one tunes in lumps of about 43Hz Thank-you Brian, but what you have URLed is already at baseband, being VLF. When moving from FORTRAN to C, the major difference (apart from the nitty-gritty of statement syntax) is that in FORTRAN, variables are always passed by reference (at least in FORTRAN '66 which I did 47 years ago) and in C you have the choice of passing by value or by reference. |
#4
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An SDR or DDS question?
On Sat, 6 Feb 2016, gareth wrote:
"Brian Howie" wrote in message ... In message , gareth writes Presumably those SDR rigs which do not work on the IF but directly from antennae must have, separately from the DSP processor, some semblance of a DDS generator (but without the final DAC) to act as the equivalent of the VFO, for I cannot perceive that a fractional-Hz tuning rate could be achieved with machine code running in the DSP processor? I'm not an expert ,but I think what you're asking is " how is the local oscillator generated" in a direct conversion SDR and "what determines its resolution" There is an example here, :- http://www.radioelementi.it/public/saqrx.pdf The "c" source code is here,which I can just about understand ( My software background is FORTRAN and Matlab) :- https://sites.google.com/site/sm6lkm/saqrx/ Softies shouldn't have a problem with it although I was able to mess about with it and recompile it successfully In this case the spectrum is dc to 22050Hz in 512 steps. It's not the LO precision ( it's floating point in this one) that limits it but the size of the FFT , the sample rate and thus the record length, that sets the minimum FFT bin width . This one tunes in lumps of about 43Hz Thank-you Brian, but what you have URLed is already at baseband, being VLF. I thought that was the norm, not much doing A/D at signal frequency. Initially, it was too fast for the hardware to handle, but there are probably some good reasons still to downconvert. Michael When moving from FORTRAN to C, the major difference (apart from the nitty-gritty of statement syntax) is that in FORTRAN, variables are always passed by reference (at least in FORTRAN '66 which I did 47 years ago) and in C you have the choice of passing by value or by reference. |
#5
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An SDR or DDS question?
"Brian Morrison" wrote in message
... On Sat, 6 Feb 2016 14:10:10 -0000 "gareth" wrote: Presumably those SDR rigs which do not work on the IF but directly from antennae must have, separately from the DSP processor, some semblance of a DDS generator (but without the final DAC) to act as the equivalent of the VFO, for I cannot perceive that a fractional-Hz tuning rate could be achieved with machine code running in the DSP processor? If you have a look here http://sdrplay.com/windows.html Gareth you will find some links to 4 or 5 pdf documents covering various aspects of the SDRplay RSP which is based on the Mirics MSI3101 chipset (comprising the MSI001 and MSI2500 chips). It provides a maximum down-conversion bandwidth of 8MHz at RF frequencies of up to 2GHz and can interface with various DSP demodulator back ends such as HDSDR or SDR-Console together with the necesssary device drivers to configure the chips and set up the data paths. That ought to help you see the topology of the receiver and you can work out some of the various clock and VCO frequencies used for the different RF bands covered by the switched front-end RF filters. OK, by following onto ... http://www.mirics.com/Mirics_MSi001_002.pdf I see fractional divide-by-N and a PLL combination integrated onto the chip, which is along the lines that I suspected, ie, a somewhat conventional approach outside of the DSP. |
#6
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An SDR or DDS question?
In message , gareth
writes "Brian Howie" wrote in message ... In message , gareth writes Presumably those SDR rigs which do not work on the IF but directly from antennae must have, separately from the DSP processor, some semblance of a DDS generator (but without the final DAC) to act as the equivalent of the VFO, for I cannot perceive that a fractional-Hz tuning rate could be achieved with machine code running in the DSP processor? I'm not an expert ,but I think what you're asking is " how is the local oscillator generated" in a direct conversion SDR and "what determines its resolution" There is an example here, :- http://www.radioelementi.it/public/saqrx.pdf The "c" source code is here,which I can just about understand ( My software background is FORTRAN and Matlab) :- https://sites.google.com/site/sm6lkm/saqrx/ Softies shouldn't have a problem with it although I was able to mess about with it and recompile it successfully In this case the spectrum is dc to 22050Hz in 512 steps. It's not the LO precision ( it's floating point in this one) that limits it but the size of the FFT , the sample rate and thus the record length, that sets the minimum FFT bin width . This one tunes in lumps of about 43Hz Thank-you Brian, but what you have URLed is already at baseband, being VLF. Well not quite. Base-band in this case is the audio pass -band which is down-converted from the RF ( if you can call it that) at up to 20KHz by the software local oscillator. You can do it mechanically as well. Http://www.wireless.org.uk/mechrx.htm Brian -- Brian Howie |
#7
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An SDR or DDS question?
In message ple.org,
Michael Black writes On Sat, 6 Feb 2016, gareth wrote: "Brian Howie" wrote in message ... In message , gareth writes Presumably those SDR rigs which do not work on the IF but directly from antennae must have, separately from the DSP processor, some semblance of a DDS generator (but without the final DAC) to act as the equivalent of the VFO, for I cannot perceive that a fractional-Hz tuning rate could be achieved with machine code running in the DSP processor? I'm not an expert ,but I think what you're asking is " how is the local oscillator generated" in a direct conversion SDR and "what determines its resolution" There is an example here, :- http://www.radioelementi.it/public/saqrx.pdf The "c" source code is here,which I can just about understand ( My software background is FORTRAN and Matlab) :- https://sites.google.com/site/sm6lkm/saqrx/ Softies shouldn't have a problem with it although I was able to mess about with it and recompile it successfully In this case the spectrum is dc to 22050Hz in 512 steps. It's not the LO precision ( it's floating point in this one) that limits it but the size of the FFT , the sample rate and thus the record length, that sets the minimum FFT bin width . This one tunes in lumps of about 43Hz Thank-you Brian, but what you have URLed is already at baseband, being VLF. I thought that was the norm, not much doing A/D at signal frequency. Initially, it was too fast for the hardware to handle, but there are probably some good reasons still to downconvert. Michael Correct , but Gareth asked about the software equivalent of a DDS frequency synthesiser or VFO. Brian -- Brian Howie |
#8
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An SDR or DDS question?
On 2/6/2016 1:07 PM, gareth wrote:
"Brian Howie" wrote in message ... In message , gareth writes Presumably those SDR rigs which do not work on the IF but directly from antennae must have, separately from the DSP processor, some semblance of a DDS generator (but without the final DAC) to act as the equivalent of the VFO, for I cannot perceive that a fractional-Hz tuning rate could be achieved with machine code running in the DSP processor? I'm not an expert ,but I think what you're asking is " how is the local oscillator generated" in a direct conversion SDR and "what determines its resolution" There is an example here, :- http://www.radioelementi.it/public/saqrx.pdf The "c" source code is here,which I can just about understand ( My software background is FORTRAN and Matlab) :- https://sites.google.com/site/sm6lkm/saqrx/ Softies shouldn't have a problem with it although I was able to mess about with it and recompile it successfully In this case the spectrum is dc to 22050Hz in 512 steps. It's not the LO precision ( it's floating point in this one) that limits it but the size of the FFT , the sample rate and thus the record length, that sets the minimum FFT bin width . This one tunes in lumps of about 43Hz Thank-you Brian, but what you have URLed is already at baseband, being VLF. When moving from FORTRAN to C, the major difference (apart from the nitty-gritty of statement syntax) is that in FORTRAN, variables are always passed by reference (at least in FORTRAN '66 which I did 47 years ago) and in C you have the choice of passing by value or by reference. Wrong on both counts. Fortran and C are both pass by value. Neither defines pass by reference in their respective standards although some recent Fortran compilers have an extension to pass by reference). -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
#9
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An SDR or DDS question?
In rec.radio.amateur.equipment Jerry Stuckle wrote:
On 2/6/2016 1:07 PM, gareth wrote: "Brian Howie" wrote in message ... In message , gareth writes Presumably those SDR rigs which do not work on the IF but directly from antennae must have, separately from the DSP processor, some semblance of a DDS generator (but without the final DAC) to act as the equivalent of the VFO, for I cannot perceive that a fractional-Hz tuning rate could be achieved with machine code running in the DSP processor? I'm not an expert ,but I think what you're asking is " how is the local oscillator generated" in a direct conversion SDR and "what determines its resolution" There is an example here, :- http://www.radioelementi.it/public/saqrx.pdf The "c" source code is here,which I can just about understand ( My software background is FORTRAN and Matlab) :- https://sites.google.com/site/sm6lkm/saqrx/ Softies shouldn't have a problem with it although I was able to mess about with it and recompile it successfully In this case the spectrum is dc to 22050Hz in 512 steps. It's not the LO precision ( it's floating point in this one) that limits it but the size of the FFT , the sample rate and thus the record length, that sets the minimum FFT bin width . This one tunes in lumps of about 43Hz Thank-you Brian, but what you have URLed is already at baseband, being VLF. When moving from FORTRAN to C, the major difference (apart from the nitty-gritty of statement syntax) is that in FORTRAN, variables are always passed by reference (at least in FORTRAN '66 which I did 47 years ago) and in C you have the choice of passing by value or by reference. Wrong on both counts. Fortran and C are both pass by value. Neither defines pass by reference in their respective standards although some recent Fortran compilers have an extension to pass by reference). In C, if an arguement to a function is defined as a pointer, then the local values are references to the storage locations of the original arguments passed in and changes will change the original value. This is called pass by reference. In C, if an arguement to a function is not defined as a pointer, then the local value is a copy of the original value which will not be changed. This is called pass by value. -- Jim Pennino |
#10
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An SDR or DDS question?
On Sat, 6 Feb 2016, Brian Howie wrote:
In message ple.org, Michael Black writes On Sat, 6 Feb 2016, gareth wrote: "Brian Howie" wrote in message ... In message , gareth writes Presumably those SDR rigs which do not work on the IF but directly from antennae must have, separately from the DSP processor, some semblance of a DDS generator (but without the final DAC) to act as the equivalent of the VFO, for I cannot perceive that a fractional-Hz tuning rate could be achieved with machine code running in the DSP processor? I'm not an expert ,but I think what you're asking is " how is the local oscillator generated" in a direct conversion SDR and "what determines its resolution" There is an example here, :- http://www.radioelementi.it/public/saqrx.pdf The "c" source code is here,which I can just about understand ( My software background is FORTRAN and Matlab) :- https://sites.google.com/site/sm6lkm/saqrx/ Softies shouldn't have a problem with it although I was able to mess about with it and recompile it successfully In this case the spectrum is dc to 22050Hz in 512 steps. It's not the LO precision ( it's floating point in this one) that limits it but the size of the FFT , the sample rate and thus the record length, that sets the minimum FFT bin width . This one tunes in lumps of about 43Hz Thank-you Brian, but what you have URLed is already at baseband, being VLF. I thought that was the norm, not much doing A/D at signal frequency. Initially, it was too fast for the hardware to handle, but there are probably some good reasons still to downconvert. Michael Correct , but Gareth asked about the software equivalent of a DDS frequency synthesiser or VFO. The "directly from antenna" in his post threw me. If there's a heterodyne conversion, which is what he was asking I see now, then there has to some sort of local oscillator. The way I read it was that he was asking how to tune something that directly converted to digital. Sorry. Michael |
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