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?

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

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.

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.

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.

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

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

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

==================

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

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