[gareth]

"gareth" wrote in message
...
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?

Thanks to all who responded, even he whose post was riddled throughout
with gratuitous rudeness, and it seems that I was almost correct, but with
the
exception of Brian Morrison's URL where the heterodyning was done
with a PLL and fractional-N synthesizer.

I wonder if Mr.Gratuitously Rude actually read through his URL reference
for therein is a clear reference to the phase accumulator, a necessary
part of the DDS process?

[Bernie[_4_]]

On Sun, 7 Feb 2016 12:40:57 -0000
"gareth" wrote:


I wonder if Mr.Gratuitously Rude actually read through his URL
reference for therein is a clear reference to the phase accumulator,
a necessary part of the DDS process?

When did you drop the "I never follow URLs" rule, Gareth?

[Jerry Stuckle]

On 2/6/2016 4:07 PM, wrote:
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 the argument to a function is defined as a pointer, then a copy
of the pointer is passed. Of course, that copy still points at the same
place as the original, but it is still a copy.

It is not called pass by reference. The pointer must still be
dereference to get to the value.

C++ does have a pass by reference, but not C.

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.


Both are pass by value. The only difference is if you are passing the
variable or a pointer by value.

Once again you argue from a position of ignorance.

--
==================
Remove the "x" from my email address
Jerry, AI0K

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

[gareth]

"gareth" wrote in message
...
"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.

Multitudinous apologies, Brian, I tell a lie, so thank-you.

I've downloaded all (and even run the prog although nothing is attached to
the
input of the sound card) and will proceed to study the code, although,
obviously in this
case, at a max freq of 22kHz, creating a VFO is quite within the
capabilities of
PC-based machine code.

Also, a study of the code should answer a previous question of mine about
how to use
the sound card in applications such as this.

As I indicated elsewhere, the nub of my question was correct, there is a
VFO-equivalent
in the front end of wide-range DSP SDR rigs, that is separate from the
DSprocessor
(except in those cases where a DFFT is applied to the whole input range)

Thanks again for your effort.

Otherwise, for light relief and to ease the aggressive tensions that my
innocent enquiry
seems to have fomented, I append an article that I wrote nearly 20 years ago
....

-----ooooo-----

Alimentary Fourier Anal-ysis
----------------------------
(C) Copyright 1997 Gareth Alun Evans G4SDW

The Fourier Transform is rather like the Human Alimentary canal....

The Alimentary Canal takes food, and then transforms it into
something that is a function of the rear end, and hence may
be referred to as, "The Food-Rear Transform".

The Fourier Transform causes integration over a one second
period, and results in an infinite series of sines.
The Food-Rear Transform causes disintegration over a 12-hour
period, and results in an infinite series of signs...."Gents",
"Ladies", "Rest Room", etc. etc.

The Fourier Transform (Tukey's reasoning?) takes Time and
transforms it to a frequency spectrum.
The Food-Rear Transform takes Parsley, Sage and Thyme (Turkey's
seasoning?) and transforms it to a frequently active rectum.

"Laplace", literally, "The Place", is how you deal with
the transform.
"Walsh" is something you do to your hands afterwards.
"JPeg" is what you hang your jacket on to. It is a form of
compression such that you take up less space and spend less time
there (although the output may be more granular).

The Fast Fourier Transform must be done through an appropriate
window, otherwise an effect known as the "Picket Fence" problem,
also known as "Spectral Leakage", can occur.
Diarrhoea is known as the FAST Food-Rear Transform, and if done
through the wrong window can result in a problem (also known
as Rectal Leakage) all over the Picket Fence.

The Picket Fence problem is also known as, "Scalloping",
something which is normally done to pie crusts. In the old
days, pies used to be made with "Four And Twenty Blackbirds";
but nowadays, members of the Jay family are used. When you go to
someone's house for tea, you politely eat everything that is
put in front of you, but your reaction might be,
"Eat the Jay (Oh my God!) Tea???".
Similarly, the Fourier Transform is a great consumer
of e^(jwT)... "E to the j, omega, t".

The Fast Fourier Transform is famous for its Butterflies.
The Fast Food-Rear Transform is famous for its
Butterflies-in-the-stomach.

Dirichlet's are the Fourier Transform's conditions, without which
the result is divergent.
Diarrhoea ****s are the Food-Rear's conditions, with which the
result is VERY divergent.

Having experienced the Fast Fourier Transform, you are then faced
with the Inverse, which can be very daunting. It is a paper
exercise but it can be quite messy.
Having experienced the Fast Food-Rear Transform, you are then
faced with the "In Verde", literally "In The Grass", which can be
very daunting indeed. (The paper exercise can be quite messy.)

[gareth]

"gareth" wrote in message
...
"Brian Howie" wrote in message
...
http://www.radioelementi.it/public/saqrx.pdf
https://sites.google.com/site/sm6lkm/saqrx/

Wow! Wow! Wow!

Dev-C++ a free C++ compiler for Windows thrown in, and much
smaller than MicroBloat's products!

Watch this space!!!!!

[gareth]

"gareth" wrote in message
...
"gareth" wrote in message
...
"Brian Howie" wrote in message
...
http://www.radioelementi.it/public/saqrx.pdf
https://sites.google.com/site/sm6lkm/saqrx/

Wow! Wow! Wow!

Dev-C++ a free C++ compiler for Windows thrown in, and much
smaller than MicroBloat's products!

Having now had time to persuse the C code, I have the answers to
all my questions!

I'd like to recommend to ALL readers of these NGs that they download
the source code and the free C compiler whilst they are available, even
if not immediately using them.

Within the AudioCallBack routine is where it all happens, including the
phase accumulation making the DDS for the local VFO, and the FFT.

It's some years aince I've seen a Windows program done at the knife-and-fork
level and so that takes me back before the times of Visual Basic, and TCL.

As Brian said, it is easy to recompile and build the program again, thus
giving
the opportunity to dabble with the code by trying out minor edits, even if
limited to the colours (colors for the yanks) of the Windows.

The program clearly relies on the speed of a PC, for example, the DDS
calculates
sin and cos on the fly from the phase accumulator rather than using a
look-up table, and
I'm afraid the dinosaur in me keeps harking back to my days of assembler
programming
on a PDP11/20 where the slowest instruction (save for RESET at 50 mSecs) was

BICB @(R1)+, @(R2)+, taking about 17 uSecs.


All-in-all, this revelation by Brian is to be recommended to those who
wish to see an example of DSP programming to run on a PC.

Well done, Brian, and many thanks!

[Stephen Thomas Cole[_3_]]

Bernie wrote:
On Sun, 7 Feb 2016 12:40:57 -0000
"gareth" wrote:


I wonder if Mr.Gratuitously Rude actually read through his URL
reference for therein is a clear reference to the phase accumulator,
a necessary part of the DDS process?

When did you drop the "I never follow URLs" rule, Gareth?

Principles have always been fluid for our Gareth.

--
STC // M0TEY // twitter.com/ukradioamateur

[FranK Turner-Smith G3VKI]

"Stephen Thomas Cole" wrote in message
...
Bernie wrote:
On Sun, 7 Feb 2016 12:40:57 -0000
"gareth" wrote:
I wonder if Mr.Gratuitously Rude actually read through his URL
reference for therein is a clear reference to the phase accumulator,
a necessary part of the DDS process?

When did you drop the "I never follow URLs" rule, Gareth?

Principles have always been fluid for our Gareth.


Eh? I thought he was teetotal.
--
;-)
..
73 de Frank Turner-Smith G3VKI - mine's a pint.
..
http://turner-smith.uk

[Brian Howie]

In message , gareth
writes
All-in-all, this revelation by Brian is to be recommended to those who
wish to see an example of DSP programming to run on a PC.

Well done, Brian, and many thanks!

Yw

Someone has modified the code to use increased sound card sample rates ,
and add other features .

https://sites.google.com/site/swljo30tb/home

I can receive MSF amongst other stations on 60KHz with the 192KHz
version on an untuned 5ft loop antenna I use on MF.


Brian




--
Brian Howie

[gareth]

"Brian Howie" wrote in message
...
In message , gareth
writes
All-in-all, this revelation by Brian is to be recommended to those who
wish to see an example of DSP programming to run on a PC.
Well done, Brian, and many thanks!
Yw
Someone has modified the code to use increased sound card sample rates ,
and add other features .
https://sites.google.com/site/swljo30tb/home
I can receive MSF amongst other stations on 60KHz with the 192KHz version
on an untuned 5ft loop antenna I use on MF.

The accompanying PPT is in foreign, presumably Swedish, but there
is an interesting page showing the VLF antenna, and the interest to me comes
from numerous tappings along the antenna with a coil down to ground.

An early form of loop antenna, perhaps?

Is there scope here for experiments on similar such tappings to bring
a Top Band antenna down to a size to fit a suburban garden?