Re: [Discuss-gnuradio] Magnitude of complex vector

[Eric Blossom]

On Tue, Aug 10, 2004 at 10:49:18PM -0500, David Carr wrote:
> Hi all,
> 
> I'm trying to implement an AM demodulator.  I was planning to send the 
> real samples through an IQ demodulator and then take the magnitude of 
> I+Q to get the demodulated audio.  I can't figure out how to implement 
> the magitude(I+Q) operation though.  Is there a provided magnitude 
> processing block or even a square root one?  This must be really easy 
> but I can't find what I want in the docs.

There is a whole list of missing signal processing blocks.  This is
one of them.  Below is a list of related blocks.  Please feel free to
write one or more of them along with test code send them to me.  I'll
add them to the gnuradio-core tree.  gr_float_to_complex is a great
example.  For examples of test code, see qa_add_and_friends.py 
Also, please take a look at README.hacking for coding conventions. 
Ask questions as they come up.  And yes, I know we're stilling missing
the "Introduction to the GNU Radio 2.x Architecture".  Generally
speaking each block requires 3 files: gr_<foo>.h, the header;
gr_<foo>.cc, the implementation; and gr_<foo>.i, the SWIG header
that's used to generate the glue to python.


Missing blocks related to your question:

  gr_complex_to_real    1 complex in; 1 float out
  gr_complex_to_imag    1 complex in; 1 float out
  gr_complex_to_mag     1 complex in; 1 float out
  gr_complex_to_arg     1 complex in; 1 float out
  gr_complex_to_float   1 complex in; 1 or 2 floats out


Other simple to implement missing blocks:

  gr_float_to_short
  gr_short_to_float
  gr_tcp_sink           look at 0.9 code plus 2.x gr_file_sink/source
  gr_tcp_source


If anyone's familiar with ALSA, or wants to be, we could use a native 
ALSA audio sink and source.  See the gr-audio-oss tarball for a
starting point.  This would allows us to transparently take advantage
of 24 bit audio cards.  The alsa module should end up in a separate
loadable module just like gr-audio-oss does.  [If you're thinking
about doing this, drop me a line, I've got some ideas.]

Eric