Re: [Discuss-gnuradio] Reading I & Q from a binary file

[Eric Blossom]

On Wed, Jun 28, 2006 at 06:00:13AM +0000, paul munro wrote:
> I have updated from CVS and re-recorded a new file using complex types and 
> the gain set to 20.

OK.

> LabView is able to read in any type, so I have defined it to read single 
> precision floats (assuming the first 32 bits are I and the second 32 bits 
> are Q). I have also read straight into a complex type and obtain the
> same results. 

OK.

> I now have I and Q values as I should. The values are in the range of 
> 10^-41. Has anyone looked at the sampled values from the USRP before??

Yes ;)

Why don't you start with something like
gnuradio-examples/python/usrp/usrp_oscope.py which will show you what
*we* think the values are.  [Sorry, no experience with LABVIEW.]

  ./usrp_oscope.py -g 20

Or if you've got octave or matlab installed, set the path for that
tool to include gnuradio-core/src/utils (take a look in that
directory).  For octave edit ~/.octaverc and put this line in it:

  LOADPATH=":~/gr-build/gnuradio-core/src/utils";

Then try:

  $ octave
  octave:1> d = read_complex_binary('name_of_file.dat', 1e6);
  octave:2> plot(real(d(1:1000)))
  octave:3> plot(imag(d(1:1000)))


> I am  using the basic daughter board with no front end. I want to check that 
> these values are reasonable.

If you've got a signal generator, try connecting a 10 MHz signal with
a peak to peak amplitude of about 0.5V to the RX-A or RX-B inputs on
the Basic Rx daughterboard.

Then try one or both of these:

  ./usrp_fft.py -f 10M -g 20

  ./usrp_oscope.py -f 10M -g 20


> D Shens tutorial mentions the PGA amplifies 
> the signal to a dynamic range of +-1???
> I want to make sure the values are ok before moving on the next stage.

The values that you'll see from usrp.souce_c(...) are in (-1.0, +1.0).
The smallest value you'll see is about +/- 3e-5 (== 1.0/32768).
If you're seeing 1e-41 I think you've still got a problem with
LABVIEW's handling of binary input values.

The -g option sets the gain of the PGA.  On the Basic Rx
daughterboard, the gain ranges from 0dB to 20dB by 0.1 dB steps.

Eric