.bin to .cfile flowgraph for GRC 3.7.2.1

Question

I have tried opening the flow graph for coverting .bin file (data captured via RTL-SDR) to .cfile for analysis. I downloaded the file from the link http://sdr.osmocom.org/trac/attachment/wiki/rtl-sd...

However, I am unable to get it working on GRC 3.7.2.1. I get a long list of error messages (given below) when I just try to open the file.

I am using Ubuntu v14.04.1.

I would be really grateful for any help to solve this or any alternate ways to convert the .bin file to .cfile (python source code?)

=======================================================
 <<< Welcome to GNU Radio Companion 3.7.2.1 >>>

Showing: ""

Loading: "/home/zorro/Downloads/rtl2832-cfile.grc"
Error:
/home/zorro/Downloads/rtl2832-cfile.grc:2:0:ERROR:VALID:DTD_UNKNOWN_ELEM:
No declaration for element html
/home/zorro/Downloads/rtl2832-cfile.grc:2:0:ERROR:VALID:DTD_UNKNOWN_ATTRIBUTE:
No declaration for attribute xmlns of element html
/home/zorro/Downloads/rtl2832-cfile.grc:9:0:ERROR:VALID:DTD_UNKNOWN_ELEM:
No declaration for element head
/home/zorro/Downloads/rtl2832-cfile.grc:10:0:ERROR:VALID:DTD_UNKNOWN_ELEM:

Answer 1

If you look at the flowgraph posted by @Kevin Reid above, you can see that it takes the input data, subtracts 127, multiplies by 0.008, and converts pairs to complex.

What is missing is the exact types. It is in the GNU Radio FAQ. From there we learn that the uchar is an unsigned char (8 bits) and the complex data type is a 'complex64' in python.

If done in numpy, as an in-memory operation, it looks like this:

import numpy as np
import sys

(scriptName, inFileName, outFileName) = sys.argv;

ubytes = np.fromfile(inFileName, dtype='uint8', count=-1)

# we need an even number of bytes
# discard last byte if the count is odd

if len(ubytes)%2==1:
    ubytes = ubytes[0:-1]

print "read "+str(len(ubytes))+" bytes from "+inFileName

# scale the unsigned byte data to become a float in the interval 0.0 to 1.0

ufloats = 0.008*(ubytes.astype(float)-127.0)

ufloats.shape = (len(ubytes)/2, 2)

# turn the pairs of floats into complex numbers, needed by gqrx and other gnuradio software

IQ_data = (ufloats[:,0]+1j*ufloats[:,1]).astype('complex64')

IQ_data.tofile(outFileName)

I've tested this translating from the rtl_sdr file format to the gqrx IQ sample input file format and it seems to work fine within what can fit in memory.

But beware this script only works with data where both input and output files can fit in memory. For input files larger than about 1/5 of system memory, which sdr recording can easily exceed, it would be better to read the bytes one at a time.

We can avoid memory-hogging by reading the data 1 byte at a time with a loop, as with the following program in gnu C. This isn't the cleanest code, I should probably add fclose and check ferror, but it works as-is for hobby purposes.

#include <complex.h>
#include <stdio.h>
#include <stdlib.h>

// rtlsdr-to-gqrx Copyright 2014 Paul Brewer KI6CQ
// License: CC BY-SA 3.0 or GNU GPL 3.0
// IQ file converter 
// from rtl_sdr recording format -- interleaved unsigned char
// to gqrx/gnuradio .cfile playback format -- complex64 

void main(int argc, char *argv[])
{
  int byte1, byte2;  // int -- not unsigned char -- see fgetc man page
  float _Complex fc;
  const size_t fc_size = sizeof(fc);
  FILE *infile,*outfile;
  const float scale = 1.0/128.0;
  const char *infilename = argv[1];
  const char *outfilename = argv[2];
  if (argc<3){
    printf("usage:  rtlsdr-to-gqrx infile outfile\n");
    exit(1);
  }
  // printf("in= %s out= %s \n", infilename, outfilename);
  infile=fopen(infilename,"rb");
  outfile=fopen(outfilename,"wb");
  if ((infile==NULL) || (outfile==NULL)){
    printf("Error opening files\n");
    exit(1);
  }
  while ((byte1=fgetc(infile)) != EOF){
    if ((byte2=fgetc(infile)) == EOF){
      exit(0);
    }
    fc = scale*(byte1-127) + I*scale*(byte2-127);
    fwrite(&fc,fc_size,1,outfile);
  } 
}

Answer 2

The cause of the errors you are seeing is that your link is bad — it is truncated and points to a HTML page, not a GRC file. The errors come from GRC trying to interpret the HTML as GRC XML instead. The correct link to the download is: http://sdr.osmocom.org/trac/raw-attachment/wiki/rtl-sdr/rtl2832-cfile.grc

However, note that that flowgraph was built for GNU Radio 3.6 and will not work in GNU Radio 3.7 due to many blocks being internally renamed. I would recommend rebuilding it from scratch using the provided picture.

Since there are no variables in this flowgraph, you can simply drag out the blocks and set the parameters as shown. Doing so will be a good exercise for familiarizing yourself with the GNU Radio Companion user interface, too.