blog/data/2023-04-07-radio-freq-scanning.txt

   1 Title: rtlsdr-scanner, software defined radio frequency scanner for Linux  - nice free software
   2 Tags: english, debian, nice free software
   3 Date: 2023-04-07 23:10
   4
   5 <p>Today I finally found time to track down a useful radio frequency
   6 scanner for my software defined radio.  Just for fun I tried to locate
   7 the radios used in the areas, and a good start would be to scan all
   8 the frequencies to see what is in use.  I've tried to find a useful
   9 program earlier, but ran out of time before I managed to find a useful
  10 tool.  This time I was more successful, and after a few false leads I
  11 found a description of
  12 <a href="https://www.kali.org/tools/rtlsdr-scanner/">rtlsdr-scanner
  13 over at the Kali site</a>, and was able to track down
  14 <a href="https://gitlab.com/kalilinux/packages/rtlsdr-scanner.git">the
  15 Kali package git repository</a> to build a deb package for the
  16 scanner.  Sadly the package is missing from the Debian project itself,
  17 at least in Debian Bullseye.  Two runtime dependencies,
  18 <a href="https://gitlab.com/kalilinux/packages/python-visvis.git">python-visvis</a>
  19 and
  20 <a href="https://gitlab.com/kalilinux/packages/python-rtlsdr.git">python-rtlsdr</a>
  21 had to be built and installed separately.  Luckily '<tt>gbp
  22 buildpackage</tt>' handled them just fine and no further packages had
  23 to be manually built.  The end result worked out of the box after
  24 installation.</p>
  25
  26 <p>My initial scans for FM channels worked just fine, so I knew the
  27 scanner was functioning.  But when I tried to scan every frequency
  28 from 100 to 1000 MHz, the program stopped unexpectedly near the
  29 completion.  After some debugging I discovered USB software radio I
  30 used rejected frequencies above 948 MHz, triggering a unreported
  31 exception breaking the scan.  Changing the scan to end at 957 worked
  32 better.  I similarly found the lower limit to be around 15, and ended
  33 up with the following full scan:</p>
  34
  35 <p><a href="http://www.hungry.com/~pere/blog/images/2023-04-07-radio-freq-scanning.png"><img src="http://www.hungry.com/~pere/blog/images/2023-04-07-radio-freq-scanning.png" width="100%"></a></p>
  36
  37 <p>Saving the scan did not work, but exporting it as a CSV file worked
  38 just fine.  I ended up with around 477k CVS lines with dB level for
  39 the given frequency.</p>
  40
  41 <p>The save failure seem to be a missing UTF-8 encoding issue in the
  42 python code.  Will see if I can find time to send a patch
  43 <a href="https://github.com/CdeMills/RTLSDR-Scanner/">upstream</a>
  44 later to fix this exception:</p>
  45
  46 <pre>
  47 Traceback (most recent call last):
  48   File "/usr/lib/python3/dist-packages/rtlsdr_scanner/main_window.py", line 485, in __on_save
  49     save_plot(fullName, self.scanInfo, self.spectrum, self.locations)
  50   File "/usr/lib/python3/dist-packages/rtlsdr_scanner/file.py", line 408, in save_plot
  51     handle.write(json.dumps(data, indent=4))
  52 TypeError: a bytes-like object is required, not 'str'
  53 Traceback (most recent call last):
  54   File "/usr/lib/python3/dist-packages/rtlsdr_scanner/main_window.py", line 485, in __on_save
  55     save_plot(fullName, self.scanInfo, self.spectrum, self.locations)
  56   File "/usr/lib/python3/dist-packages/rtlsdr_scanner/file.py", line 408, in save_plot
  57     handle.write(json.dumps(data, indent=4))
  58 TypeError: a bytes-like object is required, not 'str'
  59 </pre>
  60
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