RTL2832U SDR Logging Tool

A while back I posted about the fact that some people far smarter than me learned that some USB TV tuner dongles could be used as software defined radio receivers.

This weekend I finally had time to cook up some code that used the dongle to sweep across a given range of frequencies and record the strength of the signals received.

There are two parts to the tool.  The first is the logger, which does the actual reading and storage of the data.  The second is the plotter, which creates a graphical representation of the data points which have been stored.  We will first start with the plotter.

redacted@awesomecomputer:~/sources/pyrtlsdr$ ./freqLogger.py -h
usage: freqLogger.py [-h] [-s START_FREQUENCY] [-e END_FREQUENCY]
                     [-g GAP_START] [-f GAP_END] [-i INCREMENT]
                     [-d DESCRIPTION] [-m MINUTES]

optional arguments:
  -h, --help            show this help message and exit
  -s START_FREQUENCY, --start_frequency START_FREQUENCY
                        starting frequency for sweep
  -e END_FREQUENCY, --end_frequency END_FREQUENCY
                        ending frequency for sweep
  -g GAP_START, --gap_start GAP_START
                        start of band gap
  -f GAP_END, --gap_end GAP_END
                        end of band gap
  -i INCREMENT, --increment INCREMENT
                        frequency increment for loop
  -d DESCRIPTION, --description DESCRIPTION
                        Description for report
  -m MINUTES, --minutes MINUTES
                        Number of minutes to run scan
redacted@awesomecomputer:~/sources/pyrtlsdr$



If started with no options, the logger simply loops through those frequencies (in 1 MHz increments) which it can tune to, and logs the signal strength in the database.  Please be aware that these values are based upon what my dongle can do, and they vary somewhat.  The frequency ranges and band gap can all be set via command line arguments (or by simply editing the file, since it is written in Python).  If I wanted to scan 162 through 174 MHz for 20 minutes  I would simply run:

 redacted@awesomecomputer:~/sources/pyrtlsdr$ ./freqLogger.py -s 162 -e 174 -m 20
Found Elonics E4000 tuner

The script would  run for 20 minutes, then stop.

The plotter is quite easy to use as well.  Its options are as follows:

redacted@awesomecomputer:~/sources/pyrtlsdr$ ./reportPlotter.py -h
usage: reportPlotter.py [-h] [-r REPORT_ID] [-l] [-t] [-m MIN_FREQ]
                        [-n MAX_FREQ] [-s SAVE]

optional arguments:
  -h, --help            show this help message and exit
  -r REPORT_ID, --report_id REPORT_ID
                        report id to plot
  -l, --list_reports    list reports
  -t, --time_plot       plot signal strength vs time
  -m MIN_FREQ, --min_freq MIN_FREQ
                        minimum frequency for graph
  -n MAX_FREQ, --max_freq MAX_FREQ
                        maximum frequency for graph
  -s SAVE, --save SAVE  save graph to file (png)
Each run of the logger is listed as a report.  To list the reports currently stored in the database, execute the plotter with the -l switch.

redacted@awesomecomputer:~/sources/pyrtlsdr$ ./reportPlotter.py -l
Report Id   Minimum Frequency   Maximum Frequency  Increment   Bandgap Minimum   Bandgap Maximum Description
       16          162.000000          174.000000   1.000000       1089.000000       1252.000000 Generic Report     
       15          406.000000          420.000000   1.000000       1089.000000       1252.000000 Generic Report     
       14          406.000000          420.000000   1.000000       1089.000000       1252.000000 Generic Report     
       13          406.000000          420.000000   1.000000       1089.000000       1252.000000 Generic Report     
       12          406.000000          420.000000   1.000000       1089.000000       1252.000000 Generic Report     
       11          406.000000          420.000000   1.000000       1089.000000       1252.000000 Generic Report     
       10          566.000000          574.000000   0.001000       1089.000000       1252.000000 Scan 566 to 774    
        1           52.000000         2176.000000   1.000000       1089.000000       1252.000000 initial scan       

 Two types of reports are supported, signal strength vs frequency, and signal strength vs time.  Please be aware that strength vs time is probably only useful for a very narrow range of frequencies.

Signal Strength vs Frequency

Signal Strength vs Time

The code can be downloaded here.

In closing I must say that I actually do not know anything about digital signal processing at all.  The method I use to read the signal strength is from a script found here.    None the less, areas where high signal strength are reported correspond to known broadcasts, so I think this is correct information.  This is also one of the first actually useful things I have ever done with Python, so it is highly likely that I have done some things that would be frowned upon by the Python community.  Either way, I think I have put something useful together.