Tuesday, March 25, 2014

rtl_power (modified)

I've been working on rtl_power today and was able to accomplish the follow 3 things that are important in saving time when using GNUPLOT as well as improving rtl_power's accuracy in the resulting data it creates.

The issue is that when you run -i 1 this is a 1 second integration interval.  This means rtl_power will continue to rescan the bandwidth you specify with the -f option until the next internval and create an average based on that 1 second for each frequency it's scanned.

This average is nice if you don't really care about high resolution and can live with that.

But I want to be able to see things like Meteor Scatter on 55 Mhz TV stations in Mexico, or CW beacons rise and fall in ham radio bands, etc...

This means that we need sub-second data.  To do this I modified rtl_power as follows:

  • changed several items that relate to the 'interval' command like option so that you can now use -i .5 which is the same thing as saying do a scan every 500 milliseconds or 1/2 a minute from the time rtl_power starts.
  • added new command line option -u <upconverter frequency in hz> which will automatically 'down-convert' the frequencies being logged! (a big plus not to have to post-process for this!)
  • changed csv_dbm() so that it now only reports yyyy-mm-dd hh:ii:ss.s, freq in hz, dbm
  • changed csv_dbm() so that when a time changes it adds a blank line (required for direct import into gnuplot as 3D data.
  • These changes make is so that rtl_power is not dumping data at sub-second intervals and in a format that will directly import into GNUPLOT.  Which removes the rather complication and slow process of post-processing the old CSV style that rtl_power created.
Here is a 5 minute run of 28.0 to 28.4 Mhz at 50hz resolution and 1/2 second scans.  

NOTE: the title on this graph is incorrect (sorry) the actual data is 28.0 through 28.4 Mhz not as shown in the title 28.2 to 28.4 Mhz.

You can easily see morse code beacons around 28.2-28.25Mhz as well as SSB use between 28.3 and 28.4 Mhz and various other modes below 28.1 Mhz including PSK, and CW.