====== How To: Software-defined Radio: Exploring data in the airwaves ======
Join us for a quick 'how to' demo.  Learn how to use an RTL-SDR device to pick up data from radio waves using open source software.  Find weather reports, decode radio packet data, scan frequency ranges for local activity and much more!  You'll be surprised at what's out there!

Meetup link: https://www.meetup.com/Open-Source-Glasgow/events/277171091/

As always, join us in [[/Matrix]] room #opensource:glasgow.social if you have any questions or want me to cover something specific.

====== Links ======
  * [[https://gqrx.dk/|GQRX]]
  * [[https://github.com/EliasOenal/multimon-ng|multimon-ng]]
  * [[https://github.com/merbanan/rtl_433|RTL 433]]
  * [[https://www.ebay.co.uk/itm/203134008519|RTL SDR device on ebay]] - This is the model I use, but pretty much any RTL2832 chip device should work out of the box with Linux (performance may vary based on the the quality of the device).

===== Command Line =====
  * Tune the gqrx application to the desired frequency, then select UDP to broadcast the raw data.  Once that's done we'll use netcat to listen to that port, and sox to convert it to audio format, then multimon-ng to process the digital data into something alphanumeric:
<code bash radio-to-text.sh>
nc -l -u -p 7355 |
sox -t raw -esigned-integer -b 16 -r 48000 - -esigned-integer -b 16 -r 22050 -t raw - |
multimon-ng --timestamp -t raw -a POCSAG512 -a POCSAG1200 -a POCSAG2400  -f alpha -
</code>

To generate the heatmaps of what's happening in the radio spectrum in your area, use the ''rtl_power'' (in the rtl-sdr debian package) with  [[https://github.com/keenerd/rtl-sdr-misc/blob/master/heatmap/heatmap.py|heatmap.py]].  For more information see http://kmkeen.com/rtl-power/

Run this for 24 hours (you can also just try an hour or so and repeat to test different aerials):
<code bash>
rtl_power -f 24M:1700M:1M -i 100 -g 50 -e 24h data.csv
python heatmap.py data.csv
</code>