FLARM w szybowcu (zdjęcie: Sebastian Lampart)

Tracking gliders, airplanes, helicopters and baloons, part 3 – FLARM

We already know how to track airplanes using DVB-T USB dongle and Orange Pi or Raspberry Pi. Let’s move on to a new system that allows tracking of light aircrafts:

  • gliders
  • helicopters
  • baloons
  • smaller airplanes
Sender/reciever for glider (photo by: Sebastian Lampart)
Sender/reciever for glider (photo by: Sebastian Lampart)

FLARM – is a collision avoidance system for light aircrafts, popularized and approved by EASA, gaining traction, used mainly on gliders in Poland and Europe. We’re not going to use it to avoid collision – but to receive position and track light aircrafts – so we can share them on the OGN procest’s map – OPEN GLIDER. There are few station in Poland – let’s build a more robust network, so that gliders can be safer and their records – recorded.

What will you need?

Hardware:

  • Orange Pi Zero or RPI Zero W” rel=”noopener” target=”_blank”>Raspberry Pi Zero W
  • DVB-T USB Dongle. Look for the upgraded version in blue chassis – AKA “DVB-T RTL2832U+R820T2” – it offeres better sensitivity in interesting frequency – and will give you extra range. The most important part in that equation is the new R820T2 (version ‘2’) and of course the included antenna
  • Micro SD – could a cheap 8G for $4, but better is to use Sandisk Extreme/Ultra – at least 4GB
  • Power supply – at least 1.5 to 2A @5V with micro USB (i.e.: old charger from cellphone)
  • Two small heatsinks (radiators) for CPU and controller – for Orange Pi Zero
  • ALTERNATIVE: Raspberry Pi 2 or 3 – they have enough of CPU power, but triple the price
  • Antenna 868MHz. The one you got with USB dongle is OK for start – gives me around 50km of range without any modification. You can cut it to the lenght of single segment

Software:

    li>Armbian for Orange Pi – the best at this point is to use the Xenial NIghtly, developer/beta version, with 4.9.x kernel from https://www.armbian.com/orange-pi-zero/
  • ogn-decode i ogn-rf – software to be downloaded – ARM CPU version
  • Free ports on the Orange Pi/Raspberry Pi – 8080 and 8081 – if there’s nothing else there installed – they should be free to use.
Cokpit with FLARM  (photo by: Sebastian Lampart)
Cokpit with FLARM  (photo by: Sebastian Lampart)

Installation

First – if not installed already – we need SDR and some system libraries as well as binaries from glidernet.org:

To allow usage of the raw feed from airplanes we need to turn off the automatic loading of the DVB-T:

paste:

Reboot the Orange Pi/Raspberry Pi
Now, lets download from glidernet.org the correct file, unpack it:

Create a FIFO to allow communication between both parts of the OGN software:

View from glider (photo by: Sebastian Lampart)
View from glider (photo by: Sebastian Lampart)

Next, calibration of the USB dongle – cheap DVB-T USB tuners are not always good at tuning with high precision to given frequency – we need to correct the skew. To do that use the gsm_scan, that will give the ppm and gain correction values:

Change values so that the deviation is around 10ppm (check the best GSM frequency GSM) – write them down.
Create own configuration based on the example:

The example file contents based on my tuner: enter CORRECT values for FreqCorr, GSM: CenterFreq Gain – based on gsm_scan:

Finally – start in background two programs using very basic (or other by your choosing method) thanks to cron:
Create two files:

with:

Add rights to execute:

Second file:
nano /home/pi/rtlsdr-ogn/run_ogn-decode

with:

Rights to execute:

Now edit your crontab:

Wklejamy:

Of course in our example we’re using username “pi”.
Verify the operation by attaching screen: screecn -r XXX, or enter the URLs in we browsers: http://ADDRESS_OF_PI:8080/ oraz http://ADDRESS_OF_PI:8081/. Your station will be listed at: http://ognrange.onglide.com/, along with the range. Since FLARM changes – check every 6 months for new version.

That’s it!

Glider's tail (photo by: Sebastian Lampart)
Glider’s tail (photo by: Sebastian Lampart)