Add a PilotAware Uplink

PilotAware Uplink

A method to broadcast OGN station traffic on the PilotAware open protocol so that PilotAware equipped aircraft within range of the station see Flarm equipped aircraft on their moving map and collision avoidance systems. This being achieved with no change at all to equipment in either aircraft.

Adding the uplink to an existing RPi 2 or RPi 3 OGN station is straightforward and consists of 3 elements - transmitter, antenna and software. Stations on RPi 1 should be upgraded to RPi 2 or 3 first. Other hardware is not yet accommodated.

Pilotaware also have an active forum on the subject and detailed new build instructions using an approach suited to thier customers. The simple system below takes a different approach suitable for existing OGN members, it maintains all existing software unchanged, merely adding one executable to it.

Heat Map of PilotAware uplinks

Transmitter


This example uses the same transmitter as in the PilotAware device itself, giving a ready made, purpose designed solution. PilotAware are supportive of us doing this and have agreed to provide it (they call it the Bridge) at heavily discounted price for this purpose, circa £40, if you email them at this special email address moc.erawatolip|NGO#moc.erawatolip|NGO.

This approach offers a number of substantial advantages, not only is it physically very simple as it just plugs straight into the RPi GPIO socket but it also ensures we comply with the important transmitted power and bandwidth regulations on this radio band.

The RPi case needs to be modified to allow the antenna connection to protrude. On cases with a flat end piece this is a simple drilling or cutting job but on others it may compromise the structural integrity of the case or be totally impossible.

Antenna


Transmissions are at 869.4 Mhz, close to the Flarm frequencies but with over twice the power. The antenna generally in use is the PilotAware end fed dipole (short rubber stick) which is designed for use with the receiver.

Normal antenna siting guidance applies, as high as possible, preferable with a clear view of the distant horizon and not too near to objects that will interact with the antenna. Many current stations have it mounted on a L pole with the long arm horizontal clamped to the mast holding the OGN receiver antenna with no noticeable interaction betwen the two. (Make sure you use a propper clamp to mount it to the mast.)

Most installations protect the antenna by placing it inside a short length of plastic conduit. A common solution is to use 25mm conduit as an outer with the coax running up through a piece of 20mm conduit inside it and supporting the antenna. Use a 25mm conduit coupler to connect it to a 1 inch L pole.

The antenna needs to be connected to the receiver with a length of coax terminated in male and female SMA connectors. Make sure it is a cable with low losses at these frequencies. The shorter the cable the better but if optimising between antenna position and cable length go for position.

Do the best you can when siting this antenna as the PilotAware communication link is usually the limiting factor of the system. This tends to be due to antenna siting issues in the aircraft, with many having adequate range forward of the aircraft but little rearward or even to the sides. Aircraft equipped with external PilotAware antennas usually have excellent performance but they are a minority.

Software


Instaling the software that listens to the OGN port and runs the transmitter should only take a couple minutes. In addition you need make sure a few of the RPi configuration settings are set appropriately for the use of the GPIO.

The software requires no configuration, it reads the existing OGN station conf file for some information.

Once installed the PilotAware console is available on telnet localhost 50002 and an additional html page on port 8082.

Software Installation

(The easiest way of doing this is to copy each command from here and paste it into your SSH window)

Log in as pi

Make sure your operating system is up to date (the software works on either Jessie or Stretch)

sudo apt-get update
sudo apt-get upgrade

Become superuser, stop OGN service and install the software.

sudo su

service rtlsdr-ogn stop

wget http://fly-guy.wikidot.com/local--files/start/PAWadd.latest.tgz   -O /tmp/OGN-PAW.latest.tgz

tar --same-owner -Pxvf /tmp/OGN-PAW.latest.tgz

Edit the server config file in order to add the new software

nano /etc/rtlsdr-ogn.conf

Then add this line

50002 root /home/pi/rtlsdr-ogn ./PilotAware-OGN.exe

Save the file and exit.

Install GPIO access library

apt-get update
apt-get install wiringpi

Then check a few configuration settings, first open config.txt

nano /boot/config.txt

contains both

enable_uart=1
max_usb_current=1

If not, edit the file to contain them, save the file and exit. (It is likely that either both are missing or the first one exist at the bottom of the file requiring a zero to be changed to 1 and you will probably need to add the second one)

Then check raspi-config to ensure tty is disabled on GPIO/UART and I2C is enabled.

sudo raspi-config

The location of these configurations depends upon your version of raspi-config.

On the current version they are in :-

5 Interfacing Options > P6 Serial > No > Yes>OK
and
5 Interfacing Options > P5 I2C > Yes > Ok

In older versions they are in :-

Advanced-Options -> Serial (Disable login over serial)
and
Advanced-Options -> I2C (Yes Enable)

When you exit raspi-config it will ask if you want to reboot, select yes and it should reboot and all be working

If you have any problems please contact me Guy

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