This Week @ GGC: The tracker

I've had questions on the Open Glider Network (OGN) tracker receiver. It is a small computer (Raspberry Pi 3 in my case, though there are others, the Pi seems to be fairly standard), connected to a Software Driven Radio (SDR) receiver, and an antenna, with associated cables. If you live in a noisy (electronically) area, you probably will also need a bandpass filter to cut the noise down.
Cost of a good Pi on amazon, with software images ready to install a version of Linux, Raspbian, is about $100; you can get less powerful Pi's cheaper, but the 3 comes with wireless and bluetooth built in; you have to add that to the others, and they come with a less powerful power supply.
Cost of a SDR can vary; I bought a $27 dollar one (NooElec TV28T v2 USB DVB-T & RTL-SDR Receiver) but it turned out I needed an amplifier, since signals are weak), so I got one with an internal amp on amazon.ca for $19.00 (FlightAware Pro Stick USB ADS-B Receiver). ADS-B is near the FLARM frequency and can be adjusted for it. I was thinking of using a spare FLARM antenna I had kicking around, but Nick suggested it wouldn't be enough, so I got a 915MHz 5dBi Outdoors Omni-Directional Rigid Whip Antenna from Mouser.ca for $20.

The FlightAware 'dongle' attaches to the Pi on USB (4 ports available). Plug a cable into the FlightAware (sma connector) or if you need a bandpass filter, the filter onto the FlightAware, and the cable onto the filter, then coax cable to the antenna. I needed an adapter from SMA to N (standard communications connector) - got one at Active Electronics on Merrivale (also avail at Radio Shack in the US).

There is a good Wiki on setting up the receiver at http://wiki.glidernet.org/ , on the left side "install a receiver". This is mainly for Euro FLARM (868 Mhz vs our 902-928 Mhz), but Nick B really helped with a set of detailed instructions, which are really cut-and-paste.

I recommend anyone flying with FLARM within range of an OGN receiver register with the OGN devices database at http://wiki.glidernet.org/ddb - it takes only a minute. You need your FLARM id from your flarmcfg.txt file. I will be doing a post later on how to locate an overdue aircraft using the OGN Search and Rescue function ( http://wiki.glidernet.org/sar ). Easy and quick - if you're registered. Your data is held for 24 hours on each flight, then wiped (unless 'locked' when doing a SAR search).

So, what does it look like? Here are pics of the Pi, FlightAware dongle, the cable from the dongle out the window, then the antenna on a pole. Mount courtesy of Jarek T.; ladder courtesy of Adirondack Air Services (also their pole, wireless connection, and power). The site isn't really ideal, since the peak roof is metal, and shields the area to the North, but the installation works well from Whiteface to Mt Marcy.
Pictures: Pi and FlightAware; cable out window; antenna on pole; receiver range (green squares show good reception); and sample screen of "spot the gliders" from my iphone, looking at DB's data at the time. I get a data point about every 2 secs from gliders within range. Nick and Frank's excellent CNF3 installation on the big Hangar is excellent, seeing gliders in the wave at 8000' at a range of 174 km; my first shot at an installation is basic; I got ranges of about 20 km, and not many gliders went beyond that distance (mountains, wind, etc). Recall that the transmit power of a FLARM is 0.010 watts (Portable) or 0.018 watts (CORE). Amazing that it is detectable at all. I will also get a bigger ladder to put the antenna higher... I have about $140 invested, and am good to go (if you don't need the deluxe package, $70 CAD for the Pi will bring it down about $30). You will need access to a wireless network. I will tinker with the setup, and install it again next year at Lake Placid. The higher you get the antenna, the better; the Pendleton set-up is 30m up...

There are receivers at GGC, RVSS, MSC, SOSA and I believe Champlain clubs. It makes what we do accessible to the public, and it is a boon for the crew to wander in, look at the screen, and know whether their Sailplane Crew Union Membership (SCUM) duties will be required... You can also watch a race in near-real time, which was very popular at MayFly. We also discovered a bad FLARM A antenna in the Puchacz installation, which we fixed by using a 1/2 wave dipole antenna.

In the US , there are receivers at Minden NV, Colorado Springs, and when the GGC Lake Placid camp is operational, there (1-10 October). If the wave is up, and the gliders are above 8k you might see them on the Pendleton or Hawkesbury receivers.

To decrease noise, the pi and dongle should be separated (powered active usb cable works well, I'm told), and dongle and antenna as well (5 loops of 6" in cable also help, as do ferrities). I did learn that standard coax losses are huge, and will be replacing RG58 (standard cable tv coax) with low-loss coax (probably LM200 or LM 240) to boost my detection range. The fewer adapters, and the better the connectors, the less loss there is. Jarek and Nick improved my antenna and got a 9 dB gain on Saturday when it rained. We got at least a 10 km increase (no one got terribly far on a wave day - going up instead of out...

My next post will be a look at the October 10th wave, and the one after, using OGN for SAR. If you want to spot the gliders, go to live.glidernet.org . You can see them in the Andes, Africa, Australia, Europe, and now, North America.

A big Bravo Zulu (navy-talk for good show) to Nick for bringing the first station into life in Canada, and helping techno-bozos (me) to get the thing going.