My friend Sven (DL7AD) is deeply involved into SSR (secondary surveillance radar) reception. This is receiving position reports from commercial airplanes on 1090 MHz in a rather fast commercial data protocol. He has written a Java program to decode ADSB squitters from planes with a RTL-SDR dongle and display them on geographical vector maps on the screen. The output looks very much like a commercial flight radar screen in the cockpit of an airliner.
In order to get the best reception (at UHF this is pretty much line of sight) you’ll really want to have a very high antenna. I don’t have a huge tower in my backyard, so we were looking for alternatives. Ultimately we want to fly an ADSB receiver on a high altitude balloon payload later this summer, but we already started testing a flying payload by mounting it on a AR.Drone quadcopter.
The setup was as follows: A little 1.09 GHz ground plane antenna made from wires is fed into a Terratec T Stick PLUS RTL-SDR dongle. We’ve found that not all RTL dongles can receive 1090 MHz due to the frequency gap in the middle of the range. By testing with rtl_test -t we selected one that was stable up to 1105 MHz. We stripped off all the case and the connectors and directly mounted it to a likewise stripped Raspberry Pi PCB. The USB plugs and connectors were removed so we soldered them on 4 pins & headers so that they can be removed and remounted any time. On the other side of the Raspi PCB we mounted a 5.6 GHz Wifi dongle that was connected to a router on the roof of my car. The Raspi & dongles got their power supply from a 3.7 V, 630 mAh Lipo battery. The whole wireless construction was mounted on a AR.Drone quadcopter with it’s own 2.4 GHz Wifi connection which has a control and video link for the flight. The SSR data were received with rtl_adsb, stored on the Pi’s micro SD card (16 GByte is plenty of space for this) and at the same time transmitted through wifi for life monitoring on Sven’s laptop.
The first flight at night in my backyard was already quite successful, but steering the AR.Drone at low light levels is challenging. So we only got to 60 ft altitude. Sven has recorded one plane with complete position data, but this may be for the reason that not many planes are around at night time. So we decided to make a second try the next day on the parking lot in front of Papa’s BarBQ.
Today the weather and sight was excellent. Not much wind either, so optimal flight conditions for an AR.Drone.
On flight 1 we have captured squitters from 30 planes and got position data from 4 planes. On the second flight we got 37 planes with 3 of them with full ADSB positions. Maximum Altitude was 100 ft. Then the Wifi signal started interrupting.