Friday, 7 March 2014

Plane Weirdness

The original, suspected faulty dongle is currently plugged into my main PC, like so

The cheapo stock mini mag-mount that came with the new one is plugged into it (the modified antenna connector is open) and the antenna is set up two feet from my feet, and at least 12ft inside with the tiniest view of clear sky, atop a cable drum (empty!)

Yet, ADSBscope and ADSB# between them are tracking a good few aircraft!

So, im really none to sure why it wouldnt work before! RF overload? possibly, when I tried it at work. But maybe it doesnt like the grounded antenna? If so, why did it not work on the colinear yesterday? Maybe, the modified antenna socket is naff? Ok, i'll accept that possibility!

A few people have expressed an interest in what im doing here, so I will give a quick condensed overview, enough at least to get someone started -

ADS-B stands for Automatic Dependent Surveilance - Broadcast. It is a form of Secondary Surveilance Radar. Primary radar works by detecting the reflected pulses of a high power transmitter, and by measuring the propagation delay, working out the range to the aircraft. By using rotating antennas with known take off angles, the height and bearing of the aircraft can be determined. This requires a lot of power, and some accurate and hence expensive mechanics, so primary radar is a very expensive bit of kit. It also has very limited range as the detectable range is about half the transmitted range.

Way back in the Battle Of Britain, it was realised that our RDF (Radio Direction Finding) operators could not easily tell an RAF Hurricane from a Luftwaffe BF109 on a radar screen. This led to the invention of IFF (identification, Friend or Foe). This was the very first Secondary Surveilance Radar system. The IFF unit on the aircraft was a transponder. When 'interrogated' by a ground station, it transmitted back the aircraft callsign.

Through various incarnations of SSR to the present, and with the advent of small, cheap and amazingly accurate aeronautical GPS systems, we have ADS-B. This form of SSR requires no interrogating ground station, only receiving stations. Each equiped aircraft regularly broadcasts its callsign, flight designation, height, bearing and position, in a brief data packet, at 1.090GHz. This is known as 'squittering'. Ground receiving stations detect and decode this data burst, and via the magic of the internet, not only can plot the aircraft received on screen, but can look up all the flight details, airframe details etc. And by uploading the decodes to a server, from many different locations, a radar image of the whole airspace can be created.

The professionals use very expensive, ultra high accuracy and reliability equipment for this, but amateur plane spotters can do just as well with less money than a couple of pints! Skip a canteen breakfast two days on the trot and buy a DVB-T USB dongle!

Everything you could possibly want to know is available on but I will briefly describe my set-up

I have two dongles, both were bought off ebay from a seller in the Far East by the name easabonn. They take about a month to arrive, but cost me £5.37 each, including shipping. They come with a remote control (no use), a miniCD (no use) and a mini mag-mount antenna (reasonable for ADS-B but no use for anything else!)

OK, so you have your dongle. Now, plug it in and let windows install its driver. As soon as its done that, go online and download a program called Zadig. Run this, and follow the instructions you can find on the above website to change the driver!

With the driver changed, the dongle is now no longer a DVB-T telly stick, its a 24 - 1700MHz Software Defined Radio!

I use three programs now -

SDR# is an SDR control program. This allows you to not only receive and listen all over the dongles coverage, but to see the spectrum up to 2.4MHz wide as a waterfall. Tune to 1.090GHz and you should see a trail of brief bursts of signal go down your screen (depending where the antenna is, get it high and clear if you can), these are the ADS-B squitters.

Close SDR# and run ADSB#. This is a dedicated ADS-B receiver decoder. You wont see much happening, other than the frame rate counter hopefully go up. If you telnet to it ( you should see a stream of hex values, these are the decoded data. I have my ADSB# controls set to 'Tuner AGC'

With that running, now you need to visualise the data. Run ADSBscope. Go to Other > Network > Network setup. Click the ADSB# button, and the 48706 port number should appear. Set the URL to local. Then click on the RAW data CLIENT button. All being well, planes will start to appear on your screen! Its really as simple as that.

I have found that minimizing ADSB# stops it working, so keep that on screen.

Ideally, you want a better antenna. Get the soldering iron out and have a look at the various ideas online.

And thats all there is to it to get your very own ADS-B SSR ATC console!

No comments: