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By John AE5X, February 20, 2013

I hadn’t anticipated moving up into the GHz range with this cheap little gadget yet but as it turns out, receiving and decoding the pulse trains that make up ADS-B is even simpler than using it to explore VHF/UHF.

This is entirely due to the excellent software available for this purpose.

These dongles are not plug-n-play and there are numerous ways to configure them – all this added to initial confusion in my case as a lot of disparate software had to be downloaded to make everything work. After that learning curve, ADS-B was simple.

ADS-B is far more common among European hobbyists than it is with us here in the States due mainly to the fact that is has been in use there longer. In a nutshell, ADS-B (Automatic Dependent Surveillance – Broadcast) is the name given to the system by which commercial (and some private) aircraft transmit their GPS coordinates to each other and to air traffic controllers on 978 MHz and 1090 MHz. This allows them to be seen, plotted and directed by ATC independently of radar.

This means that air traffic control can have highly accurate aircraft positions in places where radar wouldn’t be feasible – here in Houston, that initially meant helo flights to the Gulf of Mexico to and from off-shore oil rigs, but now it’s gone mainstream.

These latest SDR dongles are the first to have the speed and resolution to be able to decode ADS-B pulses. These pulses contain an aircraft’s GPS position, ID, altitude and speed with this info being transmitted once per second. Every 5th transmission from an aircraft contains additional data (tail number, squawk code, etc). Continue reading 'Receiving ADS-B on the SDR dongle'»

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By John AE5X, February 10, 2013

Inspired by G4VXE and a few others, I recently ordered a dongle-type SDR receiver via eBay. It’s due to arrive Wednesday.

This particular dongle has a few things going for it that make it ideal for experimentation (low price being first and foremost):

• Freq coverage is 25-1700 MHz – there’s a lot of stuff going on within that range and many modulation types.
• Its broad bandwidth and a fast clock mean that pulse-type modulation can be faithfully decoded…this is where ADS-B, MLAT and Mode-S come in.

I’m not sure many people have an understanding of what these transmissions are (particularly MLAT) or how they’re generated other than the fact that they’re used for air traffic control.

I may describe some of that if I can do it without it becoming overly tedious. Continue reading 'ADS-B, MLAT and Mode-S via $18 SDR receiver'»

Comments (2)

By John AE5X, January 18, 2010

Click for larger image

Within the radio hobby, we have not only hams but shortwave listeners, scanner aficionados and many other specialties. And as in ham radio, each category has subcategories – a scanner listener may be interested only in trains. A shortwave listener may only want to listen for commercial RTTY stations.

Those interested in aviation now have another venue available to them that has never before been possible. Until fairly recently, aviation buffs listened to comms on a scanner & enjoyed the routine (and every-so-often, the non-routine) pattern of communications between pilots and air traffic controllers.

That has been the extent of their participation. Until now. Continue reading 'ADS-B: Aviation’s APRS'»