Put simply, ADS-B (Automatic dependent surveillance – broadcast) is a system used by aircraft to broadcast their position in the air.  It can be tracked by air traffic control or anyone who operates a suitable receiver.

It’s possible to build a receiving station very easily and cheaply using a Raspberry Pi, an RTL-SDR dongle and a homebrew aerial.

Two of our members (Tony and Keith) have been running ADS-B receivers for a number of years, feeding their data into various networks such as FlightAwareFlight Radar 24 and Planefinder and they decided that it would be nice to build a system to install on the Martello Tower as it’s in an excellent location to receive aircraft traffic.  This was assembled by Tony, configured by Keith and installed on the roof of the Tower on the 19th April 2019.  It consists of a Raspberry Pi 3 Model B+, an Airspy Mini receiver, an Uputronics ceramic filtered preamp and an antenna we bought from eBay. The supplier is no longer on eBay but has started his own online shop.  This is the aerial we have.  Tony and Keith have provided all the equipment themselves even though this has been built under the Martello Tower Group name.

On 30th December 2019 we replaced the preamp with an RTL-SDR-LNA and immediately noticed a significant increase in performance.

Everything was built into a single, weather proof box and mounted on the roof of the Tower with a feed to FlightAware where you can see our statistics by clicking here.

The blue ring is the theoretical maximum range for aircraft flying at FL350.

Within a few minutes of switching the receiver on, it was clear that this was going to work well.  The image below is a capture taken from the receiver and shows nearly 400 aircraft.

Although the Martello Tower is practically at sea level and the receiver only around 14m AGL, it has a completely clear view to the horizon in all directions which is an important point for ADS-B receivers.