How it works, ADS-B?

Following the crash of the Germanwings Airbus A320 (24 March 2015), many people have discovered the existence of Flightradar24.
Flightradar24 combines the ADS-B datas (Automatic Dependent Surveillance-Broadcast) provided by thousands of receivers distributed around the globe. These receptors are implemented by people and participate in the functioning of this international system. Besides Flightradar24 provides reception systems to those who apply and are eligible due to their geographical position in a poorly covered area.

Principle of ADS-B - Source © Flightradar24

The technology used by Flightradar24 to receive flight information is called ADS-B. This technology is illustrated in the image above.

  - The plane gets its location from a GPS receiver

  - The ADS-B transponder installed on the aircraft transmits a signal at 1090 MHz containing the position information and other data (Flight Number and callsign, altitude, speed, rate of climb ...)

  - ADS-B signal is received by a receiver on the ground, connected to the servers of Flightradar24

  - The receiver sends the received data to Flightradar24

  - The data are displayed on www.flightradar24.com and Flightradar24 apps.

ADS-B Transponder

ADS-B is a relatively new technology and still under development which means that currently it is rarely used for air traffic control. Flightradar24 estimated that around 65% of commercial aircraft carrying passengers (75% in Europe, 35% in the US) are equipped with an ADS-B transponder. For general aviation that number is probably less than 20%. But this percentage is increasing and ADS-B will become mandatory for most aircraft in 2020. ADS-B will replace the primary radar as aerial surveillance method used by ATC.

ADS-B Transponder

Flightradar24 (based in Stockholm) has a network of over 6000 ADS-B receivers around the world who receive flight information from aircraft equipped with ADS-B transponder and returns the information to servers. Because of the high frequency used (1090 MHz) coverage of each receiver is limited to about 250 to 400 km of the antenna depending on where it is located.
When a plane flies away from the receiver, it must fly high to be in the area covered by the receiver. The maximum range makes it very difficult to get an ADS-B coverage over the oceans.

About 99% of Europe is covered with ADS-B receivers. There is also a good ADS-B coverage in the US, Canada, Mexico, Caribbean, Brazil, Russia, Middle East, India, Japan, Thailand, Malaysia, Indonesia, Australia and New Zealand. In other parts of the world, the ADS-B coverage is very variable.

The transponders and antennas on aircraft

There are many models for aircraft transponders, such as those shown earlier in the article.

This one in two parts, with a control element that can be mounted on the dashboard, and a remote electronic unit.

This set (which includes a transponder presented above) is equipped with a display that allows the pilot to see the devices equipped with ADS-B on a map. This improves flight safety.

The antennas can also take different appearances, but most often it is this type of antenna that is used

Receivers

FR24

For receiving, many opportunities exist outside the professional equipment above.

Flightradar24 offer this model to equip the stations located in areas that are interesting for the service (not or poorly covered areas).

My station uses this receiver. My radar callsign is "F-LSGG3"

Here is approximately the reception area. It is lower in reality. The greater distances are achieved with aircraft flying over FL300

Characteristics:

  - Embedded processor - Operating without a computer
  - Received formats : 1090 MHz Mode S, ADS-B and Mode-AC
  - Reception range: more than 225 Km (depending on the quality of the antenna and its location)
  - Processing speed: over 1600 frames per second S-Mode (in areas with heavy traffic)
  - Timestamp mode or 12 MHz high resolution GPS mode
  - IP automatically assigned by DHCP
  - Works behind NAT
  - Power consumption: less than 5W
  - Bandwidth Consumption: 200 to 800 MB / month depending on the coverage

The antenna supplied by Flightradar24

Contents of the receiveing kit provided by Flightradar24

  - The FR 24 ADS-B receiver
  - The GPS antenna with 5m cable
  - Continuous power supply (110V-230V ~ input)
  - 5 m Ethernet cable
  - A Mode S antenna, 38 cm long with mounting system (0 dBd, 55 cm long, waterproof)
  - A coaxial cable 5 or 10 meters long for the Mode-S antenna with connector.
  - Cable type H 155 6mm diameter low loss. Cable equipped with SMA male connector and N-type connector

The Flightradar24 stick

On the shop Jetvision you will find DVB-T receiver solutions (Digital Video Broadcast - Terrestrial) recommended by Flightradar24. There is a version with the small antenna shown above (23 €) but you can choose an external antenna for better quality (78 €).

The possibilities to use the data provided by its multiple receiver. it is for example possible to send them directly to the Flightradar24 servers via their free software, or using the Raspberry Pi. Visit the website of "Framboise314" for more details about this solution.

To see some of the data that was sent by my Flightradar24 station, go to their website and select the display filter "Radar".
See illustration below.