Overhead 1090 Explains · Episode 1
What is ADS-B?
Updated October 2026
Every airliner overhead is broadcasting where it is, right now, on an open radio frequency. That broadcast is called ADS-B, and anyone with a small antenna can listen to it.
What's said in the video
Every plane at this airport is talking. Right now. And almost nobody is listening. It's called ADS-B. Every airliner works out exactly where it is from GPS, then broadcasts it, twice a second, to anyone nearby. Call sign. Position. Altitude. Speed. All on one frequency: 1090 megahertz. Air traffic control uses it to track planes where radar can't reach, and pilots use it to see the traffic around them. And here's the fun part: it isn't encrypted, so a little antenna on your windowsill can hear planes a couple hundred miles away.
What the letters mean
ADS-B stands for Automatic Dependent Surveillance–Broadcast. Automatic: the aircraft sends it without anyone asking. Dependent: the position comes from the aircraft's own satellite navigation, not from a radar on the ground. Broadcast: it goes out to everyone in range, not to one listener.
What's in a message
Each aircraft has a permanent 24-bit address, its “hex” code, and sends short messages built around it: the flight's call sign, latitude and longitude, altitude, ground speed, track and climb rate. Airliners and most larger aircraft send these on 1090 MHz, which is where the app's name comes from.
Who uses it
Air traffic control uses ADS-B alongside radar, and in places radar can't reach, such as over oceans and remote terrain. Pilots with the right equipment see the traffic around them on a cockpit display. Because the signal isn't encrypted, hobbyists can receive it too, and that's how flight-tracking sites and home receivers work.
Listening at home
A home station is small: an antenna, a cheap USB radio and a tiny computer such as a Raspberry Pi. Episode 2 covers what that setup hears, and Episode 3 how far it reaches. If you already run one, connect it to Overhead 1090 to see your own traffic on iPhone, iPad and Apple TV.
The series
- Ep. 1: What is ADS-B?
- Ep. 2: What does an ADS-B receiver hear?
- Ep. 3: How far can an ADS-B receiver hear?
See every plane over your house on iPhone, iPad and Apple TV: Overhead 1090 on the App Store, one purchase, no subscription.