The 1090 Megahertz Riddle (second edition)

A Guide to Decoding Mode S and ADS-B Signals
By: Junzi Sun (


In the last twenty years, aircraft surveillance has moved from controller-based interrogation to automatic broadcast. The Automatic Dependent Surveillance-Broadcast (ADS-B) is the most common method for aircraft to report their state information like identity, position, and speed. Like other Mode S communications, ADS-B makes use of the 1090 megahertz transponder to transmit data. The protocol for ADS-B is open, and low-cost receivers can easily be used to intercept its signals. Many recent air transportation studies have benefited from this open data source. However, the current literature does not offer a systematic exploration of Mode S and ADS-B data, nor does it offer an in-depth explanation of the decoding process.

This book tackles this missing area in the literature. It offers researchers, engineers, students, and enthusiasts a clear guide to understanding and making use of open ADS-B and Mode S data. The first part of this book presents the knowledge required to get started with decoding these signals. It includes background information on primary radar, secondary radar, Mode A/C, Mode S, and ADS-B, as well as the hardware and software setups necessary to gather radio signals. After that, the 17 core chapters of the book investigate the details of all types of ADS-B signals and commonly used Mode S signals. Throughout these chapters, examples and sample Python code are used extensively to explain and demonstrate the decoding process. Finally, the last chapter of the book offers a summary and a brief overview of research topics that go beyond the decoding of these signals.

About the Author

Junzi Sun is an assistant professor at TU Delft, currently working in the CNS/ATM group of the Aerospace Engineering Faculty. He is passionate about open-source, open science, and making air transportation more sustainable.

He was born in China and completed his bachelor’s degree in telecommunication at Beijing University of Posts and Telecommunications. Then, he moved to Europe and obtained his master’s degree in aerospace engineering at Polytechnic University of Catalonia. After that, he worked in Spain and France for a few years before continuing his doctoral research in the Netherlands, where he obtained his Ph.D. degree and currently works and lives.

Cite this book

    author = {Sun, Junzi}, 
    title = {The 1090 Megahertz Riddle: A Guide to Decoding Mode S and ADS-B Signals},
    publisher = {TU Delft OPEN Publishing},
    year = 2021,
    edition = 2,
    isbn = {978-94-6366-402-8},
    doi = {10.34641/mg.11}


This book is published by TU Delft OPEN Publishing as an open access book, under CC BY-NC-SA-4.0 license:

You can find the publisher’s version of the book at:

© Copyright 2021 Junzi Sun. Build with LaTeX, Pandoc, and GitHub