Spying On Planes

2026-05-05 11:10 - General

Where I'm living now is only a few miles from a major airport. Overall I'm surprised and pleased that the noise is no big deal at all. But I do notice patterns some times, which got me curious. When I lived in NYC a coworker had set up a system with an antenna that gathered data about planes flying nearby, and I thought about doing something similar. Long story short: this is ADS-B (Automatic Dependent Surveillance–Broadcast). A nifty modern technology.

To my limited understanding, and simplified a bit: air traffic control one relied upon radar to know where planes were, and voice communication over radio. In the ADS-B system the plane instead broadcasts its own position, speed, etc. Both air traffic control and other planes can receive this data and make much more well informed and rapid decisions based on it. And, anyone can receive this data! I already had an "RTL-SDR" device — "Software Defined Radio". This common cheap variety is designed for radio and/or TV reception, but being software defined, it can do many things. I plugged it in, using the antenna it came with, installed the right software, and bam I could see planes nearby.

A representative view of nearby air traffic.

So now I was interested. After looking into it, and waiting to get the one connector adapter I needed, I made my own antenna. Old TV coax cable connects up to a coupler, which is threaded into a hole in the bottom of an old can. The can functions as a sort of "ground" as I understand it. Then a carefully trimmed inner core of another old TV cable sticks out of that, aiming for exactly a quarter wavelength of the 1090 MHz signal.

The simple ADS-B antenna I built, sitting in a window.

The stock antenna was not tuned for this signal frequency, and this one I made was an improvement. But not huge. This signal does not penetrate objects well, so the house blocks a lot of it in most directions besides the window. It did let me sometimes spot planes over a hundred miles away though!

So now I can hear a plane, look at a map, and see in real time exactly where it is. No big surprise: lined up with the nearby runways for takeoff or landing. But not always! I believe the planes are directed certain ways based on weather conditions, especially wind. Prevailing winds locally seem to usually keep the planes rather far away. When they're close, it's mostly a landing approach. And now that I've got this system, it can be fun to watch...

Spotting a plane doing a grid pattern, probably taking pictures, with my new ADS-B receiver.

Like when I spotted this plane clearly making a back and forth grid pattern. Had to be collecting imagery, right?

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