xSDR

The dongle cost $40. The Wyse 5070 thin client came from eBay for less than that. And somewhere between plugging one into the other and watching aircraft appear on a map, my wife said the sentence every homelab enthusiast dreams of hearing: “Wait — can it track planes from here?”

That’s xSDR. A distributed software-defined radio platform that turns cast-off enterprise hardware into a network of radio receivers, all feeding a central brain that decodes the signals into something useful. Or at least something cool enough that your spouse stops questioning the pile of antennas on the desk.

How it works

Each node is a Wyse 5070 — those little thin clients companies throw away by the pallet — running a single job: forward raw radio samples over the LAN via rtl_tcp. No processing, no decoding, just a firehose of RF data pointed at the brain.

The brain is xtower, running a Docker Compose stack that does the actual work — Caddy for reverse proxy, readsb for ADS-B decoding, OpenWebRX+ for waterfall displays, Icecast for streaming FM, and multimon-ng for pager decoding. All self-hosted, all built with custom Docker images pushed through Woodpecker CI.

The killer app

ADS-B — Automatic Dependent Surveillance-Broadcast. Every commercial aircraft squawks its position, altitude, speed, and callsign on 1090 MHz. With a properly matched antenna — a 69mm quarter-wave element, not the WiFi whip I tried first — a $40 RTL-SDR dongle picks it all up. The tar1090 web interface plots them on a map in real-time.

Becky wanted to know what planes were flying over the house. That $40 dongle did something she wanted. If you’ve ever tried to justify a hobby purchase to a partner, you understand why this is the project’s crowning achievement.

What’s next

Three nodes doing MLAT triangulation — using time-difference-of-arrival across multiple receivers to locate aircraft that don’t broadcast position. Feeding data to ADS-B Exchange and FlightAware. GNURadio flowgraphs for real signal processing. Maybe a HackRF One for transmit capability.

But honestly? The plane tracker is already the win.