Seeing the World in Radio Waves, With a Gadget That Used to Cost a Fortune

We move through an ocean of radio waves we cannot see, and most of the time we are happy to leave them invisible. The QuadRF project^[1] is a small, pointed argument that we should be able to look anyway.

The principle behind radio direction finding is deceptively simple. Measure the tiny phase differences between several antennas, and you can work out which direction a signal arrived from. Doing it well, in a package that does not cost as much as a car, is the hard part, and the part this project is taking a swing at.

Crucially, it is open^[2], hardware and software both, which is what separates a neat demo from a tool other people can build on. Capability that used to live inside expensive, closed instruments is steadily migrating into repositories anyone can clone.

That migration is happening all across hobbyist radio right now. The same forces that put software-defined radio on a USB stick are coming for direction finding, and the result is that a curious person with a soldering iron can answer questions that once needed a lab. The waves were always there. We are finally getting affordable eyes for them.