This is a VOR.

Essentially, a VOR is a Very High Frequency Omnidirectional Range. Using fancy oscillomagicks and arcane aviationmancy, it shoots out 360 lines in the air, which an airplane equipped with a VOR system can pick up. The lines are tuned according to their compass direction (not true north-oriented, but magnetically-oriented). You tune your VOR system to this thing, and you can find out which line you’re on. Use two of them, and you can triangulate your position. You can track inbound and outbound on these lines, and use them for all sorts of navigation. They are VHF, though, so reception is largely line of sight. These are found all over the place in the US, and not so much in Canada since they are super-expensive.

tl;dr They are magic sombreros that tell you where you are.