The very first radio navigation for aircraft was the Low-frequency radio range. Marvellously simple idea: a directional radio station broadcasts the Morse code for A · – to the north and south, and N – · to the east and west. You listen to that transmission in your headset. You listen to the station in your airplane; if you hear A you're north or south of the station, N east or west. But if you're directly NW, NE, SW, or SE of the station you hear both A and N overlapping and merging into a single steady tone. Fly that tone and you're flying in a straight line right to or from the beacon. Of course the station doesn't have to be oriented to north, the actual navigation network had some 400 stations in the US defining a network of airways.
Aviation enthusiasts WWRB have built a working four course range, demonstrated in the video above. Skip to 4:28 for a technical explanation or 7:17 for a demo flight. Four course ranges were decommissioned about 40 years ago in favour of VOR, the system we use today. VOR is the same principle but lets you fly any bearing and uses electronics instead of sound to track the radial.