Ringway Manchester does a great job of explaining how, since the dawn of broadcasting, the U.S. Federal Communications Commission has been tracking radio transmissions by using direction-finding installations in remote, rural areas.
Many employ a unique antenna known as a Wullenweber array that looks sort of like a wireframe Stonehenge. Viewed from above, some of these circular setups could pass for center-pivot irrigation systems.
My favorite radio is this Panasonic RF-596 manufactured back in 1978. It tunes like a champ, has wonderful sound, and the illuminated dial and LED tuning light make every monitoring session a visually dramatic experience. Its dial is slightly off and should be recalibrated, but I don’t want to risk surgery on this otherwise perfect little beauty.