Recommend: Networked Pseudo-Doppler (a.k.a. Synthetic Doppler)
A batch of them. Networked. Providing apparent bearing back to a central server.
Back at HQ, the relative bearing lines are displayed on a map, in (effectively) real-time. Where they cross (perhaps several of them) is the location. If the point of intersection moves along a highway at 95 kmh, then (like automobile GPS systems do) you may assume that he's driving on that exact highway. A bit of intelligence can tighten the estimated location.
Sooner of later the perp will be caught on CCTV driving past an ATM or corner store security camera. Correlated with the time-stamped track (after the fact), you'll then have a grainy video of his vehicle driving by. Twice and it becomes a certainty.
Then, the next time he's on the air, you can close the net around that old truck, and catch him red-handed.
Let's say he's on the air twice a week. The mean time to catch him would be about two weeks.