[nine_k]

The comment mentions "something like a single suburban home". I suspect a line drawn on the map in the direction of the signal may give a good enough idea which few suburban homes may be the culprits, simplifying the task of locating it from a van.

I may overestimate the angular precision of that though.

[Jenda_]

The beamwidth of a standard weather radar is 1 degree. You can get to maybe 0.3° accuracy if you are pinpointing the maximum carefully. So this is 400m at 70km distance - which is not that bad. You then need to evaluate which parts of this sector are actually visible from your radar site (using a digital elevation model) and then search in them (I have never done this). Depending on the location, the entire 100km line may be visible...

But you need to specially do this scan and carefully evaluate the maximum (tricky if it's transmitting only once in a while). When you are scanning normally, you are pointing a bit above the ground (you are scanning the sky, of course) and the beam may have several degrees at the ground level.