That’s a very good question. The short answer is I have not tested a base station outside of the car simply because leaving a base station out in public while I wander around for an hour isn’t a good strategy.

I carefully place the base station in a car window to minimize loss but there is still possible loss due to the window. There’s an interesting paper here: Measurement of Radio Signal Propagation Through Window Panes and Energy Saving Windows (diva-portal.org) which shows the loss through untreated glass as near-zero.

More importantly the car has a lot of reflective metal surfaces which absolutely cause signal interference issues. Unfortunately, because I am testing the reception antennas (which I hold) any effects of the car are equally applied to all antennas and so I usually ignore any car effects.

When I tested a walkthrough in town I carefully placed the base in the back of the car and the longest walk was directly behind the car (about a mile). The walks on the side of the car (where metal columns interfere) had distinctly lower range.