I have always wondered: would a "passive repeater" (an outside antenna connected directly to an inside antenna through a short coaxial cable, with no active components at all) work in these cases, or would it attenuate the signal too much?
I believe such a "passive repeater" would not be illegal in any sane jurisdiction, since it's nothing more than metal bent in a few specific shapes connected by a cable.
Yes, a passive repeater as you described helps at least in some cases, and they are permitted. And even if the system were insane and they were not permitted, they would be practically undetectable. Active repeaters ones are illegal here. Unfortunately a passive repeater is not always enough.
I believe such a "passive repeater" would not be illegal in any sane jurisdiction, since it's nothing more than metal bent in a few specific shapes connected by a cable.