For FM Broadcasting this is VERY IMPORTANT. Originally, FM
broadcasters used horizontal polarization (usually versions of "halos"
) for their broadcast antennas. This was fine for fixed or home
listeners, who used horizontal TV/FM antennas or folder wire dipoles
(included with many stereo receivers) - BUT cars and mobile FM
receivers tended to be vertically polarized.

I believe the trend in modern cars is getting away form vertical FM
receiving antennas and going to in-glass horizontal wires for the antennas.


Ed