Dan Richardson wrote:
Roy is quite correct in stating that a vehicle's body behaves as one
side of a dipole. A lopsided dipole to be sure, but one half the
antenna just the same.

Seems the truth might lie somewhere in between. If the ground
plane of a vertical antenna is near the ground, there are
losses. If the ground plane of a vertical antenna is located
1/2WL above ground, the losses are a lot less. I'll bet that
if the vehicle were located 1/2WL in the air, the efficiency
would increase.
--
73, Cecil http://www.qsl.net/w5dxp