With a regular 1/4 wave (or 5/8) mobile whip (VHF and/or UHF) the coax
normally is grounded to the sheetmetal to form the ground plane -- but a mag
mount lacks the ground at the antenna end of the shield, though hopefully
the metal of the body is ultimately connected to the transmitter chassis and
coax braid (assumes ground braids for trunk lids etc. for rear deck lid
mounts), so is there a significant performance penalty for the mag mount vs
the same whip on a grounded base at the same location?