"K9SQG" wrote in message
...
Well, it depends. The antenna does not need a DC ground path to work
well.
Inductive/capacitive coupling to an adjacent metal surface is generally
adequate. But there are so many installation specific issues that it is
not a
simple answer. However, most people are unaware that one of the best
antennas
for 2m is a 1/4 whip in the center of the roof. At highway speeds, the
5/8
whip bends over and distorts the pattern and causes a null in the forward
hemisphere. For stationary instances, the gain antennas may indeed offer
gain
over the 1/4 wave. Just some thoughts...
73s,
Evan

There is a significant amount of capacitance between the base of the
magnet mount and the roof. Some mag mounts have special arrangements of
conductive material, sometimes a foil which is on the bottom and is
(usually) insulated by a thin plastic membrane. This provides a low
impedance or Capacitive reactance to the roof at the base of the antenna and
therefore is effectively an AC ground as far as the antenna is concerned. I
have often wanted to measure it, but haven't yet. The ground through the
coax, rig and negative power lead is completely irrelevant for the RF. This
is because the distance along this path presents a significant impedance
(without going into too much detail) and should be considered, for all
intents, an open circuit at RF.
My 5/8 MFJ has surprisingly little wind induced bend at the kind of high
speeds I travel (60 mph). Thicker whip sections are better in this regard.

--
Steve N, K,9;d, c. i My email has no u's.