"The Masked Marvel" wrote in message news:1g%hc.5154$0u6.1124791@attbi_s03...
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?

There was some difference in one case where I had the chance to
compare. I once had a larson 5/8 mag mount on the center of the roof.
You know the common model with the black box looking mag mount... It
always seemed to work pretty well as a mag mount, but eventually I
tore it up by knocking it off the car once too many times...So I had
to ditch the mag mount, and drill a hole and do a hole mount. Did it
make a difference? Yes. Quite a bit actually. It was quite noticable
anyway...I found the hole mount was superior. But I still like mag
mounts...It's nice being able to slap it on any car you are in. But on
my truck, I have a hole mount right in the center of the roof of the
cab. At the moment, I only have a homebrew 2m 1/4 wave whip on it...I
don't work a heck of a lot of 2m mobile, but I do want the antenna
there ready if needed.. MK