I have a 5" diameter 3/8-24 mag mount and was wondering if a mag mount
like that would have enough capacitance to adequately couple to the
metal surface it was on. Also is there a good rule of thumb on how much
capacitance you need to have a good ground on a mag mount at a given
frequency? I don't plan on having an HF antenna on this mag mount while
driving. I also don't plan on using it on anything below about 20 or 30
meters.

As a side note I heard someone say that the mag mount has to be on steel
for the capacitive coupling to work. I find that hard to believe.
Obviously the magnet won't hold to aluminum or copper gut setting the
antenna on any metal surface will provide the capacitive coupling, won't it?




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Chris W
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On Fri, 03 Nov 2006 12:26:09 -0600, Chris W wrote:

As a side note I heard someone say that the mag mount has to be on steel
for the capacitive coupling to work.

Hi Chris,

This is distinctly suspicious, nearly as much as the claim that
mag-mounts provide a necessary capacitance. The cable's proximity to
sheet metal leading to the mag mount easily offers MORE capacitance
than nearly any single, isolated mount.

Both claims rely on the mystery of magic (as certainly no one has ever
explained HOW they work in distinct contrast to simple cable
proximity).

73's
Richard Clark, KB7QHC

"Chris W" wrote in message
...
I have a 5" diameter 3/8-24 mag mount and was wondering if a mag mount
like that would have enough capacitance to adequately couple to the
metal surface it was on. Also is there a good rule of thumb on how much
capacitance you need to have a good ground on a mag mount at a given
frequency? I don't plan on having an HF antenna on this mag mount while
driving. I also don't plan on using it on anything below about 20 or 30
meters.

As a side note I heard someone say that the mag mount has to be on steel
for the capacitive coupling to work. I find that hard to believe.
Obviously the magnet won't hold to aluminum or copper gut setting the
antenna on any metal surface will provide the capacitive coupling, won't
it?

At 2m and above, a surface equal to or greater than a TV tray works
consistently well for me. Mounting, attaching or otherwise arranging such a
surface becomes a mechanical issue, only.

For 10 m HF, if you have a small magnetic surface (iron, mild steel, etc)
and you cement it tightly to a larger conductive surface (aluminum, copper,
stainless) that may be all you need. By "cement," I mean attaching with
some of that goop that comes out of a tube like toothpaste and then hardens.

This works like a champ at CB freqs, for sure, so it will likely work at 10
m. My buddy asked about a CB magmount for his motor home. I had him cement
a steel plate in the middle of the aluminum roof and he had excellent
performance.

The guy was a ham in high school and let his license lapse while he was in
the military. I urged him for years to retest but he never did. He's gone
now.