I want to install a Motorola (NMO) VHF hole mount in my car's trunk
lid. Like most late model vehicles however, it is made entirely of
aluminum. If your familiar with it, you know the mount fitting is
machined of brass. I've done a few of these on traditional sheet steel
trunks without thinking about this before, and never had a problem with
premature failure from galvanic type corrosion.
Besides electrical/RF degradation, I am equally concerned about the
integrity of the vehicle finish in the event of catastrophic corrosion.
I intend to run about 50w to this antenna.
My question is: If my installation is as waterproof as they always
have been, should I be more concerned about this phenomena while
dealing with brass and aluminum than I was with brass and steel?
I have found a lot of talent in this group. Thanx in advance for
your well-considered opinions.

On 3 Oct 2005 17:11:43 -0700, "Nick" wrote:

I want to install a Motorola (NMO) VHF hole mount in my car's trunk
lid. Like most late model vehicles however, it is made entirely of
aluminum. If your familiar with it, you know the mount fitting is
machined of brass. I've done a few of these on traditional sheet steel
trunks without thinking about this before, and never had a problem with
premature failure from galvanic type corrosion.
Besides electrical/RF degradation, I am equally concerned about the
integrity of the vehicle finish in the event of catastrophic corrosion.
I intend to run about 50w to this antenna.
My question is: If my installation is as waterproof as they always
have been, should I be more concerned about this phenomena while
dealing with brass and aluminum than I was with brass and steel?
I have found a lot of talent in this group. Thanx in advance for
your well-considered opinions.

Aluminum is less noble than brass, therefore there will be slightly
more galvanic action with your new installation.

Use an anti-oxidant paste to slow down or eliminate the corrosion.
Products such as Noalox or Penetrox.

Nick wrote:

I want to install a Motorola (NMO) VHF hole mount in my car's trunk
lid. Like most late model vehicles however, it is made entirely of
aluminum. If your familiar with it, you know the mount fitting is
machined of brass. I've done a few of these on traditional sheet steel
trunks without thinking about this before, and never had a problem with
premature failure from galvanic type corrosion.
Besides electrical/RF degradation, I am equally concerned about the
integrity of the vehicle finish in the event of catastrophic corrosion.
I intend to run about 50w to this antenna.
My question is: If my installation is as waterproof as they always
have been, should I be more concerned about this phenomena while
dealing with brass and aluminum than I was with brass and steel?
I have found a lot of talent in this group. Thanx in advance for
your well-considered opinions.

The threaded brass outer ring has (or should have) and O-ring embedded
in the bottom edge to provide weather proofing.

I would not be concerned with this setup. While I cannot recall ever
installing an NMO on an aluminum auto body, I have used an NMO on a
variety of other outside antenna installations with aluminum and have
never experienced an problem.

Andy

On Mon, 3 Oct 2005, Nick wrote:

I want to install a Motorola (NMO) VHF hole mount in my car's trunk
lid. Like most late model vehicles however, it is made entirely of
aluminum. If your familiar with it, you know the mount fitting is
machined of brass. I've done a few of these on traditional sheet steel
trunks without thinking about this before, and never had a problem with
premature failure from galvanic type corrosion.
Besides electrical/RF degradation, I am equally concerned about the
integrity of the vehicle finish in the event of catastrophic corrosion.
I intend to run about 50w to this antenna.
My question is: If my installation is as waterproof as they always
have been, should I be more concerned about this phenomena while
dealing with brass and aluminum than I was with brass and steel?
I have found a lot of talent in this group. Thanx in advance for
your well-considered opinions.


I am not at all familiar with the electrical requirements of your specific
mobile antenna and so my first counter-question is whether the
instructions require electrical contact between the conductive brass of
the antenna and the conductive aluminum of the trunk. If conductivity is
important, you may be able to reduce dissimilar metal electrochemical
degredation by 'painting' a narrow seal 'bead' with something like that
transparent Krylon spray (others here might have better material
suggestions). If conductivity is not required, then a thin sheet (or ring)
of parafilm, or other soft deformable but insulating and waterproof
material (even waxpaper, saranwrap), carefully cut, might 'fill' surfaces
so well as to exclude moisture that promotes electrochemical processes.

Do they give you, for example, a rubber washer for use on the inside side
of the trunk sheet?