Com Antenna Doubler Question

[szicree]

I'm mounting my Com antenna on the belly and using a rectangular doubler. The antenna base will ground to the doubler via screws into 4 riveted nutplates, and the doubler will, in turn, be pulled against the inside of the belly skin. I've removed the primer from the doubler and belly surfaces to achieve good grounding, but I worry about corrosion. Is there something I can smear on the surface that will allow good electrical contact, but prevent corrosion?

[az_gila]

Originally Posted by szicree

I'm mounting my Com antenna on the belly and using a rectangular doubler. The antenna base will ground to the doubler via screws into 4 riveted nutplates, and the doubler will, in turn, be pulled against the inside of the belly skin. I've removed the primer from the doubler and belly surfaces to achieve good grounding, but I worry about corrosion. Is there something I can smear on the surface that will allow good electrical contact, but prevent corrosion?

DC 4 is an insulator - not really suitable for the job....

Doesn't the comm. antenna come with a rubber or cork gasket for the outer surface?
If this is the case, the only primer you need to remove is on the inner surface under the mounting screw nuts.
A sealer (RTV) is usually recommended around the antenna base edges to stop moisture getting under the gasket.

The best thing is to follow the antenna manufacturer's instructions (surprise... ...)

A typical set is here....

http://www.comant.com/htmls/guide2.html

If in doubt, follow the instructions.... ... don't do a Tim Allen..

EDIT - UPDATE

Sorry ... the Comant link is for GPS ... this one is for Comm.

http://www.comant.com/htmls/guide1.html

They do talk about direct metal to metal contact... so the DC 4 comment still applies.

Not all antennae are identical... the one I mounted on my Tiger belly had a cork gasket, so removal of external paint would have had no effect. You need to check the specific instructions for your antenna...

SECOND UPDATE

This antenna from EDO (D & M) does use a 0.080 external gasket...

http://www.edocorp.com/documentation/antennas_c70.pdf

gil in Tucson

[szicree]

Gil,

I have instructions just like the ones you posted. They suggest two methods; I'm using the one that grounds through the backing plate.

[az_gila]

Originally Posted by szicree

Gil,

I have instructions just like the ones you posted. They suggest two methods; I'm using the one that grounds through the backing plate.

Steve, I think I'm getting it now....

You are only talking about the inner surfaces? ...correct?

If that's the case, just use some RTV at the seams (edges) after the antenna is bolted down to the backing plate. If you stop moisture getting between the plates, you'll be OK.

DC 4 is an insulator, and is not the best for that application where you want good conductivity...

Note that one set of the instructions called for alodine before installation.... this would really help on the long term corrosion prevention, and not upset the conductivity...

.. hope I got your installation correct... gil A

[szicree]

We're on the same page now, Gil. I saw the part about alodine and will use it. I like the idea about using rtv around the seam. Thanks.

[Jekyll]

Here's a picture from the Aero Electric Connection. Per Bob Nuckolls, step 1: discard the cork gasket.

Put a bead of RTV around the perimeter of the antenna once installed. The doubler and skin only need to be cleaned around the screw holes in a 1/4 inch radius. In other words, primer is OK except within 1/4 inch of the screw holes. The torque will create an air tight seal around the screws where you stripped to the bare metal.

http://www.aeroelectric.com/Pictures...stallation.gif

My comments are based on those from Bob Nuckolls on the Aero Electric list.

Jekyll

[Sparky]

As some have already stated, alodine provides good protection of bare metal surfaces of the skin and doubler while maintaining good electical bonding between the surfaces. An RTV bead around the perimeter of the antenna base should keep out moisture, but don't apply RTV between the antenna or doubler and the skin - it is an insulator.

An alodine "pen", such as the Touch-N-Prep 1132 sold at Aircraft Spruce, Stein Air and elsewhere, while somewhat expensive works great for this without the need for rinsing after application. If you use Alodine 1201 be sure to rinse the surfaces after application.

I am using doubler plates riveted to the skin, the Touch-N-Prep alodine pen applied to bare aluminum between the doubler and the skin - and between the skin and the antenna base, and RTV sealant (only around the perimeter of the antenna base) for all external antennas.

Hope this helps.

[BuckWynd]

Originally Posted by Jekyll

Here's a picture from the Aero Electric Connection. Per Bob Nuckolls, step 1: discard the cork gasket.

Put a bead of RTV around the perimeter of the antenna once installed. The doubler and skin only need to be cleaned around the screw holes in a 1/4 inch radius. In other words, primer is OK except within 1/4 inch of the screw holes. The torque will create an air tight seal around the screws where you stripped to the bare metal.

http://www.aeroelectric.com/Pictures...stallation.gif

My comments are based on those from Bob Nuckolls on the Aero Electric list.

Jekyll

Just to update this thread for future visitors, the above link has now changed to:

http://www.aeroelectric.com/Pictures/Antenna/Comm_Antenna_Installation.gif

.

[fehdxl]

I've heard of at tool called a burnishing brush, or at least that's what I think it's called that will make a nice primer free area around a bolt hole and is the perfect tool for this situation.

However, I have been looking a few times and not found where to purchase this tool. Anyone know where to get one?

TIA,

-Jim

[jwyatt]

I think you're looking for a "bonding brush"...

http://www.yardstore.com/browse.cfm/4,4915.html