Conductive paint for mounts?

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62Scout

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Whipped up a couple quick mounts for my antennas on my Jeep, out of steel. My plan is to weld them both to the back of the body, so there's no concern about the mounts loosening over time. They will be properly backed and welded in order to avoid tearing out the sheet metal. I'm also thinking this will easily solve bonding of the mount to the body. It's a soft top, so roof mounts are out. I can't stand antennas in my view, so the common front bumper/fender mounts are out. I've found antenna mounts on the side of the tub are rock magnets, and rear bumper mounting will have the tub blocking too much of the 2m/70cm antenna.

Of course, this means rusting will be a concern. I was thinking of picking up some the of the conductive paint I've seen online to cover the part where the antenna mount grounds to the bracket, but I'm reading that a lot of this stuff has pretty high resistance, and frankly, I don't have a clue how it may affect RF.

I suspect the proper answer here would be to just leave the conducting surfaces bare, apply a thin film of dielectric, and call it a day. I'm not trying to reinvent any wheels here, just going down a slightly different path than most, lol.
 

mmckenna

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If you are welding the mount to the body, you've already got a great ground connection. Following up with conductive paint would be of questionable usefulness.

Clean the metal well, primer and paint and you'll be OK. Conductive paint isn't required.
 

62Scout

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I may not have been completely clear, or perhaps I'm using terminology incorrectly. What I'm essentially doing is welding a chunk of plate to the tub, then installing a 3/8" stud mount into that plate (Wilson 305-610, attached photo). What I'm wondering about is the the grounding between the stud mount and that plate. If I cover the plate in paint, the mount won't be grounding through the plate.
 

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mmckenna

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OK, got it.

Ideal way to do this would be with a lock washer, either split or star. While a conductive paint might work, it's not going to be as good as a true metal to metal connection.

Other option would be to install the antenna mount, mask it, then paint.

I'd really want a good metal to metal joint for what you are doing. While a conductive paint -may- work, how it stands up to weather and time might be a better question. Also, when looking at a DC ground and an RF ground, they can be two different things. I don't know the honest answer to this, but I'd be concerned about the paint being an issue when dealing with RF energy. Seems like it's an unnecessary step.
 

WA8ZTZ

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Leave the surface bare where the stud and nut contact the plate and use a compound like Kopr-Shield by Thomas & Betts to coat the mounting stud and nut. This will protect against corrosion.
 

jbantennaman

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That might work for a receiving antenna, but it won't work for a transmitter.
The counterpoise - what you call GROUND - needs to be beneath the antenna, not along side.
Your needs would be better met using a handheld radio, at least then it would have a counterpoise - YOU!
Go back and read the license manuals.
They will explain the difference between RF ground and the ground you walk on and mechanical ground - the negative terminal on the charging system / battery in the vehicle.
 

WA8ZTZ

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That might work for a receiving antenna, but it won't work for a transmitter.
The counterpoise - what you call GROUND - needs to be beneath the antenna, not along side.
Your needs would be better met using a handheld radio, at least then it would have a counterpoise - YOU!
Go back and read the license manuals.
They will explain the difference between RF ground and the ground you walk on and mechanical ground - the negative terminal on the charging system / battery in the vehicle.
No other place on a soft top Jeep to put the antenna.

The installation may not be theorecically ideal but it will WORK.
 

mmckenna

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No other place on a soft top Jeep to put the antenna.

The installation may not be theorecically ideal but it will WORK.
Correct, it will work. Not ideal, and the radiation pattern will be lopsided.

For decades the California Highway Patrol ran 1/4 wave 40MHz antennas off the side of their cars. Worked fine for them.

Sure, center of cab roof is ideal, but you don't have one.

To be fair, I worked with a guy who had an old CJ-3. He was a very active amateur radio operator. He did mount one of his antenna smack in the middle of the hood. He'd have to remove the antenna to work on the engine.
Looked ugly, got funny looks, but given the circumstance, it worked.

_NOT_ suggesting you do that!
 

Rred

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Welding also blows off the zinc galvanize coating that normally protects body panels. And perhaps your brackets. Zinc can be toxic when inhaled, so use some care. And when you are done with the welding, a couple of coats of zinc "cold galvanize" primer paint should be used to restore the protection.

Where the antenna itself sits? In theory you don't need a direct "DC" quality connection, because at RF frequencies the capacitive connection even through some paint will be good enough. But there's nothing wrong with making that bare metal-to-metal, or using the star washer, etc., and putting a little antiseize (contains metal dust) or plain silicon dielectric (or brake) grease on the bare metal before tightening things down. Even with the non-conductive grease, you get a bare metal to bare metal contact, and the grease simply keeps out water, air, prevents corrosion.

Old standy solutions, nothing worth worrying about.
 

WA8ZTZ

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Correct, it will work. Not ideal, and the radiation pattern will be lopsided.

For decades the California Highway Patrol ran 1/4 wave 40MHz antennas off the side of their cars. Worked fine for them.

Sure, center of cab roof is ideal, but you don't have one.

To be fair, I worked with a guy who had an old CJ-3. He was a very active amateur radio operator. He did mount one of his antenna smack in the middle of the hood. He'd have to remove the antenna to work on the engine.
Looked ugly, got funny looks, but given the circumstance, it worked.

_NOT_ suggesting you do that!
Not to mention the zillions of military Jeeps with all sorts of antennas mounted on the rear.

Didn't want the OP to get discouraged by the post saying that it wouldn't work. Sounds like he has put a fair amount of work into fabricating the antenna mounts.
 

mmckenna

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Not to mention the zillions of military Jeeps with all sorts of antennas mounted on the rear.

Didn't want the OP to get discouraged by the post saying that it wouldn't work. Sounds like he has put a fair amount of work into fabricating the antenna mounts.
Exactly.
 

WA8ZTZ

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Welding also blows off the zinc galvanize coating that normally protects body panels. And perhaps your brackets. Zinc can be toxic when inhaled, so use some care. And when you are done with the welding, a couple of coats of zinc "cold galvanize" primer paint should be used to restore the protection.

Where the antenna itself sits? In theory you don't need a direct "DC" quality connection, because at RF frequencies the capacitive connection even through some paint will be good enough. But there's nothing wrong with making that bare metal-to-metal, or using the star washer, etc., and putting a little antiseize (contains metal dust) or plain silicon dielectric (or brake) grease on the bare metal before tightening things down. Even with the non-conductive grease, you get a bare metal to bare metal contact, and the grease simply keeps out water, air, prevents corrosion.

Old standy solutions, nothing worth worrying about.
Some good points to consider. ^^^

To the OP:
the welding may also burn off the paint and primer on the underside of the tub so be sure to restore the protection. Some spray undercoat would also be a good idea.

RF resistance is actually impedance. Impedance involves both a resistive component and a reactive component. There can be some capacitive coupling through paint but a bare metal to metal contact will make for a better connection because it lowers the resistance and reactance.
 

62Scout

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Didn't want the OP to get discouraged by the post saying that it wouldn't work. Sounds like he has put a fair amount of work into fabricating the antenna mounts.
Nah...not discouraging at all. I wasn't in the least bit concerned as to whether the mount would work or not. I knew signal would get through it.

I really was just wondering whether I was over thinking the corrosion aspects, lol, and just didn't want to form between the stud mount and bracket causing a poor connection. I ended up just taping off the underside of the brackets, and will apply some grease in there when I screw the mount together on it.
 

bharvey2

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Were I doing the project, I'd not worry about using conductive paint. I'd use something like Noalox at my joint connects (a conductive grease) or even mask and paint (2nd choice)

As an aside, you could make your brackets out of stainless steel and weld them to your car body. The welding purists may not like it but it will work. If you go that route, you'd want to make sure the welds themselves are painted to minimize any galvanic action.
 

Rred

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Noalox is a zinc-loaded antiseize paste. Targeted for use on aluminum parts. Conventional antiseize is usually copper-loaded, or nickel-loaded for high heat and other situations. "Conductive grease" might be too flattering a name for it though.(G)
 

bharvey2

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Noalox is a zinc-loaded antiseize paste. Targeted for use on aluminum parts. Conventional antiseize is usually copper-loaded, or nickel-loaded for high heat and other situations. "Conductive grease" might be too flattering a name for it though.(G)
True. I use it for Al and Al/Cu electrical connections and I've come to use the name generically when referring to conductive anti-oxidant paste. I should have used a generic term.
 
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