Copper bottom paint as RF ground plane

[K4TZO]

RF performance is not necessarily dependent upon ohmic conductivity, since capacitive coupling between densely packed copper particles will make the paint seem to be a continuous sheet. Magnetic and other antenna mounts make use of capacitive coupling for effective ground plane connections. I'm looking for real info and tests for use of marine copper bottom paint as a ground plane. Some knowledgeable yachting friends say their bottom paint provides a good ground plane for their vhf and ham radios when afloat. My van-sized RV has a plastic roof, so I'd like to consider copper bottom paint as a primer for an RV roof coating as ground plane for a strap-on antenna (don't want holes in my roof). Where might I contact experts on this subject and maybe even some test results? I'm wel-qualified myself, but have not (yet) experimented with this.. (was a newbie in 1957)

Chuck K4TZO

 

[slowmover]

Why not metal window screening?

What Is Copper Window Screening Used For? | Phifer

Bronze screening provides strength and durability combined with an antique look making it perfect for historic homes. Learn more about copper screening today.

www.phifer.com

 

[K4TZO]

Why not metal window screening?

What Is Copper Window Screening Used For? | Phifer

Bronze screening provides strength and durability combined with an antique look making it perfect for historic homes. Learn more about copper screening today.

www.phifer.com

Didn't say "not". Screen is not this subject. A friend uses a roll-up screen with a portable multiband vertical and has excellent results. I'm making a roll-up aluminum screen and metal tripod for myself. That is a different topic altogether.

This topic is inquiring about the RF physics of copper bottom paint. One guru has suggested that a nanoVNA can measure the reactance of my suggested test strip of about 1 inch wide and a foot long connected with chrome paper clamps to leads. Will try that soon.

 

[prcguy]

I would want to test it before committing. Maybe paint a 3ft dia circle on some cardboard and test VSWR and precise signal strength with a VHF antenna then do the same with a 3ft dia chunk of chicken wire, etc. If the results are the same and the mounting surface doesn’t flex and sever the internal conductive connections it could be good.

 

[trentbob]

I would want to test it before committing. Maybe paint a 3ft dia circle on some cardboard and test VSWR and precise signal strength with a VHF antenna then do the same with a 3ft dia chunk of chicken wire, etc. If the results are the same and the mounting surface doesn’t flex and sever the internal conductive connections it could be good.

Grew up in PA and moved to New York Great South Bay for school, the entire time I worked as a licensed Bayman in my summers. Better known as a Clam Digger. I was the first mate on several fishing boats out of Captree basin.

I agree, I would be very leery of copper bottom paint, as someone who has scraped and painted countless boats and used the best and the worst, I would think that some offerings have very little copper and so many other ingredients that could possibly impede it's use as a ground plane. If we are talking about a different kind of paint, then disregard.

 

[mmckenna]

I did foil tape on a UTV roof for a VHF antenna many years back.

It worked fine when new.
Over the years, however, temperature swings and flexing resulted in it slowly coming part and no longer having continuity.

Would it work? Probably.
Would it give you headaches down the road? Probably.

Ended up putting a sheet of sheet metal on the under side of the UTV roof. Ran a thick surface NMO mount through the roof and the sheet metal. Used pop-rivets to secure the rest of the sheet metal in place.
Worked perfectly for years.

I'd also be super careful about putting anything on the roof membrane of an RV for fear of damaging it. Unless the manufacturer approved it, I think in the long term it might be something to regret. But, RV roof tops don't last forever, so maybe when it comes time to replace it, put a layer of mesh down on the roof before the new membrane goes on.

 

[merlin]

The paint would have to be impregnated with like a copper 'chaf' to work effectively. I would question how dense the copper is in the paint.

 

[K4TZO]

Many are fixated on ohmic conductivity (DC) instead of RF reactance which is often achieved by capacitive coupling, as for magnetic antenna mounts (and others) and low reactance is likely at nearly microscopic level between copper particles in paint due to capacitive coupling. Reactance can be quite low even if DC conductivity is zilch. Note also that an antenna loading coil may have low DC resistance but be a high reactance and block RF. Note that some ohmic conductors have poor high frequency (RF) behavior. My inquiry is about the physics for RF behavior , not coppersmithing for DC.

 

[GlobalNorth]

Build it and test it. We'd be interested in your academic findings.

 

[JustinWHT]

I would want to test it before committing. Maybe paint a 3ft dia circle on some cardboard

Try zinc rich spray paint. Rust-Oleum comes to mind

 

[paulears]

I doubt the perceived effect your friends in their boats are assuming is real at all - after all it is in contacts with a much larger conductive ground plane - the sea! It is also what? At least a wavelength from the antenna. Most marine antennas don't need ground planes anyway, being balanced designs able to be on fibreglass. Musicians use copper paint in the cavities of single pickup guitars which are notorious for interference pickup and hum. They use foil and paint. Foil screening is easy to solder to, paint is not, and electrically even a copper washer screwed into the paint hard is a poor point to point path. Absolutely no use trying to use the paint to connect rather than a wire. The washer contact oxides quickly. It works effectively as a barrier though because even with imperfections, it's a shield. Any testing seems a bit pointless, because the physics already exists - hence why we still use copper ground mesh under broadcast/high power verticals, because the ground conditions are normally poor and variable. The copper paint is a plane, but an inconsistent one that is difficult to integrate into the antenna system. It's a very expensive experiment, difficult to repeat, difficult to maintain and probably not consistent across batches. I know you want precise data, but your difficulty in finding it suggests it's something nobody feels happy trying to quantify, in RF terms.

 

[N5FOG]

Living in a house with the bay only 20 feet from antenna tower, I've tried several types of ways to bond the RF ground to the seawater.

I've went down the route you are talking about with the high copper bottom anti fouling paints and most don't have elemental copper in them. Most use copper oxide of some form and its not that conductive. The only exception I've found is this stuff Antifouling Paint - Coppercoat

Several years ago I did try making a 4'x4' plywood float painted with it and hooked to the antenna system with 3" wide copper strap and allowed the float with the tide. It did give good performance but I found my other system which just has a 4 foot long piece of 1 1/8" copper pipe with four copper toilet tank float balls worked much better.

The hardest issue I found was keeping a good connection between the paint and the copper strap attached to the wood.

One place I did find that copper coating worked well was the underside of my Jeep's plastic hard top to give it a ground plan.

But just keep in mind that its actually a special epoxy with tons of a copper powder in it which is why its so expensive.

FOG