The AM Forum

Sometimes we build something and place it in a small plastic case, only later to discover that it’s effected by RF. I recently discovered that my RSP1 SDR receiver’s plastic case presented the same problem. Some users have opted to purchase aftermarket aluminum cases to address this deficiency.
I decided to fix it using a simpler method, one that could maintain the original appearance. After disassembling the case I laid down two strips of an adhesive backed copper foil (one on each half) that I use for my stained-glass work. After carefully masking the case half’s I sprayed the case’s interior with two coats of an RFI conductive shielding spray made by Miller Stephenson. The spray coats the copper foils, connects with the USB connector, and electrically bonds the entire assembly. After it dried, I powered up the RSP1 and monitored the noise. While closing the case you can literally see the noise diminish. Visually, you’d never know it was modified!

https://www.miller-stephenson.com/wp-content/uploads/2016/09/MS-487G.pdf

I'd like to try that. Where did you get the MS spray?

They don't list their dealers or I could not find them. I was looking for that kind of thing as well but did not find. I think that's an urgent matter in need of investigation.

When I worked for Motorola in the early 70s, we tamed the gremlins in the UHF HT-220 with silver conductive paint in the interior of the plastic case. We had to put a layer of insulating paint on top of that as well. It did work well and was not required for the VHF models.

73,
Jack

So they only sell direct.
I actually needed some for a work project so I called them to see if I might be able to get a sample.
Next day, I had it! I guess the company name helps ;-).
They are in CT. This is the 3rd project I've used it on, and its never let me down. 2-3 light coats - dries to a satin dark gray finish.

We used something similar on some early LEAA handy talkies and some pagers. Many moons ago. It didn't stick real well. I expect things have improved some in 30 years.

I'm not so sure I needed to lay down the two strips of copper tape, but I wanted to be sure both piece of the case were bonded to the electrical ground of the PCB. Both strips have a good contact with the shell of the USB connector. You can definitely measure resistance between any 2 points on the case. The end result is what counts, and it did the trick!

MG Chemicals is a large electronics material manfacturer who makes EMI/RFI/Static coatings in Nickel, Silver, Carbon in both spray can, and brush on forms.  Available from the usual parts houses as well as Amazon.

https://www.amazon.com/MG-Chemicals-Conductive-Coating-Aerosol/dp/B005T8O7X4

Nickel Spray Can
https://www.alliedelec.com/mg-chemicals-841-340g/70125858/

Silver Spray Can
https://www.alliedelec.com/mg-chemicals-842-140g/70635960/

Ran into "magnetic paint" a while back. Apparently allows magnets to stick to the surface applied to, I guess it would help shield RF as well:

https://www.lowes.com/pd/Krylon-Magnetic-Paint-Flat-Gray-Magnetic-Spray-Paint-Actual-Net-Contents-13-oz/1000197021

Back in the 80's I designed a transmitter facility atop South Mountain in Phoenix, AZ, aka the home of 35MW of RF.

In the day there were some 5 VHF (316kW), 5 UHF (several over 1MW), 13 FM (all 100kW), and the rest of over 200 users up there.  Some cars made it into the site, never to leave under their own power as it fried onboard computers.

The building was constructed of concrete blocks with a steel panel roof.  The panels were tack welded together to form a solid shield, then bonded with copper strap to the UFER in several locations about the perimeter.

For the walls, I applied a silver-bearing paint with my Binks spray gun, taking a couple hours.  It connected with all the copper straps.  You could stick the probes of a VOM in the wall, and get readings around 1 Ohm anywhere you liked.

At first the purchasing department of the site owner balked at $5K for a gallon of the paint, but the contractor wanted $10K to furr it out and use copper screen instead.

The paint was designed to turn blow-molded plastic microwave cavities into metal.  They thought my idea was novel and included that use in their lit afterwards.

73DG