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AMfone's Online AM Handbook => Hints and Kinks => Topic started by: WA2SQQ on October 23, 2017, 11:56:30 AM



Title: Easy RF Shielding for Plastic Cases
Post by: WA2SQQ on October 23, 2017, 11:56:30 AM
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


Title: Re: Easy RF Shielding for Plastic Cases
Post by: WB2EMS on October 23, 2017, 03:00:45 PM
I'd like to try that. Where did you get the MS spray?


Title: Re: Easy RF Shielding for Plastic Cases
Post by: Opcom on October 23, 2017, 08:22:36 PM
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.


Title: Re: Easy RF Shielding for Plastic Cases
Post by: WA9NQW on October 24, 2017, 08:35:25 AM
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


Title: Re: Easy RF Shielding for Plastic Cases
Post by: WA2SQQ on October 24, 2017, 09:09:24 AM
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.


Title: Re: Easy RF Shielding for Plastic Cases
Post by: WB2EMS on October 24, 2017, 10:18:16 AM
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.


Title: Re: Easy RF Shielding for Plastic Cases
Post by: WA2SQQ on October 24, 2017, 10:49:35 AM
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.
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!


Title: Re: Easy RF Shielding for Plastic Cases
Post by: kb4qaa on October 24, 2017, 11:01:59 AM
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/
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