Author Topic: RF shielding enclosures  (Read 1282 times)

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Offline VSV_electronTopic starter

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RF shielding enclosures
« on: May 16, 2024, 01:50:53 am »
I tried to collect some meaningful information on making DIY shielding boxes for basic RF experimental circuits and I can't find any definitive guides on how to make them. Every book on amateur RF circuits mentions them as an absolute must but none goes into any details on what metal to use, what wall thickness etc.

I went through some online one-page primitive articles and they suggest to use copper and brass for RF shielding. Some threads on EEVblog suggest using 0.3 mm copper sheet for DIY enclosures, others suggest nickel silver sheets.

What about stainless steel which is often readily available for DIY? It's probably not as easy to solder to the ground plane of the PCB compared to copper and brass?

Anyways, please give me some guidance on how to make decent DIY RF shielding enclosures for a wide range of the unwanted interference frequencies when designing basic RF circuits.
 

Online xrunner

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Re: RF shielding enclosures
« Reply #1 on: May 16, 2024, 02:07:03 am »
You can use conductive copper tape with a plastic enclosure and it works very well. I recently finished an RF power meter using this type of shielding and it worked perfectly fine. You can buy the copper tape with conductive adhesive on Amazon or perhaps other suppliers.
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Offline biastee

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Re: RF shielding enclosures
« Reply #2 on: May 16, 2024, 07:16:18 am »
Test equipment casings are universally aluminium - probably for weight saving. Car radios are steel.

Among hobbyists, sometimes PCB is used - see this Hackaday and qrpbuilder articles. However, the two aforementioned articles don't address the question of seams at the lids / covers which I feel is very critical: copper tape as gasket for PCB enclosure

I haven't seen stainless steel being used. Its rarity is probably due to it being more expensive and requiring special tools to cut & drill. 

In making RF proof enclosures, you want to pay attention to the degradation caused by seams (lids) & apertures (knobs & display, etc). My go-to reference is Chatterton & Houlden, EMC, particularly its chap 4 which describes testing methods for shielding,  equations for apertures and a graph for different seams / joints.
« Last Edit: May 16, 2024, 07:44:22 am by biastee »
 
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Offline radiolistener

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Re: RF shielding enclosures
« Reply #3 on: May 16, 2024, 07:49:49 am »
I went through some online one-page primitive articles and they suggest to use copper and brass for RF shielding. Some threads on EEVblog suggest using 0.3 mm copper sheet for DIY enclosures, others suggest nickel silver sheets.

What about stainless steel which is often readily available for DIY? It's probably not as easy to solder to the ground plane of the PCB compared to copper and brass?

Such things are explained in books about shielding theory, include formulas, so you can estimate your case.

It depends on specific case: frequency, near or far field noise source, which near field is more critical - E or H.

Regarding to steel, I don't remember exact frequencies, but at some frequencies and conditions steel material can be better than copper. But in most cases copper is better.
 
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Offline pdenisowski

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Re: RF shielding enclosures
« Reply #4 on: May 16, 2024, 08:25:43 am »
I tried to collect some meaningful information on making DIY shielding boxes for basic RF experimental circuits and I can't find any definitive guides on how to make them. Every book on amateur RF circuits mentions them as an absolute must but none goes into any details on what metal to use, what wall thickness etc.

Anyways, please give me some guidance on how to make decent DIY RF shielding enclosures for a wide range of the unwanted interference frequencies when designing basic RF circuits.

As @biastee stated, in most cases it's the seams / seals that you need to pay special attention to.  At higher frequencies, even very small gaps can act as slot antennas (i.e. if wavelength is shorter than the size of the aperture), so it's important to know what frequencies you are looking at. 

Also, unless your device is completely self-contained / battery-powered and requires no interaction with the "non-shielded" world (control lines, etc.), any penetrations made in your enclosure for passing wires, etc. through will also compromise shielding effectiveness to some degree.

It's also not clear (to me, at least - sorry :)) from your post if you are trying to stop signals from entering or keep signals from leaving the enclosure: depending on your use case, the required attenuation might be considerably different.  With regard to seams, conductive tape is often very cost-effective if your shielding requirements are modest.
Test and Measurement Fundamentals video series on the Rohde & Schwarz YouTube channel:  https://www.youtube.com/playlist?list=PLKxVoO5jUTlvsVtDcqrVn0ybqBVlLj2z8
 
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Offline David Hess

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Re: RF shielding enclosures
« Reply #5 on: May 16, 2024, 01:51:58 pm »
For single projects, I like to use double sided copper clad board because it is easier to work with than thin metal sheet.  Otherwise any thin metal sheet that you can work and solder to is acceptable.
 

Offline VSV_electronTopic starter

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Re: RF shielding enclosures
« Reply #6 on: May 16, 2024, 01:59:35 pm »
...
It's also not clear (to me, at least - sorry :)) from your post if you are trying to stop signals from entering or keep signals from leaving the enclosure: depending on your use case, the required attenuation might be considerably different.  With regard to seams, conductive tape is often very cost-effective if your shielding requirements are modest.

I'm considering very basic stage of shielding (meaning the beginner DIY experimental boards). For instance, if you open the famous 'Experimental Methods in RF Design' (I open it in the pdf form ;) ) all the component boards are shown to be enclosed and WH mentions that every time he shows a pictured board.
Also there are some brief mentions of the enclosures in the YT videos but not much can be gained from those episodes apart from the fact that RF boards need that shielding:

 

Offline VSV_electronTopic starter

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Re: RF shielding enclosures
« Reply #7 on: May 16, 2024, 02:07:28 pm »
For single projects, I like to use double sided copper clad board because it is easier to work with than thin metal sheet.  Otherwise any thin metal sheet that you can work and solder to is acceptable.

Would you say that for the amateur experimental boards like we are talking about here there is no point to overthink the shielding process? I mean - one of course has to do his best in closing all the gaps with the enclosure but the particular metal parameters don't matter much? Is that what you mean?
 

Offline pdenisowski

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Re: RF shielding enclosures
« Reply #8 on: May 16, 2024, 02:15:47 pm »
I'm considering very basic stage of shielding (meaning the beginner DIY experimental boards). For instance, if you open the famous 'Experimental Methods in RF Design' all the component boards are shown to be enclosed and WH mentions that every time he shows a pictured board.

A very underrated book - I'm surprised that it's not read more widely outside of the ham community.

But it does very much depend on the kind of circuits you are building and the environment the device is operating in.  I spent years (professionally) tracking down interference to and from all kinds of electronic devices, and I can tell you from experience that there are a lot of nominally "shielded" devices that leak RF in or out like crazy (and vice-versa). 

Also there are some brief mentions of the enclosures in the YT videos but not much can be gained from those episodes apart from the fact that RF boards need that shielding:

Alan makes such great videos :)
Test and Measurement Fundamentals video series on the Rohde & Schwarz YouTube channel:  https://www.youtube.com/playlist?list=PLKxVoO5jUTlvsVtDcqrVn0ybqBVlLj2z8
 
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Offline pdenisowski

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Re: RF shielding enclosures
« Reply #9 on: May 16, 2024, 02:17:54 pm »

One other tip: if you have a "frequency-aware" instrument (spec an, scope with FFT), you can also use a (homemade) near-field loop probe to scan around the outside (and particularly the seams / edges) of your enclosure to locate any "leaky" points.
Test and Measurement Fundamentals video series on the Rohde & Schwarz YouTube channel:  https://www.youtube.com/playlist?list=PLKxVoO5jUTlvsVtDcqrVn0ybqBVlLj2z8
 
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Offline VSV_electronTopic starter

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Re: RF shielding enclosures
« Reply #10 on: May 16, 2024, 03:33:21 pm »
...Such things are explained in books about shielding theory, include formulas, so you can estimate your case.

Please name the books with references if possible.
 

Offline VSV_electronTopic starter

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Re: RF shielding enclosures
« Reply #11 on: May 16, 2024, 03:46:14 pm »
...
I spent years (professionally) tracking down interference to and from all kinds of electronic devices, and I can tell you from experience that there are a lot of nominally "shielded" devices that leak RF in or out like crazy (and vice-versa). 
...

I perfectly understand what you say and to be honest I somewhat regret (perhaps not the best description of my feelings but anyway, sort of) that I got myself started with the RF even at the preliminary level when I can still back off.
There is so much art and science involved in this particular electronics area that it's really scary and it feels like walking in the dark with a flashlight. However it is so intriguing that it's hard to let it go.
 
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Offline VSV_electronTopic starter

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Re: RF shielding enclosures
« Reply #12 on: May 16, 2024, 04:00:39 pm »
One more thing I want to ask:
Suppose for the experimental RF boards I use double sided RF4 copper sheet and the components are mounted on top of the board while the bottom is made the common (or is it better leave it completely isolated ?) - In that case I suppose the bottom is considered shielded? I don't think the thickness of the copper layer on standard FR4 board is what makes it a good RFI shield compared to a say 0.3 mm copper sheet but since in this thread it's been already suggested to use the 'double sided copper clad boards' for making DIY shielding I suppose it works somehow.
 

Offline radiolistener

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Re: RF shielding enclosures
« Reply #13 on: May 16, 2024, 04:10:40 pm »
Please name the books with references if possible.

You can read my post here to see how to estimate it in short:
https://www.eevblog.com/forum/rf-microwave/stainless-steel-as-an-absorber-of-emi/msg3082975/#msg3082975

If you want more details, you can look for the book Gooch & Daher "Electromagnetic Shielding and Corrosion Protection for Aerospace Vehicles"
 
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Offline David Hess

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Re: RF shielding enclosures
« Reply #14 on: May 16, 2024, 05:02:38 pm »
For single projects, I like to use double sided copper clad board because it is easier to work with than thin metal sheet.  Otherwise any thin metal sheet that you can work and solder to is acceptable.

Would you say that for the amateur experimental boards like we are talking about here there is no point to overthink the shielding process? I mean - one of course has to do his best in closing all the gaps with the enclosure but the particular metal parameters don't matter much? Is that what you mean?

That is what I mean.  Mostly we are concerned with electromagnetic shielding and any conductor will work for that.

After copper clad board is cut, it is easy to sand and file the edges to make them straight and of the proper dimension.  Thin metal sheet is more difficult to work with.

 
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