RF Shielding Tips and Tricks | Hacker News Reader

RF Shielding Tips and Tricks

assemblymag.com

83 pointswalterbell57 comments

I don't know who the audience for this article is, whether it's hardware people struggling to pass regulatory compliance, or whether it's paranoid people thinking they can somehow escape surveillance.

For passing certification, the best advice is really shielding closest possible to the source. Bury all signals, have no cables, shield the die if anything. If you can, bury the die.

For escaping surveillance, make sure to never leave the shielded room, or meet with people who do. /s

This is a trade magazine for people who assemble systems from components. So they put a router in a box, or whatever, and need a power supply and amplifier and connectors to the outside world. The finished system needs to pass compliance testing, but they can't modify the parts they've selected - all they can do is fix the cabling and do things to the outside of the purchased components.

It's kind of like EMI/EMC testing of hardware you have designed yourself; it's usually much cheaper to apply a bandaid fix (add ferrite cores, shield that cable better, terminate here not there, etc.) and add to a punch list for rev 2, than to go back to the drawing board and change the board/die/whatever.

Of course if you can plan for this during design, you (and your boss/bottom line!) will be a lot happier.

In the mid 90s I had the dubious pleasure of being asked to repair a series of TEMPEST certified computers: standard Zenith 8086 clones (well, as standard as a Zenith got anyway) inside a massive steel chassis with all inputs/outputs wrapped around multiple ferrite cores before passing through some heavy-duty milspec connectors. Took a solid couple of minutes each machine pulling screws just to get the lid off so I could plug in a keyboard and monitor (Hercules Monochrome!) and assess the system. Took a dozen machines and made four or five working ones - lot of hard drive failures though Spinrite did manage to resurrect a couple. Still remember all those little jumper leads going from the peripheral cards through the ferrites and into the funky round connectors on the outside of the box.

my isp has a built in public (captive portal) wifi network that I can't turn off. They use it to provide wifi hotspots all over the country. rf shielding is a non destructive mod I can do to block the rogue wifi

if this is Comcast, you can also just buy your own modem/router

I believe you can also turn it off in your account settings.

it has been known to turn itself back on. for comcast, besides buying your own, you can also request a non-wifi router.

It’s interesting to see so many audio acoustics articles hitting the news. I’m in a crazy situation where I have a 80 meter iron fence beginning at a furnace/electric room and ending with a “L” shaped thick iron bar just below my bedroom window. The furnace buzzes every night and the fence acts like a tuning fork and hits me with 13000hz at high dB. I think I need this device.

Maybe it's my English level that isn't up par or your situation that is crazy, but I wish I could see a photo of what you describe! Inquiring mind want to know!

Sure. Imagine the small fence stretching for 80 meters and connecting to a buzzing furnace.

https://drive.google.com/file/d/13yfIYqBZsr4jH6WnnfiyfNxwchj...

btw any tips on insulating this fence post to reduce the noise? I was just think foam tubbing but maybe it should be wrapped in copper too?

Really the best thing to do would be to cut the horizontal piece with an angle grinder to give an air gap close to the furnace. The fence owner may not like that idea though.

And it wouldn't have to be a literal air gap, some kind of glue or foam would help preserve the aesthetics of the fence

You might have better luck adding weight to the fence, to change its resonant frequency.

Weight and something that absorbs and dissipates vibration. Drape rubber mats over it, or weave strips of soft material into the fence slats.

I got the fence part, but why is it connected to a furnace??? We agree that a furnace is a thing that makes heat right?

There is a room with a giant chimney right next to the fence on the other end. I think it is a furnace.

Here is some captured audio of the room from a few feet away.

https://drive.google.com/file/d/1gS1mkYPOeg25npQxWOSr_8j4I-G...

Amusing in a sad way how the site strong-arms people into accepting their tracking, if you decline they forcibly redirect you to the home page of the site ("GDPR Policy This website requires certain cookies to work and uses other cookies to help you have the best experience while on the site.")

Has the world wide web really fallen this far?

One practical advice is to install uBlock Origin + Privacy Badger and then just accept whatever they ask you to. Otherwise you'll always wonder what "essential" really means to them.

Edit: uBlock Origin, not uBlock

"For example 100 MHz = 100.000 Hz = 3 meter."

Is that a typo? 100KHz = 100,000Hz. Or is it that damn metrics system screwing with me again?

I was thinking European separation, but I can't seen any indication on the page that would confirm it.

That has to be a typo. 100 MHz frequency ≅ 3 m wavelength in air. 100 kHz would have a 3 km wavelength, which is relevant for power transmission systems but not a device that's less than 1 m^3 in volume as in the illustration.

Hz are metric system (well, both, but identical, Hz are 1/s). It's a typo.

https://archive.is/uRCdW

> For example 100 MHz = 100.000 Hz = 3 meter.

Hmm?

> [table showing 10x reduction every 20dB]

Why 20dB? I thought it was 10x every ~10dB?

I’m on my phone and it’s tricky to quote.

For the first part, the middle step is missing some zeros, but an easy approximate formula for wavelength is frequency in Hz/3e8 m/s (rough speed of light).

For the second part, that depends on whether you’re looking at voltage or power. (Because power is proportional to voltage^2, the factor of two gets pulled out)

Cant read the site as I am opting to decline the consent of being tracked by cookies and tricked by marketing to buy things I don't need.

https://web.archive.org/web/20201012122518/https://www.assem...

I've looked into creating a Faraday cage for my bedroom for the potential benefit of increasing sleep quality by blocking RF. I live in downtown Seattle where a cellular tower is visible from my house and the measured RF around me is quite noisy.

From my research it is definitely not trivial to pull off. There are RF shielding canopies you can put over your bed but they are 1k USD+ and quite unsightly. Then there is the possibility to paint the interior walls with RF shielding paint but you have to ground it correctly or you could be introducing more problems for yourself than you're solving. With either solution, I live on the 3rd floor and it's unclear if I would also have to ground the floor underneath me, or essentially "trap" RF emitting upwards into my cage which again would create more problems than they solve. After contemplating all of these possibilities and pitfalls, I decided to put it off for later until more tried techniques have been advertised.

I suspect that worrying about ambient RF is causing you the problems rather than the ambient RF.

some anecdotes:

I worked in an office with a phone tower on the roof. A couple of people complained continuously about headaches and sickness and blamed it on the tower. One quit. This was entirely related to their borderline alcoholism and terrible diet rather than the phone tower but failing to see the causality is a typical human trait. How do we know? Well when they were putting the tower up they managed to damage the roof which caused all work to stop before it was even powered up. At that point the insurance companies were duking it out.

Also I’m an amateur radio operator and ex RF engineer. I spent a number of years working in fairly high energy RF installations in the defence sector and not once did I see a reported problem from someone in the field.

I suspect you need to check your causality before being hooked on solutions which are usually sold by a combination of con artists and morons. This is one step from burning 5G towers on the thought spectrum.

Yeah, I actually sleep fine and this would be the most extreme version of proactivity that I would ever elicit. I don't really know what to make of some interesting case reports that some individuals make about being "RF sensitive" on a very rare basis; but I definitely don't fall into that camp.

However, I have done some reading on the potential long-term health consequences of non-ionizing radiation and a lot of the research is inconclusive. I believe the general consensus from empirical data is that RF has not been shown to cause cancer, but, I feel like that's a relatively low bar to meet. Certainly, there are no positive health effects to all of the extra radiation we are creating and exposing each other to; and the consequences may only be known in the future when we have more precise measurement techniques.

But yeah, even with that said, I don't know if I consider it to be enough of a problem to warrant spending more than a few hundred dollars on.

I think the point is, to steal an ironic phrase, that the signal to noise ratio of issues is utterly insignificant. Nearly all the research is inconclusive and anything which is conclusive isn’t reliable. I don’t think that is enough to act upon myself. The communications agencies around the world have provided us with well researched safe exposure limits and compliance.

If you have a few hundred dollars to burn and want to feel better, do it but that’s just bankrolling the idiots selling magic unicorns. The real solutions used in laboratories and industry run well into five figures.

Perhaps interestingly I spent a few hours the other day chasing down a prominent signal working its way into my spectrum analyser. What was it? Well it turned out to be a clock PLL harmonic off my Ryzen PC. That was far above the relative power of the WiFi router about 6 feet away from it. My interest in that signal? Purely academic as I thought my SA was broken again :)

My boss paid for decent shielded room 4x4 meters in size €80k. I wouldn’t toy with foils an the apartment walls, that sounds like complete nonsense to me when I know how industrial shielded room was build.

The common kitchen aluminium foil works. We now use it in our lab to shield stuff. A few layers of it works much better than the expensive stuff from 3M.

Is shielding affected by an insulating layer, e.g. paper or foam used in thermal insulation or vapor barriers? Those are available with two layers of aluminum, in 4' wide rolls with fiber strands for strength, at much lower cost ($0.20 per sq ft) than overpriced shielding fabrics.

There are barrier variations, some do use aluminum, e.g. https://www.radiantguard.com/products/radiant-barrier-ultima...

What frequencies are you blocking and at what powers?

I've spent a while trying to build a poor man's fariday cage for phone testing and found it almost impossible to isolate handsets.

What about reflections inside? I bet foil is very reflective and is good if you only need shielding from outer radiation.

They are usually lined with absorber foam. That's the expensive bit.

I agree with your sentiment, but let me play devil's advocate to potentially turn over a few stones.

> communications agencies around the world have provided us with well researched safe exposure limits and compliance

Based on what evidence though? Aren't their conclusions based on the general consensus that epidemiologists have gathered over the last few decades demonstrating that RFs don't cause cancer? IMO, that's a low bar; and they have a history of time and time again approving technologies, food products, and chemicals that in hindsight prove to have far worse health implications than originally believed.

I think citing any one individual study is a flawed argumentative technique, so I'll just say I was certainly surprised when Scientific American (whom I find to be in the top 5 publications in terms of credibility) published this piece[0] stating that speculating on the health effects of 5G are not completely unwarranted. The piece is an op-ed but I have found that Scientific American is very selective in what they do choose to publish. I assume the claims they are making on the effects of EMF in the piece are based on the totality of the evidence.

Practically speaking though yes, like you, I don't pay thought to it. Though if we do eventually realize that these technologies did end up having some negative health externalities I will find myself unsurprised.

[0]: https://blogs.scientificamerican.com/observations/we-have-no...

The canonical reference is by ICNIRP which references many studies at the end of the document. This is also actively reviewed based on new evidence all the time, which is the entire point of ICNIRP!

https://www.icnirp.org/cms/upload/publications/ICNIRPrfgdl20...

I make no comment on Scientific American. I don't read it and have no experience with it.

Just a point here to note ...

There are health effects from RF as it stands but it's usually localised heating, hence why some handheld radios are known as "Chinese eyeball cookers" but they tend to run +40dBm into an antenna with some gain thus ending up with 25W ERP close range strapped to your face - that's another 4dB or so. Your average phone kicks out a max of 23dBm if it's really kicking it out hard. That's 125x less power. Your wifi router is half that again. That's 250x less power than the eyeball cooker. And none of those emit ionising radiation. And your wifi router isn't strapped to your head.

As mentioned earlier my Ryzen's motherboard shows up bang on 800MHz with more ERP than my router...

Far far far more worrying for me is all the pollution and crap in the air I'm huffing up every day living near an airport.

"Far far far more worrying for me is all the pollution and crap in the air I'm huffing up every day living near an airport."

Ah yes, that reminds me of certain esoteric people, who spend lots of energy finding new things to worry about and struggle to avoid it, like bad chemicals from the washing maschine and of course 5G, while smoking the whole time.

Yep. My father is one of them. Has cancer but it's driving a couple of diesel cars that did it, not the smoking for 60 years...

> Certainly, there are no positive health effects to all of the extra radiation we are creating

Just three days ago:

Exposure to Static Magnetic and Electric Fields Treats Type 2 Diabetes (https://news.ycombinator.com/item?id=24742900)

I cannot say anything to the quality or validity of that article, but as usual absolutes are more often wrong than right.

Also you could argue that radiation levels are the lowest beneath the tower.

While a full Faraday cage can be expensive, RF from known sources can often be reduced by 90% within a specific area, with the aid of a directional RF meter, commercial-grade aluminum foil/insulation and aluminum foil tape. Window shielding would require copper mesh, which is pricier.

Start with the cheapest, simplest and most reversible approach and collect data to test assumptions as you learn about your local RF environment. Profile RF sources that are under your control. You may be able to reduce the power level of your WiFi router. Many cellphones support WiFi calling, which allows the cellular radio to be disabled.

Shield installation: http://www.eiwellspring.org/shielding.html

Skin depth calculator by RF frequency: https://www.allaboutcircuits.com/tools/skin-depth-calculator...

Since most of the strong RF around us are in the S-band, around 12cm, you could just use a metallic mesh with holes smaller than that (<1cm). I use wire fence on the walls facing the antennas and it reduces the radiation from 2 V/m to around 0.4-0.5 V/m. From my experience, everything below 0.3 V/m, or 0.2 uT on the magnetic side, is fine.

I would also recommend following the scientific research in this field and to gather your own data. Simple variables, such as pulse and blood pressure, are a good start.

Uh, why can't you just tape tinfoil on the walls, floor and ceiling and be done with it?

it's easier (and uses a lot less tinfoil) to just make a hat. it's also much more portable so you're not confined to just one room of your home.

Hard to sleep in tin foil. You need to use a meter as well. Its very easy to end up making a big reflector that just ends up amplifying the signal.

http://web.archive.org/web/20100708230258/http://people.csai...

This was fun. Thanks for sharing

"It requires no stretch of the imagination to conclude that the current helmet craze is likely to have been propagated by the Government, possibly with the involvement of the FCC."

Of course it has. They've been gaslighting us all along.

> it's unclear if I would also have to ground the floor underneath me, or essentially "trap" RF emitting upwards into my cage

Your research must not have gone really far if you're still wondering about this kind of questions... Also, Faraday cages effectiveness depends on the wavelength you're trying to block. Long story short, it's not a trivial DIY project.

Sorry, I should have clarified. I have a modem under my room, as well as a few neighbors with modems around ground level. What am I missing here? I tried as best I could to cobble together info together from around the web but it was fairly technical and sparse in the details that were relevant to my project.

Yeah, choosing the spectrum length which would be best to block was also confusing.

This is true, don't understand the down votes. You don't need a complete faraday cage, it's important to understand the direction of the source of where you are trying to block. And use a meter so you aren't guessing.

You most definitely do need a complete box. No gaps and all joins welded. And no wires passing through.

A partial box can actually make things worse:

Depending on wavelengths the intervening metal can actually focus the waves (it's called a "director").

Consider going the emf clothing route. I sleep very well this way. You can get a head and neck buff for a couple of hundred.

I'm finally going to pony up and use the Y shield HSF54 paint for the entire bed room. About $1,500 all in.

Tin foil connected to ground and you are done. What is difficult about that?

The slightest gap or join will make it useless. To be effective it must be very heavy foil with welded or bolted seams, and no wires passing through.

And contrary as it seems, earthing it won't make much difference. Especially as any earth wire will be many wavelengths long at VHF/UHF.

Reply on news.ycombinator.com