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Testing Phone-Sized Faraday Bags

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Re: Testing Phone-Sized Faraday Bags

#131

Post by teddyh »

rocqua wrote: post #82
jjoonathan wrote: post #52

Earlier quoted context omitted.

Microwave ovens make for poor Faraday cages. The problem is that you only need 30-60dB to "keep the power in" while you probably want at least 100dB to "keep the signals out." You can test this: put your phone in the microwave and try to call it. Over the years I have had about a 75% success rate. Other household appliances tend to be even worse; any gaps in metallic seals effectively turn into slot antennas and let…

For the sake of keeping people from doing stupid things. DO NOT MICROWAVE YOUR PHONE. The test involves placing your phone in the microwave and closing the door without turning the microwave on. I'd unplug the microwave before trying this.

“This is a man who has experienced The Public”

— https://www.reddit.com/r/tumblr/comments/jy8wzj/rinse_your_e...

Re: Testing Phone-Sized Faraday Bags

#132

Post by relaxing »

2rsf wrote: post #36
causi wrote: post #26

Earlier quoted context omitted.

What's the physics behind being able to make a container light-tight with a couple of right angle corners yet radio waves seem to leak out like water?

Radio waves (well, light and radio are the same thing just with different wavelength) are bounced from conductive materials, light is absorbed

Light bounces too. As you said, it’s the same thing.

Re: Testing Phone-Sized Faraday Bags

#133

Post by relaxing »

op00to wrote: post #12
bborud wrote: post #7

At my former job we had a rather large faraday cage for testing telco equipment. Two things surprised me: 1) It is more fiddly to ensure a room-sized faraday cage doesn't leak RF than I thought. It is really easy to make mistakes that compromises experiments. 2) There was a bath-towel sized piece of cloth that came with one of the expensive Rohde & Schwarz instruments that was astonishingly effective at blocking sign…

I see one of the founders (Ulrich Rhode) of Rhode and Schwarz on amateur radio some times, and I always ask for test equipment and he always says no.

I once tried to acquire a RS PR100 like the one used in the test here. Turns out they cost more than a fancy car!

Re: Testing Phone-Sized Faraday Bags

#135

Post by tablespoon »

docflabby wrote: post #134

Tinfoil hat on - has anyone considered how suspicious that only the commercial products worked, maybe the post is just a very clever shill for those products?

> Tinfoil hat on - has anyone considered how suspicious that only the commercial products worked, maybe the post is just a very clever shill for those products?

Not really, tinfoil actually worked, but it was apparently too difficult to get right:

> In my experiments, I found I could sometimes achieve approximately 90 dB attenuation by carefully wrapping the generator in foil and double folding the seams on all sides, which is quite good (comparable to commercial pouches).

This actually matches my experience with a GPS logger. It only had an on/off switch and I wanted to download the track from my trip without getting points from the download location at the end. IIRC, it was still able to get fixes even wrapped in tin foil.

Re: Testing Phone-Sized Faraday Bags

#136

Post by pfortuny »

posix_me_less wrote: post #61
pfortuny wrote: post #53

Earlier quoted context omitted.

If you consider the compactification of R^3 by a single point “at infinity”, an electric charge inside the surface is the same as the opposite charge at infinity (this is just Gauss’ result). In that sense, “infinity” acts as the opposite charge, does it not? I do not understand your question, otherwise. (Not a criticism, just an interested comment which may be very wrong though).

> If you consider the compactification of R^3 by a single point “at infinity”, an electric charge inside the surface is the same as the opposite charge at infinity (this is just Gauss’ result) This is a mental operation, not physically possible. The difference is real: for example, charge inside a perfect conductor cavity generates electrostatic field outside. A charge outside perfect conductor cavity does not genera…

Aaaahhhhh!!!!

Thank you for this comment, truly enlightening (I am a mathematician and know 0 physics). Shall have to think about it.

Re: Testing Phone-Sized Faraday Bags

#137

Post by throw10920 »

SamuelAdams wrote: post #57

This is a super cool blog post. However I think it alludes to a much larger problem. For many products today, it’s very difficult or impossible for most people to verify the product works. For a network switch, there are free and open source tools like iPerf to test and verify speeds are as advertised. For a faraday box, you have to go through all these steps (and knowledge learned) just to be able to test these. Wha…

I'd like to describe a complementary problem to yours - that it's very difficult or impossible to find out others' experiences with a product's quality, durability, and performance. That is - the complement to the problem of "it's hard to determine if some products work" is "it's hard to find other users' experiences with the product".

Amazon reviews are completely worthless, but very few other platforms have anywhere close to the same number of reviews on them. Most platforms have no verification of purchase for reviews. It's hard to determine information like "does this device require a cloud login? for which functionality? are there ads?" that isn't explicitly supplied by the manufacturer (or hidden by them). Negative reviews about product breaking quickly aren't very useful because people whose products work for a long time leave reviews at a lower rate. Google is almost useless for finding out information like this because of how SEO-gamed everything is, and the ol' "site:reddit.com" trick will only work for a while longer until these fraudsters create enough fake reviews on Reddit that it also succumbs (which is already beginning).

(rant "...and this problem will likely won't be solved anytime soon, because consumers don't care about these things. That's the reason that we're in this situation - consumer apathy. When was the last time you heard a non-tech-savvy relative say something along the lines of "Wow, this phone didn't last very long. Is there a place where I can add that data point so that other people will be more informed before they purchase one?" Users don't care about performance, privacy, or durability - they just want to watch Netflix and pay the lowest sticker price they can (regardless of annual cost of ownership). You see people self-organizing around things like video games or paintball or book clubs or whatever all the time - why won't they put even a fraction of that effort into ensuring that they buy a good car?")

Re: Testing Phone-Sized Faraday Bags

#138

Post by alecdibble »

relaxing wrote: post #132
2rsf wrote: post #36

Earlier quoted context omitted.

Radio waves (well, light and radio are the same thing just with different wavelength) are bounced from conductive materials, light is absorbed

Light bounces too. As you said, it’s the same thing.

How much EM radiation bounces and how much it gets absorbed is highly variable depending on the material and, most importantly, the frequency of the EM radiation. A great example in this article is the faraday bag that was visibly transparent but blocked the EM radiation in the 1-6gHz range. The metal tin was basically the opposite, it blocked visible radiation very effectively but not radiation in the radio frequency range.

Re: Testing Phone-Sized Faraday Bags

#139

Post by pro_zac »

IncRnd wrote: post #126

This article was a fun read, and it really highlights how we trust the words on the tin to be accurate and not mistaken marketing gibberish. However, the part about the cost ranging from $40 - $80 is simply not true. I know this, because I purchased for $20 yesterday a faraday box to hold my auto key fobs and my cell phone. [1] There are very many items for sale at this price point, fabric, pouches and boxes. [1] htt…

Key fobs! Isn't there a scheme where thieves clone the signal from a key fob when the owner is asleep in their home and drive off with their car?

Re: Testing Phone-Sized Faraday Bags

#140

Post by catlikesshrimp »

haarts wrote: post #92
catlikesshrimp wrote: post #30

Earlier quoted context omitted.

If you are concerned enough, but a phone with physical switches https://www.androidpolice.com/2020/08/22/this-smartphone-has... Or at least phone with a removable battery I know I will never buy a phone without a 3.5 audio jack

That last sentence surprises me a bit. What does a 3.5 audio jack have to with any of this?

Manufacturers are always trying to push features that are more profitable to them. As expected.

Non-removable batteries is the new standard because of that. (Also stream lining) Which is bad for security (the point of the article)

I don't use bluetooth because it is not reliable enough for me, because I don't like charging another device and, less importantly, because in the past it has been exploited to hack devices. The audio jack is the one port I prefer never to part with.

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