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Testing Phone-Sized Faraday Bags

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Re: Testing Phone-Sized Faraday Bags

#91

Post by elbasti »

rocqua wrote: post #75
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?

Also, 20-30 Db of attenuation for light is already quite a lot. Whilst for a radio signal it is still very conceivable that 30Db of attenuation still allows for a signal to be received. Our eyes simply aren't very sensitive instruments. And the visible part of the spectrum is uncharacteristically full of 'noise', so it makes some sense that our eyes don't need to detect any signals that are too far below the noise-fl…

> our eyes aren't very sensitive instruments

I take umbrage with that statement! Our eyes are exquisitely sensitive, and most importantly, have staggering dynamic range.

Our eyes are capable of perceiving a single photon [1], albeit noisily (I've been lucky enough to have performed this experiment myself!).

But the greatest thing about our eyes is the dynamic range: the difference in brightness between a moonless, starry night (which we are perfectly capable of navigating by eyesight) and a bright sunny day is nine orders of magnitude. A bright day is a billion times brighter!

Show me an RF receiver or light camera with that dynamic range!

The one place our eyes are limited is in frequency range.

[1] https://www.nature.com/articles/ncomms12172

Re: Testing Phone-Sized Faraday Bags

#92

Post by haarts »

catlikesshrimp wrote: post #30
djmips wrote: post #19

If you are sufficiently concerned, why not mod the phone to add a physical battery disconnect? Would this not provide 100% protection?

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?

Re: Testing Phone-Sized Faraday Bags

#93

Post by fsflover »

323 wrote: post #71
fsflover wrote: post #58

I prefer smartphones with kill switches, Librem 5 and Pinephone.

But you need to trust that they are actually working, and that the device was not intercepted and modified en route.

They have the schematics [0,1] for these devices and even X-rays [1] for Librem 5. Also, anti-interdiction services for the latter [2].

[0] https://wiki.pine64.org/index.php/PinePhone#PinePhone_board_...

[1] https://source.puri.sm/Librem5/community-wiki/-/wikis/Freque...

[2] https://puri.sm/posts/anti-interdiction-services/

Re: Testing Phone-Sized Faraday Bags

#94

Post by yosito »

ejolto wrote: post #28
ncmncm wrote: post #24

Earlier quoted context omitted.

It is hard to believe this would perform better than a Lazzaroni tin. And I don't recall ever finding one of these things in a hotel room, even in Europe.

Depends what the tin and shaker are made of. The tin is probably made of aluminum which has a higher skin depth than stainless steel, which I assume the shaker cups are made of. A Faraday cage of continuous surface needs walls that are thicker than the skin depth of the material the cage is made of. Since the skin depth of stainless steel is lower, the cage wall thickness can be lower while still creating an effectiv…

Reminds me of a joke my dad used to tell:

Dad: What's five plus five?

yosito: Ten!

D: How many fingers do you have?

y: Ten!

D: What's an aluminum can made out of?

y: Tin!

D: Wrong! Aluminum!

Re: Testing Phone-Sized Faraday Bags

#95

Post by rocqua »

elbasti wrote: post #91
rocqua wrote: post #75

Earlier quoted context omitted.

Also, 20-30 Db of attenuation for light is already quite a lot. Whilst for a radio signal it is still very conceivable that 30Db of attenuation still allows for a signal to be received. Our eyes simply aren't very sensitive instruments. And the visible part of the spectrum is uncharacteristically full of 'noise', so it makes some sense that our eyes don't need to detect any signals that are too far below the noise-fl…

> our eyes aren't very sensitive instruments I take umbrage with that statement! Our eyes are exquisitely sensitive, and most importantly, have staggering dynamic range. Our eyes are capable of perceiving a single photon [1], albeit noisily (I've been lucky enough to have performed this experiment myself!). But the greatest thing about our eyes is the dynamic range: the difference in brightness between a moonless, st…

I knew the dynamic range was large. I did not know about the sensitivity! That is quite impressive.

The magnitude of the dynamic range is even more impressive if converted to 'stops' from photography, yielding about 30 stops (1 stop halves the light). Whereas a really good camera will do about 15 stops. Though I suppose that the camera gets 15 stops in a single 'scene'. Whilst the 30 stop figure for the human eye does not hold up if half your vision is taken up by daylight and the other half by a night sky. For a single 'scene' I think it becomes hard to define the dynamic range of a human eye though.

Re: Testing Phone-Sized Faraday Bags

#98

Post by willis936 »

formerly_proven wrote: post #90
willis936 wrote: post #44

Earlier quoted context omitted.

Microwave-ovens definitely don't leak below 2.4 GHz. Any frequency above that is a non-issue for microwave-oven operator safety. It also wouldn't be an issue for any communication device transmitting below 2.4 GHz. If you want to shut down 5 GHz communication then a microwave-oven would be leaky. 60 GHz: it shouldn't matter since it needs LoS anyway. Also, remember to ground your faraday cages.

The width of the area around microwave doors looks suspiciously close to lambda/4 for 2.4 GHz (~3 cm) on pretty much every microwave I've ever seen - I'd almost be surprised if that construction isn't tuned to reflect 2.4 GHz, which would make it a very leaky container at say 0.9/1.8 GHz.

I think you should double-check the harmonics that would get passed relative to a quarter-wave mesh.

Re: Testing Phone-Sized Faraday Bags

#99

Post by Luc »

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.

That's very cool, he's basically test equipment royalty. But he's the son of one of the founders - Rhode & Schwarz was founded in the 1930's.

Re: Testing Phone-Sized Faraday Bags

#100

Post by sdoering »

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 agree that the free market is easily gamed and therefore I really am glad to be living in a country with relatively strong consumer protection laws.

I buy online, I can return within two weeks no question asked.

It breaks within two years - I return it. Either I get a repaired one or a new one or my money back.

There are few exceptions but mostly it makes shopping quite secure.

Yes. There are bad actors. Yes people get ripped off by shady online stores. But if using trusted shop, PayPal or one of the known big shopping brands the experience is mostly good.

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