41–50 of 205 posts
Where I live, all I have to do to block 4G is to stop standing in the far corner of the yard.
I do miss the old days of tuning the rabbit ears on top of the tv for best reception.
> While the cookie tin performed much better than the mylar bags, and could provide a modicum of useful attenuation under some circumstances, it was not sufficient to provide meaningful assurance of signal isolation at any frequency. However, it was unique among the containers tested in providing tasty snacks during measurements Back in the day working for Symbian I used to regularly have to run a load of automated B…
I really like Snowden's recommended Faraday cage for phones or other devices of similar size: two drink-shaker cups[1]. Drink shakers are cheap and widely available. The average hotel room in any medium/large hotel chain probably includes a shaker as a standard item as part of the minibar. The simple two-cup style (as seen in [1]) is preferred over the fancier "strainer top" style because you can press the two cups t…
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?
I remember going caving and we would have to go 100m or more through many different turns before we all turned our lamps off and truly experienced perfect dark.
> "Wrap it in tin foil" is perhaps the most common advice [...] Unfortunately the results were extremely inconsistent [...] 90 dB attenuation in one test would produce only 50 dB the next time [...] You would have no way to tell whether you've managed to fold and seal it adequately well On the other hand, aluminium foil is incredibly commonly available, if not in a kitchen draw, it will be at the nearest shop. Althou…
Also, remember to ground your faraday cages.
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?
A couple of right angles not really make it light tight either. I remember going caving and we would have to go 100m or more through many different turns before we all turned our lamps off and truly experienced perfect dark.
I placed my phone wrapped in a towel inside a metal box: as soon as I close the lid I can't ping the phone on local WiFi and can't reach it with call (it goes direct to voicemail as if the phone was switched off). The GPS doesn't record any position while in the box. I didn't test the Bluetooth though.
Same thing for my car keys inside a paper towel and aluminum foil: impossible to open the car even at touching distance.
I wonder if he wrapped the device before putting it in the box or aluminum.
That was really interesting. I can’t believe how poorly the metal tin box did compared to real faraday pouches.
The metal tin box will have had varnish and paint on it's surfaces. That means at the junction between the tin and the lid (and maybe other joins), there isn't an electrical connection all along. Having two metal surfaces next to eachother, but with an insulator in between, acts like a 'choke flange'[1]. However, they only work at one specific frequency - at all other frequencies they will leak either a little signal…
I wish it covered (so to speak) aluminum foil more thoroughly. In particular, foil is cheap, so rolling up in several layers (3? 5? 10?) and twisting the ends cracker-style ought to be more reliable and practical than trying to do it with one layer and fiddly seams. A suggested minimum number of layers and number of twists would be useful.
> While the cookie tin performed much better than the mylar bags, and could provide a modicum of useful attenuation under some circumstances, it was not sufficient to provide meaningful assurance of signal isolation at any frequency. However, it was unique among the containers tested in providing tasty snacks during measurements Back in the day working for Symbian I used to regularly have to run a load of automated B…
The simplest test you can make to verify that the microwave oven & biscuit tin can are good Faraday cages is to put your phone in one and try to call it - every time I did that in the past they failed to function as a Faraday cage. Edit: clarification.
It works for me with a cookie tin, the phone is wrapped in a towel.
My understanding is that a Faraday Cage, of any size, relies on a proper grounding system to work at all so these boxes and rfid blocking pockets etc all seem to be tinfoil hats parading as space age metamaterials.
Eventually it will radiate the same amount of energy as the transmitter inside it, but in infrared wavelengths and without whatever modulation was carrying the signal.