31–40 of 205 posts
I've had a lot of fun in the past trying to shield Bluetooth devices for testing... metal filing cabinet? Practically no attenuation. Biscuit tin? Minimal attenuation like in the article.
Modern radio receivers are ridiculously sensitive.
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…
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.
On the other hand, aluminium foil is incredibly commonly available, if not in a kitchen draw, it will be at the nearest shop. Although unreliable, the _potentially_ high attenuation the author shared is pretty good (we don't know his worst reading), better than all other improvised solutions tested, and similar to commercial products. I wonder if a more reliable construction method could be found.
I'm not sure what movie scene scenario I'm envisioning, but in the case you needed a Faraday cage and don't constantly carry one around, perhaps simply taking an entire kitchen roll of foil and wrapping the device into a giant unsightly ball of it would be a reliable enough process for an "emergency" (if not pocket sized). i.e rather than trying to make a neatly folded minimal version, just resort to sheer number of layers of material - unless RF doesn't care and even 1000 layers with tiny gaps is no good?
[edit] Similarly, I wonder how well (or poorly) common household appliances work as a Faraday cage, e.g a fridge, microwave-oven - From what the author described, it seems they would all have too many gaps, however they are also constructed from higher gauge metals... i'm particularly interested in a microwave-oven which is specifically designed to reflect and retain microwave frequency fields.
> 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.
Earlier quoted context omitted.
It also keeps them from drying out when you microwave them while still maintaining a crispy skin.
Also, caution: If your phone is made from a tomato or other acidic substance, the foil may corrode, further reducing RF containment.
A good portion of phones, on the other hand, do seem to be made of the fruit of the domesticated Malus.
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?
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 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…
Earlier quoted context omitted.
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.
The Faraday cage failed (the phone rang?) or the phone failed to ring (Faraday cage succeeded)?