1) what makes a good, inexpensive, and simple cage or shield
2) how to test the cage in a practical but thorough manner
3) what such a simple cage can protect against
4) whether the cage needs to be grounded to be effective (and how to do this in an apartment setting)
This post is organized by the above 4 points. Much of what I have found has been contradictory. Probably one of the best-written pieces I have read can be found here…http://www.futurescience.com/emp/emp-protection.html. Also, http://suburbansurvivalist.wordpress.com/2010/02/07/faraday-cages-to-protect-electronics/ offers a good overview, but also runs into contradictory information.
1) What makes for a good, inexpensive Faraday cage…
The winner for simplicity, size, and expense seems to be the galvanized trash can with cardboard placed inside to act as an insulator from the can’s side. A smaller version of this which I have tested myself (more below) is an empty paint can (bought from Home Depot for about $4.00).
The simplest method seems to be to wrap any electrical device in multiple layers of aluminum foil with an insulator in between such as a plastic bag.
Another alternative is a used (or working) microwave, since it is designed to contain specific microwave radiation frequency. That brings us to the second point.
2) How can a Faraday cage be tested simply and effectively?
Most of what I have found recommends testing a cage with a radio or cell phone.
The sealed paint can blocked my cell phone and radio, but I do not know what other frequencies could be getting through. When I called the cell phone, the static from the radio changed, so some type and level of signal appeared to be getting through.
Aluminum foil wrapped entirely around the cell phone and radio (with an insulator in between) appeared to block out the VHF and the cell phone signals.
The cell phone in the microwave easily received several calls. (edit... cut some information here that turned out to be incorrect).
One source (unfortunately I cannot find it now) recommended testing with the highest frequency (largest GHZ number) electronic device possible. If a metal trash or paint can protects against a high frequency, would it automatically protect against all wavelengths up to that point? Does anyone know what the frequency/ frequencies or energy levels of lightning or solar flares can be? I am probably not using the right terminology, but would like to know how these potential threats overlap.
3) What can a cage protect against?
So I know my well-sealed paint can blocks VHF and cell phone frequencies (about 1900 MHZ), but how would it work against a nearby lightning strike or EMP? According to http://www.futurescience.com/emp/emp-protection.html, “apparently DC-like currents are the problem“ from solar flares. Lightning can damage electronics through close but indirect contact.....
Last night, (edit: this was April 2011) while I was at work, lightning struck a tree on our property line. The dog run was attached to this tree, vinyl coated 1/8" braided steel cable, about 50' long. Fully half the dog's run is gone, and I mean GONE. sections of blackened, EMPTY rubber coating litter the yard, the cable vaporized right out of it. Thankfully, the dog was NOT outside at the time- all I could find of the dog lead that attaches to her collar was the pulley that rode the run cable, made of the same stuff.
The resulting magnetic wave from the strike wiped out most of the electronics in the house, including, but not limited to (we're still assessing damages) a laptop computer, cable modem (replaced it today at the cable co.) two of three phone extensions, three televisions
4) To what extent should a Faraday Cage be grounded?
After everything I have read, it seems an effective cage does not need to be grounded to offer protection. But if one was inclined to ground a cage, are there any recommendations about how to do this in an apartment setting with no direct access to the ground?