To the Moderator: I understand if you decide to move this post to another thread that is more relevant to the subject. I just wanted to get this experiment with RF shielding on record.
In my pre-compliance EMC efforts regarding my prototype medical device I must accurately measure the EMI being radiated from the DUT. To do that I need a good spectrum analyzer, an ultra-wide-band listening antenna and an RF isolation cage so as to block out virtually all RF but that coming from the DUT.
This post has to do with the RF isolation chamber. I have been experimenting with such a chamber and here are my findings, for the benefit of anyone else with similar needs.
I have a portable battery-powered transmitter-receiver pair mfg by Linx Technologies that operates at about 430 Mhz. These are being used as test assets to demonstrate when and if I have achieved a desired measure of RF isolation. I place the receiver in each of my experimental chambers and try to ping it with the transmitter from only a few feet away. If I can, then I have not achieved the level of RF isolation I am seeking. The receiver is extremely sensitive - able to receive signals at levels down to -118Dbm - which equates to little more than 1 picowatt - a very tiny signal level!
I have successfully tested this transmitter-receiver pair at a distance in excess of 2500 feet of separation from each other, with the standard whip antennas, just to illustrate how very sensitive the receiver really is. If I can get this receiver to 'go dead' within an RF isolation chamber then I have really accomplished something.
I have succeeded in doing just that. Here are the details:
I used 10 mil aluminum foil to construct a foil box with a lip all around where the lid clamps on, and a lid itself. The box itself has no holes or voids of any kind, except of course the open top where the lid fits onto it. The lid is clamped onto the box lip all around using large binder clips like you get at Staples office supplies. The box is a cube of about 18 inches square, but the shape doesn't matter. I use 10 to 12 binder clips to secure the lid in place all around, after placing the receiver inside the box. The homemade Faraday cage is not grounded. It need not be in order to snuff out RF radiation.
This cage demonstrates virtually 100% RF isolation at the 430 Mhz frequency. The transmitter is unable to reach the receiver at all. However, if I remove only a couple of binder clips from the lid and wiggle the lid edge just a little, then the signal gets thru. And I mean only a very, very slight gap being allowed between the box and lid.
But with all clamps in place, RF isolation is 'perfect'. No significant gaps exist for RF to leak into the cage, and the clamps also help ensure that box and lid are electrically One Conductor - very important for any Faraday cage.
I was very pleased to discover that this very high level of RF isolation can be achieved so easily with materials that are cheap. Now, in practice, my isolation chamber won't be made of 10 mil foil, but rather of 0.090" or 0.125" aluminum plate, so as to make a chamber with good structural integrity. But you don't have to spend a lot of money - you just have to be very careful in the design and construction of your Faraday chamber.
Soon - a post on my EMC UWB antenna that is now under construction.