jann replied to sigwinch:
Not hardly. A bandpass filter wall is simply impossible.
What's this - Argument by Authority?
Don't tell my friend that ... he'll be really pissed off when his working prototype vanishes in a puff of logic
Remember, there are experts here. In E-M radiation, I'm not an expert, although I have graduate-level course work in physics, electronics, and communications. Sigwinch may be an expert.
In other words, when Sigwinch replied to your question:
Solve the window problem (block radio waves but let sunlight through) and you may just make a lot
He is exactly right. In an earlier message I mentioned Farday cages. Read up on those. What the door to the microwave oven has is a metal sheet with holes. The holes are each about 2 mm or so, therefore they will attenuate any waves with wavelengths longer than about a centimeter. 802.11b DSSS uses a 2.4 GHz carrier, or a wavelength of 12.5 cm. Therefore a metal sheet with 2 mm solves your "window problem" - you can see through it but it will block everything with a frequency of less 5 GHz or so.
A solved problem. The door of most commercial microwave ovens lets visible light through, but is designed to
block exactly the frequencies used by wireless Ethernet.
In fact I have a supplier for copper mesh, as well as samples. The "16 mesh" - wire spacing 1/16 inch, or about 1.5 mm - will attenuate about 40dB at 1 GHz and 30dB at 2.5 GHz. The finer meshes attenuate much better. "100 mesh" will attenuate 55dB at 1 GHz and 48dB at 2.5 GHz. You can see how transparent this material is.
If you don't know what dB is: Each 3dB is a doubling or halving; 30dB means a ratio of 1000, and 60dB is a ratio of 1,000,000. The best photographic film can record a range of about 30dB.
Faster, faster, until the thrill of...
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