Jim, I really have to disagree about shielding and leakage. *** Electricity runs from a high-potential point to ground. If it isn't grounded it radiates away into space where it can be detected. If the Faraday Cage isn't grounded it simply acts as a parasitic oscillator and re-emits the signal from inside, though at a lower amplitude. Remember, charge rests on the *OUTSIDE* of a object so that any charge picked up internaly gets passed to the outside surface. *** Consider a battery-powered spark gap inside a copper box. Lots of beautiful wideband noise. I refuse to ground my copper box. I'm going to suspend it from a weather balloon over Menwith Hill. The solutions to the wave equation inside the cavity have a real part ~0 in the exponent. The boundary condition at the inside surface of the copper box splices together the solutions in the cavity and inside the conductor. Which solutions, BTW, have a real component that is non-zero so the waves are of exponentially decreasing amplitude the further into the Cu you go ( skin depth, power loss ). At the inside boundary, the higher the conductivity the smaller the E field at the surface, the shallower the skin depth and the more power is reflected with less loss. The amplitude of the internal Cu ( exponentially decreasing ) solutions at the outside surface determines the extent to which the wave leaks out because the solution is imaginary again outside. If it helps, the solution looks like the Schroedinger equation solution for a particle in a potential well when at least one boundary is a region of finite potential. Leakage has nothing to do with being grounded since the wave can be generated without the total charge residing on the surface of the box ( DC potential ) changing at all. What's there just moves around a little, that's all. I don't think it takes a whole lot of copper to do the job: the skin depth is pretty small. A copper screen behaves much like the copper sheet execept that it deviates as the wavelengths become closer to the dimensions of the holes. You might say that the resistivity increases with frequency. It leaks more. ** The 1st rule of electrons: They always take the shortest path to ground. Corollary: If they can't get to ground they radiate their excess energy away as photons. *** Oh, for crying out loud! Where did this stuff come from? I prefer the three laws of thermodynamics in layman's terms: i) You can't get something for nothing ii) The best you can do is break even iii) You can't even do that Works for my checking account too. Regards, Mike BTW - I'm still at a loss to understand what the geology has to do with RF shielding. Chaff, I think. BTW^2 - The more conductive the TARMAC the more clutter you'll get because it will be a better reflector. Ground or not. The incident waves *don't care*.