jkreznar@ininx.com (John E. Kreznar) said:

Not even the antenna should be visible. Remember, for spread spectrum radio detectable only by the intended receivers (which use the correct spread- spectrum code for coherent detection), the power density should be hardly distinguishable from the ambient noise.

This is true only for casual observers. If the FCC were after you, they could most definitely triangulate on unusual noise sources as well as they could a coherent signal. Power signals are a giveaway.

One way to arrange this is to put the antenna inside of a physically secure perimeter, outside of which the power density is too low for noncoherent detection. The perimeter can be optically opaque (e.g. a building), as long as it leaks enough r.f. in the direction of the receiver(s) for coherent detection. Preventing noncoherent detection may often require _attenuation_ of an otherwise too-powerful signal, and the building may serve part of this function.

Good enough as far as it goes. But this implies a large drop in efficiency of the transmitted signal. That's not a stopper...*if* you've got power to spare. But that implies enough power for bad guys to triangulate your noise source...ouch. If they pin you down to within a building, you've lost. There are other approaches...phase-sweeping...phase-conjugation... Doug