Secondly, the transmitter doesn't necessarily have to be exposed, it could be kept hidden and only the antenna would need to be exposed.
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. 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.
Plus the antenna would be easy to disguise or hide in many places.
Yup. John E. Kreznar | Relations among people to be by jkreznar@ininx.com | mutual consent, or not at all.