Harry Bloomfield wrote:

NY has brought this to us :
Do they use 2.4 GHz? I'd assumed/read somewhere that they didn't use a
resonant frequency of water for that very reason, and that 2.4 was only
available because no-one (eg military, broadcast) could use it for
anything else long-distance. On the other hand, with a dish aerial to
concentrate the available power into a narrower beam, maybe water
attenuation can be overcome sufficiently to transfer a usable signal at
20 km range.

Much longer distances have been managed than that.

I really don't follow how a copper tank full of water, can attenuate a
signal more than the same tank, but empty.

If something acts as an absorber of electromagnetic waves and is
lossless it also acts as a radiator. If the energy is taken out of the
system by a matched electrical connection (as in an aerial) then that
energy will not be re-radiated. I guess maybe the water could act as a
lossy absorber of electrical energy and have the same effect. Like
you, I am not very convinced that a water tank is going to act as a
highly effective 2.4GHz aerial in the first place, though.


--

Roger Hayter