I received this earlier from our man John, and with his permission, I've copied and pasted here for you guys to read.
It means absolutely zero to me, but some of you may understand what the heck he's talking about!
Hi to every one,
Over the last few months I have been playing about with low frequency for under water RF link to control a submarine, a few days ago I decided what about if all of this was joined to a piezo transducer? Yes, it can be done, the transducer in the water if it is held half inch under the surface it starts to make a whirlpool standing out the water about 2inches high, and you can see the code on the top of the whirlpool.
Hopefully when I get a bit more time I will take it a bit further and see where it goes. If you touch this whirlpool it feels like it starts to burn your finger, I know what you are going to say..'dont touch it then', but at the moment the unit is running on low power but I will hit it with more power and see if I can start a hot tub for the missus, but I don't think she will like the RF burns...
John