Hi Eric

First thought is that I have read somewhere about underwater antennas.
They were a lot shorter than what you have in air and the attenuation
was much worse. Might be worth some research. If you (say) ran a couple
of hundred kilohertz you could FSK or PSK that at some low data rate.
Perhaps even drive it with one of the older 1200/75/300 modem chips. (ie
RS232 serial data) I mean this is how the US subs get their action
messages (although this is a really low data rate)

Next one is a laser diode connection to some modem. I note that in the
cell phone world one can connect a laser/optical fibre device direct to
the RF output stage of the TX. This may sound far fetched but I wonder
about using a laser diode and phototransistor connected to an ethernet
switch. I have NOT thought this through at all so pls done burn me too hard!

I think the data rate of using an acoustic path would be way too low.
You have to allow for major multipath reflections through the medium and
I see this as bringing it down dramatically. There are probably some
signal recovery techniques that can be used in this situation but I dont
know of them. Personally I'd like to fiddle with Wyman/RDFT encoding in
a voice bandwidth and see if that works. It has adjustable forward error
correction which might just make it do-able. You tend to need a PC at
each end though!

Apologies for the waffling

Cheers Bob Vk2YQA

Eric wrote:
Hi,

Don't want to get side-threaded, but I got hit up on a project idea that
should prove practical, educational, fun, and just plain neat.

What will be required, however, is a wireless data pipe down to a depth of
~50 feet (15m). Unfortunetly, it will have to be wireless.

(Obviously, such a link will also have to be acoustic and not RF.)