Diver to shore communications?

[Angelo Farina]

40 years ago I built my first UW-wired-to-surface two-ways, half-duplex intercom.
It was intended to be used for exploration of dwells and water tanks in historical buildings and castles.
The diver was fed with an hookah system.
I employed a single RG-58 coax cable inserted inside the air hose for removing additional entanglement risks.
An electrodynamic transducer was employed in the full face mask, working both as a microphone and as a loudspeaker.
It was a special model designed for military applications and fully submersible. But it was not pressure-equalised, so I had to drill a tiny hole for allowing air to flow from the full face mask, reaching the space behind the diaphragm.
Without the equalisation hole the transducer stopped to operate at more than 3m depth, due to pressure pushing the diaphragm fully inside.
It had a 50 m long hose/cable.
The signal was good only when the hose was pressurised, as this did compress the coaxial cable, reducing its resistance thanks to better contact between the wires.
The electronic unit to be kept above water was equipped with headphones and a push-to-talk microphone. The button did act onto a relais, which switched the versus of communication.

 

[Waterwulf]

This is all feasible. The problem you'll run into is how difficult it is to speak clearly with a reg in your mouth. This likely requires a full face mask, or a reg with a custom cup-style mouthpiece. Or it may be possible to train in some alternate enunciation techniques like ventriloquists use and speak clearly through a reg, maybe.

Yeah, that takes practice. You have you put your regulator right up against the other persons ear to make yourself heard. Then speak slowly. It does work but you're not going to be planning the Birthday party that way. Short conversations.

 

[GiraffeMarineSalvage]

If the goal is purely to communication, as opposed to communicating through speech, I would highly recommend considering texting.
Amateur radio has a pretty cool set up for messaging (Global APRS Messaging Initiative) and nowadays you could do a lot with arduino or raspberry pi if it was properly potted.

 

[Failed captcha]

This is interesting. I would think you could just use a basic vhf radio. I have a Standard Horizon HX300 and have had it for years. I think the newer model has Type-C and other incremental upgrades including bluetooth. You could attach it to your marker buoy but you'd only be using it on the surface.

Are there even any earbuds made that can be used while diving? I'm guessing they'd be bone conduction like a Jabra but maybe you could have it wired to a radio.

 

[TooCold]

A button mic would be mounted inside my regulator and a waterproof earpiece inside a neoprene hood

I never thought about leaving the radio on the surface and just taking the mic/headphones down. I think (but am not sure yet) that in my case, it wouldn't work as well as taking the radio down and running an antenna wire up to the buoy.

I've sorta/kinda designed something similar, but never considered bringing the radio down to dive depths. Seemed to me much easier (and cheaper) to run low power audio signals to/from the surface than deal with UHF transmission line issues. Impedence mismatch and line losses get much worse with long lines at UHF frequencies. Also, I wanted to have GPS data at depth from a receiver on the float, so I needed more signal lanes anyway.

Cable management was another issue it seemed easier and cheaper to deal with twisted copper pair than RF coax. I want to be able to wind / unwind the cable from a reel as depth changes during a dive. This complicates the connector strategy as well as affecting the choice of cabling that can withstand expected mechanical stresses.

I've noticed with my camera in its housing that when shooting video the camera's built-in mic does a decent job of picking up the ambient sound, and its tiny built-in speaker is easily audible when playing back video underwater. Both mic and speaker work right through the camera housing, so it seemed like it was worth a try to just make a simple housing for a regular mic/speaker, instead of having to deal with separate submersible mic/speaker/earphone.

The downside to radio up top is the complication for control signals, if you want to do more than just push-to-talk. If the radio is up top you can't power on/off, change channels, adjust squelch, ... etc. A full underwater housing for the radio would solve those issues.

Interesting project - hope you go for it!

 

[Waterwulf]

Yes, that project is still on the "Active Board". I think I'm going to leave the radio on the surface and run a mic/ear cable down below. You're right about unreeling coax versus twisted copper. I was looking at the thin coax, like what's used for handheld radios but I think it's more trouble that it's worth. We shall see!