Low-frequency radio modules for under water communication

Hi Guys, I am looking for some low-frequency (with regard to the hardware I am used to at 868MHz) radio modules in the range of 50MHz up to 433MHz with good Arduino/Atmel compatibility and support base (actually, please just forward me anything). Could you please recommend sth.? Thank you!

I’ve found so far LoRa and Sigfox at 433MHz and 868MHz
I know about the nrf chips for BLE and WiFi
315MHz Linx chip: https://www.mouser.de/ProductDetail/Linx-Technologies/TXM-315-LR?qs=K5ta8V%2BWhtZaX%2Bhi0hLGmw==

My Application: radio transmission in fresh water (conductivity is not so high) for a couple of meters (around 5m).
Thank you!

Have You heard about Google?

"Arduino + 50 MHz": Arduino 50 MHz - Google Search

"Arduino + 433 MHz": Arduino 433 MHz - Google Search

Standard radio modules, used for open air communications, in a waterproof RF transparent box will work.

There are great many of those modules with 'good Arduino/Atmel compatibility and support base'

Wont go very far of course.

The lower the frequency, the better. The Navy uses 3-30 kHz for underwater radio communications.

Some people claim to get radio range of meter or two in fresh water using 27 MHz RC, but in salt water, that would be hopeless.

I've screened all modules for 868MHz communication, 433MHz and I found one from Linx:

operating at 315MHz, actually (also after using Google or several hours) one has to admit, there are not so many options for small-sized under water rf communication (30mm x 30mm x 20mm).

Underwater radio communications come up from time to time on this forum, and to my knowledge, no one has ever come back to report success.

People would be interested to know if you find something that is actually useful. If so, please update this thread.

jremington:
The lower the frequency, the better. The Navy uses 3-30 kHz for underwater radio communications.

Some people claim to get radio range of meter or two in fresh water using 27 MHz RC, but in salt water, that would be hopeless.

Actually the low frequency is only used one direction, shore to the sub. And then it is on a prearranged schedule because the sub has to reel out miles of insulated wire antenna. To communicate back to shore, the sub has to either surface or release a communication device to the surface to allow communication, and then reel it back in. The OP will have the same problem, no matter what frequency is used.
Paul

For underwater communications, read about communication between whales:

Some incredible distances are mentioned in that article. Of course, finding an Arduino module which mimics these properties is not going to be so easy.

jremington:
The lower the frequency, the better. The Navy uses 3-30 kHz for underwater radio communications.

Some people claim to get radio range of meter or two in fresh water using 27 MHz RC, but in salt water, that would be hopeless.

Thank you jremington and also the others! I've modified my question a bit since it initially did not contain too much information and left the impression that I didn't do my google homework.
@Railroader: there are quite a few 433MHz modules and also one from linx at 315MHz but i didn't find any digital 50MHz modules, where I can imagine to send some sensor values with a few bytes. Can you help me here?

mbobinger:
Thank you jremington and also the others! I've modified my question a bit since it initially did not contain too much information and left the impression that I didn't do my google homework.
@Railroader: there are quite a few 433MHz modules and also one from linx at 315MHz but i didn't find any digital 50MHz modules, where I can imagine to send some sensor values with a few bytes. Can you help me here?

If you search for ISM frequencies, you will notice there are none in the 50 mHz region.
Paul

Since when is 50MHz "low frequency"? That used to be the start of the VHF Television band.

The OP seems to be barking up the wrong frequencies.

Commercially-available hobby/model radio-controlled submarines operate at 27 MHz (as mentioned in post #3) or 40 MHz.

They are inexpensive and may be a good place to start hacking (with proper consideration of the associated regulations...)

A bit about the project might help - there may be other ways around the problem

What about light , wire , sound waves ?

Yep there are RC submarines on eBay ( no idea if they work )

I worked on a VLF xmitter/rcvr that used a piezoelectric antenna array; no long wires drug out the back. One might consider using a piezo devices mounted to the hull. Excite the piezo devices with a carrier, and then do a little frequency modulation on the carrier wave. Leave the piezoelectric antenna array in listen and when transmitting one must disable the receiver circuit.


If humans are aboard the sub, make the carrier wave above human hearing.

DaveEvans:
Commercially-available hobby/model radio-controlled submarines operate at 27 MHz (as mentioned in post #3) or 40 MHz.

And whether those frequencies are legal depends on which part of the World the OP is of course.

Idahowalker:
...excite the piezo devices with a carrier, and then do a little frequency modulation on the carrier wave...

or just do OOK?

@ OP.

What sort of communications do you want to achieve?

In typical trickle fashion, this was revealed in OP's post 8:

...send some sensor values with a few bytes...

Currently unspecified:

Sending from underwater sensor to above water receiver?
Sending from underwater sensor to underwater receiver?
Sending from above water sensor to underwater receiver?
One-way communication? Two-way?

Also left unsaid:

The Big Picture, the environment (swimming pool? lake?), fixed or random orientation between sender and receiver, why wired won't work, whether other technology (besides RF) could be entertained, such as traditional sonar, the piezo idea, blue-green laser, etc.

I was going to suggest ultrasonics. Flog a few off a wrecked car, in water they should work well.

I was going to suggest ultrasonics. Flog a few off a wrecked car, in water they should work well.

The commonly accepted wisdom around here is that ultrasonics designed for use in air function poorly, if at all, when submerged because of the vastly higher acoustic impedance presented by water. Different frequencies and higher power are said to be needed.

However, a group of (college students?) reported limited water depth ranging success with a relatively inexpensive (and crudely waterproofed) Maxbotix product intended for in-air use. See the Coconut Pi link here: Notes on Underwater Ranging | MaxBotix Inc. A model submariner also reported underwater ranging success with a Maxbotix product - up to 50 feet IIRC. See that Maxbotix URL for some of the challenges (note it mentions the acoustic impedance issue).

Also, @wvmarle has reported that another inexpensive product intended to be attached to the outside of a tank (for measuring the height of fluid in the tank) can be used to measure water depth if the business end is submerged slightly below the surface. See posts 21 and 44: https://forum.arduino.cc/index.php?topic=528653.15

Perhaps either of those sensors could be hacked for the OP's purpose. But maybe they don't have the necessary range. A fish finder-type sonar may... But echos may be a problem.