I would like to test object behavior on bottom (up to 15m depth) .. and send signal from object to surface...

Object is connected to a chain that goes to surface - can I use the chain as an antenna ?
I really need just to send short signal... would RF AM be ok lets say low frequency...
Can I pack this into a small arduino with AM transmitter?
How much power would the setup use?

What do you suggest..

P.S. I know there are some topics on this - but I really wanted to sort out this specific use case...

Looking forward to your replies and thank you very much

 

Rule of thumb for underwater rf is,, received distance is half of transmssion wavelength, so for 15M distance you need 30Mtr wavelength minimum (10Mhz max)

 

Yes, kind of. If you can run an insulated transmission line an antenna on a bouy at the surface it would be similar to communicating to a system on the surface.

 

You might be able to use ultrasonics to do this.

 

Thank you ALL for your responses. Much Appreciated.!!!!..

@AlbertHall ultrasonics would be too expensive - I am guessing?

@DickCappels so I could use a simple AM transmitter 1MHz and the buoy above the object would have an antenna looking into the water...
The box on the seabed could be plastic (do I loose any power when emitting thru plastic) with arduino inside and AM transmitter to send signal...
Would the box needed to be connected to the chain (as antenna) ... or not

@Dodgydave would 1Mhz be ok?

Looking forward to your replies and thank you ....

 

If the object is in physical contact with the surface(thru a chain)......why not use wire?

 

Ordinary coaxial cable is a good way to connect the device under water to an antenna on the surface. RF through the water is not very efficient.

If you have a real need to use wireless communications under water, you would do well to use sound as AlbertHall mentioned in post #4, or the lowest radio frequency that is practical -that would be the result of tradeoffs aming antenna size, power, and data rate.

 

Thank you ALL for your responses. Much Appreciated.!!!!..

@AlbertHall ultrasonics would be too expensive - I am guessing?

@DickCappels so I could use a simple AM transmitter 1MHz and the buoy above the object would have an antenna looking into the water...
The box on the seabed could be plastic (do I loose any power when emitting thru plastic) with arduino inside and AM transmitter to send signal...
Would the box needed to be connected to the chain (as antenna) ... or not

@Dodgydave would 1Mhz be ok?

Looking forward to your replies and thank you ....

If you are using RF then 30Mhz is the Maximum frequency to use, so 1Mhz is ideal,
However the wavelength is 300mtr so for your aerial you will need a whip type of 75mtr(1/4W) wrapped.
if you can use a long coax and float your aerial on a bouy, then any frequency of your choice will do, this will determine the aerial size.

 

Thanks....

Any suggestions what RF module should I use, let's say with arduino...
Although the depth is small 15m, will I really need a 75mtr antenna .. The signal i would send would really be just basic and would not be continuous.. like (send pause send pause send pause....... long pause(hours)... aging send pause send pause)...

tnx

 

If you connect the submerged transmitter by a coax cable up the chain to an antenna mounted on the buoy above water then you can use any frequency you like. 433MHz is popular and transmitters and receivers are available cheaply ready made and need much shorter antenna.