Transmitting video from underwater

[leepower]

Main Question or Discussion Point

hi. im looking into buying/making a wireless video camera to attach to a radio controlled submarine. im familiar with the 2.4g cctv type spycams and digital video receivers but am told water is an insulator to the fm signal being transmitted. im also aware of the rc 12 wireless mini cam which transmits a 1.2g signal "morse code" signal. the range of the rc 12 is less than im looking for of 200 yards at depths of 20 feet. can this be improved on and what are the principles of transmitting underwater. many thanks

 

[cmb]

... am told water is an insulator to the fm signal being transmitted. im also aware of the rc 12 wireless mini cam which transmits a 1.2g signal "morse code" signal. the range of the rc 12 is less than im looking for of 200 yards at depths of 20 feet. can this be improved on and what are the principles of transmitting underwater. many thanks

I'm amazed that a 200yds/20' range camera/under-water range exists at all! Water is a significant lossy dielectric to fm and above. I would simply give thanks that someone markets such a thing already, and not try to re-invent that!

 

[leepower]

thr rc 12 has a range of 30 meters im wanting 200 yards at 20 feet. ive read something about ultra long radio waves being better through water. the submarine is controlled by radio waves ? im still learning about the whole concept if that sounds stupid

 

[cmb]

thr rc 12 has a range of 30 meters im wanting 200 yards at 20 feet. ive read something about ultra long radio waves being better through water. the submarine is controlled by radio waves ? im still learning about the whole concept if that sounds stupid

Correct. But you're unlikely to transmit video on those frequencies, and you'll need to deploy a long antenna behind your submarine, fed with a lot of power to make up for its deficiencies in transmitting inefficiency.

LF and ULF transmissions are usually one way - to the subs. The message is usually some code for 'come to the surface, we need to chat over satellite comms'!!! ULF Bit-rates are in the tens of bits per minute, rather than the kB/s you'll need as a minimum.

Best option, as you don't really need the 'stealth' of military subs (presumably!) is to deploy a floating antenna that the sub drags along the surface with it.

 

[leepower]

that is an option ive looked into with a floating antenna but one i was hoping not in employ. im also thinking of the option of recording on an internal memory of the camera then transmitting once at the surface. obviously the video received wouldnt be live but then i can get away with a 2.4g type camera. the spycam type cameras all seem to have a 100 yard range is this something that could be improved on?

 

[cmb]

im also thinking of the option of recording on an internal memory of the camera then transmitting once at the surface.

...just like 'real' subs!! I think it is a good idea to stick with what is likely to work.

 

[leepower]

ha yes like real subs. could i increase the range of a 2.4g cam?

 

[cmb]

ha yes like real subs. could i increase the range of a 2.4g cam?

There are various antennas that might improve your gain that are readily available commercially for wi-fi systems (weather-proof, but you'd have to ensure water-proof), but one problem might be that you don't have a stable platform so if the antenna has higher directivity (in the horizontal plane) this might actually be to your disadvantage as the sub bounces around and you end up out of the gain lobe. I'd not like to predict the effect, nor of the influence on the water surface to the antenna gain. You're in uncharted waters! Try it! Let us know how it went!

 

[leepower]

so ok in flat calm water then? i have another question if i may.... what would you see if you looked at the suface of a lake using night vision or infra red or thermal camera as in is there an aid to being able to see the rc sub in say 6 feet of water other than attatching a very bright led on the sub

 

[leepower]

and yes i will report back with all my results in thanks for taking the time to reply to me its very much appriciated

 

[cmb]

.... what would you see if you looked at the suface of a lake using night vision or infra red or thermal camera

Very little, I expect! Water is a good absorber of the lower, red frequencies of light. (Think of all those underwater documentaries - all blue-green tinge!). Yes, I'd stick a bright flashing blue LED on the side of it. If you are worried about losing it, personally I'd also rig it to trigger into becoming postively bouyant in the event that it receives no signal for a set period of time.

If you are worried about it being visible, then I begin to wonder about the application!! I think at least in the first instance, if not for always, I would tend to think there is no big issue with attaching a trailing line to it (something that floats - e.g. polypropylene rope), maybe with a floatation device at the end of it (big orange ball), and maybe even your antenna too!

Good luck!!...

 

[leepower]

thanks again and yes i am being a bit sheepish im working on an idea to aid a hobby of mine which isnt radio controlled submarines the submarine is just a very good way of explaining what i need the camera to do which is why i have issue with the boy antenna. im an electrical contractor by trade and believe my idea may have appeal in its market aswel as helping me. im just trying to find out the best way of achieving the results to make it feasible ive spent hours already talking to cctv companies mobile phone companies invention companies its hard to find someone with the knowledge im looking for to answer my questions which is why ive found myself on this forum picking your brain. my parameters are to send a video signal either live or recorded 200 yards at 20 feet depth to a wireless digital video receiver. sorry for the eye wool :)

 

[Bobbywhy]

leepower, eye wool rarely helps us to arrive at functional engineering decisions.

Electromagentic radiation (radio frequencies) does not pass very well through water. It gets attenuated (abosorbed) quickly. As cmb pointed out above, some colors (optical frequencies) do pass with little attenuation. Blue-green is the best.

To get some idea of the propagation limitations you face, see:

http://en.wikipedia.org/wiki/Electromagnetic_absorption_by_water

If you use a powerful blue-green laser, and if you modulate it with your video signal, and if you transmit it from a depth of 20 feet directly (line-of-sight) to your receiver, and if you de-modulate the video signal, then you may be able to meet your specifications.