Homebuilt Rov Forum

What if a guy (Me), only needed to transmit a bluetooth signal, or RF signal (underwater) between two housing that are seven inches or less apart. This would be communication between my camera and the control board. Question is would it work? I know it is a crazy idea, and I know that typically wireless communication doesn't work underwater, but at what distance do we actually start losing transmission. I mean at seven inches or less that is actually a pretty negligible distance compared to the distances that most people are talking about most of the time. Meaning between the surface and the ROV. I am trying to communication between ROV and ROV then use the tether to communicate between the ROV and the Surface. Am I just crazy or just thinking outside the box? If you haven't seen the ROV that I am building then it won't make much sense so here is another picture of the "general" shape of my ROV that I am working on. There are two tubes that are in parallel from each other about seven inches apart. The back housing is for the control board, and the front one is for the camera and servos for pan and tilt. I plan on making my own pan and tilt. The whole front housing would be send its information to the back housing by means of either bluetooth or RF again my question is can it be done with such a small distance between them.

A very good question, whilst doing a bit of research I found this very good website, and although it does go into a lot of technical detail... I think I understand the idea of it.

http://www.qsl.net/vk5br/UwaterComms.htm

Basicly it is saying it isn't the best idea (as most of us know) but it does say it is possible. If in sea water then it is saying you don't have a chance because of electrical conductivity and the such unless you have a huge amount of power, a long antenna and you use a stupidly low frequency.
In fresh water however it states 'Fresh water lakes and rivers have much lower electrical conductivity than the sea and underwater transmission distances (or depths) up to 30 metres appear feasible using the lowest frequency amateur band of 1.8 MHz. Even larger distances (or depths) could be achieved if a lower frequency band allocation is available. *(Attenuation at 180 kHz is reduced to around 18 dB per metre in seawater and around 2.2 dB per metre for fresh water.)'

So basicly it looks like it is possible and you shouldn't have much problem over a short distance but considering bluetooth uses 84Mhz (I think) then you may have issues as this is considerably higher than the 1.8MHz which they used.
In tests that other people have done, they got it to about 10 inches using mobile phones and the such.
Another thing I think may cause problems however is if you have a heavily lined walls that are made out of metal as these could reflect your signal and cause other problems.

Hope this helps and good luck!

Both housings are made of polycarbonate, and like I said the only distance that I am trying to travel with the camera signal initially is 7 inches. Once I get that signal from the front housing to the back housing to the control board it will then be send to the surface by either coax or by bnc and ethernet.
Just a thought though. What if since having this new knowledge of bluetooth tech, I use a RF signal between the two. I am basically trying to eliminate some wiring between those two housings.

I am not an expert but I think you could, providing it is of a low frequency.
Some people have said that they can get about 3m, some others have said it is only a couple of feet. From looking at other peoples results, it looks like it shall vary depending on the quality of your reciever/transmitter. I suppose the only thing you can really do is try it (maybe don't put it in your ROV just yet and instead test it solo). I think it all depends on water density, salt density e.t.c.
Just a quick question, won't it make more ecenomic sence and wouldn't it be easier just to connect it via a couple of cables?

Yes it is more economic to use wires, but the point of this is is to try to reduce the number of openings in the front hull housing so that there is a reduced risk of leaking. If I can like I said just take the signal from the front hull to the back hull (wireless) that would reduce the number of openings in the front housing by three or four. Thought about using RC control crystals for this operation.

I see your idea behind the 'less holes, less leaks' principal, I however have no further knowledge on wireless technology.
Good luck with your project and I am looking forward to seeing the results.

Are you trying to send the video from the camera over bluetooth? That might be hard depending on the resolution of you camera, as bluetooth isn't exactly known for it's high bandwidth.

It sound's like a cool idea.

Oh, and I just remembered that I've read there are different classes of bluetooth devices. I can't remember the specifics, but the class most devices fall into is good for 33 feet send/receive in the air. There's another class that is good for, I think, around 90 feet. It might work better under water. I think it's basically a more sensitive reciever and a more powerful transmitter.