i want to build an ROV that can go at a depth of 800meters…So the question is what kind of a board can i use instead of fathom x?
If you really want to push that deep, I would go with fiber, but you can get away with VDSL.
SeaViwe Systems makes a good fiber modem, or you can use some Ethernet to Singlemode fiber converters from places such as Amazon.
Below is a model of VDSL I’ve used before, but know that your bandwidth will be pretty low. When we used a similar modem with 1km of cable, we were struggling to get more than 10Mbps and we were running the video at 640x480 and had only a scanning sonar. you can use a Fathom Slim single pair, but it won’t work nearly as well as a full size tether. Coax will be a little better.
If you want HD video, or imaging sonar data, you must go to single-mode fiber optic tether and modems.
It’s very likely that 800m requires a fibre-optic tether, so your best bet is probably looking for fibre optic interface boards, and a corresponding tether. I’m aware that some of our distributors offer fibre tether setups (including with appropriate end terminations), as well as some others in the community.