Ethernet over 500m (underwater)

[Moonwalker031]

Hi I am an electronics engineer and just subscribed to this forum. Its very informative - keep it up.

I have a project for building an ROV. Maximum depth is around 400m but I'm planning to use a cable of 500m for drag compenstion. My idea is to use IP camera on the ROV and send the commands via another IP. Now the problem is how to send the ethernet signal over 500m of cable. Cat5 is not possible for such lengths I guess.Fibre optic is ok but expensive and not very flexible.So I think Coax should be my choice.Well I found ethernet to coax converters which should work well with RG6 cable but I was hoping to use RG174 so that it would have the least drag possible underwater.

So has anyone worked with ethernet to coax converters using RG174? Or is there some other solution for sending ethernet using a thin wire?

 

[MacGyverS2000]

Is this a project for school?

Most FO cable is significantly more flexible than Ether cable...

Dan - Owner

http://www.Hi-TecDesigns.com

 

[biff44]

The low cost flexible coax cable will most likely get crushed at that water depth. The insulator between the two conductors is just a soft plastic wrap.

http://www.MaguffinMicrowave.com

Maguffin Microwave wireless design consulting

 

[MikeHalloran]

How do you get power down to the lights, manipulators, position & propulsion systems, ballast systems, etc?

Can you tolerate a limited time at depth and the time wasted swimming up and down to replace or recharge batteries?

How do you fish it out of the drink when everything onboard dies?

I'm suggesting that you may end up with a complex umbilical cable, including strength members and power conductors. There may be common or standard umbilicals available, that already include some kind of control/information channel. If the details are already worked out by someone else, you'd be crazy to roll your own.




Mike Halloran
Pembroke Pines, FL, USA

 

[Moonwalker031]

So to make things clear - this is not a school project - left school long time ago Since my hobby is fishing and work electronics I tought its time to build an ROV for myself.

@MacGyver - Any link where to get flexible FO? I have no experience with FO. Can I use single or dual is better? And do you know if it can handle 40bars of pressure?

@biff - If the coax gets a little crushed I dont think its a big problem. As long as the conductors dont touch it should not be a problem. And with solid core coax that should not happen at 400m depth.

@mike - The ROV will have its own power.I will pack some batteries will last long enough to go down do some observations and go up again. The umbelical will be fixed with a spectra braid so if the thing dies I should be able to fish it up. I have seen professional umbelicals but they are all thicker than what I am looking for since they are designed for much greater depths.

 

[itsmoked]

Look up 10Base2 Ethernet. I don't think it's good for 500m.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[IRstuff]

http://en.wikipedia.org/wiki/10Base5

is specified to just at 500 m, but aren't going to get much flex out of it, and 500 m of cable would be pretty darn heavy.

http://en.wikipedia.org/wiki/10Base2

is only good for 185 m.

TTFN

FAQ731-376

 

[itsmoked]

Yeah but.

I couldn't imagine horsing around 500m of 3/8" hideously stiff coax.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Moonwalker031]

Yes thats why I was looking for RG174 but I dont think it is good for such lengths.
Instead of 10Base5 or 10Base2 I was looking at this which is different

http://www.mocalliance.org/index.php

Anyone knows if this is good for my length on RG174?

Another option I tought may work is to use a Wifi router and connect the antenna to the coax. Is this possible?

 

[IRstuff]

Do you actually need ethernet?

ADSL is good for at least two kilometers, and that's with telephone cable. If your datarate requirements are less than 8 Mbps, that might be a alternative:

http://en.wikipedia.org/wiki/ADSL2+

TTFN

FAQ731-376

 

[Moonwalker031]

Hmm I didn't think about ADSL. Can ADSL be used point to point?

 

[IRstuff]

ADSL IS point to point; it goes from the telephone switchbox directly to your modem

TTFN

FAQ731-376

 

[Noway2]

Why use a heavy duty off the shelf protocol? If you are designing your own hardware, just transmit some serial data between the devices. If you have processors at both ends, they will undoubtedly have some form of serial communication hardware. The hardware will be used at logic level voltages, relative to the processor ground. You can then use a transmitter and receiver on both ends to allow the devices to talk. The choice of transmitter and receiver will be dictated by your choice of physical medium.

If you go with coax, you will need to make sure that at the length you are working with that signal attenuation isn't a problem. Also, the slower you send your data, the easier it will be to handle. Of course you will need to make this decision based upon your products needs.

 

[Moonwalker031]

@IRstuff - I can use a cheap ADSL modem on my boat but I will need a DSLAM on the ROV and that is not bought off the shelf right?

@Noway2 - Apart from the serial commands from boat to ROV, I need to transmit video signal and other parameters from the ROV to my boat and I was trying to avoid encoding the video signal over RS485. THats why I was trying to use IP camera and make to comms ethernet based.

I guess I will have to go with FO.

 

[controlnovice]

Go wireless.

______________________________________________________________________________
This is normally the space where people post something insightful.

 

[Moonwalker031]

Underwater m8!

 

[IRstuff]

Most likely you'll need a DSLAM-like device, since the upstream and downstream behavior is usually different for DSL. Note that the DSLAM device would probably wind up in the ROV, since your video must stream in the highest capacity link, which is usually the "downstream" link in DSL.

TTFN

FAQ731-376

 

[djs]

For fiber optic cable check out Corning Cable systems:

http://www.corning.com/cablesystems/nafta/en/index.aspx

 

[Henneshoe]

Here is a possible solution.

There are a few chip manufacturers that make 2 port Ethernet Switch ICs. I have used the SMSC LAN9303

http://www.smsc.com/index.php?tid=147&pid=217

You could make 4 small circuit boards with these switches and use them as repeaters every 100m in your cable. This would allow you to use standard CAT5 cable. RJ45 connecotrs would not be needed as you could solder the conductors directly to the circuit board. The extra 2 conductor pairs in CAT5 could be used to supply power to the circuit boards.

The circuit boards would need to be encased in potting material, and some sort of strain relief would be needed for the cable ends. I am not sure how CAT5 will handle the pressure of 500m depth. Also, some consideration may be needed to ensure water does not wick up into the potting material where the cable enters.

 

[VEBill]

My father used to work at an oceanographic institute designing and building similar ROVs to be used a great depths. For at least one project that he told me about, they started with the available *suitable* cable and designed the electronics to match the cable.

Keep in mind that when the ROV fails, the cable might be useful to try to retreive its waterlogged remains.