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Ethernet over 500m (underwater)

Ethernet over 500m (underwater)

Ethernet over 500m (underwater)

(OP)
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?  

RE: Ethernet over 500m (underwater)

Is this a project for school?

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

Dan - Owner
http://www.Hi-TecDesigns.com

RE: Ethernet over 500m (underwater)

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.

www.MaguffinMicrowave.com

Maguffin Microwave wireless design consulting

RE: Ethernet over 500m (underwater)

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

RE: Ethernet over 500m (underwater)

(OP)
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.

RE: Ethernet over 500m (underwater)

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

Keith Cress
kcress - http://www.flaminsystems.com

RE: Ethernet over 500m (underwater)

Yeah but.

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

Keith Cress
kcress - http://www.flaminsystems.com

RE: Ethernet over 500m (underwater)

(OP)
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?

RE: Ethernet over 500m (underwater)

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

RE: Ethernet over 500m (underwater)

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.
 

RE: Ethernet over 500m (underwater)

(OP)
@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.  

RE: Ethernet over 500m (underwater)

Go wireless.

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

RE: Ethernet over 500m (underwater)

(OP)
Underwater m8!

RE: Ethernet over 500m (underwater)

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: Eng-Tips.com Forum Policies

RE: Ethernet over 500m (underwater)

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.spin2

RE: Ethernet over 500m (underwater)

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.

 

RE: Ethernet over 500m (underwater)

(OP)
Thanks again guys. I am still trying to decide what is the best way to go.
So here are some more questions.

Can I send composite video signal over RG174 cable of 500m length?
And if yes, is there a way to also send RS485 data (low baud) over the same cable?

RE: Ethernet over 500m (underwater)

Ethernet doesn't die at 100m, like it hits a brick wall.  The 100m length limitation has something to do with propagation time for out and back and the collision detection algorithm used.

There's lots of anecdotal stories of doing ethernet over distances more than 100m.  My nephew does 500m with a ethernet surveillance camera on a 10Mb connection.  It works.

I'd be inclined to try it with ethernet over 500m, you won't have any VFD hash/noise to contend with . . .

One other thought, in commercial ethernet cable, there's 8 wires, 4 pairs, only two are used for each connection, but the other two pairs are there, idle as it were.  

You might consider streaming your camera data on 2 pair, to avoid collisions with any other data; and run your control data (or whatever else there is) on the other 2 pair.  It would take 2 ports and 'custom' connectors, but this is a hobby, right?

I've done RS-485 with CAT5, but only at distances <100m.  I suspect it will work fine at 500m, but I'd use one of the extra pairs for a ground reference.

 

RE: Ethernet over 500m (underwater)

(OP)
Thanks m8 for your explanation.
Rs485 would have no problem with limited slewrate and low baud for such lengths. I can also send composite video over 500m twisted pair cable using an amplifier. However I
Cat5 is a little thick for me since I need the least possible drag in the water.

So my options are-
RG174 - This is not good for ethernet but it should be good for composite video and maybe also for RS485. I need to find a way to encode both signals over the same cable if possible though. Also have a question if it can withstand 50bars of pressure without crushing compleatly.

Single twisted pair - Same as above but facing same encoding problem. Pressure should not be a problem here.

Plastic Fibre optic (possibly single). - Using twin fibers is ok for ethernet so would have no problems with encoding. I was hoping I can use single cable though to limit the outside diameter. Also have a question about maximum pressure it can withstand.

RE: Ethernet over 500m (underwater)

Why don't you try to call or email someone over at Woods Hole and ask what cable problems they encounter.   

www.MaguffinMicrowave.com

Maguffin Microwave wireless design consulting

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