Multiple Fathom-X on Fathom ROV Tether

Hi all ,

do you have any experience with adding additional Fathom-X to the spare conductors on the Fathom tether , and running them together ? ( for example running 2 fathom-x subsea and 2 fathom X on the surface , on the same Fathom tether )

Has anyone experienced signal interfereces as the twisted pairs are not shielded ?

Thank you .
Davide

I don’t have any firsthand experience, but my understanding is that yes you can do this with up to three in total stacked onto the same twisted pair. I would assume a separate pair works also, but maybe there’s a shielding issue being on a different pair.

@DavideROV - We have a new, soon-to-be-released, MUX that replaces the Fathom-X in the BlueROV2 and allows for dual Ethernet signals over a STP (single twisted pair). Our new MUX also has 5VDC, 12VDC and 24VDC power supplies for devices that cannot utilize the available ROV power. (There are also more advanced capabilities onboard but will leave those until the official release.)

We have 5 of these MUXs in the field and will be complete with our first production run soon. If you’d like more info, just email or message me for now. We should be releasing an official datasheet soon. jeff@blue-linked.com

Yes, you can do this, but cross talk is a problem when using more than one pair (to the point of still communicating with some devices despite being disconnected), so best to keep everything on a single pair. …Subsurface you need a fathom board for each component, connected in parallel. Then at the surface you have a single fathom board, connected to an ethernet switch, connected to your PC.

Thank you Jeff , yes I am interested on your product . Let’s keep me updated :wink:

Thanks

Thank you all for sharing your thoughts , it is much appreciated !

Hello all,

I was wondering if it is possible to get 2 pairs of FathomX board on differents Twisted Pairs on the tether, assuming they are shielded to avoid crosstalk ?

Does anyone already tried this ?

Thank you !

Hi Marcus,

Can you expand a little for a networking newbie about how best to run dual fathom boards on the same twisted pair…? I have a BR2 control system using Fathom x boards on a Subsea Crawler robot using standard 4 x TP BR umbilical cable and QGround Control. I want to add a separate IP camera to the system in addition to the BR USB camera and also run an RS485 device through the same umbilical. Do you see any issues here??
Thanks.
Gavin.

Hi @nemorov,

For adding an IP camera it’s likely simpler and cheaper to use an Ethernet Switch in the vehicle rather than adding an additional pair of Fathom-X boards :slight_smile:

RS-485 uses differential signalling, and should be fine to use through the same tether assuming the data rate isn’t too high. Section 2.2 of this Texas Instruments Application Report suggests

Accordingly, a 100m tether should not signal RS-485 faster than 1Mbit/s.

Thats great. Thanks for the reply and info. Ethernet switch sounds ideal and easy.
We’ve previously used the RS485 device through 300m of umbilical so should be fine in this application if theres no interference issues with the Fathom X signal.
Thanks,
Gavin.

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