1 twisted pair tether

Okay, dumb question here’ what protocol is used for communicating on just two wires?

RS-485 I believe is the protocol being used by the Fathom X board

Hi @model14,

We achieve communication through two wires in a tether with our Fathom X boards, which

You can read up on HomePlug AV if you want, but basically it uses AC frequency modulation to send the data efficiently. Each end sees the Fathom-X as just an ethernet device, and communicates using normal ethernet communications (e.g. IP packets).

In the specific case of our ROVs we use TCP for providing the web interface, and UDP for sending the MAVLink telemetry and the video stream :slight_smile:


@Willemb RS-485 is another robust protocol that can operate over two wires, which is common for industrial sensors and robotics (including underwater ones), but it has much lower bandwidths than HomePlug AV.

Thanks Elliot for the clarification. I was curious how video and telemetry were being delivered over what I thought was RS-485. I’ve used power line Ethernet a long time ago when living on a boat and desperate for internet. The bandwidth was severely degraded with so many junctions and noise on our dock power. What a great use of this technology.

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Williem, not to “hijack your thread” but my question may be of interest to you as well so I just tag on.

We will install a ADAM6542/W15 in the ROV and connect the two signal wires in the ROV via Ethernet connection. From there we will communicate via a fiber to the surface. Then on the topside computer the fiber is connected to another Adam unit and we take out the ethernet from there and connect it to the PC. As I understand, I then get the RS485 protocol transferred through to my PC. However, looking at the Connection Diagram, I think I will need a Fanthom-X card in both ends and the ADAM unit connected (ref diagram) after the Fantom-X in the ROV and before the Fantom X on the topside computer. Is that correct?

Hi @RURAS, welcome to the forum :slight_smile:

The Fathom-X boards convert between Ethernet <=> HomePlug AV. Your ADAM6542/W15 boards convert between Ethernet <=> WDM Fiber Optic, so with a fiber optic tether you could use your ADAM boards instead of our Fathom-X boards, not together with them.

I’ve added some notes to update our documentation so that’s clearer in future :slight_smile:

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