Fathom-X Documentation


The Fathom-X Tether Interface Boards provide a high-speed, long-distance Ethernet connection to an ROV or other remote platform. They’re designed for use with the Fathom tether, standard Cat5 cable, or even a single twisted pair of wires. This board uses the Rak Wireless LX200V20 module, which leverages the robust HomePlug AV (IEEE-1901) standard for sending Ethernet through powerlines.

The Fathom-X board is also part of the Advanced ROV Electronics Package and works well in conjunction with the Raspberry Pi, Pixhawk, and ArduSub Control Software.


  • 80 Mbps Ethernet over two wires (per our own bandwidth testing)
  • 300m+ tether length capability (published capability of 2000m)
  • Plug-and-play with no setup involved
  • Onboard switching power supply with 7-28V input range
  • USB Mini-B connector for powering directly from a computer on the topside
  • Indicator LEDs for power, link, and data
  • Included 6” Ethernet cable for connection to onboard computer

Quick Start

  1. Connect two wires from the tether cable to the terminal block
  2. Power each board with either a USB connection or a 7-28V input to the small terminal block
  3. Connect an Ethernet cable and the connection should become active immediately


Function Diagram

Specification Table

Item Condition Value
Supply Voltage Terminal Block 7-28 volts
Supply Voltage USB 5 volts
Max Power Draw 2.5 Watts
Max Practical Bandwidth   80 Mbps
Physical Layer Bandwidth   200 Mbps
Working Frequency   2-30 MHz
Max Tether Length (Published)   2000 m
Max Tether Length (Tested)   300 m
Operating Temperature   -20 to +85°C
Storage Temperature   -40 to +85°C
USB Connector Type   USB Mini B Female
Tether Wire Gauge   12-30 AWG
Power Wire Gauge   16-26 AWG
Dimensions   64 x 46 mm
Screw Hole Spacing   57 x 40 mm
Screw Hole Diameter   3.3 mm


The EagleCAD files for the schematic and board are available on our GitHub page.

2D Drawings

Fathom-X Board

3D Model

All 3D models are provided in zip archives containing the follow file types:

  • SolidWorks Part (.sldprt)
  • IGES (.igs)
  • STEP (.step)
  • STL (.stl)
Fathom-X Board  
Fathom-X Board FATHOMX-ASM-FATHOM-X-R1.zip


Normal Scenario

In most cases, the Fathom-X setup is simple. Once powered, it acts as a transparent Ethernet bridge to extend any Ethernet connection through the tether.

The four screw holes are identical to those on the Fathom-S ROV board, so they can be interchanged quickly.

With Fathom-S

The Fathom-X board can be use with the Fathom-S board to provide the features of both, simultaneously. Additionally, the screw hole pattern is identical so that they can be stacked together with stand-offs.

The use both board together:

  1. Connect the tether wires to the Fathom-S board normally.

  2. Add jumpers between “Pair 4” on the Fathom-S board and the large terminal block on Fathom-X. Connect 4+ to “+” on the terminal block and 4- to “-“ on the terminal block.

  3. That’s it, both boards will function normally, including the power on/off feature of the Fathom-S board.