Interfacing Arduino to Fathom S Topside

I am trying to use the Fathom S for an ROV I am building. I would like to use an arduino to interface to the topside board instead of a computer. I tried to use the arduino usb host example code for ftdi, but it did not seem to produce an output signal on the tx. When I use my computer to interface to the topside board, I can get a signal on the tx pin. Does anyone have experience using the topside board with an arduino and is using a usb host shield the preferred interface method?

Can you share the shield you are using, your code, and how you have things wired?

This is the link for the USB host shield running on a mega 2560:
https://store.arduino.cc/usa/arduino-usb-host-shield
This is the code:

We used the library manager in arduino to add the USB host code.
We used the USBFTDILoopback example.
We used a scope probe to check activity on the tx pin of the header.
We have screw shields providing optionally 12V, but that does not seem to effect the result.