Maximum length of tether without fathom board

We have a 150m 8-wire tether and are trying to use it directly as an ethernet cable without a Fathom board. We are having trouble getting connection with the onboard computer. Is this too long?
It says on the product page that that the maximum tether length is 300m, but is this when using a fathom board?
What is the maximum length as an ethernet cable?

I think the maximum length of standard cat6a cable is 100m.

Did a quick google search and find this article.

Cat6a maximum length

Yes. I just though it was strange that they sell 150m ethernet cable if I need to use a Fathom board anyway. Then I could just buy the 2-wire