ISO1176T: Longest cable distance can be used for ISO1176T

Part Number:ISO1176T

Hi Experts, 

When I use two ISO1176TEVM to test transmit and receive.

There is 2ns delay with 2 meters cable connection.

If I use 25 meters cable to connect with two EVM, there is no signal in receiver.

What is the longest cable length I should use for two ISO1176T/ISO3086T EVM to test ?

Thanks a lot.