Assuming the Helix 7 is a G2n version ..... You will need 2 Ethernet adapter cables and 1 Ethernet cable of the appropriate length.

http://www.humminbird.com/Products/AS-EC-QDE/

http://www.humminbird.com/Freshwater...facets=7319%2C

Humminbird also an Ethernet manual .... probably just do a google search for it.