HB Interlink (old sharing tech) and Ethernet (newer sharing tech) are 2 completely different animals ...
If there is still an xx7 series in the configuration - it will not Communicate with a HELIX series with any cable ...
If the 798 has “HD” in the model name - it will Ethernet to HELIX series ...:
https://www.humminbird.com/sites/hum...s/ethernet.pdf
Both units would need the AS EC QDE
https://humminbird.johnsonoutdoors.c...-adapter-cable
And an Ethernet cable long enough to reach
https://humminbird.johnsonoutdoors.c...letype%3A27016
Rickie