http://store.humminbird.com/media/document/798c-ci_Manual.pdf
I havent been able to find anything about the NMEA out voltage, I've tried to use a digital voltage meter to get a reading on the output voltage but it will not show any voltage. The unit operates on 12v dc and I can input the gps signal directly into my laptop via my serial input and show sentences using a program already installed,( Drdepth)