Recording signals on to a map

[sportscanuser]

I want to put a analog signal from a towed metal detector or magnetometer on a map I am using oziexplorer and need a circuit that will convert a analog signal in to a NMEA format ,the map program is set up to use a depth sounder and I wish to use the depth sounder feature to record signal strength signals from a Mag or metal detector on to the map for later use. Any help welcome