i bought a boat wiyh a hummingbird 400 tx.no manuel so i went online and studied this unit a l bit.from what i gather it has a wide range which is something like si.i think their sayind in order for that to work needa another tra sdu er with a switch added in.im confused on the whole thing.why wouldthey sell a unit with two diff transdu ers??? AM I BETTER OFF TO GIVETHIS THING TO SOMEBODYAND BUY NEW ONE OR TRY AND DO SOMETHING WITH THIS THING? does anybody here have any clue about this unit?