A VOM will tell you the end-to-end resistance of the cable. Ohms law V=IR would let you guestimate any needed voltage boost. I'm guessing it wouldn't be much if anything because of the relatively low current involved. You could always boost voltage at the handle end arbitrarily (keep it under 30V to avoid getting into potentially lethal range) and knock it down at the plane end with a little single chip voltage regulating circuit. A dead computer motherboard usually has a nice voltage regulator and heat sink on it that can be swiped.