Ultrasound can be
modulated to carry an audio signal (like radio signals are modulated). This is often used to carry messages underwater, in
underwater diving communicators, and short-range (under five miles) communication with
submarines; the received ultrasound signal is decoded into audible sound by a modulated-ultrasound receiver. A modulated ultrasound receiver is a device that receives a modulated ultrasound signal and
decodes it for use as sound, navigational-position information, etc. Its function is somewhat like that of a
radio receiver.