Modulated ultrasound


can be modulated to carry an audio signal. This is often used to carry messages underwater, in underwater diving communicators, and short-range 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.

Range limitation

Due to the absorption characteristics of seawater, ultrasound is not used for long-range underwater communications. The higher the frequency, the faster the sound is absorbed by the seawater, and the more quickly the signal fades. For this reason, most underwater "telephones" either operate in "baseband" mode, in a "UQC-1" mode with a modulated carrier of 7,500 Hz, or in "UQC-2" mode
See Sound from ultrasound for modulated ultrasound that can make its carried signal audible without needing a receiver set.