Modulated ultrasound is a technique for the transmission of audio information, comparable to radio.
Ultrasound
Ultrasound is sound with frequency, frequencies greater than 20 Hertz, kilohertz. This frequency is the approximate upper audible hearing range, limit of human hearing in healthy young adults. The physical principles of acoustic waves apply ...
can be
modulated
Signal modulation is the process of varying one or more properties of a periodic waveform in electronics and telecommunication for the purpose of transmitting information.
The process encodes information in form of the modulation or message ...
to carry an audio signal (as radio signals are modulated). It is usually used to carry messages underwater at ranges under five miles.
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
In radio communications, a radio receiver, also known as a receiver, a wireless, or simply a radio, is an electronic device that receives radio waves and converts the information carried by them to a usable form. It is used with an antenna. ...
.
Applications include use in
underwater diving
Underwater diving, as a human activity, is the practice of descending below the water's surface to interact with the environment. It is also often referred to as diving (disambiguation), diving, an ambiguous term with several possible meani ...
communicators as well as communication with
submarine
A submarine (often shortened to sub) is a watercraft capable of independent operation underwater. (It differs from a submersible, which has more limited underwater capability.) The term "submarine" is also sometimes used historically or infor ...
s.
Range limitation
Due to the absorption characteristics of seawater, ultrasound (sound at frequencies greater than human hearing, or approximately greater than 20,000 hertz) 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 (at the same frequency as the voice and is basically a loudspeaker), in a "
UQC-1" mode (as defined in
MIL-C-15240D) with a modulated carrier of 7,500 Hz, or in "UQC-2" mode (as defined in
MIL-C-22509) from around 8,500 hertz to approximately 12,000 hertz, or in the later "WQC-2" mode from 8,500 hertz to approximately 100,000 hertz - with most use around 32,500 hertz) (Also see NATO STANAG-1074 ED.4 for descriptions of internationally used frequencies.)
See also
*
Sound from ultrasound
Sound from ultrasound is the name given here to the generation of audible sound from modulated ultrasound without using an active receiver. This happens when the modulated ultrasound passes through a nonlinear medium which acts, intentionally or u ...
for modulated ultrasound that can make its carried signal audible without needing a receiver set.
References
Ultrasound
Underwater diving equipment components
Submarine tactics
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