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It’s 2015 and we still can’t talk underwater (well, we can, but at thousands of dollars per person, it’s too expensive for most recreational divers). Why is this and what is the future of underwater communication systems?
Water is significantly more dense than air and this changes not only the form of our unassisted speech (to unintelligible rumbles) but also the way in which any wireless signal can be transmitted between devices. Radio waves that work on the surface are ineffective in water, so longer wavelengths like ultrasound waves are required.
Early ultrasound underwater communication devices were based upon amplitude modulation (AM) circuitry. The receiver often heard a garbled message, as it was transmitted in the form of three simultaneously signals, which would each travel at different speeds through the water, particularly if they were reflected off surrounding objects. This problem was solved by the development of electronics able to make use of single-sideband modulation, which restricted the transmission to a single ultrasonic signal. air pocket to speak into, such as that provided by full face masks with an integrated microphone. This is currently the best solution for sports divers. Commercial divers use more reliable cabled communication systems linked to the surface or the longer range wireless options preferred by military divers (which can transmit a signal for several miles).
A range of recreational full-face masks are available, and they all designed to address problems around carbon dioxide build-up, fogging and reliability of the seal. Good gas management is essential, as talking rapidly increases air consumption and training courses are usually required with any mask purchase.
Full-face masks aren’t perfect. They are rarely used in technical diving, primarily due to the challenges of gas switching with an integrated mask/regulator. However, they’re likely to become more affordable and more widespread amongst recreational divers before long.
The original article ‘Underwater communications systems’ by Michael Menduno for Alert Diver is available here: http://www.alertdiver.com/uw_comm_systems