Underwater voice communication

Abstract

The object of this project was to familiarise oneself with the various communication systems used by divers; the problems involved and the construction of an ultrasonic voice communication system. Communication between free - swimming divers and/or surface vessels can be achieved in the following ways. i. Use of hand signals: This is the most common system employed by divers, communication is achieved by making use of a set of predetermined hand signals. It is immediately apparent that this system is very restrictive, since it is essential for the divers to be situated in close proximity of each other with good visual contact. To communicate, the divers must first attract the receiver's attention. This system is extensively used, requires no form of equipment, except a good eye and memory and costs absolutely nothing. ii. Telephone system: This is a normal telephone system, but as such, necessitates the use of cumbersome inter-connecting cables. This greatly reduces the manoeuvrability and freedom of movement of the diver. Thus only 'hard-hat' divers make use of this system. It is very reliable, and is commercially used when the diver's duties are localised. iii. Direct-Audio' System: This is basically very similar to a paging system. It is achieved by simply amplifying the audio signal and propagating it in the water using specially designed metal waterproof loudspeakers, placed beneath the surface vessel. Thus a one way communication system is achieved. iv. Ultrasonic system: This is very similar to a conventional transreceiver, utilising the same principle of modulating a carrier by the speech signal. The basic difference is that due to the inherent high attenuation of electromagnetic waves in sea water, ultrasonic acoustic radiation is employed.