The Science Of It All …
In most cases when the diver wants to talk, he simply depresses the push-to-talk (PTT ) button located on the full-face mask (FFM) and talks. The diver’s speech is picked up via the microphone installed in the FFM and sent to the communication unit. The speech is then converted into 33 kHz and sent into the water via the transducer. It goes into the water like sonar waves from a fish finder. The 33 kHz signals out omnidirectional and can bounce off the bottom and surface. When another transceiver’s transducer picks up the sonic signal, the 33 kHz is converted back to intelligible speech, amplified and sent up to the earphone. The diver has the freedom of free swimming without carrying a long wire to the surface.
Through-water communications are battery powered and are composed of a communication system with earphones. All through-water communications need a communication unit and an earphone assembly. Having one without the other is like having headphones without anything to listen to.
Note:The only exception to this is the Buddy Phone, which is both a communication unit and earphone.
Although most people prefer the push-to-talk method when communicating, some devices offer other methods to transmit speech such as Continuous Transmit, or Voice Activated Mode (VOX). Let’s take a look at the three options one might decide among.
(note: some devices only offer PTT)
PTT: This mode is quite simple, efficient, and the preferred mode of divers using through water communications. When you want to talk to your buddy simply push the PTT button and hold while you are speaking. Once you’ve finished, your buddy will do the same to respond. The PTT function is not open communication like a telephone. When one person is speaking, the other is listening.
VOX: This mode is voice activated meaning the unit transmits when your voice keys the microphone. There is no PTT – only voice activated. What’s the problem with this? False transmitting. For example, if a diver is in a panic and begins to breathe hard, he might falsely trigger the microphone and not even know it. As long as he is unknowingly transmitting, no one else can communicate.
Continuous Transmit: The name says it all. This mode is a one way line of communication where one diver is transmitting continuously. In this mode all audible noise (speech, breathing, grunts, etc.) will be heard by others on the same channel and within range.
Anyone can use underwater communications, however as with any specialty piece of equipment there can be a learning curve for some. For example, an unskilled photographer will produce unskilled photographs if they use a camera they have not yet learned to use. It took the U.S. Military three full days to become proficient with our communications. Why is this you may ask? There are several factors that can hinder communication while under the water.
- Biological Noise (critter chatter)
- Thermoclines (change in water temperature)
- Bubble Noise
- Mechanical Noise
- Shadow Zone
Can you avoid this? Not really. We have no control over the external factors that may come into play, however, understanding your communications, correctly positioning your microphone, speaking slowly and being patient while learning are all things that will help you master the use of underwater communications.