Through-water voice communications usually
relates to underwater communications that uses the water to carry
the signal. Other titles for the same type of underwater
communications are: Wireless, Sonic, Ultrasonic or Acoustic telephones.
In all, they achieve the same task, to send voice communications
through-water. This differs greatly from a Hard-wire
underwater communications device which would rely on a cable
to carry the transmission to and from the diver/s. Hard-wire
communications has the greatest potential for clear communications.
This is due to the fact little outside noise can mix with the
signal. As long as the wires are firmly connected and in good
order, the communications will be good (like a intercom).
However, the draw back is the diver has to pull a cable along
with him while he dives. As you can imagine, this would be greatly
impractical for a Sport Diver.
How are they made?
A basic Sonic underwater communication
system is usually compact in design and completely self contained.
The constructed is typically as follows: An electronic package
carefully waterproofed including a battery source, Transducer
(antenna), waterproof earphone/s, microphone and some sort of
securing device such as a belt buckle. The designer can choose
to incorporate a push-to-talk control and/or Voice Operated Transmitter
commonly known as "VOX". An assembly to either mount
to a full face mask or mouth mask is necessary.
How do they work?
Using our MKII-BUDS
Sport Diver Buddy Phone transceiver as a model, (transceiver
means the unit will both transmit and receive), the units operates
as follows: A 9 volt battery is installed into a waterproof compartment.
The Buddy Phone using 33 kHz upper sideband as the carrying frequency.
The transceiver incorporates an earphone on the back side so
the unit is mounted near the ear attaching to a full face masks
(ffm) via the head strap. A microphone assembly with a Push-to-talk
control (PTT) is installed onto the ffm. The transceiver has
a water activated switch which powers the unit ON when the diver
enters the water. The transceiver automatically switches to the
receive mode when the unit is powered ON. This means when
the diver enters the water, he will receive all transmissions
from other sonic communication systems within range and on the
same frequency.
When the diver wants to talk,
he simply depresses the PTT button located on the ffm and talks.
The divers speech is picked up via the microphone installed in
the ffm and sent to the electronic module. The speech is 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
signal goes out omnidirectional and can bounce off the buttom
and surface to ranges up to 400 yards (assuming we are using
a Buddy Phone). 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.
An option to the diver transceiver
is a Receive Only unit. This type of system is basically made
the same way but only offers the user to listen. You can hear
all underwater communications from other sonic transceiver within
range and on the same frequency. However, you can only
listen, not transmit. This device is great for instruction and
used often by professional underwater photographers and advanced
instructors.
Options:
The most common options a manufacture
can incorporate to a sonic communicator as described above are
as follows: Squelch control, VOX, multi channels, longer battery
life, longer range, surface station, more power and whatever
else the imagination can come up with. Lets take some of the
options and explain them:
Squelch: A squelch circuit allows the user to suppress
marine back ground noise commonly found in salt water.
It will also suppress man made noise which will be found anywhere
man is. The draw back to using squelch is that it not only
suppresses noise but decreases range. The more squelch you apply,
the less range you will obtain. Squelch should be used sparingly.
The squelch circuit is usually controlled by an adjusting pot
located in the battery compartment. However, on our SSB-2010,
it is electronically controlled by the diver via a voice menu
(see SSB-2010 for more information).
Voice Operated Transmission
(VOX): A VOX circuit
is designed to allow hands free operation. How the circuit operates
is simple, when the circuit hears sound, it triggers the transmitter.
As long as it hears sound it keeps the transmitter ON. When it
does not hear anything for a set time, typically about 1 to 1
1/2 seconds, it turns off the transmitter and cycles back to
the receive mode. In concept a VOX circuit is great. In practicality,
they are more complicated to use. This is due partly to how they
function in the diving environment. We already said they work
when they hear a sound. Well, divers make lots of noise in a
mouth or full face mask. When a diver off gasses, lots of noise
is created which a VOX circuit hears and triggers the transmitter.
It is for this reason most good VOX designs have some sort of
control over the sensitivity setting. A good setting is when
the unit will not trigger the transmitter when it hears breathing,
mask noise or the like but fires up when it hears the divers
speech. A typical VOX sensitivity control is a small adjusting
pot located inside the battery compartment. The diver must make
adjustments before diving. A good setting would be so the diver
can exhale into the ffm and the VOX will not trigger but when
he talks in a moderate voice, the VOX turns on the transmitter.
This adjustment should be made for each user since most people
have a different sounding voice. Regarding the VOX adjustment,
uniquely, our SSB-2010 has a voice
menu and the VOX and/or PTT can be adjusted on the fly while
diving).
Once the VOX has been triggered,
the VOX circuit will stay ON until it does not hear anything
for approximately 1 to 1 1/2 seconds. This is the biggest problem
with VOX circuits. Anyone who wants to respond back to
a VOX user, must wait at least 1 to 1 1/2 seconds before responding.
If you do not wait, the VOX user will not hear anything until
his transceiver cycles back to the listening mode. This sounds
easy but in practicality, it is hard to remember to wait. Most
of the time when a VOX diver talks to you, you answer him back
immediately. In most cases, the VOX user misses your first couple
of words and will ask you to repeat the message.
In most Search & Rescue or Military type operations, the
users will prefer PTT over VOX. They do not have time to wait
for the 1 1/2 seconds. They want to be able to answer immediately
after someone talks to them. That is exactly what happens when
you use a PTT system. As long as you depress the PTT button,
you are transmitting. As soon as you release the PTT button,
you are listening (no lag time). This seems to be a safer way
to transmit if a fast response is required.
Multi-channels: Commercial and Military divers like to
have alternate channels they can choose in the event two or more
teams are operating in the same area. Although the Buddy Phone
are being used by many Search & Rescue Teams as well as Military
divers, it is a one channel system. However, the SSB-2010 is
a four channel system and our SSB-1001M is an 8 channel system.
Power: How many watts a transceiver has usually
dictates how far it will transmit. Our Buddy Phone transceivers
are 1/2 watt system and in good conditions they can achieve ranges
to 400 yards or further. Our SSB-2010 is a 3 watt transceiver
and have achieved ranges up to 1000 yards. Our SSB-1001M is a
5 watt transceiver with ranges reported out to 3000 meters in
good conditions. Our Magnacom is a 30 watt transceiver and ranges
out to 5 miles were reported. As you can see, even a 1/2
watt transceiver with only a 400 yard range should be plenty.
Batteries: Batteries are necessary to support power.
In some cases, its the battery that dictates the size of the
unit. Electronics can be made tiny as well as the housing.
However, batteries required to support the range and longevity
cause the housings to grow in size. Todays battery technology
is getting better, but still not what we would like to see.
A few examples of what we
are up against, to make a Military unit with a 3,000 meter range,
we had to use a double Metal Hydride AA battery pack. This was
necessary to support the power and battery life required by the
client. Our SSB-2010 with a 1000 meter range and same battery
life only uses a single AA battery back where as a Buddy Phone
with a 400 yard range, 14 hour life only uses a single 9 volt
battery!
Surface Station: In order to talk to free swimming Scuba
divers using through-water communications, you must have a 
through-water device on the same frequency, be
within range and have a transducer in the water. For example,
our SP-100 Buddy Phone surface station
is basically a MKII-BUD in a box. It has a panel speaker, batteries,
hand-held microphone and transducer on the end of a 35' cable.
The user simple lowers the transducer into the water and all
divers talking within range and on the same frequency will be
heard. To talk the user depress the PTT button located on the
hand-held microphone and talks. Again, all divers within
range and on the same frequency will hear him. We have
several surface station to choose from (see Sport,
Commercial, Search
& Rescue or Military). Some
of our diver transceiver can be easily converted from a diver
unit to a portable surface station by addition of a surface conversion
kit (see SSB-2010).
For a more technical view
of sound underwater, go to "Basics
of Sound Underwater".
