Ocean Technology Systems MilCom 6000D User Manual page 26

ZONES OF SILENCE
20
Large natural or man-made objects can block acoustical transmission
under certain conditions, in much the same way that a rock blocks
a fast-moving current of water. Close to the backside of the rock, in
this example, the current is absent and the water seems still. A short
distance away, the current is flowing again.
Similarly, acoustic energy in the water can be blocked if the transmitting
source is close to a large object. On the backside of the blocking object,
a "zone of silence" is formed in which reception of the transmitted
signal is not possible. Divers can reduce "zones of silence" by moving
away from, around, or above the blocking object until communication is
reestablished.
Under some conditions, when your diving suit is directly between the
transmitting source and your MilCom, a small zone of silence may be
created that prevents reception. This effect can become greater at longer
ranges. Turning approximately 45 degrees in any direction eliminates this
zone of silence.
For more information on Wireless Communications, visit the Learning
Center on our website at: WWW.OTSCOMM.COM