2825R TWO DIVER RACK MOUNT COMMUNICATOR USER MANUAL
2825R-UM
REV 3.0
31
Communicators without both differential input and output amplifiers cannot match
the performance of Amron Diving Communicators. This is an extreme simplification
of the common-mode coupling effect and common-mode signal rejection but shows
the power of Amron's Full Duplex (4-Wire) mode of operation.
7.2.2
Isn't Round Robin The Same Thing?
In Round Robin communication systems, each diver is connected using a 4-Wire
cable like the Amron Full Duplex (4-Wire) mode. This is where the similarities end.
In Round Robin systems all the microphones are connected together in parallel
and connected to the microphone input of the communicator. All the earphones are
also connected in parallel and connected to the earphone output of the
communicator. Each microphone is loaded by all the other microphones in the
system causing lower output. In a two diver setup where the diver microphones
have a typical impedance of 8 Ohms and the tender's microphone has an
impedance of 150 Ohm, the diver microphone output level will be reduced by about
50% while the tender's microphone is attenuated by out 95%. On the earphone
side, the diver earphones commonly have an impedance of 8 Ohms while the
typical tender earphone impedance is around 175 Ohms. These two factors
combine to create a serious volume imbalance which requires higher volume
settings resulting in more noise and less system stability.
7.3 Why Full Duplex (4-Wire)?
Amron Diver Communicator uses an independent microphone amplifier for each diver circuit
as well as for the tender. This allows Amron Diver Communicators to use the power of
common-mode rejection to cancel any coupled noise for each microphone as well as
providing less loading of the microphone than in 2-Wire mode. In 2-Wire mode, the diver
microphone is wired in parallel with the diver earphones. Assuming that the impedance of the
microphone is the same as the earphones, the signal from the microphone is attenuated by
65%. By separating the microphone from the earphones, the output signal from the
microphone increases by 285%. With more signal, the volume level can be decreased
resulting in less noise and improved system stability for a significant improvement in overall
clarity.
7.4 How Do You Use Full Duplex (4-Wire)?
In order to use Amron's Full Duplex (4-Wire) mode, you need the following items:
An AMCOM series diver communicator
A good quality dive communication cable with four wires (two twisted wire pairs) like
Amron's CC1
A dive hat/helmet with connection for 4 wires such as a Marsh Marine connector
To connect the system together, refer to appropriate section of the operating manual for
AMCOM diver communicator. In general it involves three steps (using the Amron CC1 cable):