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Re: [PSUBS-MAILIST] RFC - Standard Thru-Hull Electrical Connector
Jay - you are right, and the reason is that an open-circuit comm system
would entail transmitting at all times. With radio signals, this is
obviously undesirable as an open mic steps on other persons
transmissions. With ultrasonics at identical frequencies, you just end
up with superposition of all the signals. The biggest disadvantage
would be the power consumption - PTT makes sense in that context since
in the case of a high power transmitter you aren't draining your
batteries unnecessarily. Note, however, that 4-wire comms and selective
use are not mutually exclusive. There is an argument to be made,
particularly for a sub communicating with divers, for a 4-wire open
circuit system which could be switched on only for burst sessions as
with a PTT device, and could in fact be functionally identical to a PTT
base unit with regard to a keyable microphone for switching, but the
4-wire mode would ensure that the divers voices are heard, even if two
or more divers are speaking simultaneously, and ensures that they are
never preempted during one of your transmissions. Granted, I have no
experience with one atmosphere submersible comms, but I have used both
PTT, VOX and 4-wire diver / tender systems, and the advantages of the 4
wire system have convinced me that I never want to go back. The only
real disadvantage is the extraneous non-related noise inherent to having
an always-on mic, but filters can take care of that without too much
trouble. I think what I'm getting at is that transmission can be PTT on
the sub side, but a diver in the water should have 4-wire hands free
(again, the proliferation of 2-wire systems in this application arise
from the power consumption issue when not hardwired on umbilical, and
the breathing / bubble noise issue, which while annoying, is actually
safer than eliminating these sounds as you can preemptively react to a
diver problem indicated by a breathing change), and reception ability on
the sub side even when the mic is keyed cannot be a bad thing. If we're
talking about sub-to-sub exclusively, it is less of an issue.
-Sean
Jay K. Jeffries wrote:
Sean,
I am not sure that your 4-wire mode applies here. It has been a long time
but I seem to remember that the 4-wire system is a hardwired comm system
with the diver so would not apply to a free ranging sub (i.e. not on an
umbilical). All PTT equipment is housed within the hull. We are talking
about connecting a hydrophone in most cases. Depending on how you dive, two
transducer might be used...one above the hull and one below.
R/Jay
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