Paradise Datacom P300 Series Installation & Operating Handbook page 210

signal and the ACU indicates `not blocked`. When both ACU's indicate `not blocked` (ie most of
the time) the normal modem 1 for 1 redundancy operates.
This might take a few reads to fully understand, but it is an elegant solution to the problem
requiring nothing other than a data `Y` cable, a standard 1 for 1 cable and a two wire link
(ground & `blocked`) from each ACU to the corresponding modem!
A word of advice on installation. DO NOT put the modems at opposite end of the ship and run
the 1 for 1 and data `Y` cables along the entire ships length. Instead co-locate the modems,
keep the 1 for 1 cable and data `Y` cable short, and run the modem IF along the length of the
ship. If the ACU's are located at the ends of the ship with the antennas, use coax cable to
connect the `blocked` signal from the ACU to the modem along the ships length
(screen=ground, centre=`block`).
11 Comstream Sequential Mode (Software >=V2.12)
This switches the Sequential encoder and decoder to be Comstream compatible at Rate
(in Rate 1/ it is already compatible and this flag has no effect, plus there is no Rate
CM701). Note that when interworking with Comstream equipment with Viterbi FEC: BPSK
requires P300 Tx & Rx spectrum invert, QPSK is OK without. With Sequential FEC: BPSK
requires P300 Rx spectrum invert and both Tx & Rx spectrum invert in QPSK.
12 OQPSK Compatibility Mode (Software >=V2.12)
Refer to the OQPSK Primer on page 69 before reading this section.
When using Offset QPSK (OQPSK) modulation, the in phase and quadrature components of
each symbol do not change together (as with QPSK), but instead one component is delayed by
half a symbol compared to the other. In order to be in accordance with general industry
practises Paradise Datacom has changed which of the two components is delayed with respect
to the other between the earliest of the P400 series modems and ongoing P400/P300
production. If you experience difficulty interworking in OQPSK mode between equipments,
switch on this mode at the transmit end of the link which fails.
13
Inmarsat (ISDN Backup) (Software >=V2.14)
This additional feature allows an external equipment to provide an ISDN backup of the satellite
circuit should the link fail, or degrade beyond user set Eb/No or BER parameters. The ISDN
backup being initiated from one end of the link only (in response to a failure in either direction)
by the Receiver Ready line of the interface card being dropped. Exact additions are:
A backward alarm is transmitted if the user Rx BER or Rx Eb/No pass the user set
thresholds (normally these only activate the deferred alarm). This signals the remote
end that the circuit has degraded beyond the user thresholds (although it is already
mandatory to send a backward alarm in IBS/SMS when the user BER degrades below
the fixed threshold of 1 x 10
When the user Rx BER or Rx Eb/No pass the user set thresholds OR a backward alarm is
received, the interface card Sig Valid Out line is deactivated (normally this line
deactivates only in response to a prompt Rx alarm, eg carrier loss). This line can be
used with certain ISDN equipment to initiate an ISDN call.
14-15 Used for internal Paradise testing of enhanced modes we are evaluating. Not suggested for
customer selection.
P300H P300 Series Modem Installation and Operating Handbook
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