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P300H P300 Series Modem Installation and Operating Handbook Page 204
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 ¾ (in
Rate ½ it is already compatible and this flag has no effect, plus there is no Rate
on the 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 66 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 ).
-3
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.