Paradise Datacom P300 Series Installation & Operating Handbook page 209

7 Severely Degraded Phase noise mode
In response to a customer request, to provide operation with a severely degraded receive phase
noise in QPSK, this mode can be enabled. It allows operation with up to 20dB worse phase
noise than the INTELSAT mask (DC - 1kHz), although at the cost of a degraded BER in normal
operating conditions (BER is degraded by up to 1dB compared to `Normal` mode).
8 Disable the Upper Temperature Limit
The specified upper internal temperature limit of the modem is 60C. Within three degrees of this
the unit will raise a Unit Warning (& deferred alarm relay) Warning: Int' temp 57C, Tx CARRIER
WILL MUTE outside operating range 0-60C . Above an internal temperature of 60C the carrier
mutes and a Unit Fault is raised (& Prompt Unit alarm relay), Unit Fault: Tx carrier muted, unit
temp 61C outside operating range 0-60C . Setting Fault Mode to 8 disables both the carrier
muting and the Unit Fault / Prompt alarm above 60C, however the warning/deferred alarm
above 57C is still activated. Modem operation outside the specified internal temperature
range is not guaranteed, and so this option should not be used on satellite.
9 Internal Test Mode (Disable Differential Encoder and Decoder)
10 Extended 1 for 1 for Antenna Diversity, Initially On Ships (Software >=V2.05)
The normal 1 for 1 redundancy system will cope well with each modem in the 1 for 1 pair being
connected to a different antenna (eg at opposite ends of a ship on stabilised platforms). The
modems will automatically switch traffic to whichever one remains operational. Should one of
the antennas loose its line of sight to the satellite it will cause the on-line modem receive to fail
and the modems 1 for 1 partner to come on line, conveniently also switching the Tx to the other
antenna. However one specific customer wished to integrate a `block` signal from the Antenna
Control Unit (ACU) into the 1 for 1 system, to guarantee the Tx on either antenna would be
muted when the corresponding ACU indicated `block` (ie when the antenna movement limits set
on the ACU indicated the antenna was starting to point at the ship itself, or more importantly the
crew!).
The solution is to link the `block` signal from the antenna directly to the modems external Tx
Inhibit signal on pin 7 of the alarms connector (grounded when blocked, also connect a ground
on pin 15) AND to set Fault Mode to 10. With the connection made but without the Fault
Mode set to 10 the Tx to either antenna will be muted when the corresponding ACU `block`
signal is active. It will not however immediately switch the traffic over to the other modem in the
1 for 1 pair (ie not switch the traffic to the other antenna, as the external Tx inhibit is not
considered a fault by the 1 for 1 logic). Without Fault Mode set to 10 then it would be possible
for the ACU to indicate `block`, muting the Tx carrier (because the antenna has just passed the
ACU movement limit where the beam is approaching the ship) and for the Rx carrier to remain
OK until the receive signal is fully obstructed by the ship. If this happens there will be a break in
transmission from the ship until the receive totally fails, finally causing a Rx fault which will make
the modems 1 for 1 partner take over, switching both Tx and Rx to the other antenna.
When Fault Mode is set to 10, the External Tx Inhibit is additionally considered as a fault by
the 1 for 1 logic (although it has no effect on the normal LCD display of modem faults). Now,
apart from the ACU `block` signal immediately muting the Tx carrier, the 1 for 1 modem pair will
also change over to the standby modem causing the traffic to be immediately routed to the other
antenna (provided the standby modem has no faults and the ACU of the other antenna is not
itself indicating `block` causing the standby modem External Tx Inhibit to be active). Only when
the ACU indicates `not blocked` can the traffic switch back to the first antenna. Should both
ACU's indicate `block` then Tx from both antenna will be muted, with the last one to indicate `not
blocked` remaining on-line (as far as the 1 for 1 is concerned) providing receive data. Full traffic
will switch back to the first modem, which has no faults, ie where the modem has a good receive
P300H P300 Series Modem Installation and Operating Handbook Page 209