Q-Lite Satellite Modem Installation and Operating Handbook
6-81
uncertainty in the range to the satellite (via the
Round-trip delay
setting on the
Edit->Paired Carrier
menu). This has a significant
effect on acquisition time. If using a round trip delay then try
switching to using location information.
•
Reduce the sweep width (via the
Sweep width
setting on the
Edit->Tx-Rx->Advanced
menu) as this may significantly speed
up the acquisition process.
•
Check for signs of signal degradation such as poor Eb/No
values or poor spectrum and constellation.
16. If 1:1 or 1:N redundancy is being used, Paradise recommends setting
the modems to switch on Unit Faults only (i.e. setting the Tx and Rx fail
switchovers off via the
Edit->Redundancy
menu option). This is because
when a modem is in standby, no transmit carrier is generated, therefore
there is nothing for
Paired Carrier™
to cancel and the standby
demodulator will not lock because it cannot separate the two interfering
carriers (from the online modem and the remote modem). In this case, a
switchover from the online modem can never occur since the standby
modem is, from a logical point of view, faulty and a switchover will not
occur to a standby modem deemed faulty. Please refer to application
note AN_027A (1:1 quick start guide) for further details.
17. When using
Paired Carrier
with IP as the terrestrial interface type,
Paradise recommends setting the master hub transmit timing to
Internal
,
the hub and remote receive clocking to
Satellite
and the remote transmit
clocking to
Rx reference
. This ensures only one master clock is
providing timing for both modems and can prevent data pattern clashes
(between the two overlapping carriers caused by similarities in the
satellite framing) that otherwise can degrade
Paired Carrier™
performance.
6.2.8.2 Round-trip Delay
The modem needs to know the delay to the satellite in order for
Paired Carrier™
to work.
Several methods of calculating the round-trip delay are supported, as listed in
Table 6-70
.
Set location
In this mode the modem automatically calculates the satellite round trip
delay using coordinates that you enter for the modem and satellite
positions.
Set delay
This mode uses user-entered minimum and maximum satellite round-trip
delay times and searches for the satellite between the limits. The size of
the delay window directly affects the carrier acquisition time and should
be reduced to +/-0.5ms around the actual measured satellite delay (as
shown on the
Status->Paired Carrier
screen) once this has been
established following
Paired Carrier™
achieving lock.
Use GPS
This mode allows mobile
Paired Carrier™
operation (for example, on
ships) without ever having to change location or satellite delay information
for
Paired Carrier™
. Any change in location will not affect
Paired
Carrier™
operation. A GPS source must be attached to the modem via
the modem’s remote serial control port, which will be automatically
