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C.2.4
Demod Unlock
This defines the action the modem will take if the remote demodulator loses lock. The two
choices are:
•
NOMINAL (reduce the Tx Output Power to the nominal value) – default setting.
•
MAXIMUM (increase the Tx Output Power to the maximum value permitted by the
parameter MAX RANGE).
If the local demod loses lock, then the modem automatically moves its output
power to the nominal value.
C.3
Compensation Rate
As with any closed-loop control system, you must choose loop parameters that ensure stability at
all times. Several features ensure that the AUPC system does overshoot, or oscillate:
•
Corrections for which the output power can be made are fixed at the rate of once every
four seconds. This takes into account the round trip delay over the satellite link, the time
taken for a power change to be reflected in the remote demodulator's value of Eb/No,
and other processing delays in the modems.
•
If the comparison of actual and target Eb/No yields a result that requires a change in
output power, to avoid the possibility of overshoot the first correction made will be at 80%
of the calculated step. Subsequent corrections are made until the difference is less than
0.5 dB. At this point, the output power is only changed in increments of 0.1 dB to avoid
'hunting' around the correct set point.
Appendix C
CDM-425 Advanced Satellite Modem
C–3
Revision 0
MN-CDM-425
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