Comtech EF Data CDM-570A - Manual (Page 505)

CDM-570A/570AL Satellite Modem with Optional Packet Processor MN-CDM570A
Appendix E Revision 2
E–3
E.2.4 DemodUnlock
Set the action the modem will take if the remote demodulator loses lock. The two choices are:
• Nom-Pwr reduces the Tx Output Power to the nominal value – default setting.
• Max-Pwr increases 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.
E.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:
• First, corrections for which the output power can be made are fixed at the rate of once
every 4 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.
• Second, 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.
E.4 Monitoring
CAUTION – Comtech EF Data strongly cautions against the use of large values of
permitted power level increase under AUPC control. Users should consider using the
absolute minimum range necessary to improve rain-fade margin.
The remote demodulator’s value of Eb/No can be monitored at all times, either from the front
panel (SELECT: Monitor  AUPC) or via the remote control interface. The resolution of the
reading is 0.2 dB. For all values greater than or equal to 16 dB, a value of 16.0 dB will be
displayed. As long as framing is enabled, the value will still be available, even though AUPC may
be disabled.
The current value of Tx power increase is also displayed. If EDMAC framing is enabled but AUPC
is disabled, this will indicate 0.0 dB. This value is also available via the remote control interface.