Comtech EF Data CDM-760 Installation And Operation Manual page 106

Front Panel Operation
CDM-760 Advanced High-Speed Trunking Modem
AUPC Compensation Rate: As with any closed-loop control system, the loop parameters must
be chosen to ensure stability at all times. Several features are incorporated to ensure that the
AUPC system does overshoot, or oscillate:
•
In Normal (GEO, or geosynchronous satellite) operating mode, the rate at which
corrections are made to the output power is fixed at 1X/second. 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.
•
In MEO (Medium Earth Orbit satellite ) operating mode, the rate at which a message is
processed and the modem acts on the message, is 1X/250 ms. This takes into account the
lower round trip delay.
•
If the comparison of actual and target Eb/No yields a result that requires a change in output
power, the first correction made will be 80% of the calculated step, up to a maximum
change of 1 dB/message (1X/second in Normal Mode and up to 4X/second in MEO Mode).
This avoids the possibility of overshoot. 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.
The maximum change per message (1X/second in GEO mode and 1X/250 ms in
MEO Mode) will be 1 dB. Any request for more than 1 dB of power delta will take
more than one update period to perform. This is to keep the demodulator from
unlocking due to an instantaneous power change.
AUPC and ACM: AUPC and ACM operate autonomously:
•
AUPC drives the modem to a Tx power level that meets the target Es/No at the remote site.
•
ACM transmits the "best fit" ModCod for the current Es/No.
Because AUPC and ACM function independently, there should be no reason to link them, as one
does not affect the other. In fact, run independently, each feature safeguards the other's
function from a loss of lock.
(CONFIG: Tx) Power  AUPC  Target
This is the Target Es/No value that you wish to keep constant at the remote modem. Use
the  arrow keys to set the value. Press ENTER. Valid settings are:
Minimum
If the current Es/No exceeds this value, the AUPC control decreases the local modem's
Tx output power but never drops below the configured Nominal value.
If the far side modem's Es/No falls below this value, the AUPC control increases the local
modem's Tx output power but never exceeds the Nominal value + Range.
For example: When you set the Nominal value to -25.0 dBm and the Range value to
03.0 dBm, then the maximum Tx power that AUPC drives the modem to will be -22
dBm.
Range
Maximum
0.0 dB 23.5 dB
Step Size
0.1 dB
6–17
Revision 4
MN-CDM760