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CDM-625A Advanced Satellite Modem
Appendix M
The graph shows the switch points with the Target Eb/No margin set to 0dB. However, the
switch points can be moved (increased) by configuring the Target Eb/No margin parameter,
which can vary from 0 to 4.5 dB, in 0.5dB steps. In a fading environment it is highly
recommended to add sufficient margin to maintain an adequate link quality (and to maintain
demod lock) during the interval between the Eb/No degrading and the ACM controller
responding by lowering the ModCod. See Sect. M.12 Notes and Recommendations.
To continue with the configuration:
Step
Task
6
(SELECT) CONFIG: IP Switch-set-up WAN
Enter t he desired s ize of t he W AN B uffer. T he
minimum size is 20 milliseconds, and is referred to the
data rate c orresponding t o Mo dCod0. In order to
achieve minimum system latency, do not make this
value unnecessarily large.
M.9
Monitoring ACM performance
The CDM-625A provides several ways to determine the current state of the ACM system.
Use the front panel menu to select MONITOR: ACM. The the current Tx and Rx ModCod, along
with the Local and Remote SNR, are displayed here. The SNR displays values between –3.0 dB
and +22.0 dB, with a resolution of 0.1 dB. If either the local or remote demod is unlocked, the
SNR will show 'No Sync'. Of course, under MONITOR: Rx PARAMETERS, the Eb/No continues to
be displayed corrected for modulation type and code rate, in case you do not wish to deal with
SNR values.
Figure M-3. CDM-625A – ACM ModCod Switch Points
Front Panel Mnemonic
Ethernet Switch: Mode
MAC-Learning VLAN Qos Stats
M–11
Revision 0
MN-CDM625A
WAN
PerPortCnfg
()
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