Switch Points - Comtech EF Data CDM-570A Installation And Operation Manual

Step
2c. (SELECT) CONFIG: TI  IP-ACM  Target SNR
Margin
Use the ▲▼ arrow keys to select a margin value from
0.0 to 4.5 dB, in 0.5 dB increments. Press ENTER.
This is a VERY important parameter. The ACM system is
designed to switch based on thresholds that correspond to a
BER of 5 x 10
prevent oscillation around two ModCods at this exact value,
0.3 dB of hysteresis has been added. The switch points and
the hysteresis are shown in Figure P-2.
P.6.3

Switch Points

Figure P-2 shows the switch points with the Target Eb/No margin set to 0 dB. 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 0.5 dB steps. In a fading environment, it is strongly
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 Secion P.9, Notes and Recommendations.
Adaptive Coding and Modulation (ACM) Option
CDM-570A/570AL Satellite Modem with Optional Packet Processor
Task
for each ModCod. However, in order to
-8
Figure P-2. CDM-570A/570AL-IP ACM ModCod Switch Points
Front Panel VFD Mnemonic
Target SNR Margin:
1.0 dB (0.0 – 4.5)
P–11
Revision 5
(▲ ▼)
MN-CDM570A