Comtech EF Data CDM-570A Installation And Operation Manual page 661

Step
8a. (SELECT) CONFIG: TI  V2-ACM  ModCod
Use the ◄ ►arrow keys to select the Min(imum) (on the
top line) or Max(imum) ModCod range setting (on the
bottom line). Then, use the ▲▼ arrow keys to define
the range of ModCods over which the system will
operate. Press ENTER.
The minimum setting for VF2S (VersaFEC-2 Short Block)
and VF2L (VersaFEC-2 Long Block) is fixed at ModCod 00
(BPSK Rate 0.489 (0.49 bps/Hz)).
•
•
8b. (SELECT) CONFIG: TI  V2-ACM  Unlock-Action
This screen is read-only. Press ENTER or CLEAR to
return to the previous menu.
In the event that the distant-end demod loses lock, the Tx
ModCod will automatically go to ModCod 0.
8c. (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 1 x 10
prevent oscillation around two ModCods at this exact value,
0.3 dB of hysteresis has been added.
Adaptive Coding and Modulation (ACM) Option
CDM-570A/570AL Satellite Modem with Optional Packet Processor
Task
For VF2S, the maximum selectable ModCod
35 is 32-ARY Rate 0.831 (4.153 bps/Hz)
For VF2L, the maximum selectable ModCod 37
is 32-ARY Rate 0.879 (4.397 bps/Hz)
In VersaFEC-2, the Minimum ModCod is fixed at 00, and the user cannot change it.
CAUTION – The value of Max ModCod may be limited by other FAST codes installed. For
example, suppose the 3000 ksps FAST option is installed, and the symbol rate set to
3000 ksps, the theoretical maximum data rate would be 10.239 Mbps at ModCod 27.
However, if CnC is being used, with a 5 Mbps FAST limit, the ACM Max ModCod will be
limited to ModCod 10, or 4.8 Mbps.
for each ModCod. However, in order to
-8
Front Panel VFD Mnemonic
Min ModCod:00 BPSK .489
Max ModCod:37 32ARY .879
Distant-end loses lock:
Go to Min Tx Modcod(▲ ▼)
Target SNR Margin:
1.0 dB (0.0 – 4.5)
P–15
Revision 5
(▲ ▼)
MN-CDM570A