Comtech EF Data CDM-750 - Manual (Page 108)

CDM-750 Advanced High-Speed Trunking Modem Revision 2
Front Panel Operation MN-CDM750
5–30
5.2.2.5 CONFIG: ACM (Adaptive Coding and Modulation)
Appendix C. ADAPTIVE CODING AND MODULATION (ACM) OPTION.
ACM Config: Min/Max-ModCod Unlock-Action
Target-EbNo-Margin Degradation (
v)
Use the W X arrow keys to select Min/Max‐ModCod, Unlock‐Action, Target‐EbNo‐Margin, or
Degradation, and then press ENTER.
5.2.2.5.1 (CONFIG) ACM Config: Min/Max-ModCod
If the user wishes to constrain the system to run at a fixed ModCod, set the Min and
Max ModCod values to be equal.
The value of Max ModCod may be limited by other FAST Access Codes installed for
Modulation and Symbol Rate.
Min Modcod: QPSK 1/2
Max Modcod: 32APSK 9/10
To define the range of ModCods over which the system will operate (i.e., the range for the
modem’s Tx capability): First, use the W X arrow keys to select the Min or Max ModCod. Then,
use the ST arrow keys to select the available ModCod (see Table 5‐2 for the available
ModCod, modulation, and code rate combinations). Press ENTER when done.
5.2.2.5.2 (CONFIG) ACM Config: Unlock-Action
When distant-end demod loses lock:
Go to min Tx ModCod (Maintain,Min) (
v)
Use this submenu to establish the desired action when the remote demod loses lock. This is
important, as the ACM system depends on the feedback of the SNR metric from the remote
demod to determine the optimum ModCod.
On the bottom line: Use the ST arrow keys to select Go to min Tx ModCod (recommended)
or Maintain Tx ModCod, and then press ENTER. The ACM Æ Unlock selection will trigger
when three consecutive ACM messages are missed (ACM messages are sent and received
roughly every 250 ms).