Comtech EF Data CDM-760 Installation And Operation Manual page 109

Front Panel Operation
CDM-760 Advanced High-Speed Trunking Modem
Table 6-3, Table 6-4, and Table 6-5 list the permitted ModCod, modulation, and code rate
combinations. These tables have some roundoff of the last number in the Data Rate Range
columns.
(CONFIG: Tx) ACM ConfigUnlock-Action
When distant-end demodulator loses lock:
Go to min Tx ModCod (Maintain,Min)
The modem sends and receives ACM messages roughly every 250 milliseconds. This Unlock-
Action occurs when the remote demodulator loses lock and the modem misses three
consecutive ACM messages.
Use the  arrow keys to select an action. Press ENTER.
Comtech EF Data recommends that you use "Min" as the go-to option. This is
important, because the ACM system depends on the feedback of the SNR metric from
the remote demodulator to find the optimum ModCod.
(CONFIG: Tx) ACM ConfigTarget-EsNo-Margin
Target Es/No Margin = 1.0 dB (0.0 – 4.5)
Use the  arrow keys to select a margin value. Press ENTER. Valid settings are:
Minimum
0.0 dB
The ACM system is designed to switch based on thresholds that correspond to a QEF of 1E
for each ModCod. The Target Es/No Margin value is used as a tool to compensate for fade. This
margin is ADDED to the QEF published specification to all ModCods. The QEF specification for a
ModCod plus the Target Es/No margin plus the Modulation Degradation for a modulation type
sets the "shift up" and "shift down" points for the ACM operation.
Using this table as a guide for calculating the Target Es/No Margin:
Symbol Rate
Range (Msps)
1.0<SR<5.0
5.0<SR<15.0
15.0<AR
Range
Maximum
4.5 dB
Messaging/
GEO Round
Processing
Trip Time (ms)
(ms)
1016 560
303 560
267.8 560
6–20
()
()
Step Size
0.1 dB
MEO Round Total GEO
Trip Time (ms) Comms (ms)
150 1756
150 863
150 827.8
Revision 4
MN-CDM760
Default
1.0 dB
-7
PER
Total MEO
Comms (ms)
1166
453
417.8