Front Panel Operation Revision 4
CDM-760 Advanced High-Speed Trunking Modem MN-CDM760
6–20
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 ConfigUnlock-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 ConfigTarget-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:
Step Size Default
Maximum
The ACM system is designed to switch based on thresholds that correspond to a QEF of 1E
-7
PER
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)
Processing
GEO Round
Trip Time (ms)
MEO Round
Trip Time (ms)
Total GEO
Comms (ms)
Total MEO
Comms (ms)
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