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CDM-625A Advanced Satellite Modem
Appendix M
Step
Task
5
(SELECT) CONFIG: ACM
Configure the desired ACM operating parameters,
by selecting the ACM submenu from the CONFIG:
menu branch.
Proceeding from the CONFIG: ACM submenu:
i. Min/Max-ModCod: Define t he r ange of
ModCods ov er w hich t he s ystem will op erate.
ModCod0 is BPSK Rate 0.488 (0.49 bps/Hz), while
ModCod11 is 16-QAM Rate 0.853 (3.41 bps/Hz).
ii. Unlock-Action: Choose t he de sired ac tion
when t he remote demod l oses lock. T his i s
important, as t he A CM s ystem de pends o n t he
feedback o f t he S NR m etric f rom the remote
demod t o determine the optimum M odCod. T he
choices are:
Go to min Tx ModCod (recommended)
–or– Maintain Tx ModCod
iii. Target E b/No m argin: This i s a V ERY
important parameter. The ACM system is designed
to switch based on thresholds that correspond to a
BER o f 5 x 10
order to prevent oscillation around two ModCods at
this exact v alue, 0 .3 dB o f h ysteresis ha s b een
added. T he s witch po ints and t he hy steresis ar e
shown in
found.
If you wish 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 codes installed. For example, suppose the
4100 ksps FAST option is installed, and the symbol rate set to 4100 ksps, the theoretical maximum
data rate would be 14 Mbps at ModCod 11. However, is CnC is being used, with a 10 Mbps FAST limit,
the ACM Max ModCod will be limited to ModCod 7, or 9.6 Mbps.
for ea ch Mo dCod. However, i n
-8
Error! Reference source not
:
Front Panel VFD Mnemonic
CONFIG: All
Mode Tx
CnC
EDMAC
Misc Mask
ACM Config: Min/Max-ModCod
Target-EbNo-Margin
Min Modcod: 00 (B
Max Modcod: 00 (B
When distant-end demod loses lock:
Go to min Tx ModCod (Maintain,Min)
Target Eb/No Margin = 1.0 dB (0.0 – 4.5)
M–10
Revision 0
MN-CDM625A
Rx
Clocks
ACM
Remote
IP ()
Unlock-Action
()
0.488 0.488 bps/Hz)
0.488 0.488 bps/Hz)
()
()
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