Comtech EF Data CDM-625A, Инструкция по установке и эксплуатации

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CDM-625A Advanced Satellite Modem MN-CDM625A
Appendix S Revision 4
S–2
•
At lower symbol rates, particular care needs to be taken with the frequency accuracy and
stability of the RF carriers. It is your responsibility to determine if sufficient guard band is
built into the frequency plan to avoid carriers moving towards each other and overlapping
at the edges.
Now that you can choose between six different values of Tx α , it now becomes
important to match the Rx Alpha (Rx α) accordingly . Comtech EF Data has analyzed
the effect of mismatching Tx α and Rx α , and has concluded that there is little benefit
in providing six values of Rx α . It has been determined that just two values of Rx α –
0.35 and 0.12 – are required to match all six Tx cases.
In order to correctly set Rx α – this assumes that you have knowledge of the Tx α being
transmitted – follow these guidelines:
•
For a Tx α of 0.05, 0.10, 0.15, or 0.20, use Rx α = 0.12.
•
For a Tx α of 0.25 or 0.35, use Rx α = 0.35.
If these rules are followed, then the amount of degradation due to mismatch will be < 0.05 dB.
If these rules are not followed, then the amount of degradation due to mismatch can be > 0.3
dB.