Comtech EF Data CDM-570A Installation And Operation Manual page 634

•
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 Txα, it now becomes
important to match the Rx Alpha (Rxα) accordingly. Comtech EF Data has
analyzed the effect of mismatching Txα and Rxα, and has concluded that there is
little benefit in providing six values of Rxα. It has been determined that just two
values of Rxα – 0.35 and 0.12 – are required to match all six Tx cases.
In order to correctly set Rxα – this assumes that you have knowledge of the Txα being
transmitted – follow these guidelines:
•
For a Txα of 0.05, 0.10, 0.15, or 0.20, use Rxα = 0.12.
•
For a Txα of 0.25 or 0.35, use Rxα = 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.
In Chapter 6. FRONT PANEL OPERATION, see:
•
•
Transmit Spectrum Filtering Options
CDM-570A/570A Satellite Modem with Optional Packet Processor
Sect. 6.3.2.3.11 (Config: Tx) α (Tx Alpha Filter Rolloff Factor)
Sect. 6.3.2.4.11 (Config: Rx) α (Rx Alpha Filter Rolloff Factor)
M–2
Revision 5
MN-CDM570A