Table of Contents
Advertisement
CDM-625A Advanced Satellite Modem
Appendix S
The recommended minimum carrier spacing equals(1 + Txα) x symbo l rate ,
•
assuming equal symbol rates for all carriers and zero frequency error between carriers.
•
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.
S–2
Revision 0
MN-CDM625A
Advertisement
Chapters
Table of Contents
