M7/M7L/M7LT Modular Satellite Modem Operation
M7/M7L/M7LT - Rev. 0.05 1-13
A significant benefit of this technology is the reduction in carrier pacing required on the satellite. With
a filter roll-off of 0.4, the carrier spacing would be 1.4 times the carrier symbol rate. When the carriers
are changed to a 0.08 roll-off, this carrier spacing can be reduced by more than 20% to 1.1 times the
carrier symbol rate. A spectrum analyzer plot that demonstrates this capability is shown in Figure
1-10.
Figure 1-10 – Carrier Alpha = 0.08, 1Msps x1.10 Carrier Spacing
For example, in a typical 36MHz transponder configured with 1Msps carriers with a 0.4 roll-off there
could be twenty-five (25) carriers. If the 1Msps carrier roll-off was changed to 0.08, there could now
be 32 carriers – a 28% increase in transponder throughput. Table 1-1 shows the relative
improvement that can be gained in a bandwidth limited 36MHz transponder be changing the carrier
Alpha settings from 0.4.
Table 1-1 – Bandwidth Savings Related to Carrier Alpha
Carrier Alpha 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.08 0.05
25 26 27 28 30 31 32 33 34
% improvement
from 0.4 Alpha
0% 4% 8% 12% 20% 24% 28% 32% 36%
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