2 selecting the adjacent carrier curve – Mocomtech CDM-QX User Manual
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CDM-Qx/QxL Multi-Channel Satellite Modem with DoubleTalk™ Carrier-in-Carrier® Revision
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DoubleTalk™ Carrier-in-Carrier® (CnC)
MN/CDMQX.IOM
9–7
Carrier
Spacing
Adjacent
Carrier
Level
Desired
Carrier
Desired
Carrier(s)
R = +3 dB
R = +3 dB
A
B
D
R = +3 dB
Desired
Carrier(s)
C
R = +3 dB
Adjacent
Carrier
Adjacent
Carrier
Desired
Carrier
9.4.2
Selecting The Adjacent Carrier Curve
The information presented earlier characterizes the case for one or two adjacent carriers relative to
the desired carrier. The desired and adjacent carriers may also be CnC carriers occupying the
adjacent slots. These cases are summarized by several variants shown in Figure 9-7. Understanding
the relationship between the variants illustrated here assists in selection of the correct adjacent
carrier degradation curve.
Case
Desired
Carrier
Adjacent Carrier
(See Note)
Curve To Use In Figure
Curve To Use For
Any Ratio R (dB)
A
1 Carrier
1 Adjacent Carrier
0dB
R – 3dB
B
1 Carrier
2 Adjacent Carriers
+3dB
R + 0dB
C
1 CnC Carrier
1 Adjacent Carrier
+3dB
R + 0dB
D
1 CnC Carrier
2 Adjacent Carriers
+6dB
R + 3dB
Note: The adjacent carrier is the composite power for either a conventional carrier or CnC carrier.
Figure 9-7. Adjacent Carrier Cases
Case ‘A’ illustrates the way the adjacent carrier testing is conducted. It shows a single adjacent
carrier 3dB higher than the desired carrier, equivalent to two like-modulated adjacent carriers on
either side of the desired carrier, each at the same level as the desired (0dB higher).
Case ‘B’ shows two adjacent carriers, each 3dB higher than what is desired.
Case ‘C’ illustrates a CnC with a pair of co-located desired carriers (CnC ratio is 0) and a single
adjacent slot with pair of CnC carriers whose total composite power is 3dB higher than the
desired pair. The total adjacent power to one of the CnC carriers is 6dB, or the equivalent of two
single adjacent carriers (one on each side of the desired) each 3dB higher than “one” of the
desired CnC carriers. It does not matter whether the adjacent carrier is a pair of CnC carriers or a
standard carrier. It is based on the power.
Case ‘D’ shows two desired CnC carriers accompanied by a CnC carrier on each side. Again, it
does not matter whether the adjacent carriers are CnC or conventional carriers, just the total
power. This situation is equivalent to adjacent carriers each 6dB greater than the one desired CnC