Comtech EF Data SLM-5650A - Manual (Page 303)

SLM5650A_CDM625 Satellite Modem Revision 8
DoubleTalk Carrier-in-Carrier Option MN-SLM5650A
15–5
15.4 System Functionality and Operational Considerations
Figure 15-2 illustrates a conventional, full duplex satellite link where two carriers are placed in
non-overlapping channels. Figure 15-3 shows the same link using the SLM-5650A equipped
with the DoubleTalk Carrier-in-Carrier option. Note that only 50% of the bandwidth is being
used, as both carriers are now occupying the same bandwidth.
The transponder downlinks the composite signal containing both carriers on the same band to the
SLM-5650A, which then translates the signal to near-baseband where it can be filtered
(decimated) and then processed as a complex envelope signal. The SLM-5650A then suppresses
the version of the near-end carrier on the downlink side, and then passes the desired carrier to the
demodulator for normal processing.
To further illustrate, as shown in Figure 15-4, without CnC, the two carriers in a typical full
duplex satellite link are adjacent to each other. With CnC, only the composite signal is visible
when observed on a spectrum analyzer. Carrier 1 and Carrier 2, shown here for reference only,
are overlapping, thus sharing the same spectrum.
Figure 15-2. Conventional FDMA Link