Comtech EF Data SLM-5650A Installation And Operation Manual page 472

G.3 System Functionality and Operational Considerations
Figure G-2 illustrates a conventional, full duplex satellite link where two carriers are placed in
non-overlapping channels. Figure G-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 G-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.
Appendix H
Figure G-2. Conventional FDMA Link
G–6
SLM-5650A Satellite Modem
Revision 10
MN-SLM-5650A