System Functionality And Operational Considerations - Comtech EF Data CDM-570A Installation And Operation Manual

G.4

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 CDM-570A/AL 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
CDM-570A/AL which then translates the signal to near baseband where it can be filtered
(decimated) and then processed as a complex envelope signal. The CDM-570A/AL 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 DoubleTalk Carrier-in-Carrier, the two
carriers in a typical full duplex satellite link are adjacent to each other. With DoubleTalk Carrier-in-
Carrier, 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.
DoubleTalk Carrier-in-Carrier Option
CDM-570A/570AL Satellite Modem with Optional Packet Processor
Figure G-2. Conventional FDMA Link
G–5
Revision 5
MN-CDM570A