Cisco DNCS System Release 2.8.1 3.8.1 4.3.1 User Guide

Systems using the Overlay option require an RF GoQAM modulator or an IF GoQAM modulator. These modulators
are required because they produce partially encrypted broadcast sessions, which feed DHCTs manufactured by
us and by other vendors.

Note: Depending upon system architecture, GoQAM modulators can be used in headends or hubs.

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RF GoQAM Modulators are used only in a DBDS that uses Overlay technology. An RF GoQAM

modulator receives both clear and encrypted content data in an MPEG format from two pairs of ASI
inputs.  Each pair consists of an encrypted stream and its corresponding clear stream. The RF GoQAM
receives RF GoQAMs filter, modify, synchronize, and combine the two data streams into a single
transport stream and send this stream to hubs. Once processed by the RF GoQAM, the transport stream
can be used by DHCTs from third-party vendors, without regard to the type of encryption method that
each DHCT uses. From the QAM List, you can 

, 

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IF GoQAM Modulators are used only in a DBDS that uses Overlay technology. An IF GoQAM modulator

receives both a clear and an encrypted data stream. IF GoQAM modulators filter, modify, synchronize,
and combine the two data steams into a single transport stream using an IF (intermediate frequency) of
44MHz. Once processed by the IF GoQAM, the transport stream can be fed to DHCTs from different
manufacturers, without regard to the type of encryption method that the DHCTs use. Because the
modulator uses an IF frequency, it supports applications that require operation below 55 MHz or above
860 MHz. From the QAM List, you can 

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