The SCT2X4 includes two satellite tuners and demodulators that are used to recover an IP encapsulated, MPEG2 transport stream from the satellite-downlinked transmissions. The SCT2X4 can demodulate QPSK signals with various FEC modes and it can also demodulate 8PSK modulation using DVB-S2 FEC.
After demodulation and deencapsulation, all of the single program MPEG2 transport streams (MPEG2 or MPEG4/H.264 payload) from the received satellite transmissions, from one or two transponders, are listed so that the user can select desired program streams and map each program to one or more of the four output QAM channels. The programming of the program filter may be conveniently accomplished by means of a RS232 user interface and PC. After this program filtering, a multiplexer section combines selected programs into a multiprogram transport stream, one for each of the four outputs. The data rates are such that when the satellite transmissions are 8PSK with DVB-S2 FEC, the programs from two transponders will usually require four QAM output channels if all programs are selected.
The satellite delivered streams end up with quite a bit of timing jitter when the IP encapsulation process is used at the uplink. The SCT2X4 contains special circuitry that is used to reduce this jitter to an acceptable level for MPEG delivery.
The SCT2X4 does not alter the scrambling that is likely to be in place on the program streams. The scrambled streams pass intact through the transcoder and are delivered to the set top box where the descrambling will occur. The SCT2X4 does provide a data output that can be used to direct satellite delivered data, such as EMM streams, to the local headend. Usually a local headend controller will process this data and a Drake OBM100 Out of Band Modulator will be used to send data from the headend controller to the set top boxes.
The SCT2X4 also provides an ASI input where additional locally generated programs can be input. This allows these programs to be added to one or more of the output multiplexes, as selected by the user. These programs may be MPEG2 or H.264 transport streams that have been encoded with a local MPEG encoder.
The SCT2X4 may be remotely monitored and controlled via its RS232 interface. The SCTeci Ethernet Control Interface may be used to provide an IP interface for all SCT2X4 units that are being used in the headend.