How It Works
Each satellite receiver in the installation has a dedicated user band of a bandwidth approximately the same as a transponder. The receiver requests a particular transponder frequency via a DiSEqC-compliant command. A mixer in the dish-end equipment (an LNB or distribution unit) converts the received signal to the correct user band IF centre frequency for that receiver.
The converted transponders of the various users are then combined, and sent via the single coaxial cable to the receivers. The combined signal is tapped or split to reach every user.
Silicion vendors have developed complex Integrated Circuits that greatly reduce the cost of implementing the single cable distribution function. Entropic offers multiple versions of Channel Stacking Switchs to support specific applications. A Channel Stacking Switch IC is a multiple-input multiple-output device. It typically has N 1.2 GHz inputs that can be cascaded to additional chips as required (to expand output capacity). These inputs are fed into a large N-pole M-Throw switch that outputs to M mixers. Each mixer path then translates only the user requested transponder to a predetermined fixed frequency within the 950-2150 MHz band. This fixed frequency is unique for each tuner on the single cable output. Each tuner in the STB always stays at this fixed frequency while the CSS IC translates the user requested content down the cable to this exact frequency. This architecture requires no hardware change to the STB design. Communications protocol between the CSS IC and the STB is handled via the CENELEC EN50494 standard or proprietary systems.
Read more about this topic: Single Cable Distribution
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