A descrambler is a device that reverses the effect of signal scrambling on the receiving side. A descrambler corrects a video signal that has been intentionally distorted to prevent unauthorized viewing. Descramblers are typically used with satellite TV systems.
When a descrambler is added to the Cable Converter Box in the same chassis, it is referred to as a Converter/Descrambler or sometimes a Combination Unit, and is a type of Set-top box, it allows: local broadcast channels, basic cable channels, authorized premium channels, "Pay-Per-View" (PPV), and “Video On Demand” (VOD) services to be viewed. A Combination Converter/Descrambler is generally called a Set-top box or STB it is a single (one-piece) system installed in a single cabinet and represents a single component that is capable of descrambling premium services, like HBO or Showtime, pay-per-view cable channels., Video on Demand, Games or other specialty pay services, and transposes the cable signal for RF output on channel 3 or 4. This unit contains a converter and a descrambler, enclosed in a common box, and outputs the signal directly to a TV, VCR, DVR, PC, DVD or video projector.