4DTV Satellite receiver By Lawrence E. Ullman   •   February, 1999 When it comes to delivering audio/video programming to the home, there's no substitute for bandwidth. Typically measured in megahertz (MHz) for analog signals or megabits per second (Mbps) for digital datastreams, the amount of bandwidth your system can access determines how much programming you can receive and at what level of quality.

Bandwidth can be piped into the home using a variety of media, including telephone, coaxial, and fiber-optic cable as well as a rooftop antenna. But the most effective and practical way for most people to access a lot of bandwidth today is with a satellite dish. And the bigger the dish, the better.

Dishing it up
Although direct broadcast satellite (DBS) systems such as DSS can deliver a lot of bandwidth, the very thing that makes them popular—that small, fixed dish—limits their ultimate capacity. To understand why, you need to know a bit about how satellite television works.

There are currently 22 C-band (3.7-4.2GHz) and nearly as many Ku-band (11.7- 12.2GHz) satellites in orbit. Each of these "birds" contains a number of transponders, which receive signals from a program provider's uplink antenna and then rebroadcast, or downlink, the signal back to earth. As you might expect, each satellite's bandwidth is strictly limited by the number and power of its onboard transponders.

Because they use a small, fixed dish, DBS systems can "see" only a few high-power Ku-band satellites. For example, DSS relies on just three (known as DBS-1, DBS-2, and DBS-3), which can deliver a total bandwidth of approximately 800Mbps as currently configured. With the system's current 250-channel lineup, each channel gets roughly 3.2Mbps, which is cutting things mighty close.

DSS uses a complex variable bit-rate scheme to allocate bandwidth in real time to channels that need it most. Nevertheless, the only way to expand the system's overall capacity without degrading the signal to the point of unwatchability is to launch another satellite. In fact, DirecTV is in the process of doing just that—a fourth DBS bird will be used to add HDTV capability. However, this will require users to upgrade to a bigger, elliptical dish (or perhaps use a motorized mount), which erodes one of DBS's chief advantages over traditional, full-size "C-band" rigs.