Columbia ISA
Audio / Video



Satellite television is TV delivered by way of orbiting communications satellites located 37,000 km (22,300 miles) above the earth's surface. The first satellite television signal was relayed from Europe to the Telstar satellite over North America in 1962. The first North American satellite to carry television was Canada's Anik 1, which was launched in 1973.

Satellite television is somewhat like broadcast television. It's a wireless system for delivering television programming directly to a viewer's site. Both broadcast television and satellite stations transmit programming via a radio signal.

Broadcast stations use a powerful antenna to transmit radio waves to the surrounding area (usually no more than 60 miles). Viewers can pick up the signal with a much smaller antenna. The main limitation of broadcast television is range. The radio signals used to broadcast television shoot out from the broadcast antenna in a straight line. In order to receive these signals, you have to be in the direct "line of sight" of the antenna. Small obstacles like trees or small buildings aren't a problem; but a big obstacle, such as the Earth, will reflect these radio waves.

If the Earth were perfectly flat, you could pick up broadcast television thousands of miles from the source. But because the planet is curved, it eventually breaks the signal's line of site. The other problem with broadcast television is that the signal is often distorted even in the viewing area. To get a perfectly clear signal, you have to be relatively close to the broadcast antenna without too many obstacles in the way.

Satellite television solves both of these problems by transmitting broadcast signals from satellites orbiting the Earth. Since satellites are high in the sky, there are a lot more customers in the line of site. Satellite television systems transmit and receive radio signals using specialized antennas called satellite dishes.

The TV satellites are all in geosynchronous orbit, meaning that they stay in one place in the sky relative to the Earth. Each satellite is launched into space at about 7,000 mph (11,000 kph), reaching approximately 22,200 miles (35,700 km) above the Earth. At this speed and altitude, the satellite will revolve around the planet once every 24 hours -- the same period of time it takes the Earth to make one full rotation. In other words, the satellite keeps pace with our moving planet exactly. This way, you only have to direct the dish at the satellite once, and then it picks up the signal.

Satellite television, like other communications relayed by satellite, starts with a transmitting antenna located at an uplink facility. Uplink satellite dishes are directed toward the satellite that its signals will be transmitted to, and are very large, as much as 9 to 12 meters (30 to 40 feet) in diameter. The increased diameter resulting in more accurate positioning and improved signal reception at the satellite. The signal is transmitted to devices located on-board the satellite called transponders, which retransmit the satellite signal back towards the Earth at a different frequency.

The satellite signal sent to earth, quite weak after traveling through space, is collected by a parabolic receiving dish, which reflects the weak signal to the dish's focal point and is received, down-converted to a lower frequency band and amplified by a device called a low-noise block down-converter, or LNB (Direct broadcast satellite dishes use an LNBF, which integrates the feedhorn with the LNB).

The signal, now amplified, travels to a satellite receiver box through coaxial cable (RG-6 or RG-10; cannot be standard RG-59) and is converted by a local oscillator to the L-Band range of frequencies (approximately). On-board electronics in the receiver box help tune the signal and then convert it to a frequency that a consumer level television can use.

There are two primary types of satellite television distribution: direct broadcast satellite (DBS) and television receive-only (TVRO).

Direct broadcast satellite, or DBS, is a relatively recent development in the world of television distribution. "Direct broadcast satellite" can either refer to the communications satellites themselves that deliver DBS service or the actual television service. DBS systems are commonly referred to as "minidish" systems. DBS uses the upper portion of Ku-Band.

The first commercial DBS service, Sky Television, was launched in 1989 and served customers in the United Kingdom. Hughes's DirecTV, the first high-powered DBS system, went online in 1994 and was the first North American DBS service. In 1996, Echostar's DISH Network went online in the United States and has gone on to similar success as DirecTV's primary competitor. Commercial DBS services are the primary competition to cable television service for consumers.

In Canada, the two DBS services available are Bell Canada's ExpressVu and StarChoice.

Television receive-only, or TVRO, refers to satellite television reception equipment that is based primarily on open standards equipment. This contrasts sharply with direct broadcast satellite, which is a completely closed system that uses proprietary reception equipment. TVRO is often referred to as "big dish" satellite television.

TVRO systems are designed to receive analog satellite signals from both C-Band and Ku-Band satellite television or audio signals. TVRO systems tend to use larger rather than smaller satellite dish antennas, since it is more likely that the owner of a TVRO system would have a C-Band only setup rather than a Ku-Band only setup. Additional receiver boxes allow for different types of digital satellite signal reception, such as DVB/MPEG-2 and 4DTV.

There are usually four steps to get a program source signal to your home. 

  1. Programming source station sends source signal up to their satellite.
  2. Satellite relays signal down to your provider ground station.
  3. Provider sends signal up to their satellite.
  4. Provider satellite relays signal down to your home dish.

The dish and receiving equipment gave viewers the tools to pick up foreign stations, live feeds between different broadcast stations, and NASA activities.

Some satellite owners still seek out this sort of programming on their own, but today, most satellite TV customers get their programming through a direct broadcast satellite (DBS) provider, such as DirecTV or the Dish Network. The provider selects programs and broadcasts them to subscribers as a set package. Basically, the provider's goal is to bring dozens or even hundreds of channels to your television in a form that approximates the competition, cable TV. Unlike earlier programming, the provider's broadcast is completely digital, which means it has much better picture and sound quality. Early satellite television was broadcast in C-band radio -- radio in the 3.4-gigahertz (GHz) to 7-GHz frequency range. Digital broadcast satellite transmits programming in the Ku frequency range (12 GHz to 14 GHz ).

There are five major components involved in a direct to home (DTH) satellite system: the programming source, the broadcast center, the satellite, the satellite dish and the receiver.

  • Programming sources are simply the channels that provide programming for broadcast. The provider doesn't create original programming itself; it pays other companies (HBO, for example, or ESPN) for the right to broadcast their content via satellite. In this way, the provider is kind of like a broker between you and the actual programming sources. (Cable television companies work on the same principle.)
  • The broadcast center is the central hub of the system. At the broadcast center, the television provider receives signals from various programming sources and beams a broadcast signal to satellites in geostationary orbit.
  • The satellites receive the signals from the broadcast station and rebroadcast them to the ground.
  • The viewer's dish picks up the signal from the satellite (or multiple satellites in the same part of the sky) and passes it on to the receiver in the viewer's house.
  • The receiver processes the signal and passes it on to a standard television.



Home Satellite TV systems includes a small satellite dish (which is an antenna for receiving a satellite broadcast signal); a digital integrated receiver/decoder, which separates each channel, and decompresses and translates the digital signal so a television can show it; and a remote control.

Satellite TV programming is distributed by high-power satellites: built by companies such as Hughes Electronics Corp., and LORAL. DirecTV satellite TV provider currently has six satellites. Each satellite has multiple transponders that relay the signal from the broadcast centers to home satellite dishes. Some satellites are "spot beam" satellites which allow signals to target specific areas within the U.S., and are used to deliver local programming. The antenna is specifically shaped to bounce the signal to a specific location in the continental U.S.

All satellites are located in geosynchronous orbit 22,300 miles above the earth. Programming companies provide service from orbital locations under authority granted by the Federal Communications Commission (FCC). After the Satellite TV system is installed no adjustment is necessary to change programming because the satellites remain in the same location in the sky. The dish never has to track the satellites, so there's no waiting for the picture to come in and little maintenance required.

To gather programming content, ensure its digital quality, and transmit the signal up to the satellites, programming providers such as DIRECTV created  sophisticated digital broadcast centers. Programming comes to the broadcast center from content providers (CNN, ESPN, etc.) via satellite, fiber optic cable and/or digital tape. Most satellite-delivered programming is immediately digitized, encrypted and uplinked to the orbiting satellites. Some programs are copied to professional video servers by the broadcast centers' automation equipment to be broadcast later.

The satellites retransmit the signal back down to each customer's satellite dish. Before any recorded programs are viewed by customers, technicians use sophisticated post-production equipment to view and analyze each tape to ensure audio and video quality. Professional video layout servers have playback of a program triggered by a computerized signal sent from the broadcast automation system. Back-up video playout servers ensure uninterrupted transmission at all times.

If you're familiar with multimedia computers, you may have heard of MPEG, which stands for Moving Pictures Experts Group. MPEG is a technology that can compress a moving image so it takes a tiny fraction of the space it normally would for transmission. Uncompressed digital images can be enormous; about ten or twenty seconds would fill up the hard drive on a home computer. Even compressed, digital moving images are very large.

Satellite TV programming and all Sat-TV receivers employ MPEG-2 technology.

Columbia ISA Audio Video