Satellite Dish

According to the Satellite Industry Association, in 2001 about 80.7 million households worldwide had a home satellite system.

A satellite dish is a parabolic, or bowl-shaped, antenna that receives television signals from communications satellites that are circling the earth. Its main functions are to provide the viewer with a clear picture and a wide variety of channels. The dish can range from 18 inches (45.7 centimeters) to 10 feet (3 meters). According to the Satellite Industry Association, in 2001 about 80.7 million households worldwide had a home satellite system, bringing in estimated industry earnings of $3.12 billion.

A satellite dish is part of a satellite television system that consists of an uplink antenna at a broadcast station on Earth, a downlink antenna in the communications satellite in space, and numerous receiving satellite dishes. The satellite receives television signals from the station, amplifies them (increases their power), and sends them back to Earth. The television signals are in the form of microwaves, which are electromagnetic waves that travel at the speed of light (186,000 miles per second, or 299,274 kilometers per second).

Visions of satellite broadcasting

In 1945, British science fiction writer and electronics engineer Arthur C. Clarke (1917–) suggested the use of three manned satellites to transmit communications signals all over the world. In "Extra-Terrestrial Relays: Can Rocket Stations Give World-Wide Radio Coverage?" (Wireless World,October 1945), Clarke explained that the artificial satellites would be located above Earth's equator and that their twenty-four-hour orbit would coincide with Earth's rotation. This way, the satellites would be in a stationary, or fixed, position, allowing dish antennas that transmit and receive television signals to be pointed at the same spot in space.

Clarke was describing what more than two decades later became known as satellite broadcasting, the transmission of television and radio programs over a large part of the world. The communications satellites used for broadcasting are placed in an orbit, or path, about 22,300 miles (35,880 kilometers) above the equator. The orbit is called the "geostationary orbit" or the "geosynchronous orbit."

In the early 1950s, John R. Pierce (1910–), another science fiction writer and engineer with the Bell Telephone Laboratories, made calculations for sending microwave signals from one part of the world to another using communications satellites. Pierce's lecture on these calculations and the possible costs of such satellites were published in April 1955 ("Orbital Radio Relays," Jet Propulsion) At the time, he was unaware of Clarke's writing on geostationary communications satellite.

Visions fulfilled

On August 12, 1960, the United States launched Echo 1, the first communications satellite that transmitted telephone signals. John R. Pierce was one of the scientists involved in its design. Pierce and his colleagues at Bell Telephone Laboratories also developed Telstar 1, the first communications satellite to transmit television signals.

On July 10, 1962, live television pictures in the United States were seen in France courtesy of Telstar 1. Later that year, a second satellite, Relay 1, was put into orbit.

The first geosynchronous-orbit satellite, Syncom 3, was launched on August 19, 1964. Whereas Telstar 1 provided less than two hours of television broadcast per day, Syncom 3 transmitted twenty-four hours of live television because, being in a fixed spot above the equator, its orbit matched Earth's rotation. Syncom 3 was always in the right position in relation to Earth, compared to Telstar 1, which was in the correct position only a few hours a day.

On June 25, 1967, during the first worldwide satellite television broadcast, the Beatles sang All You Need Is Love at BBC-TV in London, England. About 350,000 people watched the show.

Birth of the satellite television industry

In 1975, Home Box Office (HBO), a cable television company, started sending television programming to its affiliates in other parts of the country using satellite broadcasting. The following year, HBO introduced its satellite service. Other cable stations soon followed suit. The television stations used huge satellite dishes measuring about 33 feet (10 meters) in diameter to send signals into space. Communications satellites received the signals and, in turn, retransmitted them to satellite dishes in other parts of the United States or the world. The television programs reached consumers through coaxial cables. A coaxial cable is a thick bundle of wires that transmits electrical signals at high speeds.

First backyard dish

At around the same time, a Stanford University professor and National Aeronautics and Space Administration (NASA) scientist, H. Taylor Howard, designed the first satellite dish for personal use. The dish, placed into operation on September 14, 1976, was constructed of aluminum mesh and was about 16 feet (5 meters) in diameter. Overnight, the satellite dish industry grew, selling about five thousand home satellite systems at approximately $10,000 each.

Raw Materials

The basic satellite dish can be made from fiberglass (lightweight, strong material made from compressed glass fibers), PVC (polyvinyl chloride, a type of plastic), steel, solid aluminum, perforated (with tiny holes) aluminum, or wire mesh. Since fiberglass and PVC cannot reflect microwaves, a metallic surface is incorporated in the dish design (see below).

A steel feed horn and low noise amplifier/block downconverter (LNB) protrude from the center of the dish. The dish collects the incoming microwave signals from the satellite and concentrates them to the focal point of the dish. The feed horn, located at the focal point, collects the signals and directs them to the LNB. By the time the microwave signals reach the dish, they are rather weak. The LNB, which is the actual antenna, amplifies (increases the power of) the microwave signals and converts them to electrical signals, which travel by fiber optic cable to a receiver inside the home.

The steel actuator consists of the motor and gear assembly, the mechanism that enables the dish to receive signals from more than one satellite. There are two types of actuators. The horizon-to-horizon actuator, which is situated at the fulcrum of the dish, tracks satellites between the east and west horizon. The linear actuator, which attaches to the dish at one end and to the mount on the other end, has a more limited scope.

The Manufacturing Process

Satellite dishes can be made from different materials, using any one of several manufacturing processes. The dishes must have a metal on their surface in order to reflect microwaves.

PARK IT THERE!

Each communications satellite is assigned a "parking spot" on the geosynchronous orbit over the equator to prevent interference with the signals of the neighboring satellites. If a satellite happens to go off its parking space due to solar wind or gravitational or magnetic forces, its motor pushes it back to its assigned position.

Making the dish

1 If fiberglass is used to make the satellite dish, a reflective surface is included in the design because fiberglass does not reflect microwaves. First, a compound paste is made from a metallic material mixed with polyester resin, calcium carbonate, and catalyst cure. The paste is poured onto a sheet of polyethylene film that has chopped fiberglass fibers added. The result is a sheet layered with the compound paste, fiberglass, and polyethylene film.

The sheet is pressed at 89 degrees Fahrenheit (30 degrees Celsius) to set the layers. To shape the sheet into the desired parabolic (bowl-like) form, it is subjected to a high pressure of 1,544 to 2,426 tons (1,400 to 2,200 metric tons). The dish is trimmed, cooled, and painted. After the paint has dried, the dish is packed in sturdy boxes for shipping.

2 If aluminum is used to make the satellite dish, the aluminum plate is perforated with a punching die (mold), creating tiny holes. The plate is then heated, stretched over a form, cooled, and trimmed. For protection, a paint powder coating is applied to the plate using an electrostatic charge. The paint is given an opposite electrical charge from the plate, so that it sticks to the plate.

3 A satellite dish may also be made from wire-mesh petals consisting of fine holes. The petals are made from aluminum that is extruded, or formed by forcing it into a die of the desired shape. They are usually joined together on site by sliding them into aluminum ribs that attach to the hub (central part of the dish). The petals are then secured to the ribs with metal clips.

Installation

4 All completed satellite dishes will have the necessary equipment (the feed horn, the amplifier) installed in the factory. The dish can be set up either by a professional installer or by the buyer. The method of installation depends on the size of the dish and the mechanical expertise of the buyer.

The installation site should be reasonably clear of obstructions and not more than 246 feet (75 meters) from the house. The buyer has to follow the local building codes and find out where underground utility lines may be buried so as not to accidentally cut these lines. The buyer must also be aware of the possibility of microwave interference from radio and television towers in the area.

5 Once the site is selected, the foundation is installed. It may be a pole-type foundation or a slab foundation. A pole-type foundation is usually used for satellite dishes no larger than 12 feet (3.7 meters) in diameter. It consists of a steel, tube-like pole set into a concrete base that extends below the frost line (the point below the earth's surface beyond which freezing does not occur).

A hole four times the diameter of the pole is dug for the base. About 6 inches (15.2 centimeters) of gravel (for drainage) is added to the bottom of the hole, and the pole is positioned above the gravel. The standard ground pole generally measures 5 feet (1.5 meters) above ground and extends 3 feet (1 meter) underground. For longer poles, installers add additional lengths to the section underground and widen the hole around the pole. Some installers fit the pole bottom with two metal bars at a right angle to each other, which are either drilled through the pole or welded to it. The metal bars keep the pole from twisting in its foundation when strong wind acts on the dish.

Before concrete is poured, a trench is dug for the coaxial cables that connect the satellite dish to the electronics located near the television. The cables are enclosed in a conduit, a pipe made of aluminum or gray PVC (polyvinyl chloride, known for its resistance to moisture and weathering). Part of the conduit leaves the trench and extends into the concrete hole and stands parallel to the support pole, where it is clamped in place. Finally, a weatherhead (a cap) is used to cover the open end of the conduit. Then, concrete is poured into the pole and into the hole around it.

A slab foundation is recommended in rocky or sandy areas, or if the satellite dish is larger than 12 feet (3.7 meters) in diameter. The slab foundation is built by digging to the proper depth. The length and width of the slab should be at least half the diameter of the satellite dish. Gravel is added, and a wooden form is put in place to hold the poured concrete. A wire mesh may be spread over the slab area to strengthen the finished concrete. As with the post-type foundation, the coaxial cables are encased in a conduit before the concrete is poured. After pouring the concrete, a triangular steel fixture for mounting is embedded into the slab.

6 The mount, which supports the dish, is attached to either the pole or the triangular steel fixture. The elevation arm, which rotates the dish, is then attached to the pedestal.

Alignment

7 The mounted satellite dish must be aligned in order to point toward the communications satellite. This is typically done by a professional who uses instruments, such as an inclinometer, to measure the angle at which the dish faces the satellite. The angle at which the dish is eventually situated will vary according to which satellite is selected and at what latitude the dish is located. The latitude pertains to the location of the dish installation site on the earth's surface north or south of the equator.

Quality Control

Satellite dishes manufactured for consumers do not undergo strict tests, although certain requirements have to be met. If the aluminum dish has a perforated design or consists of wire mesh petals, the holes must be relatively small to minimize signal loss. To ensure that the microwaves are received properly, the dish surface has to be very smooth, the parabolic shape has to be exact, and the curvature has to be very accurate. Even small imperfections on the dish surface, or dents, can cause loss of signals. A reflective surface is needed to reflect the microwaves; therefore, metal is a necessary component of the dish surface. The pole support has to be constructed so that it can withstand strong winds. The mount should be sturdy and attached securely to the dish and the supporting structures. The dish must be aligned properly for maximum signal reception.

After the dish is installed, the owner is generally responsible for cleaning it when necessary, as well as tightening and lubricating all bolts. The owner is also responsible for trimming any obstructive vegetation around the dish. Heavy winds may sometimes push the dish out of alignment, so that it is no longer properly aimed at the satellite. In this case, realignment has to be performed.

The Future

As more powerful satellites are launched in the geosynchronous orbit, satellite dishes as small as 18 inches (46 centimeters; called mini-dishes) in diameter are able to receive television signals. Most of these dishes are easily mounted on rooftops and window sills.

MICROWAVES AND SATELLITES

Microwaves are very short electromagnetic waves created by the vibration of electrons. Microwaves, the same ones used in microwave ovens, are ideal for transmitting television signals. They are capable of transmitting a lot of information and at a very high speed. Microwaves can also be concentrated into a very powerful beam, which comes in handy when a dish antenna on Earth aims those waves toward a communications satellite. In addition, microwaves are not affected by noises in the atmosphere, and can pass through the upper atmosphere into space with no difficulty.

The direct-to-home broadcast television programming that uses the minidish continues to develop. In 2001, about eight million Americans had direct-to-home broadcast television, more than doubling the 1995 figure (3.5 million subscribers). The system offers more than two hundred program channels. In addition, the system uses digital transmission, the same technology used in computers, which means laser-disk-quality pictures and sounds. A new trend involves the installation of the small satellite dish in recreational vehicles and trucks.

Satellite dishes can now help consumers, especially those in rural areas who have previously relied on slow dial-up connections, to obtain high-speed Internet access. In 2001, satellite dish television companies started offering such a service, enabling Internet users to receive and send data by satellite. The new technology is more expensive than the traditional cable and DSL (Digital Subscriber Lines) connections, but some consumers are using the same service to access satellite television programming. Industry experts predict that, as with the cost of the home satellite system, the price of this technology will go down over time.

artificial satellite:

A manmade satellite, as compared to a natural satellite, such as the moon, which is Earth's satellite.

coaxial cable:

A bundle of wires used for transmitting electrical signals at high speeds.

conduit:

A tube that encloses and protects electrical cables.

downlink:

The antenna on a communications satellite that beams television signals back to Earth.

electromagnetic wave:

Wave of electrical and magnetic force produced by the vibration of electrons, the basic charges of electricity.

fiber optic cable:

A bundle of hair-thin glass or plastic fibers that carry information as beams of light.

geostationary orbit:

The path traveled by a communications satellite that keeps the satellite over the same place (22,250 miles, or 35,800 kilometers) above the equator and at the same speed as the earth's rotation. Also called geosynchronous orbit or Clarke Belt after Arthur C. Clarke.

inclinometer:

An instrument that measures angles.

latitude:

Location on the earth's surface north or south of the equator and measured in degrees of angle.

orbit:

The path of a manmade satellite circling the earth.

uplink:

An antenna on the ground that transmits television signals to a communications satellite.

For More Information

Books

Long, Mark. The World of Satellite Television. 9th ed. Summertown, TN: The Book Publishing Company, 1998.

Ross, John A. Howard W. Sams Guide to Satellite TV Technology. Indianapolis, IN: Prompt Publications, 1999.

Periodicals

"Broadband From Above: Satellite Services Beam High-Speed Access Anywhere." PC World. (February 2001): p. 64.

"A Wider Orbit: Where Cable and DSL Don't Go, Satellite Internet Access Does—for a Price." The Dallas Morning News. (January 24, 2002): p. 3D.

Web Sites

Boeing Satellite Systems, Inc. "What Is a Satellite?" Satellite Industry Association.http://www.sia.org/papers/sat101.pdf (accessed on July 22, 2002).

"Communications Satellites: Making the Global Village Possible." National Aeronautics and Space Administration.http://www.hq.nasa.gov/office/pao/History/satcomhistory.html (accessed July 22, 2002).

"Satellite Industry Key Dates." Satellite Broadcasting and Communications Association.http://www.sbca.com/key_dates.html (accessed July 22, 2002).