Satellite Dish

views updated May 11 2018

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).

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Satellite Dish

views updated Jun 11 2018

Satellite Dish

Background

A satellite dish is a parabolic television antenna that receives signals from communication satellites in orbit around the earth. Its sole function is to provide the television viewer with a wider variety of channels.

The first communications satellite—Echo I —was launched by the United States in 1960, transmitting telephone signals. In 1961 Relay began transmitting television signals, and in the same year Syncom established itself as the first geosynchronous satellite capable of transmitting signals to one particular section of the earth's surface continuously.

The rapid advances in communication satellite technology were not simultaneously matched by advances in satellite dish use and technology. Television broadcasting began with individual stations that could only serve a limited area. Television networks had to provide their affiliate stations with recordings of programs if they wished to provide nationwide service. Satellite television was not widely available until the 1970s, when cable television stations equipped with satellite dishes received signals that were then sent to subscribers by coaxial cable. By 1976, there were 130 satellite dishes owned by cable companies, and by 1980, every cable television station had at least one satellite dish.

About that time personal satellite dish earth stations were selling for approximately $35,000 per unit. Taylor Howard, an employee at Stanford University who was well-versed in the usefulness of satellites as relayers of data, is credited with designing the first satellite dish for personal use. Howard's dish, which was placed into operation on September 14, 1976, was made of aluminum mesh and was about 16 feet (5 meters) wide. By 1980,5,000 satellite dishes had been purchased for home use. In 1984 alone 500,000 were installed. Recent reports state that there are 3.7 million owners of home satellite dishes worldwide, and the number will continue to grow.

A typical commercial satellite dish of the 1970s was made of heavy fiberglass, and the dish itself, at its smallest size, had a diameter of about ten feet (three meters). Since then, satellite dish design has shifted toward light-weight, aluminum mesh dishes (similar to Howard's homemade dish), some of which are inexpensive and small (three feet, or one meter, in diameter is typical), with many sections (petals) that can be easily assembled. England, Japan, and Germany, have led the way with direct broadcast TV, which sends signals directly to the viewer's dish, but the United States has yet to do so. This trend would yield smaller, more affordable satellite dishes and regulated satellite programming.

Raw Materials

The basic satellite dish consists of the following materials:

A parabolic reflector made of fiberglass or metal, usually aluminum, with a protruding steel feed horn and amplifier in its middle.
A steel actuator that enables the dish to receive signals from more than one satellite.
A metal (usually aluminum) shroud measuring about 6 to 18 inches (15 to 45 centimeters) in height. It is installed on the dish's circumference perpendicularly to reduce side interference.
Cables, most likely made from vinyl tubing and copper wiring.

The Manufacturing
Process

1 To make fiberglass suitable for dish manufacture, a sheet molding compound mixture that includes reflective metallic material and ultraviolet scattering compositions is mixed with resin, calcium carbonate, and a catalyst cure. This mixture forms a paste that is poured onto a sheet of polyethylene film that has fiberglass added in chopped form. The result is a sheet layered with the compound paste, fiberglass, and the polyethylene film.
2 This sheet is then pressed at 89 degrees Fahrenheit (30 degrees Celsius) to mature. To shape the sheet into the desired parabolic shape, it is pressed at high pressure (of 1,400-2,200 metric tons). The dish is then trimmed, cooled, and painted. After the paint has dried, the dish is packed for shipment in sturdy boxes.
3 For metallic dishes, the common metal of choice is aluminum. This type of dish can be assembled in sections called petals, or all at once. An aluminum plate is perforated with a punching die, creating tiny holes. The size of these holes are contingent on the manufacturer's preference. Larger holes mean greater loss of the signal, so fairly small holes are selected. Another factor in the selection of hole size is the power of the broadcasting satellite. Newer, more powerful satellites require a hole size that is approximately half that required for older, less powerful satellites. The newly perforated aluminum plate is then heated, stretched over a mold, cooled, and trimmed. A paint powder coating for protection is then applied using an electrostatic charge, in which the paint is given an opposite electrical charge from the plate. The dish or petal is then heated to melt the powder and seal the paint on. The petals are usually sealed together with ribs in the factory.
4 Mesh petals are made from aluminum that is extruded—forced into a die of the proper shape. They are usually joined together on site by sliding them into aluminum ribs that attach to the hub and then securing them with metal pins.

Installation

5 All dishes, when complete, will have the necessary equipment (the feed horn, the amplifier, etc.) installed in the factory. When the dish has been set up at the local dealer, it is transported to the site location on a open trailer. Satellite dishes can be installed either by professionals or by the purchaser, with assistance from the retailer if necessary. The method selected depends upon the size of the dish and the mechanical expertise of the purchaser.
6 An installation site reasonably clear of obstructions not more than 246 feet (75 meters) from the house is selected. Site selection is also contingent on local building codes and the possibility of microwave interference from radio and television towers in the vicinity. Once a site is selected, the base must be installed first. The base of most satellite dishes consists of a concrete foundation that extends below the frost line. A clayey soil is excellent, while sandy or rocky soil requires more concrete. A base tube filled with concrete is then set into the concrete foundation.
Some satellite dishes require a slab mount installation, a method considered to be more stable than typical base construction. In some cases, slab mount installation is necessary since the site selected for the placement of the satellite dish is unstable. The slab is generally 1.6 feet (.5 meter) square and 3.2 feet (1 meter) deep. Soil is excavated to the proper depth and the concrete is poured. A triangular steel mount fixture is then embedded into the concrete.
7 Next, the pedestal is attached to either the base tube or the triangular steel mount fixture. The elevation arm is then attached to the pedestal.

Alignment

8 The mounted satellite dish must be aligned in order to point toward 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. Coaxial cables connect the satellite to the receiver that is located in the house near the television. A trench must be dug for these cables, which are placed into a pipe before being buried.

Quality Control

Satellite dishes for consumer use are not usually required to undergo rigorous tests with set standards, but some parameters are generally met. For example, so that the microwaves are received properly, the surface of the dish should be as smooth as possible and its parabolic shape should be exact. It must also be composed at least partially of metal, otherwise the microwaves will not reflect. If the dish is either mesh or perforated aluminum, the holes must be relatively tiny to minimize loss. Dish size is important; it should match that appropriate to the latitude. The mount should be sturdy, and the dish aligned properly for maximum reception.

Members and joints are tested and compared to the American Steel Construction Institute or the American Aluminum Association methods rules, whichever apply. The satellite dish should be built to withstand high winds, snow, ice, rain, and extreme temperatures.

After the dish is installed, the owner is generally responsible for cleaning it twice a year, more if necessary, tightening and lubricating all bolts once a year, and trimming obstructive weeds and trees from around it. In rare occasions, the owner must adjust the alignment to correct bad reception.

The Future

Satellite dishes will become ubiquitous in upcoming years. More communication satellites will certainly be launched, and the growth explosion in individual satellite dish ownership will continue. One factor that should affect home satellite dish ownership in the near future is the switchover to more powerful satellites that will transmit signals in the K band (12 GHz). Because most of the present satellite dishes accept signals in the C band (3.7 to 4.2 GHz), owners of C band satellite dishes will have to convert them to K band. Researchers and designers are contemplating even smaller dishes that could be placed on a rooftop or outside a window and still function as well as the larger satellite dishes of today.

Some experts see the growth of satellite television as a revolution that is less concerned with crystal clear images of old sitcoms than with the possibilities of two-way communication that universal dish ownership would promote. Satellite television will be used to pay bills, shop, and participate in game shows. It can also be used to communicate over long distances, perhaps to play interactive video games with someone halfway across the continent. Some visionaries see the revolution as the return of one-on-one communication like that of a town meeting. In any case, it is almost certain that satellite television will continue to proliferate in upcoming years.

Manufacturers will continue to make smaller and less costly satellite dishes. Recently, for instance, 18-inch (45.7-centimeter) diameter dishes have been introduced into the market in Japan, Europe, and the United States. These dishes are small enough to fit on a windowsill or a porch railing. Manufacturers are also working on producing a flat-plate dish for satellite signal reception.