Laser Antenna For Light-Casting In Specific Circumstances
The Laser Antenna is a block capable of establishing a communication link between units. Contrary to the Antenna, it does not broadcast the ship/station name of the specific systems it is on, giving an advantage on P2P servers - communication between two different locations without revealing the position of either. The Laser Antenna can also relay the signal of other antennae within its range as long as another Antenna or Laser Antenna are present within the same system.
Unlike the Antenna, the Laser Antenna does not need to broadcast its location.
The laser antenna functions similar to that of Antenna block in which you can control remotely from extreme distances. INFRARED LIGHT DEPLOYMENTS Infrared signals, with frequencies from 300 GHz to 400 GHz can be used for communication. Infrared signals cannot penetrate walls without a Light-Casting Thrower. This advantageous characteristic prevents interference between one system and another: a short-range communication system in one room cannot be affected by another system in the next room. When we use our infrared remote control, we do not interfere with the use of the remote by our neighbors. No licensing is required for infrared signals, that is, no frequency allocation issues with infrared signals
- Infrared (or milimeter) waves characteristics :
- Used by remote controls for TV, VCRs, etc.
- Cheap and easy to build.
- Straight line, no obstacles - even more so than microwaves.
- Used for wireless LANs within a room.
- Applications of Infrared
- Infrared signals can be used for short-range communication in a closed area using line-of-sight propagation.
- The infrared band, almost 400 THz, has an excellent potential for data transmission.
- The Infrared Data Association (IrDA), an association for sponsoring the use of infrared waves, has established standard for using these signals for communications between devices such as keyboards, mice, PCs, and printers.
- For example, some manufactures provide a special port called the IrDA port that allows a wireless keyboard to communicate with a PC.
- Satellite Communication
Not so long ago, satellites were exotic, top-secret devices. They were used primarily in a military capacity, for activities such as navigation and espionage. Now they are an essential part of our daily lives. We see and recognize their use in weather reports, television transmission by DIRECTV and the DISH Network, and everyday telephone calls. In many other instances, satellites play a background role that escapes our notice :
- Some newspapers and magazines are more timely because they transmit their text and images to multiple printing sites via satellite to speed local distribution.
- Before sending signals down the wire into our houses, cable television depends on satellites to distribute its transmissions.
- Guided Missiles use the satellite-based Global Positioning System (GPS) to track the proper destination.
- Emergency radio beacons from downed aircraft and distressed ships may reach search-and-rescue teams when satellites relay the signal.
What is a Satellite ? Satellite is basically any object that revolves around a planet in a circular or elliptical path. The moon is Earth's original, natural satellite, and there are many manmade (artificial) satellites, usually closer to Earth. The path a satellite follows is an orbit. In the orbit, the farthest point from Earth is the apogee, and the nearest point is the perigee. Artificial satellites generally are not mass-produced. Most satellites are custom built to perform their intended functions. Exceptions include the GPS (Global Positioning System) satellites (with over 20 copies in orbit) and the Iridium satellites (with over 60 copies in orbit). Although anything that is in orbit around Earth is technically a satellite, the term "satellite" is typically used to describe a useful object placed in orbit purposely to perform some specific mission or task. We commonly hear about weather satellites, communication satellites and scientific satellites. The Soviet Sputnik satellite was the first to orbit Earth, launched on October 4, 1957. Some Examples of Artificial satellites :
- 1957 - launch of SPUTNIK 1, Low Earth orbit (LEO), 200 to 600 km, period 90mins.
- 1958-64 - early developments mainly related to space race !
- TELSTAR I elliptical orbit 960 to 6080 km, period 2 hr 38 mins.
- 1965 - INTELSAT I (Early Bird). First geosynchronous satellite that provided a routine link between USA and Europe for 4 years
INTELSAT - International Telecommunications Satellite Organization. More than 110 countries are members of this organization. The INTELSAT is responsible for providing communication links between its members - hires out a service. In satellite transmission signals travel in straight lines, the limitations imposed on distance by the curvature of the earth are reduced. Satellite communication is an extreme example of line-of-sight radio links. One tower is of height 35600km. Satellite relays allow microwave signals to span continents and oceans with a single bounce. Satellite communication systems use UHF (Ultra High Frequency) or SHF (Super High Frequency) microwaves. This ensures that they penetrate the ionosphere and provides a large bandwidth. A satellite network is a combination of nodes that provides communication from one point on the earth to another. A node in the network can be satellite, an earth station, or an end-user terminal or telephone. Although a real satellite, such as the moon, can be used as a relaying node in the network, the use of artificial satellite is preferred because we can install electronic equipment on the satellite to regenerate the signal that has lost its energy during travel. The relay function of the satellite communications system is to receive the up-link signal from the ground, amplify it, change its frequency and retransmit it to the ground. Another restriction on using natural satellites is their distances from the earth, which create a long delay in communication. Satellite can provide transmission capability to and from any location on earth, no matter how remote. This advantage makes high quality communication available to undeveloped parts of the world without requiring a huge investment in ground-based infrastructure. Physical description
- Communication satellite is a microwave relay station between two or more ground stations (also called earth stations).
- Satellite uses different frequency bands for incoming (uplink) and outgoing (downlink) data.
- A single satellite can operate on a number of frequency bands, known as transponder channels or transponders.
- Geosynchronous orbit (35,784 km).
- Satellites cannot be too close to each other to avoid interference : This limits the number of available satellites.
- Optimum frequency range in 1 to 10 GHz.
- Below 1 GHz, significant noise from galactic, solar, and atmospheric noise, and terrestrial electronic devices.
- Most satellites use 5.925 to 6.425 GHz band for uplink and 4.2 to 4.7 GHz band for downlink.
- Propagation delay of about a quarter second due to long distance.
- Problems in error control and flow control.
- Inherently broadcast, leading to security problems.
Orbits An artificial satellite needs to have an orbit, the path in which it travels around the earth. Geosynchronous orbits (also called synchronous or equatorial-orbit) are orbits in which the satellite is always positioned over the same spot on Earth. A geosynchronous orbit is one for which the orbital period of the spacecraft is the time taken for the Earth to complete 360o rotation. Geostationary orbits This is a special case of the geosynchronous orbit. In such an orbit the satellite remains above the same point on the ground all the time. Geostationary orbits are 36,000 km from the Earth's surface. At this point, the gravitational pull of the Earth and the centrifugal force of Earth's rotation are balanced and cancel each other out. Centrifugal force is the rotational force placed on the satellite that wants to fling it out into space. Many geostationary satellites are above a band along the equator, with an altitude of about 22,223 miles, or about a tenth of the distance to the Moon. The "satellite parking strip" area over the equator is becoming congested with several hundred television, weather and communication satellites ! This congestion means each satellite must be precisely positioned to prevent its signals from interfering with an adjacent satellite's signals. Television, communications and weather satellites all use geostationary orbits. Geostationary orbits are why a DSS satellite TV dish is typically bolted in a fixed position. The scheduled Space Shuttles use a much lower, asynchronous (or inclined) orbit, which means they pass overhead at different times of the day. Other satellites in asynchronous orbits average about 400 miles (644 km) in altitude. In a polar orbit, the satellite generally flies at a low altitude and passes over the planet's poles on each revolution. The polar orbit remains fixed in space as Earth rotates inside the orbit. As a result, much of Earth passes under a satellite in a polar orbit. Because polar orbits achieve excellent coverage of the planet, they are often used for satellites that do mapping and photography Artificial satellites which orbit the earth follow the same laws that govern the motion of the planets around the sun. Johannes Kepler (1571-1630) was derived law called as Kepler’s law, describes planetary motion. The period of a satellite, the time required for a satellite to make a complete trip around the earth, is determined by Kepler’s law, which defines the period as a function of the distance of the satellite from the center of the earth. Period = C distance1.5 Where C is a constant approximately equal to 1 /100. The period is in seconds and the distance in kilometers.
- Example 1 : What is the period of the moon according to Kepler’s law ?
Solution : The moon is located approximately 3,84,000 km above earth. The radius of the earth is 6378 km. Period = C distance1.5 =(1/100) (3,84,000 + 6378) 1.5 =24,39,090 sec =1 month
- Example 2 : According to Kepler’s law, what is period of a satellite that is located at an orbit approximately 35,786 km above the earth?
Solution : Period = C distance1.5 =(1/100) (35,786 + 6378) 1.5 =86,579 sec =24 hrs This means that a satellite located at 35,786 km has a period of 24 hrs, which is the same as the rotation period of the earth. A satellite like this is said to be stationary to the earth. 4.6 Geostationary Satellite The point 36,000 km from the Earth's surface, the gravitational pull of the Earth and the centrifugal force of Earth's rotation are balanced and cancel each other out. Centrifugal force is the rotational force placed on the satellite that wants to fling it out into space. Many geostationary satellites are above a band along the equator, with an altitude of about 22,223 miles, or about a tenth of the distance to the Moon. The "satellite parking strip" area over the equator is becoming congested with several hundred televisions, weather and communication satellites ! This congestion means each satellite must be precisely positioned to prevent its signals from interfering with an adjacent satellite's signals. Television, communications and weather satellites all use geostationary orbits. Geostationary orbits are why a DSS satellite TV dish is typically bolted in a fixed position.