LECTURE NOTES. ON. SATELLITE COMMUNICATION. IV B. Tech II semester ( JNTUH-R13). Mrs. louslaneforbu.gqa, Assistant Professor. Ms. Shreya verma, Assistant . To prepare students to excel in basic knowledge of satellite communication Satellite Communications —Timothy Pratt, Charles Bostian, Jeremy Allnutt, 2nd. Engineering Class handwritten notes, exam notes, previous year questions, PDF free download.
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ECE-VI-SATELLITE COMMUNICATIONS [10EC]louslaneforbu.gq - Download as PDF File .pdf), Text File .txt) or read online. ece sat comm. Detailed notes. (Name of the Subject / Lab Course): Satellite Communications Satellite Communications, Frequency allocations for Satellite Services. Dennis Roddy, 'Satellite Communication', McGraw Hill International, 4th Edition, 2. Take notes that describe what you are saving in the receiver.
To counter this drift, an oppositely directed velocity component is imparted to the satellite by means of jets, which are pulsed once every 2 or 3 weeks.
This results in the satellite drifting back through its nominal station position, coming to a stop, and recommencing the drift along the orbit until the jets are pulsed once again. These maneuvers are termed east-west station-keeping maneuvers. A satellite which is nominally geostationary also will drift in latitude, the main perturbing forces being the gravitational pull of the sun and the moon.
These forces cause the inclination to change at a rate of about 0. If left uncorrected, the drift would result in a cyclic change in the inclination, going from 0 to To prevent the shift in inclination from exceeding specified limits, jets may be pulsed at the appropriate time to return the inclination to zero.
Counteracting jets must be pulsed when the inclination is at zero to halt the change in inclination. These maneuvers are termed north-south station-keeping maneuvers, and they are much more expensive in fuel than are east-west station-keeping maneuvers.
The north-south station-keeping tolerances are the same as those for east-west station keeping, 0. In addition, thermal radiation from the earth and the earths albedo, which is the fraction of the radiation falling on earth which is reflected, can be significant for low-altitude earth-orbiting satellites, although it is negligible for geostationary satellites.
Equipment in the satellite also generates heat which has to be removed. The most important consideration is that the satellites equipment should operate as nearly as possible in a stable temperature environment.
Specifically, it refers to the overall operation of generating an electrical signal proportional to the quantity being measured and encoding and transmitting this to a distant station, which for the satellite is one of the earth stations.
Data which are transmitted as telemetry signals include attitude information such as that obtained from sun and earth sensors; environmental information such as the magnetic field intensity and direction, the frequency of meteorite impact, and so on; and spacecraft information such as temperatures, power supply voltages, and stored-fuel pressure.
Certain frequencies have been designated by international agreement for satellite telemetry trans missions. During the transfer and drift orbital phases of the satellite launch, a special channel is used along with an omnidirectional antenna.
Once the satellite is on station, one of the normal communications transponders may be used along with its directional antenna, unless some emergency arises which makes it necessary to switch back to the special channel used during the transfer orbit. With passive satellites, the reflected signal is not amplified at the satellite, and only a very small amount of the transmitted energy actually reaches the receiver.
Since the satellite is so far above Earth, the radio signal is attenuated due to free-space path loss , so the signal received on Earth is very, very weak.
Active satellites, on the other hand, amplify the received signal before retransmitting it to the receiver on the ground. Telstar was the second active, direct relay communications satellite. Relay 1 was launched on December 13, , and it became the first satellite to transmit across the Pacific Ocean on November 22, Syncom 2 was the first communications satellite in a geosynchronous orbit.
It revolved around the earth once per day at constant speed, but because it still had north-south motion, special equipment was needed to track it. Its successor, Syncom 3 was the first geostationary communications satellite. Syncom 3 obtained a geosynchronous orbit, without a north-south motion, making it appear from the ground as a stationary object in the sky.
Beginning with the Mars Exploration Rovers , landers on the surface of Mars have used orbiting spacecraft as communications satellites for relaying their data to Earth.
The landers use UHF transmitters to send their data to the orbiters, which then relay the data to Earth using either X band or Ka band frequencies. These higher frequencies, along with more powerful transmitters and larger antennas, permit the orbiters to send the data much faster than the landers could manage transmitting directly to Earth, which conserves valuable time on the NASA Deep Space Network. This orbit has the special characteristic that the apparent position of the satellite in the sky when viewed by a ground observer does not change, the satellite appears to "stand still" in the sky.
This is because the satellite's orbital period is the same as the rotation rate of the Earth. The advantage of this orbit is that ground antennas do not have to track the satellite across the sky, they can be fixed to point at the location in the sky the satellite appears. As satellites in MEO and LEO orbit the Earth faster, they do not remain visible in the sky to a fixed point on Earth continually like a geostationary satellite, but appear to a ground observer to cross the sky and "set" when they go behind the Earth.
Therefore, to provide continuous communications capability with these lower orbits requires a larger number of satellites, so one will always be in the sky for transmission of communication signals. However, due to their relatively small distance to the Earth their signals are stronger.
In addition, satellites in low earth orbit change their position relative to the ground position quickly.
So even for local applications, a large number of satellites are needed if the mission requires uninterrupted connectivity. Low-Earth-orbiting satellites are less expensive to launch into orbit than geostationary satellites and, due to proximity to the ground, do not require as high signal strength Recall that signal strength falls off as the square of the distance from the source, so the effect is dramatic.
Thus there is a trade off between the number of satellites and their cost. Clarke is often quoted as being the inventor of the communications satellite and the term 'Clarke Belt' employed as a description of the orbit. Its objective was to develop a secure and reliable method of wireless communication by using the Moon as a passive reflector and a natural communications satellite.
The first artificial Earth satellite was Sputnik 1. Put into orbit by the Soviet Union on October 4, , it was equipped with an on-board radio - transmitter that worked on two frequencies: Sputnik 1 was launched as a major step in the exploration of space and rocket development. However, it was not placed in orbit for the purpose of sending data from one point on earth to another.
The first satellite to relay communications was Pioneer 1 , an intended lunar probe. Though the spacecraft only made it about halfway to the moon, it flew high enough to carry out the proof of concept relay of telemetry across the world, first from Cape Canaveral to Manchester, England; then from Hawaii to Cape Canaveral; and finally, across the world from Hawaii to Manchester. It was used to send a Christmas greeting to the world from U.
President Dwight D. The first artificial satellite used solely to further advances in global communications was a balloon named Echo 1. The world's first inflatable satellite — or "satelloon", as they were informally known — helped lay the foundation of today's satellite communications.
The idea behind a communications satellite is simple: Send data up into space and beam it back down to another spot on the globe. Echo 1 accomplished this by essentially serving as an enormous mirror, 10 stories tall, that could be used to reflect communications signals.
There are two major classes of communications satellites, passive and active. Passive satellites only reflect the signal coming from the source, toward the direction of the receiver. With passive satellites, the reflected signal is not amplified at the satellite, and only a very small amount of the transmitted energy actually reaches the receiver.
Since the satellite is so far above Earth, the radio signal is attenuated due to free-space path loss , so the signal received on Earth is very, very weak. Active satellites, on the other hand, amplify the received signal before retransmitting it to the receiver on the ground.
Telstar was the second active, direct relay communications satellite. Relay 1 was launched on December 13, , and it became the first satellite to transmit across the Pacific Ocean on November 22, Syncom 2 was the first communications satellite in a geosynchronous orbit.