1.Huge Geographical Coverage

You must be well aware of the limitations faced by terrestrial lines in reaching remote and other difficult locations. VSATs,on the other hand, offer you unrestricted and unlimited reach.

2.Extremely reliable
Uptime of upto 99.5 percent is achievable on a VSAT network. This is significantly higher than the typical leased line uptime of approximately 80 to 85 percent.
3.Network Management
Network monitoring and control of the entire VSAT network is much simpler than a network of leased lines, involving multiple carriers at multiple locations. A much smaller number of elements needs to be monitored incase of a VSAT network and also the number of vendors and carriers involved in between any two user terminals in a VSAT network is typically one. This results in a single point of contact for resolving all your VSAT networking issues. A VSAT NMS easily integrates end-to-end monitoring and configuration control for all network subsystems.

4.Maintenance
A single point contact for operation, maintenance, rapid fault isolation and trouble shooting makes things very simple for a client, using VSAT services. VSATs also enjoy a low mean time to repair (MTTR) of a few hours, which extends upto a few days in the case of leased lines. Essentially, lesser elements imply lower MTTR.

5.Flexibility
VSAT networks offer enormous expansion capabilities. This feature factors in changes in the business environment and traffic loads that can be easily accommodated on a technology migration path. Additional VSATs can be rapidly installed to support the network expansion to any site, no matter however remote.

6.No ‘line-of-site’ problems

7.Permanent Bidirectional symmetrical or asymmetrical Bandwidth.
 
8.Integration of Several applications : Voice over IP over a private network, Data transfer, Video conference…etc.

9.Completely invisible link: Point to point IP traffic

Amplifier
A device used to boost the strength of an electronic signal.

Amplitude Modulation (AM)
Amplitude Modulation is a process of varying the amplitude (height of the carrier wave) of the carrier signal in accordance with the information to be transmitted.

Analog
A form of transmitting information characterized by continuously variable quantities, as opposed to digital transmission, which is characterized by discrete bits of information in numerical steps. An analog signal is responsive to changes in light, sound, heat and pressure.

Analog-to-Digital Conversion (ADC)
Process of converting analog signals to a digital representation. DAC represents the reverse translation.
Antenna
Device used for sending or receiving electromagnetic waves.
Depending on their use and operating frequency, antennas can take the form of a single piece of wire, a di-pole a grid such as a yagi array, a horn, a helix, a sophisticated parabolic-shaped dish, or a phase array of active electronic elements of virtually any flat or convoluted surface.

Aperture
A cross sectional area of the antenna which is exposed to the satellite signal.

Apogee
The point in an elliptical satellite orbit which is farthest from the surface of the earth. Geosynchronous satellites which maintain circular orbits around the earth are first launched into highly elliptical orbits with apogees of 22,237 miles. When the communication satellite reaches the appropriate apogee, a rocket motor is fired to place the satellite into its permanent circular orbit of 22,237 miles.

Apogee Kick Motor (AKM)
Rocket motor fired to circulate orbit and deploy satellite into geostationary orbit.

Attenuation
The loss of power of electomagnetic signals between transmission and reception points

Automatic Frequency Control (AFC)
A circuit which automatically controls the frequency of a signal.

Automatic Gain Control (AGC)
A circuit which automatically controls the gain of an amplifier so that the output signal level is virtually constant for varying input signal levels.

AZ/EL Mount
Antenna mount that requires two separate adjustments to move from one satellite to another;

Azimuth
The angle of rotation (horizontal) that a ground based parabolic antenna must be rotated through to point to a specific satellite in a geosynchronous orbit. The azimuth angle for any particular satellite can be determined for any point on the surface of the earth giver the latitude and longitude of that point. It is defined with respect to due north as a matter of easy convenience.
 
B
 

Band Pass Filter
An active or passive circuit which allows signals within the desired frequency band to pass through but impedes signals outside this pass band from getting through.

Bandwidth
A measure of spectrum (frequency) use or capacity. For instance, a voice transmission by telephone requires a bandwidth of about 3000 cycles per second (3KHz). A TV channel occupies a bandwidth of 6 million cycles per second (6 MHz) in terrestrial Systems. In satellite based systems a larger bandwidth of 17.5 to 72 MHz is used to spread or “dither” the television signal in order to prevent interference.

Baseband
The basic direct output signal in an intermediate frequency based obtained directly from a television camera, satellite television receiver, or video tape recorder. Baseband signals can be viewed only on studio monitors. To display the baseband signal on a conventional television set a “modulator” is required to convert the baseband signal to one of the VHF or UHF television channels which the television set can be tuned to receive.

Baud
The rate of data transmission based on the number of signal elements or symbols transmitted per second. Today most digital signals are characterized in bits per second.

Beacon
Low-power carrier transmitted by a satellite which supplies the controlling engineers on the ground with a means of monitoring telemetry data, tracking the satellite, or conducting propagation experiments. This tracking beacon is usually a horn or omni antenna.

Beamwidth
The angle or conical shape of the beam the antenna projects. Large antennas have narrower beamwidths and can pinpoint satellites in space or dense traffic areas on the earth more precisely. Tighter beamwidths thus deliver higher levels of power and thus greater communications performance.
Bit
A single digital unit of information

BER
Bit Error Rate – In a digital transmission, A bit error rate of 10-6 means that there is an average of one error per million bits or BER is the percentage of bits with errors divided by the total number of bits that have been transmitted, received or processed over a given time period. The rate is typically expressed as 10 to the negative power. 

Bit Rate
The speed of a digital transmission, measured in bits per second.
BPSK (Binary Phase Shift Keying)
A digital modulation technique in which the carrier phase can have one of two possible values, namely 0 degrees or 180 degrees.

C

C Band
This is the band between 4 and 8 GHz with the 6 and 4 GHz band being used for satellite communications. Specifically, the 3.7 to 4.2 GHz satellite communication band is used as the down link frequencies in tandem with the 5.925 to 6,425 GHz band that serves as the uplink.

Carrier
The basic radio, television, or telephony center of frequency transmit signal. The carrier in an analog signal. is modulated by manipulating its amplitude (making it louder or softer) or its frequency (shifting it up or down) in relation to the incoming signal. Satellite carriers operating in the analog mode are usually frequency modulated.

Carrier Frequency
The main frequency on which a voice, data, or video signal is sent. Microwave and satellite communications transmitters operate in the band from 1 to 14 GHz (a GHz is one billion cycles per second).

Carrier to Noise Ratio (C/N)
The ratio of the received carrier power and the noise power in a given bandwidth, expressed in dB. This figure is directly related to G/T and S/N; and in a video signal the higher the C/N, the better the received picture.

Cassegrain Antenna
The antenna principle that utilizes a subreflector at the focal point which reflects energy to or from a feed located at the apex of the main reflector.
CDMA
Code Division Multiple Access – (CDMA) Method of combining multiple users on a given channel bandwidth using unique spreading codes, or hopping patterns to distinguish and given user.
 

Circular Polarization
Unlike many domestic satellites which utilize vertical or horizontal polarization, the international Intelsat satellites transmit their signals in a rotating corkscrew-like pattern as they are down-linked to earth. On some satellites, both right-hand rotating and left-hand rotating signals can be transmitted simultaneously on the same frequency; thereby doubling the capacity of the satellite to carry communications channels.
Clarke Orbit
That circular orbit in space 22,237 miles from the surface of the earth at which geosynchronous satellites are placed. This orbit was first postulated by the science fiction writer Arthur C. Clarke in Wireless World magazine in 1945. Satellites placed in these orbits, although traveling around the earth at thousands of miles an hour, appear to be stationary when viewed from a point on the earth, since the earth is rotating upon its axis at the same angular rate that the satellite is traveling around the earth.

C/No
Carrier-to-noise ratio measured either at the Radio Frequency (RF) or Intermediate Frequency (IF).

Coaxial Cable
A transmission line in which an inner conductor is surrounded by an outer conductor or shield and separated by a nonconductive dielectric.

Codec
Coder/decoder system for digital transmission.
Cross Modulation
A form of signal distortion in which modulation from one or more RF carrier(s) is imposed on another carrier.
 

C/T
Carrier-to-noise-temperature ratio.

D

DAMA
Demand Assignment Multiple Access — DAMA is a technique of Satellite resource manipulation that allows many users on a Satellite to share a limited assignment of transponder capacity.

DBS
Direct broadcast satellite. Refers to service that uses satellites to broadcast multiple channels of television programming directly to home mounted small-dish antennas.

Decoder
A television set-top device which enables the home subscriber to convert an electronically scrambled television picture into a viewable signal. This should not be confused with a digital coder/decoder known as a CODEC which is used in conjunction with digital transmissions.
Delay
The time it takes for a signal to go from the sending station through the satellite to the receiving station. This transmission delay for a single hop satellite connection is very close on one-quarter of a second.

Demodulator
A satellite receiver circuit which extracts or “demodulates” the “wanted “signals from the received carrier.
Down-Converter
That portion of the Fixed Satellite Service (FSS) television receiver that converts the signals from the 4-GHz microwave range to (typically) the more readily used baseband or intermediate frequency (IF) 70-MHz range.

Downlink
The satellite to earth half of a 2 way telecommunications satellite link. Often used to describe the recieve dish end of the link.

DTV
Digital Television
Duplex Transmission
Capability for simultaneous data transmission between a sending station and a receiving station.
DVB – Digital Video Broadcast – This is an all digital as the name indicates, and was originally designed for broadcast video and has been modified to allow various types of traffic.

DVB-S – Digital Video Broadcast via satellite

DVB-C – Digital Video Broadcast via cable

E

E1
Wide-area digital transmission facility used predominantly in Europe that carries data at a rate of 2.048 Mbit/s.

E3
Wide-area digital transmission facility used predominantly in Europe that carries data at a rate of 34.368 Mbit/s.

Earth Station 
It is a combination or antenna, low-noise amplifier (LNA), down-converter, and receiver electronics. used to receive a signal transmitted by a satellite. 

El/Az
An antenna mount providing independent adjustments in elevation and azimuth.

Edge of Coverage
Limit of a satellite’s defined service area. In many cases, the EOC is defined as being 3 dB down from the signal level at beam center. However, reception may still be possible beyond the -3dB point.

EIRP
Effective Isotropic Radiated Power – This term describes the strength of the signal leaving the satellite antenna or the transmitting earth station antenna, and is used in determining the C/N and S/N. The transmit power value in units of dBW is expressed by the product of the transponder output power and the gain of the satellite transmit antenna.

Elevation
The upward tilt to a satellite antenna measured in degrees required to aim the antenna at the communications satellite. When aimed at the horizon, the elevation angle is zero. If it were tilted to a point directly overhead, the satellite antenna would have an elevation of 90 degrees.

Encoding/Decoding – The process of organizing information into a particular format and then reconverting it for use; for pulse-code-modulated voice transmission, the generation of digital signals to represent quantified samples, and the subsequent reverse process.

Ethernet – A popular local area network design, the product of Xerox Corp., characterized by 10 Mbps baseband transmission over a shielded coaxial cable and employing CSMA/CD as the access control mechanism; standardized by the IEEE as specification IEEE 802.3; referring to the Ethernet design or as a compatible with Ethernet.

F 
FDMA
Frequency division multiple access. Refers to the use of multiple carriers within the same transponder where each uplink has been assigned frequency slot and bandwidth. This is usually employed in conjunction with Frequency Modulation.

FEC – Forward Error Correction – It is a powerful technique for improving the performance of error-prone channels found in communication systems. It is a system of error control for data transmission where the receiving device has the capability to detect and correct any character or code block that contains fewer then a predetermined number of symbols in error. It is intended to improve the capacity of a channel by adding some carefully designed redundant information to the data being transmitted through the channel.

Feed
This term has at least two key meanings within the field of satellite communications. It is used to describe the transmission of video programming from a distribution center. It is also used to describe the feed system of an antenna. The feed system may consist of a subreflector plus a feedhorn or a feedhorn only.

Feedhorn
A satellite TV receiving antenna component that collects the signal reflected from the main surface reflector and channels this signal into the low-noise amplifier (LNA).

Focal Length
Distance from the center feed to the center of the dish.

Focal Point
The area toward which the primary reflector directs and concentrates the signal received.

Footprint
A map of the signal strength showing the EIRP contours of equal signal strengths as they cover the earth’s surface. Different satellite transponders on the same satellite will often have different footprints of the signal strength. The accuracy of EIRP footprints or contour data can improve with the operational age of the satellite. The actual EIRP levels of the satellite, however, tends to decrease slowly as the spacecraft ages.

FEC – Forward Error Correction – It is a powerful technique for improving the performance of error-prone channels found in communication systems. It is a system of error control for data transmission where the receiving device has the capability to detect and correct any character or code block that contains fewer then a predetermined number of symbols in error

Frequency
The number of times that an alternating current goes through its complete cycle in one second of time. One cycle per second is also referred to as one hertz; 1000 cycles per second, one kilohertz; 1,000,000 cycles per second, one megahertz: and 1,000,000,000 cycles per second, one gigahertz.

FTDMA – frequency time division multiple access – The FTDMA features a unique and patented two-dimensional satellite access scheme, which combines the TDMA slotted ALOHA and FDMA techniques. Remote terminals burst in randomly-selected frequency channels at each transmission. Occasional high traffic sites are automatically off-loaded from the shared resources and have dedicated frequency channels allotted to them upstream communications are transmitted using a patented, proprietary technology – Frequency/Time Division Multiple Access, or FTDMA. Downstream transmissions, however, use the industry standard Digital Video Broadcast (DVB) carrier.

G

Gain
A measure of amplification expressed in dB.
Geostationary
Refers to a geosynchronous satellite angle with zero inclination. so the satellite appears to hover over one spot on the earth’s equator.

GEO (GEOSYNCHRONOUS EARTH ORBIT)
This is the orbital altitude of 35,580 km (22,237 miles) above the earth’s surface where a satellite’s velocity matches with the rotation of the earth. The geosynchronous earth orbit is also referred to as the Clarke Orbit .

Gigahertz (GHz)
One billion cycles per second. Signals operating above 3 Gigahertz are known as microwaves. above 30 GHz they are know as millimeter waves. As one moves above the millimeter waves signals begin to take on the characteristics of Iightwaves.

G/T
A figure of merit of an antenna and low noise amplifier combination expressed in dB. “G” is the net gain of the system and “T” is the noise temperature of the system. The higher the number, the better the system.

Guard Channel
Television channels are separated in the frequency spectrum by spacing them several megahertz apart. This unused space serves to prevent the adjacent television channels from interfering with each other.

H

Hertz (Hz)
The name given to the basic measure of radio frequency characteristics. An electromagnetic wave completes a full oscillation from its positive to its negative pole and back again in what is known as a cycle. A single Hertz is thus equal to one cycle per second.

High Frequency (HF)
Radio frequencies within the range of 3,000 to 30,000 kilohertz. HF radio is known as shortwave.

High-Power Satellite
Satellite with 100 watts or more of transponder RF power.
Hub
The master station through which all communications to, from and between micro terminals must flow. in the future satellites with on-board processing will allow hubs to be eliminated as MESH networks are able to connect all points in a network together.

I
IBS
INTELSAT Business Services.

Inclination
The angle between the orbital plane of a satellite and the equatorial plane of the earth.

Interference
Energy which tends to interfere with the reception of the desired signals, such as fading from airline flights, RF interference from adjacent channels, or ghosting from reflecting objects such as mountains and buildings.

ISDN – Integrated Services Digital Network.
A CCITT standard for integrated transmission of voice, video and data. Bandwidths include: Basic Rate Interface – BR (144 Kbps – 2 B & 1 D channel) and Primary Rate – PRI (1.544 and 2.048 Mbps).

J
Jammer -
An active electronic counter-measures (ECM) device designed to deny intelligence to unfriendly detectors or to disrupt communications.

K
Ka Band
The frequency range from 18 to 31 GHz.

Kbps
Kilobits per second. Refers to transmission speed of 1,000 bits per second.

Kelvin (K)
The temperature measurement scale used in the scientific community. Zero K represents absolute zero, and corresponds to minus 459 degrees Fahrenheit or minus 273 Celsius. Thermal noise characteristics of LNA are measured in Kelvins.

Kilohertz (kHz)
Refers to a unit of frequency equal to 1,000 Hertz.

Klystron
A microwave tube which uses the interaction between an electron beam and the RF energy on microwave cavities to provide signal amplification. The klystron operates on principles of velocity modulation very similar to those in a TWT except that klystron interaction takes place at discrete locations along the electron beam. Common types of klystrons are the reflex klystron (an oscillator having only one cavity), two-cavity klystron amplifiers and oscillators, and multi-cavity klystron amplifiers.

Ku Band
The frequency range from 10.9 to 17 GHz.

L

L-Band
The frequency range from 0.5 to 1.5 GHz. Also used to refer to the 950 to 1450MHz used for mobile communications.

Latency – In a network, latency, a synonym for delay, is an expression of how much time it takes for a packet of data to get from one designated point to another.

Leased Line
A dedicated circuit typically supplied by the telephone company.

LNA – Lowe Noise Amplifier – Special type of amplifier used in communication systems to amplify very weak signals captured by an antenna.

LNB – Low Noise Block – take a block or band of relatively high frequencies and convert them to similar signals carried at much lower frequencies (intermediate frequency or IF).

Low Noise Amplifier (LNA)
This is the preamplifier between the antenna and the earth station receiver. For maximum effectiveness, it must be located as near the antenna as possible, and is usually attached directly to the antenna receive port. The LNA is especially designed to contribute the least amount of thermal noise to the received signal.

Low Noise Block Downconverter (LNB)
A combination Low Noise Amplifier and downconverter built into one device attached to the feed.

Low Noise Converter (LNC)
A combination Low Noise Amplifier and down converter built into one antenna-mounted package.

Low Orbit
At an altitude of 200 to 300 km this orbit is used for certain types of scientific or observation satellites, which can view a different part of the Earth beneath them on each orbit
 
M

Megahertz (MHz)
Refers to a frequency equal to one million Hertz, or cycles per second.

Microwave
Line-of sight, point-to-point transmission of signals at high frequency. Many CATV systems receive some television signals from a distant antenna location with the antenna and the system connected by microwave relay. Microwaves are also used for data, voice, and indeed all types of information transmission. The growth of fiber optic networks have tended to curtail the growth and use of microwave relays.

Microwave Interference
Interference which occurs when an earth station aimed at a distant satellite picks up a second, often stronger signal, from a local telephone terrestrial microwave relay transmitter. Microwave interference can also be produced by nearby radar transmitters as well as the sun itself. Relocating the antenna by only several feet will often completely eliminate the microwave interference.

Modem
A communications device that modulates signals at the transmitting end and demodulates them at the receiving end.

Modulation
The process of manipulating the frequency or amplitude of a carrier in relation to an incoming video, voice or data signal.

Modulator
A device which modulates a carrier. Modulators are found as components in broadcasting transmitters and in satellite transponders. Modulators are also used by CATV companies to place a baseband video television signal onto a desired VHF or UHF channel. Home video tape recorders also have built-in modulators which enable the recorded video information to be played back using a television receiver tuned to VHF channel 3 or 4.

 Multiplexing
Techniques that allow a number of simultaneous transmissions over a single circuit.

Mux
A Multiplexer. Combines several different signals (e.g. video, audio, data) onto a single communication channel for transmission. Demultiplexing separates each signal at the receiving end.

N

Noise
Any unwanted and unmodulated energy that is always present to some extent within any signal.

Noise Figure (NF)
A term which is a figure of merit of a device, such as an LNA or receiver, expressed in dB, which compares the device with a perfect device.

O

Orbital Period
The time that it takes a satellite to complete one circumnavigation of its orbit.

P

Packet Switching
Data transmission method that divides messages into standard-sized packets for greater efficiency of routing and transport through a network.
 

Parabolic Antenna
The most frequently found satellite TV antenna, it takes its name from the shape of the dish described mathematically as a parabola. The function of the parabolic shape is to focus the weak microwave signal hitting the surface of the dish into a single focal point in front of the dish. It is at this point that the feedhorn is usually located.

Perigee
The point in an elliptical satellite orbit which is closest to the surface of the earth.

Perigee Kick Motor (PKM)
Rocket motor fired to inject a satellite into a geostationary transfer orbit from a low earth orbit especially that of a STS or Shuttle-based orbit of 300 to 500 miles altitude.

Period
The amount of time that a satellite takes to complete one revolution of its orbit.

Phase-Locked Loop (PLL)
A type of electronic circuit used to demodulate satellite signals.

 Polarization
A technique used by the satellite designer to increase the capacity of the satellite transmission channels by reusing the satellite transponder frequencies. In linear cross polarization schemes, half of the transponders beam their signals to earth in a vertically polarized mode; the other half horizontally polarize their down links. Although the two sets of frequencies overlap, they are 90 degree out of phase, and will not interfere with each other.

Polarization Rotator
A device that can be manually or automatically adjusted to select one of two orthogonal polarizations.
Polar Orbit
An orbit with its plane aligned in parallel with the polar axis of the earth

Pulse Code Modulation
A time division modulation technique in which analog signals are sampled and quantized at periodic intervals into digital signals. The values observed are typically represented by a coded arrangement of 8 bits of which one may be for parity.

Q

QPSK
Quadrature Phase Shift Keying is a digital modulation technique in which the carrier phase can have one of four possible values of 0, 90, 180, 270 degrees on the equivalent of a 90 degrree rotation. There are even more advanced concepts based upon 8-phase (45 degree rotation), 16 phase (22.5 degree rotation) and so on to 32 phase, etc. 
 
 R

Rain Outage
Loss of signal at Ku or Ka Band frequencies due to absorption and increased sky-noise temperature caused by heavy rainfall.

Receiver (Rx)
An electronic device which enables a particular satellite signal to be separated from all others being received by an earth station, and converts the signal format into a format for video, voice or data.

Router
Network layer device that determines the optimal path along which network traffic should be forwarded. Routers forward packets from one network to another based on network layer information.
  
S

Satellite
A sophisticated electronic communications relay station orbiting 22,237 miles above the equator moving in a fixed orbit at the same speed and direction of the earth (about 7,000 mph east to west).

Sidelobe
Off-axis response of an antenna.

Signal to Noise Ratio (S/N)
The ratio of the signal power and noise power. A video S/N of 54 to 56 dB is considered to be an excellent S/N, that is, of broadcast quality. A video S/N of 48 to 52 dB is considered to be a good S/N at the headend for Cable TV.
 

Single-Channel-Per-Carrier (SCPC)
A method used to transmit a large number of signals over a single satellite transponder.

 Solar Outage
Solar outages occur when an antenna is looking at a satellite, and the sun passes behind or near the satellite and within the field of view of the antenna. This field of view is usually wider than the beamwidth. Solar outages can be exactly predicted as to the timing for each site.
 

Spin Stabilization
A form of satellite stabilization and attitude control which is achieved through spinning the exterior of the spacecraft about its axis at a fixed rate.

Splitter
A passive device (one with no active electronic components) which distributes a television signal carried on a cable in two or more paths and sends it to a number of receivers simultaneously.

Spot Beam
A focused antenna pattern sent to a limited geographical area. Spot beams are used by domestic satellites to deliver certain transponder signals to geographically well defined areas such as Hawaii, Alaska and Puerto Rico.

Spread Spectrum
The transmission of a signal using a much wider bandwidth and power than would normally be required. Spread spectrum also involves the use of narrower signals that are frequency hopped through various parts of the transponder. Both techniques produce low levels of interference Between the users. They also provide security in that the signals appear as though they were random noise to unauthorized earth stations. Both military and civil satellite applications have developed for spread spectrum transmissions.

Star Topology – Network designed in the shape of a star, where all end points are connected to one central switching device, or hub. Star networks are easier to manage than ring topology but are slower because every message must pass through the central point.

SSPA
Solid state power amplifier. A VSLI solid state device that is gradually replacing Traveling Wave Tubes in satellite communications systems because they are lighter weight and are more reliable. 
 

T

T1
The transmission bit rate of 1.544 millions bits per second. This is also equivalent to the ISDN Primary Rate Interface for the U.S. The European T1 or E1 transmission rate is 2.048 million bits per second.

TDMA
Time division multiple access – is digital transmission technology that allows a number of users to access a single radio-frequency (RF) channel without interference by allocating unique time slots to each user within each channel.

Transmitter
An electronic device consisting of oscillator, modulator and other circuits which produce a radio or television electromagnetic wave signal for radiation into the atmosphere by an antenna.

Transponder
The transponder is a broadband RF channel used to amplify one or more carriers on the downlink side of a geostationary communications satellite. It is part of the microwave repeater and antenna system that is housed onboard the operating satellite.

Transponder Hopping
A single TDMA equipped earth station can extend its capacity by having access to several down-link beams by hopping from one transponder to another. In such a configuration the number of available transponders must be equivalent to the square of the number of beams that are interconnected or cross-strapped.

TSS
Telecommunications Standardization Sector. The world standards setting organization resulting from the combination of the CCITT (Consultative Committee on Telephony and Telegraphy) and the CCIR (Consultative Committee on International Radio).

Turnkey
Refers to a system that is supplied, installed and sometimes managed by one vendor or manufacturer.

TVRO
Television Receive Only terminals that use antenna reflectors and associated electronic equipment to receive and process television and audio communications via satellite. Typically small home systems.

Tweeking
The process of adjusting an electronic receiver circuit to optimize its performance.

TWT (Traveling-wave tube)
A microwave tube of special design using a broadband circuit in which a beam of electrons interacts continuously with a guided electromagnetic field to amplify microwave frequencies.

TWTA
Traveling-wave-tube amplifier

U

Ultra-high Frequency (UHF)
Officially the band of frequencies ranging from 300 to 3000 MHz. In television use, refers to the set of frequencies starting at 470 MHz, The UHF channels are designated as 14 through 70.
Uplink
The earth station used to transmit signals to a satellite

USAT
Ultra Small Aperture Terminal. This refers to very small terminals for DBS and other satellite applications where the terminal can be very small (under 50 cms).

V

V.35
ITU-T standard describing a synchronous, physical layer protocol used for communications between a network access device and a packet network.

Viterbi Encoding/Decoding – is widely used for satellite and other noisy communication channels. There are two important components of a channel using Viterbi encoding: the Viterbi encoder (at the transmitter) and Viterbi Decoder (at the receiver). A Viterbi encoder includes extra information in the transmitted signal to reduce the probability of errors in the received signal that may be corrupted by noise.
Very High Frequencies (VHF)
The range of frequencies extending from 30 to 300 MHz.

VSAT
Very small aperture terminal. Refers to small earth stations, usually in the 1.2 to 2.4 meter range. Small aperture terminals under 0.5 meters are sometimes referred to Ultra Small Aperture Terminals (USAT’s)

VSWR
Voltage Standing Wave Ratio. A measurement of mismatch in a cable, waveguide, or antenna system.
 
W
Waveguide
A metallic microwave conductor, typically rectangular in shape, used to carry microwave signals into and out of microwave antennas.

X

X-Band
The frequency band in the 7-8 GHz region which is used for military satellite communications

X.25
A set of packet switching standards published by the CCITT.

8PSK – 8 Phase-Shift Key – data modulation is performed to the bits from the output of the physical channel mapping procedure. Modulation 3 consecutive binary bits are represented by one complex valued data symbol. 8PSK deals with bandwidth by reducing spectral occupancy compared to lower order modulation methods.

In July 1964, INTELSAT, a multinational organization, was formed with the purpose to design, develop, construct, establish, and maintain the operation of the space segment of a global commercial communications satellite system.
In April 1965, Early Bird (INTELSAT I), a geostationary communications satellite was launched.
In a span of seven years, four generations of satellites – INTELSAT I through IV were launched and placed in commercial operation.

Satellite communication utilizes electromagnetic waves to carry information from the ground to space and back. An electromagnetic wave consists of an electric field and a magnetic field that are perpendicular to each other and to the direction of propagation

The frequency of an electromagnetic wave is defined as the number of times it cycles in one second and is measured in Hertz (Hz).
1 Hertz = 1Hz (one hertz)
1,000 Hertz = 1kHz (one kilohertz)
1,000,000 Hertz = 1MHz (one megahertz)
1,000,000,000 Hertz = 1GHz (one gigahertz)

What is a Satellite?
A satellite is any object that orbits or revolves around another object. For example, the Moon is a satellite of Earth, and Earth is a satellite of the Sun.In SATCOM parlance it’s a man- made machine orbiting Earth / Sun. Acting as a repeater in the sky, permitting communication over long distances at high bandwidths and relatively low cost.

Types of Satellites
Communications Satellites
Remote Sensing Satellites
Weather Satellites
GPS Satellites
Science Research Satellites – SOHO

Communications Satellites
Communications satellites act as relay stations in space.
Used for bouncing messages from one part of the world to another.
The messages can be telephone calls, TV pictures, or even Internet connections.

Remote Sensing Satellites
Remote-sensing satellites study Earth’s surface.
From 300 miles (480 km) up, these satellites use powerful cameras to scan the planet.
The instruments on remote-sensing satellites study Earth’s plant cover, chemical composition, and surface water, among many other features.
The satellite then sends back valuable data about global environments.
Farming, fishing, mining, and many other industries find this information very useful.
Remote sensing satellites can also be used to study changes in the Earth’s surface that are caused by people. Examples of this include the parts of West Africa that are turning into desert (desertification), and the destruction of the rainforest in South America (deforestation).

Weather Satellites
Also called TIROS (Television Infrared Observational Satellite).
It records weather patterns around the world. Many countries use TIROS data to forecast weather, track storms, and do scientific research.

GPS Satellites
GPS satellites are a group of satellites that can tell you your exact latitude, longitude, and altitude.
People everywhere are using these satellites to determine where in the world they are.
GPS satellites are used for navigation almost everywhere on Earth — in an airplane, boat, or car, on foot, in a remote wilderness, or in a big city.

Science Research Satellites
Many satellites in orbit conduct scientific experiments and observations.
For example SOHO, which studies the Sun.
Hubble Space Telescope is a satellite in orbit around Earth, and its mission is to study distant planets, stars and galaxies.

Satellite Orbits
Definition :
Orbit – path of a satellite around a body (e.g. the earth) which is stable under the influence of gravity.
Types :
Equatorial
Elliptical
Polar
Equatorial / Geosynchronous Orbit :
A satellite in geosynchronous equatorial orbit (GEO) is located directly above the equator, exactly 22,300 miles out in space. At that distance, it takes the satellite a full 24 hours to circle the planet. Since it takes Earth 24 hours to spin on in its axis, the satellite and Earth move together. So, a satellite in GEO always stays directly over the same spot on Earth.It is also called a Clarke Orbit or Geostationary Orbit.
Elliptical Orbit :
A satellite in elliptical orbit follows an oval-shaped path.
One part of the orbit is closest to the center of Earth (perigee) and the other part is farthest away (apogee).
A satellite in this orbit takes about 12 hours to circle the planet. Elliptical orbits move in a north-south direction. Also known as Super-synchronous Orbits or Molniya Orbits.
Polar Orbit :
A Polar orbit is a particular type of Low Earth Orbit. The only difference is that a satellite in polar orbit travels a north-south direction, rather than the more common east-west direction.
These orbits are at a typical height of 850 Km and a period of 100 minutes.
Polar Coverage
While most communications satellites are in Clarke Orbit, the footprints of GEO satellites do not cover the polar regions of Earth. So communications satellites in elliptical orbits cover the areas in the high northern and southern hemispheres that are not covered by GEO satellites.

Low Earth Orbit (LEO)
When a satellite circles close to Earth it is said to be in Low Earth Orbit (LEO).
Satellites in LEO are just 200 – 500 miles (320 – 800 kilometers) high.
Satellites in LEO speed along at 17,000 miles per hour (27,359 kilometers per hour)!
They circle Earth in about 90 minutes.
A Low Earth Orbit is useful because its nearness to Earth gives it spectacular views.
Remote Sensing and Weather satellites often travel in LEOs because from this height they can capture very detailed images of Earth’s surface.

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