Satellite Terminology

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AM Modulation

The term AM is formed by the initials of the words "amplitude modulation". As the name suggests, what is essential in AM is to provide the change of the amplitude. In order to achieve this, the signal to be transmitted is multiplied by a signal having a higher frequency. When a mathematical analysis is done, the frequency of the signal obtained by multiplying the two signals would be close to the frequency of the carrier signal.

Analog

These are the signals being a continuous function of time. In other words, these signals change constantly.

AZIMUTH

It means horizontal angle according to true north. It is the direction to which the satellite antenna must face towards a certain satellite on the horizontal direction. It is the direction to which the satellite antenna must face towards a certain satellite on the horizontal direction. It would be 0 degrees North, 180 degrees South when viewed through a compass. It is the angle obtained as a result of moving the dish antenna clockwise.

Viewpoint

It is the angle of dish antenna facing towards the satellite for receiving the broadcast of the satellite smoothly.

Bandwidth

It is the frequency range defined within the frequency spectrum. It is also used for the capacities used by various broadcasts from satellite such as TV, Radio, and Internet.

BSS

It is the abbreviation of "Broadcast Satellite Service". It means TV/Radio Satellite Broadcast.

Dish Antenna

It is the antenna having a parabolic geometry collecting the signals coming from satellite.

Clarke Belt

In Clarke's own words: ...An artificial satellite at the correct distance from the earth would make one revolution every 24 hours. In other words, it would remain stationary above the same spot and would be within optical range of nearly half the earth's surface. Three repeater stations, 120 degrees apart in the correct orbit, could give television and microwave coverage to the entire planet.

Compression

Decreasing the bandwidth used is a procedure for decreasing the bandwidth of voice and image signals for the sake of the most effective usage. A compressed signal occupies less space on the satellite transponder and the capacity of the transponder in the space is used more effectively.

dB

Decibel is the analog measurement unit expressing logarithmically the amount of signal attenuation due signal magnitude, volume, or resistance.

Demodulation

It is the procedure of receiving back the information a carrier's signal modulated on a carrier.

Digital

Signals getting specific values within a certain time interval. Digital systems are basically composed of 0 and 1 values.

Downlink

Sending a signal, which is sent to satellite, to the earth.

EIRP (Equivalent Isotropic Radiated Power)

It is the value obtained by multiplying the power transferred from the transponder to the antenna by the gain of the satellite antenna.

ELEVATION (Elevation Angle)

It is the dish antenna's viewpoint in vertical direction towards a specific satellite. It is the angle obtained as a result of moving the dish antenna up or down.

Interference

It is the phenomenon of unintentional interference (frequency interference) of signals going up to a satellite or sent from a satellite with all kinds of receiver-transmitter stations and with other satellites.

FM Modulation

In this type of modulation, the signal required to be transmitted creates a phase difference on the carrier signal. Thus, a signal the frequency of which changes over time is obtained. The changes in the frequency of the signal created are the indicator of the changes in the signal required to be transmitted. The frequency of the created signal is close to the frequency of the carrier signal. The signal required to be transmitted is transmitted with a frequency different from its own frequency in this method as well.

FSS

It is the abbreviation of "Fixed Satellite Service". It means Constant Satellite Broadcast.

G/T (Gain-Noise Equivalent Temperature Ratio)

It is a parameter used to determine the quality of the receiver of a satellite or a ground station.

High Definition Television

It is the technology raising the resolution of video signals increasing the picture quality so dramatically compared to the existing PAL and NTSC standards. It has a resolution higher than today's NTSC televisions, which is approximately twice the horizontal resolution and approximately twice the vertical resolution. Its resolution has an image information approximately five times of today's standard televisions, whereas it has a sound quality similar to CD (6-channel cd-quality surround sound).

INMARSAT

It is the abbreviation of "International Maritime Satellite Organization". 

INTELSAT

It is the abbreviation of "International Telecommunications Satellite Organization". 

ITU

It is the abbreviation of "International Telecommunications Union". 

Geosynchronous Orbit

Only the position of one of the satellite orbits, the number of which is infinite, remains always constant with respect to a specific point on the earth. This is the specific and unique circular orbit over the equatorial plane where the speed of the satellite on it is equal to the angular speed of the earth around its own axis. This orbit is referred to as the geosynchronous satellite orbit or the Clarke orbit, where its distance to earth is 35,784 km. Remaining stable of a satellite on such an orbit is determined with three conditions: a- Rotation of the satellite in the same direction with the earth, b- Position of the satellite on the equator latitude, c- Full rotation of the satellite every 23.94 hour.

KU Band

It is the band gap on the frequency spectrum as the following based on European standards; Uplink: 13750 MHz / 14500 MHz Downlink: 10950MHz-11700MHz and 12500MHz-12750 MHz.

LNB (Low Noise Block Convertor)

It is an electronic equipment strengthening the signal coming from a satellite and reducing the frequency of the strengthened signal to a level suitable for the digital satellite receiver.

Modulation

Some adverse impacts are exposed to the signal by the environment where it is carried. Changes in the external world or other signals cause disruption of the carried signal. Furthermore, there are some restrictions introduced by the environment. Therefore, in order to achieve the least possible disruption of the signal, some procedures are held on the signal. In other words, the signal is needed to be processed to make it suitable for the environment where it is carried. This procedure, which gives the required structure to the signal, is called modulation.

MPEG

A committee called MPEG (Motion Picture Experts Group), participated by the leading telecom organizations and research groups, has been created in order to eliminate the problems experienced during transition to digital technology, set a global standard considering the consumers as well, and to develop this standard. This committee has compiled the studies of the international communication engineers in many parts of the world and prepared some standards acceptable by all countries as a result a meticulous work on these studies. The standards prepared by the committee are MPEG1, MPEG2, etc. The work of this committee can be categorized as follows: determining the worldwide standard for video and audio encoding based on application, preparing and developing procedures appropriate for system assessments, determining the frame of bit group for transmission, coding, multiplexing, and decoding, and introducing a common standard for devices used for these procedures.

MPEG1

This is the first standard created by the MPEG group. Covers digital video and audio of 1.5 Mbit/s and equivalent to VHS quality. The CDIC (Compact Disc Interactive) has been developed and used in decoder chips manufactured as the easiest way of obtaining a broadcast with television quality in CD players and multimedia PCs. In this standard, a system developed additionally has enabled to merge multiple signals and transfer them to satellite as a single signal. MPEG-1 has been developed to be used in the professional television technology.

MPEG2

Developments experienced in the digital TV technology have led to creation of a more complex standard. This standard, which is called MPEG-2, has a flexible structure defining broadcast standards of every quality from the local standard quality up to HDTV quality by using 2-15 Mbps data ratios. A decoder using in accordance with the MPEG-2 standard is able to decode MPEG-1-standard broadcasts and to process signals of video telephone structure of the CCITT H216 standard. This feature is called "Backward compatible" which means the feature of supporting the previous system. Since the standards are comprised of the encoding range and compression techniques, the systems developed include the previous standards to avoid losing the usability of the previous systems in time (against future developments) and not to cause discarding them.

Polarization

An electromagnetic signal moves up and down or left and right when going on its own direction. Polarizing filters allows the passage of the signal's waves vibrating in only one direction. Having the light vibrating one-way like this is called polarization.

Oscillatory Orbit

Since the angular velocity of each geosynchronous satellite is equal to the angular velocity of the earth around its own axis, its coverage range on the earth is constant, where its distance from the ground surface is 35786.4 km. Although the satellite is expected to maintain this position, due to the reasons such as the gravity effects of the sun, moon, and the other celestial bodies, the shape of the earth which is not completely round and homogeneous, and the thrust effect of sunbeams, the latitude of the satellite (referenced to the equator) fluctuates during the day within ± i (inclination) interval, and its longitude value oscillates during the day in proportion to eccentricity (the parameter indicating the ellipse ratio of the orbit). The life of a geosynchronous satellite can be extended by operating it on a oscillatory (inclined) orbit as a strategy adopted by satellite operators as well. In such a case, the periodic North maneuvers would not be made anymore and the inclination angle, which is the natural increase inclination, would be released, so the satellite would be controlled on the inclined orbit. However, since the satellite communication systems are very sensitive to changes in latitudes and longitudes of satellites, the signals sent from the satellite would be received only by antennas equipped with tracking units.

SCPC (Single Channel Per Carrier)

It is the allocation of one carrier, i.e. frequency range, in the satellite for each link necessary for communication. Accordingly, all kinds of link requirements can be quickly and safely met in scalable manner.

Tracking

This is function of the antenna which tracks the satellite in a manner minimizing the disruption of the signal coming from the satellite.

Transponder

The collective name of the satellite's electronic equipment receiving the signal coming to the satellite, reducing its frequency to the satellite receiving frequency, and ensuring radiation of the signal to the regions specified within the coverage range.

Uplink

Sending a signal to a satellite to be transferred or accessing a satellite from a ground station is basically called up-link.

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