EARTH STATIONThe earth-based communications station providing the communication link to a communications satellite. The earth station itself is usually an antenna that includes a low-noise amplifier, a down-converter, as well as an electronics receiver. The antenna itself can vary in size from at little at 3 to 30 meters, depending on its usage. May also be called a satellite earth station.

SATELLITE COMMUNICATION

1957 Sputnik first rocket for metrological purpose16 revolution per day.

There are two forces act on the satellite to revolve it in its orbit• Centrifugal- for revolution• Gravitational- to attach to the earth

Fc =mv2/(r+h)Fg= G M m/(r+h)2

Therefore and conditions must be fullfilled.

30 E -- Africa and Europe.

150 E -- China and Oceana.

90 W -- The Americas.

Range given to different continents to establish their satellite

• Block diagram of uplink and downlink

Types of satellite1. BSS – broadcasting satellite system2. MSS – mobile satellite system3. FSS – fixed satellite system

Azimuth angle Az =Or Az= α where α=For earth station in the northern hemisphereAz= α when earth station is west of satelliteAz= α when earth station is east of satelliteFor earth station in the southern hemisphereAz= α when earth station is west of the satelliteAz= α when earth station is east of satellite

Angle of elevation El=

r = Radius of the earthR = radius of the orbitᶲ = latitude of the earth stationD = difference in longitude of earth station & satellite

Antenna gain S band, 26+20log DM C band, 29.9+20log DM Ex C band, 31+20log DM

Where DM = diameter of PDA in meter

DISH TRACKING

Looking angles of the satellite

Azimuth angle Az =

Angle of elevation El=Where ᶿ = ᶿe - ᶿs

d=slant hieghta= 35786+6378=42164b=6378

INTEGRATED RECEIVER DECODER

PAL DECODER

BASIC T.V. SYSTEM AND SCANIMAGE CONTINUITYWhile television elements of the frame by means of scanning process, it is necessary to present the picture to the eye in such a way that an illusion of continuity and any motion of the scene appears on the picture tube screen as a smooth and continuous change to achieve this, advantage is taken of “persistence of vision (1/16 sec)” or storage characteristic of human eye thus if scanning rate per second is more than 16 the eye is able to integrate the changing levels of brightness in the screen. So when the picture elements are scanned rapidly enough they appear to eye as a complete picture unit, with none of the individual elements visible separately.SCANNINGA similar process is carried out in television system. The screen is scanned rapidly both in the horizontal and vertical directions simultaneously to provide sufficient number of complete picture of frame per second to give to give the illusion of continuous motion. Instead of 24 in commercial motion picture practice, the frame repetition rate is 25 per second in most television systems.

INTERLACED SCANNINGFrom consideration of flicker it has been found that 50 picture frames per sec. is the minimum requirement in television scanning. For a 625 line system this means that the horizontal line scanning frequency is 15625 Hz with the line period of 64 µsec. for a desired resolution of 546/2 alternations in horizontal line, this leads to very high bandwidth requirement viz. ((546/2)*(32-6))= 10 MHz, if the line scanning is the simple sequential way.An ingenious method of reducing the bandwidth requirement, while still maintaining an effective vertical picture scan rate of 50 Hz is to employ “interlaced scanning” rather than the simple sequential raster in interlaced scanning, the picture is divided into two more sets of fields each containing half or other fractional number of interlaced lines. And fields are scanned sequentially in 2:1 interlace, the 625 lines are divide into two sets of 312.5 lines each.The first set of 312.5 odd number of lines in the 625 lines, called the first field or the odd lines are first scanned sequentially, halfway through the 313th line, the spot is returned to the top of the screen and remaining 312 even number lines, called the second field or the even field are then traced interleaved between the lines of the first set.

This is done by operating the vertical fields scan at 50Hz so that the two successive interlaced scans each at 25 Hz make up the complete picture frame. This keeps the line scanning speed down as only 312.5 lines are in 1/50 second. The 612 lines of the full picture are scanned in 1/25 second, thus keeping down the bandwidth requirement.Here, through the picture is scanned 25 times per second the area of the screen is converted in an interlaced fashion at twice the rate, viz. 50 times per second. A closed examination may reveal the small area ‘interlaced flicker’ as actually individual line repeats only 25 times per second. But this is tolerable and the overall effect is closer to that of a 50 Hz scanning. The flicker becomes noticeable at high brightness only. In practice, the playback after each of the two fields that makes the complete picture. This means that out of 625 lines, only 585 line actually bears picture information. These are called the active lines.

HORIZONTAL RESOLUTION AND VIDEOO BANDWIDTHIn a 625 lines system there are effectively about 410 lines of vertical resolution. The horizontal resolution should be of the same order. Because of the aspect ratio of 4:3 the number of vertical lines for equivalent resolution will be (410*(4/3))= 564 black and white alternate lines, which means (546*1/2)= 273 cycles of black and white alternations of elementary areas. For the 625 lines system ,the horizontal scan or line frequency is given by:-Fh= no. of lines per picture Picture scan rate= 625*25 =15625 HzAs each picture lines is scanned 25 times in one second. The total line period is thusTh = 1/fh = 1/15625=64 µs.Of this period, 12 µs. is used are used for blanking of the playback retrace. Thus 546 black and white alternations, i.e. 273 cycles of complete square waves, are scanned along a horizontal raster line during the forward scan time of(64-12)= 54 micro sec. the period of this square wave is 52/273=0.2 µs. giving the highest fundamental frequency 5 MHz which is adequate as the highest video frequency in the signal.The highest fundamental video frequency in a scanning system is thus given byfmax= (active lines *kell factor *aspect ratio)/2 *line forward scan period

fmax≈5 MHz