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Satellite Television 1 It’s out of sight! 22,300 miles in fact!

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Presentation on theme: "Satellite Television 1 It’s out of sight! 22,300 miles in fact!"— Presentation transcript:

1 Satellite Television 1 It’s out of sight! 22,300 miles in fact!

2 Satellite Television 2 From How Stuff Works

3 Satellite Television Commercial Satellites H In Geo-Stationary Orbit 22,300 miles away.... H All in a band over the Equator H They have a revolution of once per day. H Just like us!... That makes them geo- stationary. H They have a useful life of 10 years.

4 Satellite Television 4 Boeing 702 the most widely used satellite

5 Satellite Television 5 Hughes HS601

6 Satellite Television 6 Forces at work H A satellite spins around the planet H What holds these satellites in place ? H Gravity will try to pull the mass back to earth H The force of a centrifuge pushes the satellite out into space..

7 Satellite Television 7 Geo-stationary Orbits H The force of gravity, Fg, is equal to H The centripetal force, Fc H AT 22,300 miles, Fg = Fc if the velocity is one revolution per day ! H This was first proposed byArthur C. Clarke...

8 Satellite Television 8

9 9 The Clarke Belt H These satellites appear to be in the same position in the sky at all times. H They are directly over the equator but not directly over us. H They are in a line that starts 14 degrees above our Western Horizon. H And rises to 42 degrees elevation in the South

10 Satellite Television 10 Original figure from Clarke's article in the October 1945 edition of Wireless World

11 Satellite Television 11 Elevation and Azimuth H The Elevation is the number of degrees above the horizontal... H The Azimuth is a degree reading with North being 0 and 360 degrees, East being 90, South at 180, and West at 270. H Degree readings are allways ‘True’ and not ‘Magnetic’

12 Satellite Television 12

13 Satellite Television 13 Uplink antenna Elevation and Azimuth are adjusted to point to the satellite

14 Satellite Television Channels on a Satellite H Numbered 1 to 24 H Odd Number Channels are often Vertically Polarized... H Even Number Channels are often Horizontally Polarized. H The antenna must line up with the polarization..

15 Satellite Television 15 C Band and Ku Band H The C Band uses 4 GHz for the down link and 6 GHz for the up link. H The Ku Band uses 12 GHz for the down link and 14 GHz for the up link. H A ground station monitors each satellite 24 hours a day. H Friction tends to move them from their orbit ! (Magnetic friction..)

16 Satellite Television 16 A ‘downlink’ Much less expensive than the uplink..

17 Satellite Television 17 Analog vs Digital H The largest commercial system is an Analog system, subject to noise and signal strength. H The newer Digital dishes can easily remove the nose and can produce crystal clear pictures with weak signals. H The Digital dishes are smaller..

18 Satellite Television 18 A digital dish.. MPEG2 is used as a format for the data stream..

19 Satellite Television 19 A satellite uses 300 Watts H Which must come from solar power H This power is distributed over 24 small transmitters... H The surface area of the US is 3,000,000 Square Miles. H That’s 100 Micro Watts per square mile H But only 5 Micro Watts per channel...

20 Satellite Television 20 The signals are very very weak. H A large ‘dish’ is used to focus the power received onto a small 1.5 CM antenna.. H A 12 Foot dish, has an area of Pi X R 2 or 108 Sq Feet. H Calculate the power the dish receives from a 300 Watt Satellite....

21 Satellite Television 21 An 18” Digital Dish... H Has a much smaller surface area H Receives a much smaller amount of power... H But delivers a better signal due to the cleanliness of ‘bits’ !

22 Satellite Television 22 Satellite ‘Sighting’ H We point the dish at specific azimuths and elevations to find a satellite. H From 14 Degrees Elevation and 270 Degrees Azimuth (W) H To 42 Degrees Elevation and 180 Degrees Azimuth (S) H A set of tables lets us find the data for a particular satellite.

23 Satellite Television 23 Latitude and Longitude H Binghamton... H Is at 70 Degrees E Longitude and 42 Degrees N Latitude H East of Grenich, and North of the Equator H The calculations for finding a satellite 22,300 miles over the equator are complex

24 Satellite Television 24 Longitudes for US View

25 Satellite Television 25 A recent copy of ORBIT H Shows us the longitude of the various satellites. H They are spaced 3 to 6 degrees apart H Their longitude, entered into an equation gives us Elevation and Azimuth.

26 Satellite Television 26

27 Satellite Television 27 The Satellite RECEIVER H The signal is collected by the ‘dish’ H Focused on the ‘Feed Horn’ Assembly H Amplified by a Low Noise Amplifier H Converted to a much lower frequency H Carried by shielded cable to the receiver H And delivered to your TV set..

28 Satellite Television 28 Satellite Feed Horn Assembly

29 Satellite Television 29 The ‘Polarotor’ H A small motor turns the antenna to accomodate the ‘polarization’ of the signal. H The ‘plane’ of the signal ‘skews’ as we point the dish to the west H The ‘polarotor’ must compensate for this skew

30 Satellite Television 30 Satellites H Are also used for ‘Pager Service’ H Cellular Telephone H Other types of communication including the monitoring of vehicles like Federal Express H Global Positioning ( GPS)

31 Satellite Television 31 Satellite in low Earth Orbit

32 Satellite Television 32 For more.. Go to the web..


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