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Satellite Television

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# Satellite Television - PowerPoint PPT Presentation

Satellite Television. It’s out of sight! 22,300 miles in fact!. From How Stuff Works. 20 + Commercial Satellites. In Geo-Stationary Orbit 22,300 miles away.... All in a band over the Equator They have a revolution of once per day. Just like us!... That makes them geo-stationary.

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### Satellite Television

It’s out of sight!

22,300 miles in fact!

20 + Commercial Satellites
• In Geo-Stationary Orbit 22,300 miles away....
• All in a band over the Equator
• They have a revolution of once per day.
• Just like us!... That makes them geo-stationary.
• They have a useful life of 10 years.
Forces at work
• A satellite spins around the planet
• What holds these satellites in place ?
• Gravity will try to pull the mass back to earth
• The force of a centrifuge pushes the satellite out into space ..
Geo-stationary Orbits
• The force of gravity, Fg, is equal to
• The centripetal force, Fc
• AT 22,300 miles, Fg = Fc if the velocity is one revolution per day !
• This was first proposed byArthur C. Clarke...
The Clarke Belt
• These satellites appear to be in the same position in the sky at all times.
• They are directly over the equator but not directly over us.
• They are in a line that starts 14 degrees above our Western Horizon.
• And rises to 42 degrees elevation in the South
Elevation and Azimuth
• The Elevation is the number of degrees above the horizontal...
• The Azimuth is a degree reading with North being 0 and 360 degrees, East being 90, South at 180, and West at 270.
• Degree readings are allways ‘True’ and not ‘Magnetic’

Uplink antenna

Elevation and Azimuth are adjusted to point to the satellite

24 Channels on a Satellite
• Numbered 1 to 24
• Odd Number Channels are often Vertically Polarized...
• Even Number Channels are often Horizontally Polarized.
• The antenna must line up with the polarization..
C Band and Ku Band
• The C Band uses 4 GHz for the down link and 6 GHz for the up link.
• The Ku Band uses 12 GHz for the down link and 14 GHz for the up link.
• A ground station monitors each satellite 24 hours a day.
• Friction tends to move them from their orbit ! (Magnetic friction..)

A ‘downlink’

Much less expensive than the uplink ..

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

A digital dish ..

MPEG2 is used as a format for the data stream ..

A satellite uses 300 Watts
• Which must come from solar power
• This power is distributed over 24 small transmitters...
• The surface area of the US is 3,000,000 Square Miles.
• That’s 100 Micro Watts per square mile
• But only 5 Micro Watts per channel...
The signals are very very weak.
• A large ‘dish’ is used to focus the power received onto a small 1.5 CM antenna..
• A 12 Foot dish, has an area of Pi X R2 or 108 Sq Feet.
• Calculate the power the dish receives from a 300 Watt Satellite....
An 18” Digital Dish...
• Has a much smaller surface area
• Receives a much smaller amount of power...
• But delivers a better signal due to the cleanliness of ‘bits’ !
Satellite ‘Sighting’
• We point the dish at specific azimuths and elevations to find a satellite.
• From 14 Degrees Elevation and 270 Degrees Azimuth (W)
• To 42 Degrees Elevation and 180 Degrees Azimuth (S)
• A set of tables lets us find the data for a particular satellite.
Latitude and Longitude
• Binghamton...
• Is at 70 Degrees E Longitude and 42 Degrees N Latitude
• East of Grenich, and North of the Equator
• The calculations for finding a satellite 22,300 miles over the equator are complex
A recent copy of ORBIT
• Shows us the longitude of the various satellites.
• They are spaced 3 to 6 degrees apart
• Their longitude, entered into an equation gives us Elevation and Azimuth.
The Satellite RECEIVER
• The signal is collected by the ‘dish’
• Focused on the ‘Feed Horn’ Assembly
• Amplified by a Low Noise Amplifier
• Converted to a much lower frequency
• Carried by shielded cable to the receiver
• And delivered to your TV set..
The ‘Polarotor’
• A small motor turns the antenna to accomodate the ‘polarization’ of the signal.
• The ‘plane’ of the signal ‘skews’ as we point the dish to the west
• The ‘polarotor’ must compensate for this skew
Satellites
• Are also used for ‘Pager Service’
• Cellular Telephone
• Other types of communication including the monitoring of vehicles like Federal Express
• Global Positioning ( GPS)