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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

Satellite Television

It’s out of sight!

22,300 miles in fact!

20 commercial satellites
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
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
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
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
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’
slide13

Uplink antenna

Elevation and Azimuth are adjusted to point to the satellite

24 channels on a 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
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..)
slide16

A ‘downlink’

Much less expensive than the uplink ..

analog vs digital
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..
slide18

A digital dish ..

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

a satellite uses 300 watts
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
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
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
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
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
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 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
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
Satellites
  • Are also used for ‘Pager Service’
  • Cellular Telephone
  • Other types of communication including the monitoring of vehicles like Federal Express
  • Global Positioning ( GPS)