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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.


Boeing 702 the most widely used satellite
Boeing 702the most widely used satellite



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 edition of Wireless World

  • 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 edition of Wireless World

Elevation and Azimuth are adjusted to point to the satellite


24 channels on a satellite
24 Channels on a Satellite edition of Wireless World

  • 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 edition of Wireless World

  • 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’ edition of Wireless World

Much less expensive than the uplink ..


Analog vs digital
Analog vs Digital edition of Wireless World

  • 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 .. edition of Wireless World

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


A satellite uses 300 watts
A satellite uses 300 Watts edition of Wireless World

  • 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. edition of Wireless World

  • 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... edition of Wireless World

  • 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’ edition of Wireless World

  • 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 edition of Wireless World

  • 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


Longitudes for us view
Longitudes for US View edition of Wireless World


A recent copy of orbit
A recent copy of ORBIT edition of Wireless World

  • 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 edition of Wireless World

  • 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..


Satellite feed horn assembly
Satellite Feed Horn Assembly edition of Wireless World


The polarotor
The ‘Polarotor’ edition of Wireless World

  • 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 edition of Wireless World

  • Are also used for ‘Pager Service’

  • Cellular Telephone

  • Other types of communication including the monitoring of vehicles like Federal Express

  • Global Positioning ( GPS)


Satellite in low earth orbit
Satellite in low Earth Orbit edition of Wireless World


For more go to the web
For more .. Go to the web .. edition of Wireless World


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