satellite television 1 it’s out of sight! 22,300 miles in fact!

Satellite Television 1

Satellite TelevisionSatellite Television

It’s out of sight!

22,300 miles in fact!

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From How Stuff WorksFrom How Stuff Works

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20 + Commercial Satellites20 + Commercial Satellites

In Geo-Stationary Orbit 22,300 miles away....

All in a band over the EquatorThey have a revolution of once per day. Just like us!... That makes them geo-

stationary.They have a useful life of 10 years.

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Boeing 702the most widely used

satellite

Boeing 702the most widely used

satellite

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Hughes HS601Hughes HS601

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Forces at workForces at work

A satellite spins around the planet

What holds these satellites in place ?Gravity will try to pull the mass back to

earthThe force of a centrifuge pushes the

satellite out into space ..

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Geo-stationary OrbitsGeo-stationary Orbits

The force of gravity, Fg, is equal toThe centripetal force, FcAT 22,300 miles, Fg = Fc if the velocity

is one revolution per day !This was first proposed byArthur C.

Clarke...

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The Clarke BeltThe 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

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Original figure from Clarke's article in the October

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

1945 edition of Wireless World

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Elevation and AzimuthElevation 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’

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Uplink antenna

Elevation and Azimuth are adjusted to point to the satellite

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24 Channels on a Satellite24 Channels on a Satellite

Numbered 1 to 24Odd Number Channels are often

Vertically Polarized...Even Number Channels are often

Horizontally Polarized.The antenna must line up with the

polarization..

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C Band and Ku BandC 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..)

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A ‘downlink’

Much less expensive than the uplink ..

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Analog vs DigitalAnalog 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..

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A digital dish ..

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

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A satellite uses 300 WattsA satellite uses 300 Watts

Which must come from solar powerThis 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 mileBut only 5 Micro Watts per channel...

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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....

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An 18” Digital Dish...An 18” Digital Dish...

Has a much smaller surface areaReceives a much smaller amount of

power...But delivers a better signal due to the

cleanliness of ‘bits’ !

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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.

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Latitude and LongitudeLatitude and Longitude

Binghamton... Is at 70 Degrees E Longitude and 42

Degrees N LatitudeEast of Grenich, and North of the

EquatorThe calculations for finding a satellite

22,300 miles over the equator are complex

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Longitudes for US ViewLongitudes for US View

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A recent copy of ORBITA recent copy of ORBIT

Shows us the longitude of the various satellites.

They are spaced 3 to 6 degrees apartTheir longitude, entered into an

equation gives us Elevation and Azimuth.

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The Satellite RECEIVERThe Satellite RECEIVER

The signal is collected by the ‘dish’Focused on the ‘Feed Horn’ AssemblyAmplified by a Low Noise AmplifierConverted to a much lower frequencyCarried by shielded cable to the

receiverAnd delivered to your TV set..

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Satellite Feed Horn AssemblySatellite Feed Horn Assembly

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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

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SatellitesSatellites

Are also used for ‘Pager Service’Cellular TelephoneOther types of communication including

the monitoring of vehicles like Federal Express

Global Positioning ( GPS)

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Satellite in low Earth OrbitSatellite in low Earth Orbit

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For more .. Go to the web ..For more .. Go to the web ..