Transcript Satellite Television - SUNY Broome Community College

Satellite Television
It’s out of sight!
22,300 miles in fact!
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From How Stuff Works
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20 + Commercial Satellites
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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 geostationary.
They have a useful life of 10 years.
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Boeing 702
the most
widely
used
satellite
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Hughes HS601
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Forces at work
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A satellite spins around the planet
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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 ..
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Geo-stationary Orbits
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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...
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The Clarke Belt
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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
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Elevation and Azimuth
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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 Satellite
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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..
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C Band and Ku Band
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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 Digital
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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 Watts
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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...
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The signals are very very
weak.
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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...
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Has a much smaller surface area
Receives a much smaller amount of
power...
But delivers a better signal due to the
cleanliness of ‘bits’ !
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Satellite ‘Sighting’
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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 Longitude
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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
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Longitudes for US View
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A recent copy of ORBIT
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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.
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The Satellite RECEIVER
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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..
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Satellite Feed Horn Assembly
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The ‘Polarotor’
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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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Satellites
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Are also used for ‘Pager Service’
Cellular Telephone
Other types of communication including
the monitoring of vehicles like Federal
Express
Global Positioning ( GPS)
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Satellite in low Earth Orbit
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For more .. Go to the web ..
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