Satellite communication Flashcards

1
Q

How are microwave signals sent?

A
  • Microwave signals are sent into space from a parabolic transmitter.
  • The signals are received, amplified and re-transmitted back to the Earth by a geostationary satellite
  • The signals are picked up by a parabolic receiver.
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2
Q

Why are digital signals used for satellite communication?

A
  • They do not attenuate as quickly.
  • There is less noise.
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3
Q

What does mega mean?

A

Million 106

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4
Q

What does giga mean?

A

Thousand million 109

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5
Q

What happens to different waves of frequency?

A
  • The ionosphere reflects radio waves with frequencies below 30 mHz
  • Frequencies above 30 GHz are absorbed and scattered. This reduces signal strength.
  • The frequencies used for satellite communication are between 3 GHz and 30 GHz.
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6
Q

Geostationary orbit

A
  • Geostationary satellites orbit Earth about 36,000 km above the equator.
  • All geostationary satellites are in the same orbit which is very crowded.
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7
Q

Microwaves and communication

A
  • Microwaves pass through the Earth’s atmosphere and because they have a very small wavelength, they do not spread out very much.
  • The narrow microwave beams are able to target one satellite without interfering with another.
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8
Q

Why are aerial dishes large?

A
  • The size of the aerial dish is many times the microwave lwavelength so there is very little diffraction. It produces a narrow beam that does not spread out.
  • This means the receiving this and satellite need extra alignment to ensure that the signals do not ‘miss’ the geostationary satellite.
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9
Q

Where is the ionosphere?

A

The ionosphere is a region between 100 km and 500 km above the Earth’s surface.

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10
Q

Radiowaves and the Ionosphere

A
  • Radio waves undergo a series of refractions and speed up as they enter different layers. Eventually, the waves are totally internally reflected.
  • Radio waves also reflect off the Earth’s surface. It means they can travel around the world.
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11
Q

Diffraction

A
  • The smaller the size of a gap, the greater the diffraction.
  • Maximum diffraction occurs when the wavelength is equal to the size of the gap.
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12
Q

Radio waves and diffraction

A
  • Long and medium wave radio waves diffract around buildings, hills and follow the curvature of the Earth.
  • Radio waves have long wavelengths compared to the distance between hills so diffract easily.
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13
Q

Why don’t TV signals diffract?

A

TV signals have much shorter wavelengths so do not show much diffraction. Television aerials must be in the line of sight with the transmitter.

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