Satellite communication

Question 1

How are microwave signals sent?

Answer 1

• 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.

Question 2

Why are digital signals used for satellite communication?

Answer 2

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

Question 3

What does mega mean?

Answer 3

Million 10⁶

Question 4

What does giga mean?

Answer 4

Thousand million 10⁹

Question 5

What happens to different waves of frequency?

Answer 5

• 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.

Question 6

Geostationary orbit

Answer 6

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

Question 7

Microwaves and communication

Answer 7

• 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.

Question 8

Why are aerial dishes large?

Answer 8

• 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.

Question 9

Where is the ionosphere?

Answer 9

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

Question 10

Radiowaves and the Ionosphere

Answer 10

• 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.

Question 11

Diffraction

Answer 11

• 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.

Question 12

Radio waves and diffraction

Answer 12

• 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.

Question 13

Why don’t TV signals diffract?

Answer 13

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