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.
2
Q
Why are digital signals used for satellite communication?
A
- They do not attenuate as quickly.
- There is less noise.
3
Q
What does mega mean?
A
Million 106
4
Q
What does giga mean?
A
Thousand million 109
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.
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.
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.
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.
9
Q
Where is the ionosphere?
A
The ionosphere is a region between 100 km and 500 km above the Earth’s surface.
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.
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.
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.
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.