Wireless signals

Question 1

What uses wireless technology.

Answer 1

• Radio and television
• Laptops
• Mobile phones.

Question 2

What happens to radio waves in the atmosphere?

Answer 2

• Radio waves are reflected and refracted in the Earth’s atmosphere.
• The amount of refraction depends on the frequency of the wave
• There is less refraction at higher frequencies.

Question 3

Radio stations broadcast…

Answer 3

Signals with a particular frequency.

Question 4

The same frequency can be used by more than one radio station:

Answer 4

• The radio stations are too far away from each other to interfere
• But in unusual weather conditions, the radio waves can travel further and the broadcasts interfere.
• Interference is reduced if digital signals are used.

Question 5

DAB

Answer 5

Digital Audio Broadcasting

Question 6

What does DAB do?

Answer 6

• DAB provides a greater choice of radio stations but the audio quality is not as good as the FM signals currently used.
• DAB also eliminates interference between other radio stations.

Question 7

What happens to radio waves when they reach the ionosphere?

Answer 7

Radio waves are reflected from the ionosphere. They behave like light in an optical fibre and undergo total internal reflection.

Question 8

What else reflects radio waves?

Answer 8

• Water reflects radio waves but land mass does not.
• Continued reflection by the ionosphere and the oceans allows radio waves to be received from an aerial that is not in line of sight.

Question 9

What happens to microwave radiation when it reaches the ionosphere?

Answer 9

• Microwaves pass through the ionosphere.
• Microwave signals are received by orbiting satellites, amplified and retransmitted back to Earth.

Question 10

Orbit of a communication satellite.

Answer 10

24 hours.

Question 11

Communication problems

Answer 11

• Radio waves are diffracted when they meet an obstruction.
• Refraction in the atmosphere needs to be taken into account when sending a signal to a satellite.
• The transmitting aerial needs to send a focused beam to the satellite because its aerial is very small.
• The transmitted beam is slightly divergent.
• Some energy is lost from the edge of the transmitting aerial because of diffraction.