P1g: Wireless Signals

P1g: Wireless Signals

1. Radio Refraction and Interference

   • 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
   • Radio stations broadcast signals with a particular frequency
   • The same frequency can be used by more than one radio station: ––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.
   • Wireless technology is used by: ––radio and television ––laptops
   • Digital Audio Broadcasting or DAB also provides a greater choice of radio stations but the audio quality is not as good as the FM signals currently used.
   • DAB eliminates interference between other radio stations

2. Radio Reflection

   • Radio waves are reflected from the ionosphere. They behave like light in an optical fibre and undergo total internal reflection.
   • Microwaves pass through the ionosphere.
   • Communication satellites orbit above the equator and take 24 hours to orbit Earth
   • 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.
   • Microwave signals are received by orbiting satellites, amplified and retransmitted back to Earth.

3. Communication Problems

   • 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
   • 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.