P5e radio communication By the end of this lesson you should be able to: Describe how the amount of diffraction depends upon the size of the gap and the wavelength of the wave. State that maximum diffraction occurs when the wavelength equals the size of the gap. Describe that radio waves are readily diffracted so are more suitable for broadcasting. Describe that long wave radio waves have a very long range because they diffract around hills and over the horizon. Explain how long wavelength radio waves are diffracted around hills and over the horizon. Describe that longwave radio waves carry signals by amplitude modulation (AM).

information can be transmitted using microwaves to orbiting artificial satellites and then retransmitted back to Earth Why microwaves Microwaves have a frequency of 300MHz to 30 GHz (1cm to 100 cm) Microwaves only diffract by a small amount due to their short wavelength they can be sent as a thin beam Waves of frequency less than 30MHz (wavelength> 10 m) are reflected by the ionosphere For waves with a frequency above 30GHz (wavelength<1cm), rain, dust and other atmospheric effects reduce the strength of the signal due to absorption and scattering; Using microwaves for satellite communication

Waves diffract when they pass an obstacle or go through a gap Longer waves diffract more than short ones. Waves diffract more when they pass through a smaller gap. Maximum diffraction occurs when the gap is the same size as the wavelength

Microwaves do not diffract around hills Greater diffraction occurs when long wavelength radio waves pass between hills radio waves are readily diffracted so are more suitable for broadcasting because they have a long wavelength long wave radio waves have a very long range because they diffract around hills and over the horizon.

longwave radio waves carry signals by amplitude modulation (AM). The amplitude of the sound wave is added to the carrier wave and resulting modulated wave is transmitted. The carrier wave is removed by the radio receiver. The carrier wave frequency is the radio station’s frequency e.g. Radio 4 200kHz