COMMUNICATIONS

COMMUNICATIONS

1. Radio communications

   • 1.Radiowaves are emitted from an aerial when an alternating voltage is applied.
     • The frequency of the alternating voltage is the same as the frequency from the aerial
   • 2. Then, when the radio waves pass across a receiver aerial, they cause a tiny alternating voltage in the aerial
     • This is the same frequency of the radio waves the aerial receives.
   • 3. The alternating voltage from the aerial is used to make the loudspeaker send out sound waves
   • The radio and microwave spectrum is divided into bands of different wavelength ranges
     • This is because when the wavelength of the waves is shorter...
       • They carry more information
       • They have a short range (absorbed by atmosphere)
       • They spread out less (diffract less)

2. Radio wavelengths

   • Microwaves
     • Satellite phone
     • TV links
     • Satellite TV broadcasting
     • Can travel between satellites in space and on ground
     • Spread out less than radio waves so signal doesn't weaken too much.
   • Radio waves with wavelengths less than 1 metre
     • TV broadcasting from TV masts
     • Carry more information than waves with longer wavelengths
   • Radio waves with wavelengths of 1m to 100m
     • Used by local radio stations and emergency services
     • Their range is limited to the area round the transmitter
   • Radio waves of wavelengths greater than 100m
     • Used by national and international radio stations
     • Longer range than shorter wavelength radio waves

3. Optical fibre communications

   • Optical fibres are thin glass fibres
   • Used to transmit signals carried by light or infrared radiation
   • Light rays can't escape fibre as when they reach surface they are reflected back in.
   • Optical fibres carry more information than radio or microwaves
   • Optical fibres are more secure because signals stay within fibre