1. 6.9 How radio works
January 29, 2015
What is this image? What
other information can
you get from it?

2. Aims
• Review knowledge of AC
• State the difference between AM and FM
• Describe how a simple radio works

7. Sending sounds by radio
RF Oscillator Modulator Amplifier
Microphone
AF signal
RF carrier Modulated RF carrier

8. Sending sounds by radio
Amplifier demodulator Tuning circuit
Loudspeaker
AF signal Modulated RF carrier

9. Radio gaga
• AF signal: varying voltage
• RF oscillator creates high frequency AC, this is the
carrier
• AF signals modulate the RF waves
• RF wave is then amplified
• RF waves then generate a voltage in the aerial
• The tuning circuit decides which frequency of RF
carrier to detect
• The demodulator then removes the carrier wave
leaving on AF
• This is amplified and then converted to sound

10. AM and FM
• This is amplitude modulation or AM
• You can also use frequency modulation (FM)
• FM has less noise so this is better