i) Frequency Modulation


  • Frequency Modulation where the modulating signal causes changes to the frequency of the carrier signal.



  • This gives a more complex spectrum than AM and as a result occupies more bandwidth.


ii) Amplitude Modulation


  • Amplitude Modulation where the modulator causes the envelope of the carrier frequency to follow the waveform of the modulating signal.



  • The demodulator recovers this modulating signal from the envelope.


iii) Pulse Amplitude Modulation


  • Carriers are modulated with a train of pulses where a train of direct current digital signals is converted into a train of carrier frequency samples.



  • These samples are applied to an Analogue-to-Digital Converter (ADC) resulting in a series of on-off pulses.