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.