Terminology » Modulation » AM vs FM vs PM: Modulation Techniques Compared

AM vs FM vs PM: Modulation Techniques Compared

amplitude modulation frequency modulation phase modulation analog modulation radio broadcasting

This page compares Amplitude Modulation (AM), Frequency Modulation (FM), and Phase Modulation (PM). All these modulation types are analog modulation techniques used to transmit information from one place to another, often employed in wireless communication.

For any analog modulator, there are two inputs and one output:

  • Modulating signal: The analog information to be transmitted.
  • Carrier signal: The waveform used to carry the information.
  • Modulated waveform: The output signal.

Amplitude Modulation (AM)

amplitude modulation

Amplitude Modulation (AM) is a modulation technique where the carrier amplitude varies based on the analog baseband information signal to be transmitted. A common application is radio broadcasting. AM broadcast signals propagate mainly by ground waves during the day and by sky waves at night.

Advantages, Disadvantages, and Applications of AM

Different amplitude modulation techniques have their own pros and cons:

  • DSB-SC (Double-Sideband Suppressed-Carrier):

    • Advantages: Lower power consumption and simple modulation.
    • Disadvantages: Complex detection at the AM receiver.
    • Applications: Analog TV transmission systems for color information.

  • SSB-SC (Single-Sideband Suppressed-Carrier):

    • Advantages: Efficient spectrum management.
    • Disadvantages: Difficult SSB modulation generation and complex receiver detection.
    • Applications: Two-way radio FDM (Frequency Division Multiplexing).

  • VSB-SC (Vestigial Sideband Suppressed-Carrier):

    • Advantages: Compromise between DSB and SSB.
    • Disadvantages: Complex demodulation system. Bandwidth is 25% higher than SSB-SC.
    • Applications: Analog TV broadcast systems.

Frequency Modulation (FM)

frequency modulation

Frequency Modulation (FM) is a modulation technique where the carrier frequency varies based on the analog baseband information signal to be transmitted.

FM is generally considered superior to AM due to its better noise immunity and ability to reject interfering signals thanks to the capture effect.

Advantages, Disadvantages, and Applications of FM

  • Advantages: Increased immunity to noise.
  • Disadvantages: Requires larger bandwidth.
  • Applications: Radio broadcasting, direct satellite broadcasting.

Phase Modulation (PM)

phase modulation

Phase Modulation (PM) is a modulation technique where the carrier phase varies based on the analog baseband information signal to be transmitted.

When a constant amplitude and frequency sine wave carrier is given to a phase shifter, the output is a phase-modulated signal. Phase modulation is also known as indirect frequency modulation because it produces frequency modulation. The change in phase shift is proportional to the change in the carrier frequency.

Advantages, Disadvantages, and Applications of PM

  • Advantages: Increased immunity to noise.
  • Disadvantages: More complex hardware at the receiver.
  • Applications: Data communication systems.

Comparison Table: AM vs FM vs PM

FeatureAMFMPM
FunctionAmplitude of carrier wave varies as per the amplitude/voltage of the modulating signal input.Frequency of carrier wave varies as per the voltage of the modulating signal input.Phase of carrier wave varies as per the voltage of the modulating signal input.
Carrier ParameterFrequency of the carrier wave is kept constant.Amplitude of the carrier wave is kept constant.Amplitude of the carrier wave is kept constant.
TypesAM types include DSB-SC, SSB, VSB, etc. Refer DSB-SC vs SSB-SC and SSB vs VSB modulation.Digital FM types include FSK, GFSK, Offset FSK, etc. Refer MSK and GMSK modulation.Digital PM types include BPSK, QPSK, QAM (combination of amplitude and phase modulation types).