AM vs FM: Advantages and Disadvantages of Modulation Techniques

This page covers the advantages and disadvantages of AM and FM modulation techniques.

AM stands for Amplitude Modulation, and FM stands for Frequency Modulation.

AM is a modulation technique where the amplitude of the RF carrier signal is varied in accordance with the amplitude of the modulating input signal.

FM is a modulation technique where the frequency of the RF carrier signal is varied in accordance with the frequency of the modulating input signal.

Both AM and FM are used as analog modulation techniques.

Figure 2 depicts AM propagation and FM propagation. As shown, AM propagation happens due to reflection from the ionospheric layer. FM propagation relies on a Line of Sight communication path.

Advantages of AM (Amplitude Modulation)

The following are the advantages of AM:

• AM signals are reflected back to earth from the ionosphere layer. Due to this, AM signals can reach far places, thousands of miles from the source. Hence, AM radio has wider coverage compared to FM radio.

Disadvantages of AM

The following are the disadvantages of AM:

• The most natural as well as man-made radio noise is of the AM type. AM receivers do not have any means to reject this kind of noise.
• Weak AM signals have low magnitude compared to strong signals. This requires an AM receiver to have circuitry to compensate for the signal level difference.

Advantages of FM (Frequency Modulation)

The following are the advantages of FM:

• In FM, the recovered voice depends on frequency and not amplitude. Hence, the effects of noise are minimized.
• FM bandwidth covers the entire frequency range humans can hear. Hence, FM radio has better sound quality compared to AM radio.

Disadvantages of FM

The following are the disadvantages of FM:

• At higher frequencies, FM modulated signals pass through the ionosphere and do not get reflected. Hence, FM has lesser coverage compared to AM signals.