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Difference between Frequency Modulation and Amplitude Modulation

Difference between Frequency Modulation and Amplitude Modulation

Did we ever think about how we transfer the data? How does data transferring take place? Well, we can transfer data through electromagnetic waves. Physicists choose a certain frequency and wavelength of the electromagnetic waves to transfer data to a longer distance without weakening the main data signal. However, there will be some weakening in the signals due to noise present in our surroundings.

To transfer electromagnetic waves, we use frequency modulation and amplitude modulation techniques. In frequency modulation, the wave's amplitude remains constant, and the transfer of wave occurs through altering the frequencies of the electromagnetic waves. Contrastingly, in amplitude modulation, the frequency of the electromagnetic wave is kept constant, and the amplitude is altered to meet the signal strength. Both frequency and amplitude modulation are used to broadcast and encode radio signals.

Frequency modulation (FM)

In frequency modulation, the waves that transfer information, usually known as carrier waves, are modified according to the signal. The frequency modulation technique was invented in 1930. At that time, frequency modulation was considered an advancement in transmitting information through radio waves of the electromagnetic spectrum.

It must be noted that the bandwidth of the frequency modulation radio signals is larger than the amplitude modulation radio signals. Because of this reason, the sound quality of FM signals is better than other modulation techniques.

Frequency modulation formula

Frequency modulation is given by:

m (t) = Am cos (ωm t + Ɵ)
Here, m (t) stands for modulating signal
Am is the amplitude of the modulating signal
ωm is the angular frequency of the modulating signal
Ɵ is the phase of the modulating signal

Advantages of frequency modulation

1) It is more power-efficient than amplitude modulation systems.
2) Noise can be easily removed in frequency-modulated waves.
3) The amplitude in frequency-modulated waves is constant over time.
4) There is little or no interference between adjacent FM signals. Due to this, the transmitted power increases.

Amplitude modulation (AM)

Amplitude modulation was invented in the late 19th century. It was during this time, the concept of broadcasting audio signals was discovered. At the same time, amplitude modulation was also invented. In AM, the amplitude of the carrier wave varies according to the signal strength.

If we need a high strength signal, the amplitude will be increased more than the optimized level. On the other hand, if we need low signal strength, the signal amplitude will be made optimum. This is because the bandwidth of amplitude-modulated waves is lesser than frequency-modulated waves.

Under AM, radio signals use low carrier frequencies. This way, they can travel a farther distance than FM waves. The sound quality in AM is compromised. Therefore, only data information is sent via AM waves.

Types of amplitude modulation

  • Single Sideband Modulation (SSB) – In this, the amplitude-modulated wave consists of either an upper sideband or a lower sideband.
  • Double Sideband-suppressed Carrier Modulation (DSB-SC) – It also contains either an upper sideband or a lower sideband. However, the bandwidth remains constant throughout the transmitted wave.
  • Vestigial Sideband (VSB) Modulation – In this, a part of the signal, known as a vestige, is only modulated, including a single sideband.

Amplitude modulation formula

Amplitude modulation is given by:

Y (t) = A . sin (ωc t)+ A M2 sin ((ωc + ωm) t + φ) sin ((ωc + ωm) t + φ) + A M2 sin ((ωc − ωm) t − φ) sin((ωc − ωm) t − φ)

Here, c is the carrier amplitude
φ is a phase of the signal at the beginning of the reference time
M is carrier amplitude
Modulation Index (µ) = Ac / Am
Ac = amplitude of carrier wave
Am = Amplitude of modulating signal

Advantages of amplitude modulation

1) It is economical and can be obtained easily.
2) Amplitude modulation can be implemented without much difficulty.
3) It can easily be demodulated with lesser components only by using a circuit.
4) The materials used in amplitude modulation are cheap and easy to process.

Difference between AM and FM

Amplitude modulation 

Frequency modulation 

In amplitude modulation, the frequency wave is kept constant and the amplitude carrier wave is modified. 

In frequency modulation, the amplitude carrier wave is kept constant and the frequency carrier wave is modified. 

The range of AM is between 500 to 1800 kiloHertz. 

The range of FM is 80 to 120 megaHertz. 

It consists of two sidebands. 

It consists of infinite sidebands. 

The modulation index can vary between 0 and 1.

The modulation index is always greater than 1. 

It delivers low sound quality. 

It delivers good sound quality. 

The circuits are simple and cheap. 

The circuits are complex and can be expensive. 

Power consumption is an issue. 

No issues in power consumption. 

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