An Introduction
People of this generation may not be aware of this thing called FM radio, where people listen to the newest pop songs over blur and static. Before FM radio it was AM radio, which has the worst sound quality ever. Both FM and Am are still with us till today. But they are used to send high-speed digital data over high-frequency carrier waves. Amplitude modulation is used in technologies like WiFi, while other radio technologies still use digital frequency modulation.
Amplitude Modulation
Back in the 1870s, the concept of broadcasting any audio production through radio waves was discovered, and that is when the AM method was also introduced. To explain the Amplitude modulation definition, it can be mentioned that, in this modulation technique, depending on the information signal, the amplitude of a carrier varies. Radio broadcast signals under AM use lower carrier frequencies, and thus they can travel long distances, and that is larger than FM.
Amplitude modulation is the process in which the wave signals are transmitted by modulating the amplitude of the signal. The amplitude modulation is often called AM. This technique was established by Landell de Moura and Reginald Fessenden in the 20th century when conducting radiotelephone experiments. It is used to transfer information through a radio wave. It is mostly used in electronic communications like portable two-way radios, citizens band radio, VHF aircraft radio, etc.
Y(t) = A sin (ωct) + A M2sin((ωc + ωm) t + φ) + A M2sin((ωc − ωm) t − φ)
Where,
C is the carrier amplitude
φ is the phase signal of the initial reference time
M is the carrier amplitude
Modulation Index (µ) = Ac / Am
Ac is the amplitude of carrier wave
Am is the amplitude of modulating signal
Types of Amplitude Modulation
Three types of amplitude modulation can be found -
Single Sideband (SSB) Modulation
In the case of SSB modulation, between an upper sideband and lower sideband, the amplitude-modulated wave contains either one of two.
Double Sideband-suppressed Carrier Modulation
In the case of DSB-SC modulation, bandwidth remains constant even though the transmitted wave contains only upper and lower sidebands.
Vestigial Sideband (VSB) Modulation
In the case of VSB modulation, the vestige which is a part of the signal is only modulated, including one sideband.
Frequency Modulation
Frequency modulation is the process of encoding information on a particular analogue or digital signal by varying the carrier wave frequency in accordance with the frequency of the modulating signal. The Frequency Modulation is often called FM. As we know, a modulating signal is the transmitting of information or message after being converted into an electronic signal.
m (t) = A m cos (ωmt + Ɵ)
Where,
m(t) is the modulating signal
Am is the amplitude modulating signal
ωm is the angular frequency
Ɵ is the phase of the modulating signal
Difference between Amplitude Modulation and Frequency Modulation
Frequency Modulation is the advanced method of transmitting information when compared to Amplitude Modulation in various aspects. Here are some of the differences between Frequency Modulation and Amplitude Modulation.
Pros and Cons of Amplitude Modulation
The advantages of AM include its affordability, ease in detecting using simple equipment even in a weak signal. Also, AM has a narrow bandwidth and broader coverage as compared to frequency modulation. Some of the disadvantages include signal getting affected by electrical storms, or any radiofrequency or noise interferences, low signal quality, and also the applications being restricted to one-sided communication.
Pros and Cons of Frequency Modulation
A significant advantage found in FM is that it possesses better sound quality since an FM wave remains constant, unlike AM. Therefore, encoders can remove the received noise, and better sound quality can be achieved. Also, frequency modulation can be used for low power transmitters, and power consumption also remains limited. On the other hand, some disadvantages can also be found in FM, such as the frequency modulated continuous wave cannot be broadcasted over a longer distance since the signal is more local. Also, another requirement for FM is a complicated receiver and transmitter, and the cost becomes automatically high because of that.
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FAQs on Frequency Modulation Vs. Amplitude Modulation
1. What is the fundamental difference between Amplitude Modulation (AM) and Frequency Modulation (FM)?
The core difference lies in which property of the carrier wave is altered to encode information. In Amplitude Modulation (AM), the amplitude (signal strength) of the carrier wave is varied in proportion to the message signal, while its frequency and phase remain constant. In contrast, in Frequency Modulation (FM), the frequency of the carrier wave is varied, while its amplitude and phase are kept constant.
2. In simple terms, what is Amplitude Modulation (AM)?
Amplitude Modulation is a technique where an information signal, like an audio wave, is superimposed onto a high-frequency carrier wave. The amplitude of this carrier wave is made to change in sync with the amplitude of the information signal. You can think of it as making the carrier wave 'louder' or 'quieter' to match the pattern of the original sound. This modulated signal can then be transmitted over long distances.
3. How is Frequency Modulation (FM) different from AM in its process?
In Frequency Modulation, instead of altering the carrier wave's strength, its frequency is altered. The frequency of the carrier wave increases or decreases based on the amplitude of the input message signal. The original amplitude of the carrier wave is kept constant throughout this process. This method makes the FM signal significantly less prone to noise, which often manifests as unwanted changes in signal amplitude.
4. Where are AM and FM used in everyday technology?
Both modulation techniques are vital in modern communication. Their distinct properties make them suitable for different applications:
- AM Applications: AM is traditionally used for long-wave and medium-wave radio broadcasting because its signals can travel farther, especially by following the Earth's curvature. It is also found in VHF aircraft radio and citizens band (CB) radio.
- FM Applications: FM is famous for high-quality, static-free music broadcasting on FM radio. Due to its superior noise immunity, it is also used in two-way radio systems, mobile communication, telemetry, and for high-fidelity sound synthesis.
5. Why does FM radio generally have better sound quality than AM radio?
FM's superior sound quality is due to its immunity to noise. Most natural and man-made electrical noise (from thunderstorms, motors, etc.) creates interference by adding unwanted amplitude variations to a signal. In an AM signal, where information is stored in the amplitude, this noise directly distorts the original audio. Since an FM signal's information is encoded in frequency changes and its amplitude is constant, an FM receiver can simply ignore these amplitude-based noise spikes, resulting in a much clearer sound.
6. Why are FM transmitters and receivers generally more complex and expensive than AM ones?
The circuitry required for Frequency Modulation is inherently more complex. Accurately varying a signal's frequency in proportion to an input signal (using components like a voltage-controlled oscillator) and then precisely demodulating it at the receiver end requires more sophisticated electronics than the relatively simple circuits needed for AM. This increased complexity in both the transmitter and receiver leads to higher manufacturing costs for FM equipment.
7. How does the modulation method in AM make it more susceptible to noise than FM?
AM's vulnerability lies in its core principle. Since information in AM is encoded in the amplitude of the carrier wave, any external interference that changes this amplitude is interpreted by the receiver as part of the original signal. In contrast, FM encodes information in frequency shifts. An FM receiver is designed to track only these frequency changes and disregard amplitude variations, making it highly resilient to the most common types of electrical noise.
8. What does the modulation index signify in AM and FM, and why is it different for both?
The modulation index is a critical parameter that measures the extent of modulation. Its meaning and limits differ significantly between AM and FM:
- In AM, the modulation index (μ) is the ratio of the modulating signal's amplitude to the carrier wave's amplitude. Its value must be kept between 0 and 1 to prevent a type of distortion called over-modulation.
- In FM, the modulation index (β) is the ratio of the frequency deviation to the modulating frequency. It can be, and often is, greater than 1. A higher index in FM means a wider bandwidth is used, which results in better noise immunity and overall signal quality.
