Amplitude Modulation: Types, Need, Wave, Advantages and Disadvantages
Table of Contents
Amplitude modulation involves modifying the wave signal’s amplitude before it is transmitted. As a result, it is frequently used to transmit data over a radio carrier wave and is referred to as AM. Amplitude modulation is most frequently used in electronic communication. So many different communication channels, such as computer modems, VHF aircraft radios, citizens band radios, and portable two-way radios, currently use this technique. Amplitude modulation is another name for mediumwave AM radio broadcasting.
What Is Amplitude Modulation?
One of the earliest modulation techniques used for radio communication is amplitude modulation, or simply AM. This approach was develope in the 20th century, when Landell de Moura and Reginald Fessenden were testing radiotelephones in the 1900s. The modulation technique was develope and put to use in electronic communication after several attempts that were successful. A type of modulation called amplitude modulation is one in which the carrier wave’s amplitude changes in relation to the data or signal being modulated in some way.
A variation in the carrier’s amplitude occurs when amplitude modulation is use, which is the mechanism. The carrier’s amplitude is altered in this case by the voltage or power level of the information signal. The carrier’s amplitude doesn’t change in AM. However, the modulating information is present as signal elements with frequencies that are either higher or lower than the carrier frequency. Sideband power, one of the signal’s constituents, is what causes the signal’s overall amplitude to vary. Sidebands are known as signal components. The frequency modulation (FM) and phase modulation (PM) techniques, in which the carrier signal’s frequency or phase is change, respectively, are completely different from each other and the AM technique.
Types of Amplitude Modulation
There are three main types of amplitude modulation. They are
- Double Sideband-suppressed Carrier Modulation (DSB-SC)
- Single Sideband Modulation (SSB)
- Vestigial Sideband Modulation (VSB)
Designations by ITU
In 1982, the International Telecommunication Union (ITU) classified various amplitude modulation types. These are what they are:
|Double-sideband a full-carrier
|Linked compressor and expander
Communication Systems and Modulation
We are researching communication system modulation. They function in two different ways and are used to send and receive messages (information) in the form of electronic signals from one location to another.
(i) Analog signal transmission
(ii) Digital signal transmission
So, we can represent an analogue electronic signal (information) as follows:
m(t) = Am cos (ωmt + Ɵ)
m(t) = Am sin (ωmt + Ɵ)
The analogue electronic signal can be visualized as either a sine wave or a cosine wave. There will be an amplitude and phase for every wave.
Where m(t) = Modulating signal (input signal) or baseband signal
Am = Amplitude of the modulating signal
What Is Modulation?
Essentially, it is a communication system process. There are some basic components we need for communication. The information that needs to be transmitted (the modulating signal) or input signal comes in two forms: a high-frequency carrier wave and an input signal. These are necessary for device-based communication from one location to another. All in all, the communication system is something we need. Our message (information) is transformed into an electronic signal by an electronic communication system, and the electronic signal is then sent over carrier waves to its intended location.
The superposition of modulating signal onto a carrier wave is known as modulation.
Modulation is defined as,
So adjusting any of a carrier wave’s fundamental parameters in response to the modulating signal. A sine or cosine can be used to represent a carrier wave.
C(t) = Ac sin (ωct + Ɵ)
Amplitude modulation is the process of changing the carrier wave’s amplitude in response to the input signal that is modulating it. The same can be said for phase and frequency modulation. Modulation is the process of “superimposing the modulating signal (input signal) into the carrier wave,” to put it another way.
Why Do We Need Modulation?
Practically speaking, modulation is required for
- Quality of transmission
- High range transmission
- To avoid the overlapping of signals
High Range Transmission: (Effective Length of Antenna)
For effective communication, the length of the antenna should be λ/4 times the modulating signal.
Hmin = λ/4
λ – Wavelength of the modulating signal or transmitting signal H> λ/4
For example, if I need to transmit a signal of a frequency of f = 20 kHz
As we know, c = f λ
3 × 108 = 20 × 103 (λ)
Hmin = 3750 m
Hmin = 3750 m is practically impossible;
So for that, we can transmit our modulating signal onto a carrier wave of frequency 1MHz. What we did here is we raised our transmission frequency from 20kHz to 1mHz.
Now, let us find out what the Hmin is needed for good transmission.
c = fλ
3 × 108 = 1×106 (λ)
If we increase the transmitting frequency, wavelengths
(3×108−6 ) /1=λ
will decreases so, Hmin also decreases.
3 × 102 = λ
Hmin = λ/4 = 300/4 = 75
Since this is technically feasible, modulation is required to raise the transmission frequency and send a low-frequency signal.
Avoiding the Overlapping of Signals
The same frequency is use by two different transmitting stations to transmit their signals. They will overlap or become mixed up. We must modulate these signals using various carrier waves in order to prevent this. So Amplitude modulation is a method use to adjust the high-frequency carrier wave’s amplitude in accordance with the amplitude of the modulating signal. However, the carrier wave’s frequency doesn’t change. Let’s examine the definitions of modulating signals and carrier waves now.
Carrier Wave (High Frequency)
A carrier wave’s frequency and amplitude don’t change. It is typically a high frequency electronic signal in the form of a sine or cosine wave; it can be visualized as
C(t) = Ac sin wct ……………. 1
The input signal (electronic signal), which must be transmitted, serves as the modulating signal. Additionally, it is a sine or cosine wave, and it looks like
m(t) = Am sin wmt
Ac and Am = Amplitude of the carrier wave and the modulating signal
sin wct = Phase of the carrier wave
sin wmt = Phase of the modulating signal
Bandwidth: (BW) It is the difference between the highest and lowest frequencies of the signal.
BW = Upper sideband frequency – Lower sideband frequency (fc – fm)
BW = fc + fm – fc + fm = 2 fm
BW = 2fm = Twice the frequency of the modulating signal
It is the ratio of the amplitude of the modulating signal to the amplitude of the carrier wave.
µ=Amplitude of modulating signal / Amplitude of carrier wave
Amplitude Modulated Waveform
Below is a waveform illustration of an amplitude modulated wave.
1. Carrier wave
2. Modulating signal
3. Superposition of the carrier wave and modulating signal
4. Amplitude modulated wave
Carrier wave, c(t) = Ac sin wct
Modulating single m(t) = Am sin wmt
Amplitude modulate wave (m(t) = (Ac + Am sin ωmt) sin ωct
µ=Amplitude of modulating signal / Amplitude of carrier wave
Frequencies of modulated wave → fc, fc + fm, fc – fm
Disadvantages of Amplitude Modulation
When it comes to power usage, it is not efficient.
It needs an extremely wide bandwidth, which is equal to the highest audio frequency.
Noise interference is highly noticeable.
Implementing amplitude modulation is simpler.
A circuit and a few components can be used to demonstrate.
AM receivers are very inexpensive.
Applications of Amplitude Modulation
Amplitude modulation has fewer applications today than it did in the past, but it is still use in some transmission areas. Below, we’ll take a look at them.
- Air-band Radio: Many airborne applications, such as ground-to-air radio communications or two-way radio links for ground staff personnel, use AM in VHF transmissions.
- Broadcast Transmissions: Broadcasting transmissions using AM are made using short, medium, and long wavebands. Amplitude modulation radio receivers are therefore simpler and more affordable to produce because AM is simple to demodulate.
- Quadrature Amplitude Modulation: AM is heavily utilize in the transmission of data over a variety of different mediums, including short-range wireless connections like Wi-Fi to cellular telecommunications and others.
- Single Sideband: So This type of amplitude modulation is use for point-to-point or HF radio links.AM makes better use of the transmitted power and has a smaller bandwidth.
A diode that serves as an envelope detector makes up the simplest AM demodulator. Another type of demodulator, the product detector, can provide better demodulation but requires a complicated additional circuit.