What is Demodulation ?

The modulation is the technique by which data is converted into electrical or digital signals for transferring that signal over a medium. Signal modulation is done to carry the signal over large distances. After the signal transmission, the modulated signal must be converted back into the original signal to retrieve the original information. This back-conversion is done with the help of various demodulation techniques. Hence, it means the separation of the signal from the modulated carrier. In this article, we will study these techniques in detail, their applications, advantages and disadvantages, etc.

Demodulation

To understand the concept of Demodulation, we need to study the Modulation first. Modulation is the process where properties of the carrier signal like amplitude, frequency, or phase change according to the baseband or message signal. It is the reverse process of the modulation to recover the signal from modulated signal and hence obtain the original signal, so the need of the demodulation is to get the original information or signal from the modulated one.

Demodulation

Demodulation is the technique to recover the original signal from the modulated signal. The demodulation is done with the help of a demodulator. A demodulator will convert the carrier variation of amplitude, frequency, or phase back to the message signal. There are three different types of demodulators for converting the AM (amplitude modulation), FM (frequency modulation), and PM (phase modulation) modulation schemes.

Demodulation Techniques

There are various demodulation techniques depending on the type of modulation. Some of the technique are listed below:

• Diode rectifier envelope detector
• Product detector
• Synchronous detection

Diode Rectifier Envelope Detector

It is used to demodulated the amplitude modulated signal. The simple diode detector circuit is given below. It is the simplest form of detector because it comprises of a single diode and a capacitor. Since it does not meet the standard of the other techniques related to it but this is the most basic type of the detector and detects the envelope of the AM signal.

Simple Diode Detector Circuit

The working the circuit is as follows:

• The signals from the previous stages is applied to the diode. The capacitor helps in removing the unwanted radio frequency (RF) elements.
• When the radio signal is applied to the diode, only half the waveform passes through it and half of the waveform is removed. This is due to the property of diode i.e., current can flow only in one direction through the diode.
• The resulting signal is applied to the audio output which is seen in the above diagram. This resulting signal is the demodulated signal.

Diode rectifier envelope detector is a very simple circuit. Due to its simplicity, it is very low cost. But it also has some disadvantages like it is not linear due to the diode characteristic which leads to the distortion in the signal. It is less sensitive and its performance is affected by the selective fading.

Product Detector

The product detector circuit is used to demodulate the SSB (single side band) signal. In SSB amplitude modulation, the first carrier signal is suppressed, and then either the upper-side band or lower-side band is suppressed. The circuit diagram of the product detector is given below.

Product Detector

The working the circuit is as follows:

• The SSB signal is passed from the IF transformer. It uses a crystal oscillator which produces the local oscillator signal. The generated local oscillator signal has a frequency similar to the carrier signal.
• The SSB signal is then multiplied by the local oscillator signal. This leads to the creation of different frequencies i.e., sum and difference of the frequencies.
• The resulting signal is then passed to the low-pass filter. It will pass only the low frequency signal which is the baseband signal. Hence, in this way, we extract the original signal.

This technique is used in the various communication application during demodulation. Also, this circuit can be used to intercept Morse Code signal.

Synchronous Detection

It is also known as coherent detection and is used to demodulate the amplitude-modulated signal. It also comprises the oscillator which generates the local oscillator signal. It is then multiplied with the incoming modulated signal. The resulting signal is then passed through the low-pass filter to remove the high-frequency components. The block diagram for the Synchronous Detector is given below.

Synchronous Detection

The filtered signal contains the original baseband signal. The received signal is then decoded to extract the original information. It helps in providing better performance. It is used in various applications of broadcast receivers like radio communication equipment or walkie-talkies because it is easy to incorporate.

Challenges and Need for Demodulation

Some challenges and need for the demodulation technique is discussed below:

Challenges

There are two main challenges while performing demodulation. The challenges are:

• Synchronization: It is very typical to maintain the synchronization between the incoming modulated signal and the demodulator. To overcome this challenge carrier synchronization is used.
• Noise and interference: While recovering the original signal, it might be distorted due to the noise and interference in the channel. To overcome this problem, error correction methods are used.

Need for Demodulation

Demodulation is the process of recovering the original signal from the modulated signal. The modulation of the signal is done to transmit the signal over long distances by decreasing the bandwidth requirements. It also helps in multiplexing which means that multiple signals can be transmitted over a single channel resulting in the efficient use of the spectrum. The modulation is done with the help of radio frequency which is outside the audible range of the human ear. To retrieve the original information and make it in the audible range for humans, the demodulation process is required.

Difference between Modulation and Demodulation

Modulation	Demodulation
It is the process where properties of the carrier signal like amplitude, frequency, or phase change according to the baseband or message signal.	Demodulation is the technique to recover the original signal from the modulated signal
Modulation of the signal is done at the transmitter side.	Demodulation of the signal is done at the receiver side.
It is performed to transmit the signal over the long distance.	It is performed to extract the original information from the modulated signal.
It is a simple process as compared to demodulation.	It is a complex process.
It converts low-frequency signals into high-frequency signals.	It converts high-frequency signal into low-frequency signal.
To perform modulation, modulator (electronic circuit) is required.	To perform demodulation, demodulator or detector (electronic circuit) is required.
It is the mixing of two signals of different parameters.	It is the process of recovery of original signal from the mixed signal.

Advantages and Disadvantages of Demodulation

There are some list of Advantages and Disadvantages of Demodulation given below :

Advantages

• It helps in the efficient use of the bandwidth by allowing multiple signals to pass through a single channel.

• It helps in the recovery of the original signal which is essential to retrieve the original information from the signal.

• It improves the noise immunity which helps in improving the reliability of the signal.

• It can demodulate the AM, FM, and PM signals. This helps in improving the diversification of demodulation and can be used in a wide range of applications.

Disadvantages

• Some of the demodulation techniques, like coherent demodulation, are a very complex process. Due to the complexity of the process, the cost of the system increases.

• It is sensitive to channel conditions like attenuation, and distortion. It can lead to poor quality of the obtained signal.

• Power consumption is high in some of the demodulation techniques like digital demodulation.

• When the frequency spectra are crowded, it might lead to crosstalk and interference.

Applications of Demodulation

• Radar System: The demodulation technique is used in the radar system to extract information about range, velocity, angle, and many more. It helps in navigation, weather monitoring, and defense.
• Television: The demodulation technique is used to recover the video and audio signals which helps in proper displaying of the television programs.
• Radio broadcasting: Demodulation is used to extract the audio signals which is to be broadcast. It can retrieve AM and FM signals to broadcast over a wide range of frequency spectra.
• Underwater communication: For underwater communication, acoustic signals are used. These acoustic signals needed to be demodulated, to receive the original information coming from the deep sea.
• Medical: The demodulation technique is used to generate the image of internal organs. It is widely used in MRI and ultrasound.

Conclusion

In the above article, we have studied the demodulation process. There are various techniques involved during the demodulation. There are various demodulation systems for demodulating AM, FM, and PM signals. We have studied the workings of the various systems. The article also covers the application, need, advantages, and disadvantages of the demodulation technique. This perform the vital performance by converting the signal and extracting the original signal from that and that too by enabling the transmission of information from various platforms or devices .

FAQs on Demodulation

In wireless technologies like Bluetooth, how does demodulation work?

Demodulation is used to extract the original information that is being transmitted between the two devices. It helps in connecting the device wirelessly and transferring the information.

What happens when demodulation is not properly performed?

When demodulation is not properly performed, it can lead to distorted audio, and video signals, loss of original information, and loss of data integrity.

Can we see demodulation happening?

You cannot directly see the demodulation but you can find many practical applications where demodulation is helping in retrieving the original signal. For example: Connection to Wi-Fi, television channel broadcasting, and many more.