An outline of dsbscssbsc modulation and demodulation. The dsbsc wave st is applied to a product modulator in which it is multiplied with the locally generated carrier cos 2. In this experiment you will design an analog modulator and an analog demodulator. Modulation is the process of influencing data information on the carrier, while demodulation is the recovery of original information at the distant end from the carrier. Answer to here is the matlab code for dsbsc modulation. The incoming dsbsc signal is multiplied by a pure sinewave that must be the same frequency as the dsbsc signals suppressed carrier. Analog communications dsbsc modulation intro youtube. The methods include the use of matlab commands from the command window and simulink. A sscsc signal is much easier to demodulate than dsbsc one. Double sideband dsb is one of the easiest modulation techniques to understand, so it is a good starting point for the study of modulation. Hey guys, in studying dsb demodulation, it is said that the demodulator has a to generate a synchronis carrier signal to multiply with the dsb using a multiplier to extract the modulating signal and when the generated carrrier signal is not synchronis, the extracted signal is distorted. Previous frequencydoubling techniques generally fall into two categories.
Double sideband suppressed carrier dsb sc demodulation. The modulated signal s dsbsc amt looks similar to st but has a temporal but not spectral carrier component. A modem is an equipment that performs both modulation and demodulation. Single sideband modulation ssb standard am and dsb sc techniques are wasteful of bandwidth because they both require transmission bandwidth of 2b hz, where b is the bandwidth of the baseband modulating signal mt. This is an increase compared to normal am transmission dsb that has a maximum efficiency of 33. Amplitude modulation am frequency modulation fm lin dai city university of hong kong ee3008 principles of communications lecture 3. Remember, neither yt, nor the oscillator signal, appears at the multiplier output. Let us examine the spectrum of the demodulated dsbsc signal. Dsbsc can be demodulated if modulation index is less than unity. Both the input and output signals are real scalar signals.
It simply is an analysis of am and dsbsc modulation and demodulation of a periodic square wave. Coherent detection of dsbsc waves electronics post. This method tries to aeoid the phase shift of audio frequencies and combine the. Demodulation of dsbsc signal by means of a product detector dsbsc modulator coherent dsbsc demodulator recovered carrier remarks.
Pdf a tunable frequencydoubling optoelectronic oscillator oeo is proposed and. Dsb sc is basically an amplitude modulation wave without the carrier, therefore reducing power waste, giving it a 50% efficiency. Output of this filter is the desired message signal. Dsb modulation and demodulation this tutorial describes the use of matlab to simulate dsb modulators and demodulators along with their spectra. For the love of physics walter lewin may 16, 2011 duration. The signal output from a demodulator may represent sound an. Demodulation is done by multiplying the dsbsc signal with the carrier signal. Learning how to use product detector in communication receivers.
It is an expensive technique when it comes to demodulation of the signal. Analog communication dsbsc modulation tutorialspoint. Dsbsc is a subset of am techniques, i think you mean to compare dsbsc with dsblc. The theory of dsb scssbsc modulation and demodulation double sideband suppressed carrier modulation at the beginning of the explanation of amplitude modulation, we explained the am radio system, but the term for amplitude in the theoretical expression was complex. Pdf frequencydoubling optoelectronic oscillator using dsbsc. Doublesideband suppressed carrier modulation dsbsc in full am dsbam, the carrier wave ct is completely independent of the message signal mt, which means that the transmission of carrier wave represents a waste of power. This points to a shortcoming of amplitude modulation, that only a. Below is what happen when you overmodulate a little bit, leaving some carrier behind but going beyond the am broadcast levels of modulation. Dsbsc is double sideband suppressed carrier modulation and ssbsc is single. The modulated signal s dsb sc amt looks similar to st but has a temporal but not spectral carrier component. From this equation, it is obvious that the carrier component in am wave remains constant in amplitude and frequency. As its name implies, the product detector uses multiplication and so mathematics are necessary to explain its operation. Then inner products dot products are 1 1 0 can interpret inner product as projection of vector 1 v1 onto vector 2 v2in other words, inner product of v1 and v2 tells us how much of vector 1 is there in the direction of vector 2.
Double sideband suppressed carrier dsbsc modulation. A regular am receiver will produce distortion as per the topright diagram due to the modulation being greater than 100%. But the common sense says recovering the baseband from two side bands should be much easier than from just one side. There are many types of modulation so there are many types of demodulators. The transmission of a signal, which contains a carrier along with two sidebands can be termed as double sideband full carrier system or simply dsbfc. Unit 4 week3 power efficiency, dsbsc modulation and. Vectors and modulation cse 466 interfacing 3 spose m and n are orthogonal unit vectors. Doublesideband suppressed carrier modulation dsb sc in full am dsb am, the carrier wave ct is completely independent of the message signal mt, which means that the transmission of carrier wave represents a waste of power.
Frequencydoubled signals are generated via the dsbsc modulation, which is. In both cases the transmission bandwidth b t is occupied by the upper sideband usb and lower sideband lsb. Amplitude modulation am is similar to dsb but has the advantage of permitting a simpler demodulator, the envelope detector. Demodulation is extracting the original informationbearing signal from a carrier wave. As in the case of dsb, product detector recovers the message signal without any distortion g. Ssb ds generation gsrq igys balanced modulator ls dsbsc tujsv. Introduction to double sideband suppressed carrier dsbsc. Lab 2 dsbsc generation and demodulation nick patino ece 458. Sc signal can be generated from two am modulator as shown in fig. Because, twothirds of the power is being wasted in the carrier, which carries no information. In the doublesideband suppressedcarrier transmission dsbsc modulation, unlike am, the wave carrier is not transmitted. The acronym stands for double sidebandsuppressed carrier modulation. For obtaining the dsbsc wave multiply both carrier signal and message signal hence.
The dsbsc am demodulator passband block demodulates a signal that was modulated using doublesideband suppressedcarrier amplitude modulation. The resulting signal is then passed through a low pass filter. In doing so, we explored the effects of both modulation and demodulation on the frequency spectrum of the signal,the. Recovering the modulating signal of a dsbsc signal is much harder than of a. Both simple multiplier type and nonlinear element type modulatorsdemodulators will be constructed. A demodulator is an electronic circuit or computer program in a softwaredefined radio that is used to recover the information content from the modulated carrier wave. Demodulation of dsb sc signal by means of a product detector dsb sc modulator coherent dsb sc demodulator recovered carrier remarks. It is achieved by combining ssbsc signal and an unmodulated carrier by a. In order to demodulate single sideband, ssb, it is necessary to reintroduce the carrier. Double sideband suppressed carrier dsb sc modulation. This is what i done with matlab coding for modulation and demodulation. As described in previous pages, single sideband is a form of amplitude modulation where the carrier and one sideband have been suppressed or reduced in level. In order to transmit 2 channel stereo signals, dsb signals are used in television and fm broadcasting.
By this test, i liked to prove the opposite of the statement that says. Doublesideband suppressedcarrier transmission dsbsc is transmission in which in the dsbsc modulation, unlike in am, the wave carrier is not transmitted. Both processes aim to achieve transfer information with the minimum distortion, minimum loss and. Am and dsbsc modulation and demodulation of a periodic. Ordinary am amplitude modulation as used in traditional am broadcasting results in a signal which, when analyzed as to its frequency spectrum is seen to consist of a centr. In the course of demodulating, this block uses a filter whose order. The spectrum of the dsbsc signal is the convolution of the input signal spectrum mf and the spectrum of the cos2 pft carrier. Single sideband modulation ssb standard am and dsbsc techniques are wasteful of bandwidth because they both require transmission bandwidth of 2b hz, where b is the bandwidth of the baseband modulating signal mt. Understand amplitude modulation and the difference between suppressed and. In this process, the message signal can be extracted from dsbsc wave by multiplying it with a carrier, having the same frequency and the phase of the carrier used in dsbsc modulation. Doublesideband suppressedcarrier transmission wikipedia. Mathematical analysis of a modulated carrier wave the equation of an unmodulated carrier wave is ec ec sin 2. During the transmission of binary data, dsb sc system is used in phase shift keying methods.
A type of dsb, called binary phaseshift keying, is used for digital telemetry. In the doublesideband suppressedcarrier transmission dsb sc modulation, unlike am, the wave carrier is not transmitted. Modulation and demodulation in communication engineering. The differential amplifier, q5 and q6, is used to drive the differential amplifiers q1q2 and q3q4.
If the amplitude of the carrier wave is simply changed and mathematised, it is. Demodulation or detection is nothing but the process of extracting a. Modulation is classified into two types they are, analog modulation and digital. Let the equation of the singlefrequency sinusoidal modulating signal be em em sin. Double sideband suppressed carrier dsb sc system definition and mathematical expression. Thus by suppressing the carrier, we obtain a modulated wave that is proportional to the product of the carrier and the message signal as shown in fig 1. Test the product detector by feeding in digitally synthesized singletone am and dsbsc signals with varying snr. Test the circuit by feeding in an external modulation multitone am signal from the arb. Analog amplitude modulation and demodulation part 2. About 37 years ago, i built, as a test, a simple linear demodulator for a doublesideband suppressedcarrier dsbsc signal. We once had a homework way back when decided to share it. For demodulation, the modulation oscillators frequency and phase must be exactly the same as the demodulation oscillators otherwise, distortion andor attenuation will occur.
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