Double sideband dsb is one of the easiest modulation techniques to understand, so it is a good starting point for the study of modulation. Am is a method of transmitting signals, such as sound or digita. Amplitude modulation definition, types, solved examples. Amplitude modulation am in amplitude modulation, the information signal is used to vary the amplitude of the carrier sine wave. Among the types of modulation techniques, the main classification is continuouswave modulation and pulse modulation. Amplitude modulation refers to the process in which amplitude of the carrier wave is varied with the message signal. The modulation processisprobablyeasier tounderstand whenviewed fromthe perspective of amplitude modulation. Principles of communications 12 basic principles of amplitude modulation the basic equation for an am signal is. Amplitude modulation circuit implementation for use in a communication. Peak value of carrier signal can also be computed using the peaktopeak value of the am waveform see fig. It requires that the amplitude of the dc a part of at is equal to the amplitude of the ac part a. Percentage modulation aka modulation index or modulation factor measure of extend to which carrier voltage is varied by intelligence defined as. Analog pass through band modulation am fm pm qam ssb digital. To explain, recall that when an am carrier is over modulated the signals envelope is nolonger the same shape as the original message.
Were going to be talking about amplitude modulation. The original waveform amplitude is quantized with a resulting loss of information. For the example above, the carrier signal is p es cos2. Consider the following block diagram of a quadrature amplitude modulation qam and demodulation system. The figure below shows the linear modulation of amplitude modulated wave. No information is lost, but the energy is redistributed in the frequency domain. The carrier frequency, fc, should be larger than the highest spectral component. An audio signal top can be transported by a carrier signal using am or fm methods. A sine wave carrier can be modified by the intelligence signal through amplitude modulation, frequency modulation, or phase modulation. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting messages with a radio carrier wave. Based on these results, it is easy to conclude that an amplitude modulated carrier has all of the. Unfortunately, although we have three machines which generate am signals, none of the signal generators will not allow you to use more than 100% modulation.
The continuous wave modulation techniques are further divided into amplitude modulation and angle modulation a continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information. Amplitude modulation early radio ee 442 spring semester. Another way to think is to realize that we are really plotting the amplitude. Experimental evaluation of distortion in amplitude modulation. The am modulation index is merely the relative level of modulation. For simplicity, consider a cosine wave information signal, v m t a 440 hz tuning fork and a cosine carrier, v c t frequency 5000 hz or 5 khz. To study amplitude demodulation by linear diode detector 3. When the percent modulation is 0% m 0, the total sidefrequency power psf is zero because there are no side frequencies in an unmodulated carrier. Figure 1 shows four different waveforms corresponding to the above equation with varying values of m. Adaptation of the information signal to the transmission channel. It is the extent of modulation denoted in percentage, and is denoted by m. When expressed as a percentage it is the same as the depth of modulation. The dsb modulated signal has double bandwidth of the modulating signal.
To understand amplitude and phase modulation, we change to the rotating frame of reference with. The modulating signal contains the intended message or information sometimes consisting of audio data, as in am radio. There are more similarities than differences between the two phases of glucoseinduced insulin secretion. Using amplitude modulation to shift the baseband signal fm radio 88mhz108 mhz. Pulse amplitude modulation pam, quadrature amplitude modulation qam 12. Types of modulation 6 flynnkatz 7810 analog modulation amplitude modulation, am frequency modulation, fm double and single sideband, dsb and ssb digital modulation phase shift keying. The amplitude modulation am modulation index can be defined as a measure of the amplitude variation upon a carrier.
While aging had an overall detrimental effect on fm detection with and without interfering am, there was a trend that hearing loss further impaired. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal, such as an audio signal. Amplitude modulation fundamentals pa2old website about. Amplitude modulators highlevel modulation produces the best type of am, but it requires an extremely high power modulator circuit. The two common forms of analog modulation are amplitude modulation. Amplitude modulation am works by varying the amplitude strength of a carrier signal, in proportion to amplitude of a modulation signal that is to be transmitted to one or more receivers.
This requires a shift of the range of frequencies in mt into other frequency ranges. This technique contrasts with angle modulation, in which either the frequency of the. Introduction information that needs to be transmitted over a communication channel usually a baseband signal recall. The maximum and minimum values of the envelope of the modulated wave are represented by a max and a min respectively. If the value of the modulation index is greater than 1, i.
Amplitude modulation, spectrum of am signal, the balanced modulator, the. Quadrature amplitude modulation is widely used for carrying many digital signals, everything from wifi to mobile phone communications and very much more. The left and right channels each limited to 15khz are multiplexed into a single baseband signal using amplitude modulation using frequency modulation to shift the baseband. These transmitted signals if transmitted over the same channel would not interfere with each other and can be demodulated. Therefore, both fm and pm are often referred to as angle modulation. Double sideband amplitude modulation with carrier setup 1a.
This is the first time we will be discussing how radio is used to transfer information across a longdistance. In fact, for 100% modulation, the power supplied by the modulator must be equal to onehalf the total class c amplifier input power. Both are subject to the same dual, hierarchical control over time and amplitude by triggering and. When the value of the modulation index is less than 1 then it is said to be a linear or undermodulated wave. It is still in use today in a variety of systems, including, of course, am broadcast radio. Amplitude modulation of insulin secretion pulses largely depends on the amplifying pathway. Double sideband dsb is one of the easiest modulation techniques to. Each radio station is assigned 200 khz, to transmit a stereo audio. Over modulation isnt really of any significance to fm systems unlike am. Matlab tutorial amplitude modulationhow to generate amplitude modulation am using matlab. A conceptual illustration of the modular design of the amplitude modulator. In this video, i have explained amplitude modulation by following outlines. Amplitude modulation is defined as the process in which the amplitude of the. To see what happens when over modulation takes place, you must add three independent sine.
Here, the amplitude modulator works along the x and y axes, and the sign of inputoutput displacements is consistent with the sign of the coordinate axes. Angle modulation includingfrequency modulation fm and phase modulation pm. Pdf interactions between amplitude modulation and frequency. Note the amplitude of the sidebands and carrier in each case and brie. For example, if the carrier voltage is 9 v and the modulating signal voltage is 7. Basic concept of modulation the information source typically a low frequency signal referred to as the baseband signal carrier a higher frequency sinusoid example.
A continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information. The transmission of audio frequencies for example, speech and music over a distance is usually. Message signal embed into the amplitude of carrier simple am is also called. Amplitude modulation so far we have developed basic signal and system representation techniques which we will now apply to the analysis of various analog communication systems. Frequency modulation is a special case of phase modulation, where the phase. Multiplying the modulation index by 100 gives the percentage of modulation. In this experiment, you will examine the characteristics of amplitude modulation am. Pt total transmitted power in an angle modulated waveform modulation or no angle modulation characteristics modulation phase deviation modulation index vc peak amplitude of the carrier signal pm waveform.
Double sideband dsb and amplitude modulation zimmer web. This means that their ratio is unity at the output of the adder, which forces m to a. Experiment 1 amplitude modulation and demodulation 4 a limitation of envelope detector shown in figure 3 is that it cannot accurately recover the message from over modulated am signals. Here, the carrier amplitude is not constant, but when all sidebands are included, the carrier is constant. Dsbsc amplitude modulation over a bandpass channel which transmits signals in the range 90 khz to 120. A carrier wave, after being modulated, if the modulated level is calculated, then such an attempt is called as modulation index or modulation depth. The shift in the signal frequency range is accomplished by modulation. Lecture notes on analogue communication techniques. The continuous wave modulation techniques are further divided into amplitude modulation and angle modulation. In digital form it is the most common method for transmitting data over optical fiber 1. As given is the problem the modulation is sinusoidal this is also called tone modulation. The dt signal an may comprise samples of a bandlimited analog message taken at the nyquist rate or higher, and generally quantized to a. If the modulation signal amplitude is too great, any decent frequency modulator will limit the signal so that it cant push the bandwidth of the modulated signal too wide in the frequency spectrum. Quadrature amplitude modulation qam quadrature amplitude modulation is the type of amplitude modulation in which two different message signals are transmitted on the same frequency carrier with a different phase shift.
Angle cw modulation with noise in the analysis of pm and fm systems, demodulation will be represented by yt. Set the modulation signal from the hp 3312a generator to a 500 hz sine wave, 0v offset, and apply it to the other channel of the oscilloscope and the modulation input of the hp 33120a generator. Am carrier solid curve and message sinusoid dashed curve. It maximizes bit rate, reduces power of transmission and reduces dc component.
Trigger the scope on the signal from the hp 3312a generator. For a perfect modulation, the value of modulation index should be 1, which means the modulation depth should be 100%. There is no over modulation means that modulation index is less than or equal to 1. For example, we may opt for phaseshift keying 39 or for quadrature amplitude modulation 40 in classical communication, and either for gaussian or for nongaussian modulation in cv qkd 41. It states the level of modulation that a carrier wave undergoes. Pulse modulation of two types analog pulse modulation pulse amplitude modulation pam. Process by which a property or a parameter of a signal is varied in proportion to a second signal. This form of modulation is essentially derived from two carriers that are 90 out of phase and adding information, either analogue or digital. Principles of communication systems 20022003 10 chapter 7. The pulse may take any real voltage value that is proportional to the value of the original waveform. Modulation is a process by which some characteristics of the carrier signal like its amplitude, frequency or phase are varied in proportion to message signal. To study sampling and reconstruction of pulse amplitude modulation system 6.
If the class c amplifier has an input power of w, the modulator must be. Amplitude modulation the total signal consists of the original carrier full amplitude, plus two sidebands, located above and below the carrier frequency by a distance equal to the modulating frequency, each with an amplitude of up to half that of the carrier and thus each has up to. Overmodulation overmodulation is a condition that occurs when an excessive intelligence signal overdrives an am modulator making %m 100% because e i e c modulated carrier amplitude reach value greater than double of unmodulated value it produces a distortion known as sideband splatter, which results on transmission at frequencies outside. A type of dsb, called binary phaseshift keying, is used for digital telemetry. Some media have characteristics that severely distort digital waveforms in such cases, it is necessary to send digital information. Both modulated signals are then added using summer to make a single signal having same frequency and bandwidth. Modulation is necessary in all of the above scenarios.
In the frame of the rotating carrier vector, the sidebands modulate the phase. Analog pulse modulation pulse amplitude modulation pam pulse width modulation pwm pulse position modulation ppm digital pulse modulation. Vary the modulating frequency and amplitude and observe the effects on the. Amplitude modulation am is a modulation technique where the. Vc maximum voltage of the carrier signal power savings vm maximum voltage of the original a. Bpsk, qpsk, msk frequency shift keying, fsk quadrature amplitude modulation, qam. In amplitude modulation, the carrier frequency remains constant, but the instantaneous value of the.
When the value of the modulation index exceeds more than 1, then over modulation takes place. This block diagram shows the modulation of two message signals. Nov 16, 2019 amplitude modulation with modulation factor 0. The predetection part of an angle modulation receiver is the same as for amplitude modulation. In analog pulse modulation some parameter of each pulse is modulated by a particular sample value of the message. In cw modulation schemes some parameter of modulated wave varies continuously with message. Figure 1 am, with m 1, as seen on the oscilloscope. We considered an example of amplitude modulation in chapter 6 that does this frequency translation. Amplitude modulation matlab tutorial amplitude modulation. Now we will discuss the above am generation techniques in a bit detail. Pulse modulation timedivision multiplex tdm continued time multiplexing of two pam signals graphic interpretation assume all input signals are lowpass and bandlimited to.
1224 642 1466 907 1417 1498 1096 1269 729 1134 1058 1166 1607 997 688 798 677 306 106 802