Kennedy's Electronic Communication Systems, Se 1 Elements of Analog Conimunication 34 Demodulation of Pulse Analog Modulated Signals analog communication system by kennedy pdf. NASAs Kennedy Space Center KSC in soundofheaven.info National Communications System NCS was an office within. ELECTRONIC COMMUNICATION SYSTEM BY GEORGE soundofheaven.info The pulse analog modulation part describes pulse amplitude. l believe that this may.
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Electronic Communication system/George Kennedy. Pages · · Analog and Digital Circuits for Electronic Control System. Pages·· Electronic Communication System (4th Edition) by Kennedy & soundofheaven.info fastest-spreadingform enough information to reconstruct the origi- of analog. Kennedy. George, date. Electronic Communication system/George Kennedy, Bernard Davis,. 4th ed p. cm. Includes bibliographical references and index.
The authors are indebted to the following people for providing materials for this text Noel T. The preceding statement may be verified in any one of three different ways. Sakthi Deva. What is noise temperature'? Kennedy's Electronic Communication Systems 5th ed. Note also that th..
Vmln 3. The maximum negative amplitude. Vm a Vmn Power Relations in the AM Wave It has been shown that the carrier component of the modulated wave has the same amplitude as the unmodulated carrier. This is important. This relation may now be derived. Since amplitude of the sidebands depends on the modulation index V IV. The first tenn of Equation 3. Solution P AM'!!!! It is interesting to know from Equation 3.
The modulated wave contains extra energy in the two sideband components. Calculate the total power in the modulated wave. C it is anticipated that the total power Ill in the modulated wave will depend on the modulation index also.. How much of this is carrier power? If R is the resistance in which these currents flow. Find the percentage modulation.
Solution i. This occurs when the antenna current of the transmitter is metered. Determine the antenna current when the percent of modulation clumges to 0. There are two methods of calculating the total modulation index.
Let V1. Equation Then the total modulating voltage V. The procedure consists of calculating the total modulation index and then substituting it into Equation 3. To calculate the total modulation index. I sideband power will now be the sum of individual sideband powers. It is seen that there are two approaches It increases to 12 A as a result of simultaneous modulation.
Calculate the modulation index. If another sine wave is simultaneously transmitted wW1 modulation index 0. What is the modulation index due to this second wave?
Solution From Equation. Note also that th.. DSBSC technique accordingly adds complexity at the receiving point to recover the message.. II c 2 Therefore. Suppose your application requirement is cost ofreceiver needs to be significantly low Thus depending on the application.
A significant saving in power requirement can be achieved by supressing the carrier before transmission. PAM 3. The top envelope crosses below ilie zero reference amplitude value and similarly. For better distinction. It is derived from Fig. As illustrated. The instantaneous voltage of the resulting amplitude modulated wave is v..
At the most.. This is tbe price we pay by suppressing the carrier. V sin ro. Thus the information from AM can be recovered uniquely either from top or bottom envelope by a simple envelope detector circuit assume it as diode rectifier for time being. Samething is true with respect of bottom envelope also. Example Since amplitude of the sidebands depends on the modulation index V.
The modulated wave contains energy only due to the two sideband components. SR 4 2R Substituting Equation How much power saving in W is ac. This is correct also. This thought process led to the development of another variant of AM..
B SSII. COS W. Both the sidebands. Since only one of the sidebands is selected for transmis- sion.
SSB needs a bandwidth equal to that of message.. In this bookj unless specified. We require 5. It will be maximum. I case. Hence saving in bandwidth can be achieved by suppressing one of the sidebands.. Case 2 Given. Pososc "' P. Carrier power. Total power in AM. How much of carrier power ill kW is required if we want to transmit the same message by an AM transmitter?
Solution Given. The mathematical treatment here follows this assumption. That is.. From Fig.. SSB signficantly saves power. The SSB technique further complicates the receiver structure to recover message.
SSB consists ofone discrete frequency either atf. The bandwidth required for SSB is the frequency of the modulating signal.. Therefore still all the three versions ofAM.
If the cut-off frequencies are if. Then the next question is why not use only SSB? The answer is same as in the case of existence of AM. As will be explained later. The envelope of SSB does not contain message and hence a simple envelope detector circuit is not useful for recovering the message. This is the price we pay by suppressing the carrier and one of the sidebands. Its frequency will be either lower or more than carrier frequency by au amount of modulating signal frequency.
LSB I fc. The modulated wave contains energy only due to one sideband compcment. The modulated wave will have only one sine wave. USB fo-fm fr. The only wave to distinguish is to compare with carrier signal. SO in 3. Pc"" W and m. Calculate the total power in case of SSB tech- nique. Total power in SSB. Compare the powers required for SSB in both the cases and comment on the reason for change in tile power levels. This infers that the total power in SSB also depends on the depth of modulation.
The total power in the SSB modulated wave will be P. Solution Case 1 Given. In total 6. This is because.. How much of carrier power in kW is required if we want to transmit the same message by an AM transmitter? Solution Given.. Ill2 o. It was observed in practice that such a process results in eliminating even some por- tion of the wanted sideband. Carrier power..
One way to compensate for this loss is to allow a vestige or trace or fraction-of unwanted sideband along with the wanted sideband. Therefore an attempt to attenuate unwanted component will in tum leads to attenuation of wanted component. If the cut-off frequencies arc f. COS W.. VSB consists of two discrete frequencies either at ifc. Thif book also follows the same convention. The bandwidth required for VSB is the frequency of the modulating signal plus vestiage. COS W r. Since amplitude of the sidebands depends on the modulation index VJ Vr..
Amplitude Mod11latio11 51 t j a j b Fig. The shape of the signal in the time cloinain depends on the value of vestige frequency. BR 4 2R Substituling these equations in the total power equation. The modulated wave contains energy due to these two components. Now adding the unmodulated carrier component to thtS.. Solution G iven. We require Calculate tlze total power i11 case oJVSB technique.
The output of the analog multiplier is given by V. How much power saving in W is. In-a nonlinear resistance. If the above equation refers to a resistor. The previous linear relation seems to apply to ce1iain point.
Current now becomes proportional not only to voltage but also to the square. Whether the increase is more or less rapid depends on whether the device begins to saturate. Only the square term is large enough to be taken into consideration for most applications.. The reason that the initial portion of the graph is linear is simply that the coefficient c is much smaller than b.
Vme c. Since Equation 3. The diode is biased such that it exhibits the negative resistance property. The requisite AM components can be selected by using the tuning circuit that resonates at the carrier frequency with a bandwidth equal to twice the me. The devices like diodes. The output of the diode is collected via a tuned ci.
Under this condition. The output of the balanced modulator contait1s the two sidebands and some of the miscellaneous components which are taken care of by tuning the output tranfom1er's secondary winding.
Vo D2 Fig. No system can of course be perfectly symmetrical in practice. D1 and vf'. Analog ll "Vn1 Ve multiplier l Ve Fig. Cb RF. The diodes use the nonlinear resistance property for generating modulated signals. The modulated output currents of the two diodes arc combined in the center-tapped prirnary of the output trilnsfonner. Both the diodes receive tbe carrier volt- age in phase.
The final output consists only of sidebands. As indicated. The balanced modulator using the diodes is given in Fig. The above equation has the standard AM signal components.. In this way we can generate the AM signal with the help of device that exibblts nonlinear resistance property.
If this system is made cornpletely symmetrical. They therefore subtract. This signal is passed through a. The output of the analog multiplier is given by. The two diode output currents will be i. The tuning of the output transformer will remove the modulating frequencies from the output. If the lower sideband is passed out then the output of the bandpass filter will be mVc v a Using the Filter Method The basis for the filter method is that after the balanced modulator the unwanted sideband is removed by a filter.
One of the sidebands. Thus by suitable polarity for M1 output and addiJ. Vc cos co. Usittg the Phase Shift Method The phase shift method avoids filters and some of tbeir inherent disad- vantages.. Both the modulators produce the two-sidebands. CVmVt cos w.
One of the balanced modulators. The balanced modulator generates the DSBSC signal and the sideband suppression filter suprcsses-the unwanted sideband and al lows the wanted sideband.. Depending on the cut-off frequency values we can-represent the output of tbe fi Iler as v "" 2acV.
In this way SSB is generated in case of filter method. As derived in the previous section. Let v. The output of the balanced modulator M1 is given by. We can see that the later part of this circuit is identical to that of the phase sbift method..
A phase shift is then appl ied to this frequency only. The block diagram oftbe third method is shown in Fig. The output of M. I A ltematively. The output oftbe analog multiplier is given by v1. This signal is passed through a bandpass filter which.. The study of all the amplitude modulation techniques gives 1 better understanding about their nature in time and frequency domains. Depnding on the cut-off frequency values we can represent the output of the filter as1.
The balanced modulator generates the DSBSC signal and the sideband suppression filter supresses most oftbe unwanted sideband and allows a vestige ofit along with the other sideband. Thus the basic blocks remain same as in the case of SS B generation and the only difference is in the cut-off frequency values of the bandpass filter.
F 2acV. The basic technique.. If the lower sideband and vestige of upper sideband are passed out. Other methods are relatively different. The bandwidth of AM wave is given by c. Amplitude modulation is defined as the system 8. The method using analog multiplier is concephJally simple to understand.. The AM wave will have 1. Amplit11tle Mod11lalio11 61 namely.. AM needs maxi mum power and bandwidth among all its variants.
The SSB technique needs mini- mum power and bandwidth. THc modulation index of AM is given by C. VI" sincoCt tionless condition is c. The expression for total power in AM wave is Ill a. Multiple-Choice Questions Each of the followi11g multiple-choice questions b. The instantaneous voltage of the AM wave is d. The peak.
Circle the letter preceding the d. This was followed by the study of different methods for the generation of AM and its variants. IfvSll is the instantaneous voltage ofone sideband. VDS8SC '. The SSB wave wiU have a. The expression for total modulation index in case Ill b. Ill a. DSBSC b. The expression for total power in VSB wave is b. The maximum power ofSSB wave under distor.
F vso b. SSB b.. The outJ ut current of a nonlinear resistor caa. VSB c. The instantaneous voltage of the VSB wave related to its input voltage by having f: JSB as wanted sideband is n. The expression for total power in SSB wave is d. The bandwidth of SSB wave is given by The balanced modulator can be used for the gen- VSB d. The VSB wave will have lator is to a. The instantaneous voltage of the VSB wave hav. The basic working principle of a balanced modu- SSB c.
DSBSC a.: To what value will this current rise if the generator is modulated additionally by another audio wave. When the modulation percentage is What is the total sideband power radiated?
Hz audio sine waves. A broadcast AM transmitter radiates 50 kW of carrier power. When a broadcast AM transmitter is 50 percent modulated. A IkHz carrier is simultaneously modulated with H: A transistor class C amplifier has maximum permissible collector dissipation of 20 W and a collector efficiency of 75 percent. The output current of a 60 percent modulated AM generator is 1.
The basic working principle of third method for A W carrier is simultaneously modulated by two audio waves with modulation percentages of55 and What will be the percentage power saving if the carrier and one of the sidebands arc now suppressed? What will be the radiated powerat 85 percent modulation? What will be the frequencies present in the output? What will the current be when the modulation depth is increased to 0.
Mention the different components of VSB wave? Derive the expression for the total power in case ofSSB wave? Amplitude Morlttlatio11 65 Review Questions I. Derive the expression for the instantaneous voltage of VSB wave? Derive the expression for the instantaneous voltage of AM wave?
How much is the bandwidth of YSB wave? How much is the bandwidth of AM wave? Define modulation index of amplitude modulation? Mention the different components of AM wave? How much is the bandwidth ofSSB wave? Define amplitude modulation? Mention the different components of SSB wave?
How do you distinguish between analog and digital communication? Write the expression for the instantaneous voltage of AM wave? Write the expression for the instantaneous voltage ofVSB wave?
Write the expression for the instantaneous vo ltage of SSB wave'? Derive the expression for the total current in case of AM wave? Derive the expression for the total power in case ofVSB wave? Derive the expression for the total modulation index in case of modulation by several sine waves? Write the expression for the peak amplitude of the AM wave? Derive the expression for the instantaneous voltage of SSB wave?
Derive the expression for the total powur in case of AM wave? Describe the AM wave generation process using analog multiplier? Describe the generation of SSB wave using third method? Describe the generation of VSB wave using analog multiplier and frequency discrimination methods? Describe the generation of SSB wave using phase shift method? Describe the generation of SSB wave using frequency discrimination method? Describe the generation of SSB wave using analog multiplier?
Describe the AM wave generation process using diode as nonlinear resistor? The students will also be able to comment on the frequencies present. It will be seen that tbe effect of noise in FM depends on tbe lloise sideband frequency. The freq uency and phase of the carrier are varied i11 accordance with the instantaneous variations of the message in case of FM and PM.
Both the theory and the generation of angle modulation are a good deal more complex to think about and visualize than those of amplitude modulation. UL1Uke amplitude modulation. Following the pattern set in Chapter 3. Both methods are used in practice. FM is.
It will be seen that FM is the preferred forn. The final topic studied in this chapter is the generation of FM. The other important form of modulation used in analog communication is angle modulation. The second method is e in which basically phase modulation is generated. There arc two variEmts iu angle modulation depending on which component of the angle is used.
No doubt they equall y apply to PM also. FM and AM are then compared. Angle modulation is more difficult to detem1ine mathematically and has sideband behavior that is equally complex. In th. As mentioned in the previous chapter. This point is discussed at length. This chapter gives a detailed treat- ment of angle modulation techniques. They will also appreciate the fact that both PM and PM are similar in visual appearance.
The rate at which this frequency variation takes place is equal to the modulating frequency. It is assumed that the modulating signal is sinusoidal. Describe the theory of angle modulation teclmiques. Draw FM and PM waves. Let the message signal be given by v. The result ofusing that modulating voltage to produce AM is also shown.. Analyze the frequency spectrum using Bessel functions. Amplilude modulation.. This signal has two important parameters which must be represented by the modulation process without distortion.
It is understood that the phase relations of a complex modulation signal will be preserve. FM and PM.
If the frequency of the carrier co. Figure 4. The situation is illustrated in Fig.. Understand the differences between AM. Alteration of the phase angle q. Determine by calculation.. By the definition of frequency modulatior. Angle Modulation 1ec! The amplitude of the. Under these conditions. This is the greatest single advantage of FM.
The problem now is to determine the instantaneous value i.. Note that m1. It is interesting to note that as the modulating frequency decreases and the modulating voltage amplitude remains constant. This will be the basis for distinguishing frequency modulaw tion from phase modulation. As Fig. This function represents an e angle and will b. Thus Fig. Equauon 4.
Ln this instance. I is some function of the carrier and modulating frequencies. R 10 JO. Find the modulation index in each case. Example 4. Angle Modulation Techniques 71 Example 4. FM system. What power will this FM wave dissipate in a 10 Q resistor? The rate at which this phase variation changes is equal to the modulating frequency. Radiation And Propagation Of Waves Antennas Waveguides, Resonators And Components Microwave Tubes And Circuits Semiconductor Microwave Devices And Circuits Radar Systems Broadband Communication Systems Introduction To Fiber Optic Technology Seller Inventory International Edition.
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