LABORATORY MANUAL

ON

ANALOG COMMUNICATION TECHNIQUES

DEPARTMENT OF ELECTRONICS &TELECOMMUNICATION ENGINEERING

Contents

Sl.no Experiments to be performed Page no

1 Analyze and plot the spectrum of following signals with aid of spectrum analyzer: Sine wave, square wave, triangle wave, saw-tooth wave of frequencies 1KHz, 10Khz, 50Khz, 100KKz and 1 MHz

5

2 Analyze the process of frequency division multiplexing& time division multiplexing and de-multiplexing. Of FDM & TDM

7

3 Study and design of AM modulator and demodulator. (Full AM, SSB, DSBSC, SSBSC)

9

4 Study of FM modulation and Demodulation Techniques 135 Observer the process of PAM, quantization and determination of

quantization noise15

6 Multiplex 2-4 PAM/ PPM and PWM signals. 177 Using MATLAB/ SCILAB generate a carrier and a modulating signal.

Modulate the carrier using AM. Show the waveform in time domain and analyze its frequency spectrum. Repeat the simulation for modulating signal being square, triangular and other forms waveform.

19

8 Using MATLAB/ SCILAB generate a carrier and a modulating signal. Modulate the carrier using FM. Show the waveform in time domain and analyze its frequency spectrum. Repeat the simulation for modulating signal being square, triangular and other forms waveform.

22

9 Using Lab-View software simulate AM modulation and demodulation system 2510 Using Lab-View software simulate FM modulation and demodulation system 27

Rules & regulations

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(1) Each student must contain a lab record for each laboratory module, recording their individual work & results for each experiment.

(2) For most lab modules you will be assigned to a lab group. Each group typically consisting of five students, who are required to complete each exercise as a team. The detailed organization of work within a group should be agreed by the group members themselves. Every student is required to be familiar with all the aspects of each exercise, to participate actively in carrying it out, and to maintain his/her own individual lab record. Any disagreements over the organization of group work should be referred to a demonstrator.

(3) It is essential to study the lab manual, in detail in advance of each exercise.

(4) Students are required to attend the lab sessions. Neither the demonstrator nor the academic supervisors are responsible for missing a lab session. But missing a single session without explanation will normally mean you that you will be deemed to have extra compensatory lab for that experiment or you will be awarded no marks for that lab session.

(5) Arrive prepared with your lead kits, tools, pens, pencils, scales & calculator.

(6) Keep the equipments with care & use those for intended purposes. You are completely financially responsible for loss or damage to equipments signed out to you.

(7) While performing experiments be aware about the electrical supplies.(8) After the completion of the experiment properly keep the equipments in

their respective positions.(9) Only one compensatory lab class can be arranged for those students who

miss an experiment only on the medical ground.(10) Mobile phones are strictly prohibited inside the laboratory.(11) The student has to come to the lab class with proper dress code offered

by the institution.(12) The student is not allowed to bring his /her shoes, bags inside the lab

except lab record, pens, and pencils etc, which are required for the experiment.

(13) Any misconduct by the student, either to the demonstrator or to the supervisor, will lead to suspension of the student from the lab classes.

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LAB PLAN

Total experiments to be held : 10

Full mark of each experiment : 10

No of sub groups in a batch : 10

No of students in each group : 3

Division of mark in each Experiment:

SL.NO CATEGORY MARKS1 Viva voce 32 Experiment 33 Record 24 Attendance 15 Discipline 1

TOTAL MARKS 10

Grades awarded to the Student:

Grade MarksO 90 -100 marksE 80-89 marksA 70-79 marksB 60-69 marksC 50-59 marksD 40-49 marks

EXPERIMENT NO:-1

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Aim of the Experiment:

Analyze the spectrum of Sine wave, square wave, triangle wave, saw-tooth wave signals

Objective:

Analyze and plot the spectrum of following signals with aid of spectrum analyzer: Sine wave, square wave, triangle wave, saw-tooth wave of frequencies 1KHz, 10Khz, 50Khz, 100KKz and 1 MHz

Equipments required:

Sl. No. Name of the Equipment Specification

1 Signal/ function generator 1MHz

2 Spectrum analyzer 100MHz

3 Power supply (ac) 230v

Theory :

Frequency spectrum:-The frequency spectrum of a time-domain signal is a representation of that signal in the frequency domain. The frequency spectrum can be generated via a Fourier transform of the signal, and the resulting values are usually presented as amplitude and phase, both plotted versus frequency.

Spectrum analysis:-Spectrum analysis is the technical process of decomposing a complex signal into simpler parts. As described above, many physical processes are best described as a sum of many individual frequency components. Any process that quantifies the various amounts (e.g. amplitudes, powers, intensities, or phases), versus frequency can be called spectrum analysis. Spectrum analysis can be performed on the entire signal. Alternatively, a signal can be broken into short segments (sometimes called frames), and spectrum analysis may be applied to these individual segments. Periodic functions (such as sin(t)) are particularly well-suited for this sub-division. General mathematical techniques for analyzing non-periodic functions fall into the category of Fourier analysis.

Diagram:

5

Precautions :

Don’t give the power supply if the connections were properely made.

Don’t touch the uncovered part of patch cord.

Switch off the power supply after the experiment.

Procedure :

At first the function generator was used to give the input of various signals to the spectrum analyser.

Square wave, triangular wave , sine wave are given as the input to the spectrum analyser.

Tracing was done on each output of spectrum analyser.

Tabulation:

Sl. No

Type of waveform

Bandwidth

Saanwidth(mhz/div)

Frequency=bandwidth*saanwidth

1

2

3

Calculation:

Conclusion:

6

EXPERIMENT NO:-2

Aim of the Experiment:

Study of FDM & TDM

Objective:

Analyze the process of frequency division multiplexing& time division multiplexing and de-multiplexing. Of FDM & TDM

Equipments required:

Sl. No. Name of the Equipment Specification

1 FDM kit ST2211

2 TDM kit ST2503

3 CRO 50MHz

4 Patch cords --------

5 CRO probes 10:1

6 Power supply(AC) 230V

Theory :

Multiplexing: In telecommunications and computer networks, multiplexing (also known as mixing) is a process where multiple analog message signals or digital data streams are combined into one signal over a shared medium. The aim is to share an expensive resource. A device that performs the multiplexing is called a multiplexer (MUX), and a device that performs the reverse process is called a demultiplexer (DEMUX).

Frequency-division multiplexing: Frequency-division multiplexing (FDM): The spectrums of each input signal are sifted in several distinct frequency ranges. Frequency-division multiplexing (FDM) is inherently an analog technology. FDM achieves the combining of several digital signals into one medium by sending signals in several distinct frequency ranges over that medium. One of FDM's most common applications is cable television.

Time-division multiplexing:-Time-division multiplexing (TDM) is a digital technology. TDM involves sequencing groups of a few bits or bytes from each individual input stream, one after the other, and in such a way that they can be associated with the appropriate receiver.

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If done sufficiently and quickly, the receiving devices will not detect that some of the circuit time was used to serve another logical communication path.

Precautions :

Don’t give the power supply if the connections were properely made.

Don’t touch the uncovered part of patch cord.

Switch off the power supply after the experimentDiagram:

(FDM & TDM)

Procedure :

For frequency division multiplexing:-

At first connections were made properly.

Supply is given to connections.

Then individual signal processed & sketched from CRO with a given frequency range.

The frequency is calculated.

Finally the resultant signal (after multiplexing) is sketched.

For time division multiplexing:-

At first connections were made properly.

Supply is given to connections

Then individual signal processed & sketched from CRO

Finally the resultant signal (after multiplexing) is sketched.

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Calculation:

Conclusion:

EXPERIMENT NO:-3

Aim of the Experiment:

Study of Amplitude Modulation Processes

Objective:

Study and design of AM modulator and demodulator. (Full AM, SSB, DSBSC, SSBSC)

Equipments required:

SL.NO Equipments used Specification

1 CRO 50MHz

2 Function generator 10MHz

3 Patch cord ----------

4 CRO probe 10:1

5 DSB-SC TRAINER KIT VCT-47

6 SSB-SC TRAINER KIT VCT-42

7 DSB-FC TRAINER KIT VCT-26

8 Power Supply(AC) 230V

Theory :

Modulation is defined as the process by which some characteristics of a carrier signal is varied in accordance with a modulating signal. The base band signal is referred to as the modulating signal and the output of the modulation process is called as the modulation signal. The modulation is of following types.

Double-sideband modulation with carrier (DSB-WC) (used on the AM radio broadcasting band) (normal AM)

Double-sideband suppressed-carrier transmission (DSB-SC)

Single side band suppressed carrier(ssb-sc)

Amplitude modulation is defined as the process in which is the amplitude of the carrier wave is varied about a means values linearly with the base band signal. The envelope of the modulating wave has the same

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shape as the base band signal provided the following two requirements are satisfied

1. The carrier frequency fc must be much greater then the highest frequency components fm of the message signal m (t) i.e. fc >> fm

2. The modulation index must be less than unity. if the modulation index is greater than unity, the carrier wave becomes over modulated.

Double-sideband suppressed-carrier transmission (DSB-SC):The transmission in which (a) frequencies produced by amplitude modulation are symmetrically spaced above and below the carrier frequency and (b) the carrier level is reduced to the lowest practical level, ideally completely suppressed.

Single-sideband suppressed-carrier transmission (SSB-SC):-As we know the information content in upper sideband is equivalent to the information contained in the lower side band. So we can consider single side band by suppressing the carrier signal and hence the amplitude modulation is called single side band suppressed carrier.

Demodulation is the reverse process of modulation. The detector circuit is employed to separate the carrier wave and eliminate the side bands. Since the envelope of an AM wave has the same shape as the message, independent of the carrier frequency and phase, demodulation can be accomplished by extracting envelope.

Modulation index:It can be defined as the measure of extent of amplitude variation about an unmodulated maximum carrier. As with other modulation indices, in AM, this quantity, also called modulation depth, indicates by how much the modulated variable varies around its 'original' level. For AM, it relates to the variations in the carrier amplitude and is defined

Ma=(Vmax-Vmin)/(Vmax+Vmin)

Percentage of modulation=Ma*100 %

Output waveform:

(Information signal)

(DSB-FC)

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(DSB-SC)

( SSB-SC)

AM waveform Amplitude demodulation

Precautions :

Don’t give the power supply if the connections were properely made.

Don’t touch the uncovered part of patch cord.

Switch off the power supply after the experiment

Procedure :

Make the connections as per the circuit diagram. Do not connect modulating signal generator and connect emitter

resistor to ground.. Feed carrier signal at constant frequency and adjust its amplitude to

get good trace onCRO. Measure the amplitude Vc.

Remove carrier signal and apply modulating signal of 1KHz in the emitter circuit.

Adjust the amplitude of modulating signal to get good trace on CRO. Apply the carrier signal and observe the AM output. Vary the amplitude of modulating signal to observe the depth of

modulation. Change the frequency of the modulating signal and observe the effect

on the envelope of AM signal. Draw the waveform of modulating signal, carrier signal, AM

wave.

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Tabulation:

Sl.No

Amplitude of modulated

signal

Amplitude of carrier

signal

Maximum amplitude of modulated signal(Vmax)

Minimum amplitude of the

modulated signal(Vmin)

Modulation index

Calculation:

Ma=(Vmax-Vmin)/(Vmax+Vmin) &

Percentage of modulation=Ma*100 %

Conclusion:

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EXPERIMENT NO:-4

Aim of the Experiment:

Study of FM modulation and Demodulation Techniques

Objective:

Analyze the process of frequency modulation & demodulation techniques

Equipments required:

Sl.No Equipments required Specification

1 CRO 50MHz

2 CRO Probe 10:1

3 Patch cords -----------

4 FM trainer kit VCT-11

5 Power supply 230V(AC)

Theory :

frequency modulation:-frequency modulation may be defined as the process by which frequency of carrier varies in accordance with amplitude of base band signal.

Modulation factor:-It is defined as the difference between upper frequency & lower frequency of carrier wave to frequency of base band signal.

Modulation factor/index (β)=δF(freq. deviation)/Fm(freq. of the BBS)

δF=Kf*Am

where Am=Amplitude of base band signal

if β<1,then the signal is narrow band signal.

Β>1,then the signal is wide band signal

Diagram:

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Precautions:

Don’t give the power supply if the connections were properly made.

Don’t touch the uncovered part of patch cord.

Switch off the power supply after the experiment

Procedure :

Connections were made as per the circuit diagram given.

The input signal amplitude was varied.

The frequency modulated output at the FM output terminal was observed.

Modulation index was calculated.

Tabulation:

Signal Amplitude Time period frequency

Base band signal

Carrier signal

Modulated signal

Calculation:

Modulation index(β)=δF(freq. deviation)/Fm(freq.of the BBS)

Conclusion:

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EXPERIMENT NO:-5

Aim of the Experiment:

Study of the process of Pulse amplitude Modulation & Quantization

Objective :

Observe the process of PAM, quantization and determination of quantization noise

Equipments required:

Sl.No Equipments required Specification

1 PAM Trainer Kit HUD-59XLR

2 Patch Cords -------------

3 CRO 50MHz

4 Probes 10:1

Theory :

Pulse amplitude modulation is a scheme, which alters the amplitude of regularly spaced rectangular pulses in accordance with the instantaneous values of a continuous message signal. Then amplitude of the modulated pulses represents the amplitude of the intelligence. A train of very short pulses of constant amplitude and fast repetition rate is chosen the amplitude of these pulse is made to vary in accordance with that of a slower modulating signal the result is that of multiplying the train by the modulating signal the enve lope of the pulse height corresponds to the modulating wave .the Pam wave contain upper and lower side band frequencies .besides the modulating and pulse signals. The demodulated PAM waves, the signal is passed through a low pass filter ha ving a cut –off frequencies equal to the highest frequency in the modulating signal. At the output of the filter is available the modulating signal along with the DC component PAM has the same signal to noise ratio as AM and so it is not employed in practical circuits

Waveform:-

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(modulator and demodulator output)

Precautions :

Don’t give the power supply if the connections were properly made.

Don’t touch the uncovered part of patch cord.

Switch off the power supply after the experiment

Procedure :

Modulation1. Make the circuit as shown in circuit diagram2. Set the pulse generator output to be 41Vpp at 100HZ3. Set AFO output at 2 Vpp 100HZ4. Observe the output wave form on a CRO5. Tabulate the reading.

Demodulation1. Connect the circuit as shown in figure2. Given the modulated output with AFO used to the input of the circuit.3. Vary the potentiometer so that modulating signal is obtained.4. Measure the amplitude of the signal and verify with that of the input.

Conclusion:

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EXPERIMENT NO:-6

Aim of the Experiment:

Study of PAM,PPM,PWM Signals

Objective :

Multiplex 2-4 PAM/ PPM and PWM signals.

Equipments required:

SL No Equipments Required Specification

1 PAM Trainer Kit HUD-59XLR

2 PPM Trainer Kit HUD-59XLR

3 PWM Trainer Kit HUD-59XLR

4 Multiplexer Trainer Kit ST2503

5 CRO 50MHz

Theory :

PAM(Pulse Amplitude Modulation):-PAM may be defined as that type of modulation in which the amplitudes of regularly spaced rectangular pulses vary according to the instantaneous value of the modulating or message signal.

PPM(Pulse position Modulation):-In pulse position modulation ,the amplitude & width of the pulses are kept constant, while the position of each pulse ,with reference to the position of a reference pulse is changed according to the instantaneous sampled value of the modulating signal.PPM system is needed for the transmitter & receiver synchronization.

PWM(Pulse Width Modulation):-PWM is also known as Pulse Duration Modulation(PDM).In PWM , the width of the pulse is made proportional to the amplitude of signal at the sampling instant. Three variations of the pulse width modulation are possible. In one variation , the leading edge of the pulse is held constant & change in pulse width with signal is measured with respect to the leading edge. In second type of variation ,the tail edge is kept constant & with respect to it , pulse width is measured. In third variation , centre of the pulse is kept constant & pulse width changes on either side of the centre of the pulse.

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Diagram :

Precautions :

Don’t give the power supply if the connections were properly made.

Don’t touch the uncovered part of patch cord.

Switch off the power supply after the experiment

Procedure :

Connections are made as per the circuit diagram.

Connect the required supply to the kit and switch on the unit.see that the supply indicator glows.

Connect the CRO at the PWM output terminals and observe the waveforms.

Observe the waveforms at various test points and draw the same.

Vary the pulse input signal frequency from 20 KHz to 100 KHz and observe the PWM output.

Vary the sine wave signal and observe its effect on the effect on the output.

Conclusion:

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EXPERIMENT NO:-7

Aim of the Experiment:

Using MATLAB/ SCILAB generate a carrier and a modulating signal. Modulate the carrier using AM. Show the waveform in time domain and analyze its frequency spectrum. Repeat the simulation for modulating signal being square, triangular and other forms waveform.

Software used:

MATLAB7.1

Theory:

Introduction to MATLAB:Mat lab (R) is a high performance

language for technical computing it integrates computation,

visualization and programming in an easy way to use environment

where problem and solutions are expressed in family mathematical

relation. Thus, collection includes following topic.

MATLAB WINDOWS

MATLAB has 3 windows ie.

command window

graphics window

edit window

Command window: It is the main window here the program is to be

executed. As it depends upon the only commands it is called

“command window” Here all the command can be typed in a single line

by command in between the command.

Edit window :As the name indicates here editing can be done and it is

called script file. It is written by the user. If it is define by the user. If it

is define by the program it self then it is called function file.

Graphics window: In this window the out put of the programme will

display in graphical form.

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OPERATORS: Expression used familiar arithmetic operation and

procedure role.

Operator Operation

+ Addition

- Subtraction

* multiplication

/ Division

\ Left division

^ Power

I complex conjugate transpose

( ) Specify evaluation orders

Source code:

clct=0:0.001:5;m=cos(2*pi*.5*t);fs=100fc=1;y=modulate(m,fc,fs,'am');subplot (3,1,1);plot(t,m);grid on;ylabel('Amplitude');title('information signal');subplot(3,1,2);plot(t,y);grid on;ylabel('Amplitude');title ('Am modulated signal');

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s=demod(y,fc,fs,'am');subplot(3,1,3);plot(t,s);xlabel('time(s)');ylabel('amplitude');title('demodulated signal');

Waveform:-

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-1

0

1

Am

plitu

de

information signal

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-1

0

1

Am

plitu

de

Am modulated signal

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-1

0

1

time(s)

ampl

itude

demodulated signal

Conclusion:

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EXPERIMENT NO:-8

Aim of the Experiment :

Using MATLAB/ SCILAB generate a carrier and a modulating signal. Modulate the carrier using FM. Show the waveform in time domain and analyze its frequency spectrum. Repeat the simulation for modulating signal being square, triangular and

other forms waveform.

Software used:

Mat lab 7.1Theory :

Introduction to MATLAB

Mat lab (R) is a high performance language for technical computing it integrates computation, visualization and programming in an easy way to use environment where problem and solutions are expressed in family mathematical relation. Thus, collection includes following topic.

MATLAB WINDOWS

MATLAB has 3 windows ie.

command window graphics window edit window

Command window

It is the main window here the program is to be executed. As it depends upon the only commands it is called “command window” Here all the command can be typed in a single line by command in between the command.

Edit window

As the name indicates here editing can be done and it is called script file. It is written by the user. If it is define by the user. If it is define by the program it self then it is called function file.

Graphics window

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In this window the out put of the programme will display in graphical form.

OPERATORS : Expression used familiar arithmetic operation and procedure role.

Operator Operation

+ Addition

- Subtraction

* multiplication

/ Division

\ Left division

^ Power

I complex conjugate transpose

( ) Specify evaluation orders

Source code:-

t=0:0.001:5;x=cos(2*pi*0.5*t);fs=100;fc=1;y=modulate(x,fc,fs,'fm');subplot(3,1,1);plot(t,x);ylabel('amplitude');title('information signal');subplot(3,1,2);plot(t,y);ylabel('amplitude');title('fm modulated signal');s=demod(y,fc,fs,'fm');subplot(3,1,3);

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plot(t,s);xlabel('time(s)');ylabel('amplitude');title('demodulated signal');

Waveform:-

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-1

0

1

ampl

itude

information signal

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-1

0

1

ampl

itude

fm modulated signal

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-0.2

0

0.2

time(s)

ampl

itude

demodulated signal

Conclusion:

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EXPERIMENT NO:-9

Aim of the Experiment:

Study of AM modulation and demodulation system

Objective:

Using Lab-View software simulate AM modulation and demodulation system with carrier frequency 10KHz.

Soft ware used:

Lab-View-5.1

Theory :

Amplitude modulation is defined as the process in which is the amplitude of the carrier wave is varied about a means values linearly with the base band signal. Demodulation is the process of recovering the original base band signal from the amplitude modulated signal.

The AM Wave is given by

X(t)=[A+M(t)]cosωct

Where A=Amplitude of the carrier signal

M(t)=Baseband signal

Diagram:

AM MODULATOR :

25

.Procedure :Make the circuit connections as shown in figure using lab view software.

Then simulate the circuit to observe the output waveforms.

The output wave form is shown below.

Result:

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Conclusion:

EXPERIMENT NO:-10

Aim of the Experiment :

Study of FM modulation and demodulation system

Objective :

Using Lab-View software simulate FM modulation and demodulation system with carrier frequency 10KHz.

Soft ware used :

Lab-View-5.1

Theory :

frequency modulation:-frequency modulation may be defined as the process by which frequency of carrier varies in accordance with amplitude of base band signal.

Circuit Diagram :

27

Procedure :

Make the circuit connections as shown in figure using lab view software.

Then simulate the circuit to observe the output waveforms.

The output wave form is shown below

Result :

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0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-1

0

1

am

plitu

de

information signal

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-1

0

1

am

plitu

de

fm modulated signal

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-0.2

0

0.2

time(s)

am

plitu

de

demodulated signal

Conclusion :

Questions :

1. Based upon your general knowledge of AM and FM broadcasting by listening to the radioname the frequency occupied by AM and FM broadcast stations?2. What will happen, if modulation index is greater than 100%?3. Audio signals are not transmitted by electromagnetic waves. Justify the statement.4. An amplitude modulated amplifier has a radio frequency output of 50w at 100% modulation.

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The internal loss in the modulator is low. What output power is required from the modulator?5. In what stage modulation is done in high – power A.M transmissions?

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