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EC 4112: ANALOG COMMUNICATION LABORATORY

LIST OF EXPERIMENTS:

COMPULSORY EXPERIMENTS:

1. Generation of AM wave using 2N2222 BJT Modulator circuit

2. Implementation of Voltage to Frequency Converter using IC 555 Timer

3. Generation of FM wave and its detection using ACL 03 and ACL 04 FM

Trainer kit

4. AM wave detection using Series Envelope detector stage in radio receiver

GR3151

5. Generation of Frequency Modulated wave using IC 8038

6. Design and Implementation of 2nd and 4th order LP Butterworth Filters

7. Design of Amplitude Modulation and Demodulation System using

Commsim

8. Design of Frequency Modulation and Demodulation System using

Commsim

9.

Design of DSSBSC Modulation and Demodulation System using

Commsim

10. Design of SSBSC Modulation and Demodulation System using Commsim

11. Generation of the Amplitude modulated wave and Calculation of %

Modulation using ACL01 kit & ACL02

12. Design of PAM Modulation and Demodulation System using Commsim

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OPTIONAL EXPERIMENTS:

13. Generation of DSBSC Modulated wave using Anacom-1/1 Trainer kit

14. Design of a Class B push- pull Complimentary Amplifier using Multisim

15. Design of Series / Shunt Voltage regulator circuit for given specification

using Multisim

16. Design of 2nd and 4th order LP Butterworth Filters using Multisim

17. Design of an AM Superhetrodyne receiver using Commsim

18. Design of an FM Superhetrodyne receiver using Commsim

19.

Voice transmission using Varactor Modulator and the Foster Seeley

Detector

20. Voice Transmission using Phase modulation and Demodulation system

21. Design of Pre-emphasis and De-emphasis circuits and determination of

their Frequency Response

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DEPARTMENT

OF

ELECTRONICS AND COMMUNICATION ENGINEERING

ANALOG COMMUNICATION LABORATORY

LAB INSTRUCTIONS FOR CARRYING OUT PRACTICAL

ON

GENERATION OF AM WAVE USING 2N2222

BJT MODULATOR CIRCUIT

BIRLA INSTITUTE OF TECHNOLOGY

MESRA, RANCHI

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AIM: Generation of AM wave using 2N2222 BJT Modulator circuit

APPARATUS REQUIRED:

1.

Circuit board with components of desired values.2. Function generator (2-Nos)

3. Transistor Power Supply (0-30V)

4. CRO

OTHER ACCESSORIES:Connecting wire and probes.

THEORY:

When a low frequency signal controls the amplitude of high frequency signal,

we get amplitude-modulated wave. The high frequency signal is known as carrier andlow frequency signal is called the modulating signal.

PERCENT MODULATION: Ideally a sinusoidal modulating signal produces a

sinusoidal variation in voltage gain, which is expressed by: -

A=A0 (1+m sinyt)…………………………..(i)

Where A= Instantaneous Voltage Gain

A0= Quiescent Voltage Gain

M= Modulation co-efficient

As the sine function varies between – 1 to+1 the voltage gain varies

sinusoidally between A0(1-m) and A0(1+m). For example, if A0=100 and m=0.5 then

the voltage gain varies sinusoidally between a minimum voltage gain of Amin=100(1-

0.5)=50 and a maximum voltage gain of Amax=100(1+0.5)=150. In equation (i) m

controls the amount of modulation. The larger m is the greater the change in voltage

gain. Percent modulation is typically used to measure the amount of amplitude

modulation. It is given by m x 100%

2Vmax-2Vmin

Where m= ------------------------- where 2Vmax=max peak to peak Voltage

2Vmax+2Vmin 2Vmin= min peak to peak Voltage

PROCEDURE:

1. Connect the circuit as shown in the figure.

2. Carrier signal frequency is set at 80KHz and modulating frequency at 514 Hz.

3. Keep the carrier voltage signal at 25mV and modulating signal at 2V.

4. Set Vcc at 12 V from transistor power supply then see output waveform on

CRO. Calculate Vmax and Vmin from AM wave.

5. Vary the modulating voltage and see waveforms.

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OBSERVATIONS AND CALCULATIONS:

Sl.

No

Modulating

Signal/

Voltage

Carrier

Signal/

Voltage

A=2Vmax(Volts)

B=2Vmin

(Volts)

%mod =

(A-B)/(A+B)

x 100

Efficiency

=m2/(m2+2)

x 100

RESULT:

PRECAUTIONS:1. All the connections should be perfect.

2. At the time of taking reading from the measuring equipments the errors of

reading must be avoided

REFERENCES:1. Pamphlet to be supplied

2.

Electronics Principle by Malvino.

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2N222

10kohm

2.2kohm

2.2kohm

12kohm

4.7kohm

0.22uF

2200pF

0.15uF

Vc

fc=80KHz

Vo

Vcc(+12V)

514HzModulatingsignal

CKT DIAGRAM FOR AMPLITUDE MODULATION

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DEPARTMENT

OF




ON

IMPLEMENTATION OF VOLTAGE TO FREQUENCY

CONVERTER USING IC 555 TIMER


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AIM: - To Design a voltage to frequency converter using IC 555 Timer.

APPARATUS REQUIRED:1. Breadboard with components.

2.

Transistor power supply – 2 No’s 3. CRO

PIN DIAGRAM OF THE 555 TIMER

Functions of pins:

1. Ground: All voltages are measured with respect to this terminal.

2. Trigger: It is the external input that will be applied to the inverting input of the

lower comparator & will be compared with Vcc/3 coming from the potential divider

network.

3. Output: Complement of the output of the flip-flop acts as the final output of timeras it passes through a power amplifier with inverter. Load can either be connected

between pin 3 & ground or pin 3 & Vcc.

4. Reset : This is an input to the timing device which provides a mechanism to reset

the flip-flop in a manner which overrides the effect of any instruction coming to the

FF from lower comparator. This is effective when the reset input is less than

0.4V.When not used it is returned to Vcc.

5. Control Voltage input: Generally the fixed voltages of 1/3Vcc & 2/3Vcc also aid in

determining the timing interval. The control voltage at 5 can be used when it is

required to vary the time & also in such cases when the reference level at V- of the

UC is other than 2/3Vcc.

Generally when not used a capacitor of 0.01uF should be connected between 5 &ground to bypass noise or ripple from the supply.

6. Threshold: An external voltage by means of a timing capacitor & resistor is applied

to this pin. When this voltage is greater than 2/3Vccoutput of UC is 1 which is given to

the set input of FF thereby setting the FF making Q=1 & Q=0.

7. Discharge: This pin is connected to the collector of the discharge transistor

Q1.When Q output of the FF is 1,then Transistor Q1 is on due to sufficient base drive

hence driving transistor into saturation.

When output of the FF is low Transistor Q1 is off hence acting as a open circuit to any

external device connected to it.

8. +Vcc (Power Supply): It can work with any supply voltage between 5 & 18V.

Threshold

Control voltage

Discharge

out ut

IC 555

+ VccGND

Trigger

Reset

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RESULT:

PRECAUTIONS:

1. All the connections should be perfect.

2. At the time of taking reading from the measuring equipments the error of

reading must be avoided.

3. Vcc should not exceed 10V.

REFERENCE:1. Pamphlet to be supplied.

2. Electronic Principle by A.P. Malvino.

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DEPARTMENT

OF




ON

GENERATION OF FM WAVE AND ITS DETECTION

USING ACL 03 AND ACL 04 FM TRAINER KIT


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B. To calculate the modulation sensitivity of FM modulator. :

EQUIPMENT:

Modules ACL-03 Power supply +/-12 V

20 MHz oscilloscope

Voltmeter.

Frequency meter.

Connecting Links.

PROCEDURE:

1. Perform the procedure as done in Exp: 1(A).

2.

Consider the modulator operation in the segment of curve within 700 to 1300kHz, with central frequency of 1000 kHz. From the analysis of the curve of

fig. 1.8 it is possible to calculate the modulation sensitivity of the modulator.

3. The modulation sensitivity S is defined as:

S= dF (v)

dv

Where F (v) is the instantaneous frequency function of the modulating voltage

v. The last relation can be approximated writing the incremental ratio:

S=F

v

With reference to the curve of fig. 1.8, in correspondence to the central

frequency (1000kHz) you obtain:F=50kHz v 125mv from which: So=50/125=0.4kHz/mv

RESULT:

PRECAUTION:

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C. To observe and measure frequency deviation and modulation index of

FM.

EQUIPMENT:

Modules ACL-03

Power supply +/-12 V

Oscilloscope

Voltmeter

Frequency meter

Connecting Links

PROCEDURE:

1.

Refer to the fig. 1.6 & carry out the following connections.2.

Connect the power supply with proper polarity to the kit while connecting this;

ensure that the power supply is OFF.

3. Connect the o/p of function generator OUT post to the modulation IN of

FREQUENCY MODULATOR MOD IN post.

4. Switch ON the power supply and carry out the following presetting:

FUNCTION GENERATOR: sine wave (J1); LEVEL about 0.2Vpp;

FREQ. About 1kHz.

FREQUENCY MODULATOR LEVEL about 2Vpp; FREQ. on the

center; switch on 1500kHz

5. Connect the oscilloscope to the output of the modulator FM/RF OUT. You

obtain a waveform similar to the one of Fig.1.10.6. The frequency deviation F can be calculated as follows (refer to fig. 11).

From the oscilloscope evaluate FM and Fm, detecting the periods of therespective sine waves

The frequency deviation F is defined as: F = (FM – Fm)/2 and F

You can note that if the modulator operates in a linear zone so FM and Fmare over and under the central frequency F of the same quantity F,

otherwise this does not occur.

7.

The value of the modulation index mf is calculated by the relation mf = F/f,

where f is the frequency of the modulating signal.

8.

Then observe the FM signal as shown in fig. 1.1 in theory

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DEPARTMENT

OF




ON

AM WAVE DETECTION USING SERIES ENVELOPE

DETECTOR STAGE IN RADIO RECEIVER GR3151


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AIM: AM wave detection using Series Envelope detector stage in radio

receiver GR3151

APPARATUS REQUIRED:1) Circuit board with components of desired values.

2)

Standard AM Signal Generator range (5KHz-50MHz)3) CRO.

OTHER ACCESSORIES:

Connecting Wires, Probes.

THEORY:

The process of demodulation is used to recover the original modulating signal

from the incoming modulated wave. In effect, the demodulation is the reverse of the

modulation process. As with modulation, the demodulation of an AM wave can be

accomplished by using various devices. Here we describe simple and highly effectivedevice known as Envelope Detector. Some version of this demodulator is used in

almost all commercial radio receivers. However the AM wave has to be narrow band,

which requires that carrier frequency be large compared to message bandwidth.

Moreover the percentage modulation must be less than 100%.

An envelope detector of series type is shown in the fig, which consist of diode

and RC filter.

PROCEDURE:


2. Apply 30% amplitude-modulated signal to the I/P terminal using signal

generator.

3. Measure frequency Vmax, Vmin on Cro.

4. Take output from RC combination circuit on CRO.

5. Measure frequency of output signal.

6. Repeat the process for another value of AM wave.

PRECAUTION:

2.

All the connections should be perfect.3. At the time of taking reading from the measuring equipments the errors of


REFERENCES:

1. Pamphlet to be supplied.

2.

Electronics Communication system by George Kennedy.

3. Communication system by S. Haykin, IInd Edition.

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D

1N4007GP

Rs

C

0.22uF

Rl

22kohm Vo

-----

-----

+

-

CIRCUIT DIAGRAM FOR SERIES ENVELOPE DETECTOR

AMWAVE

I/P

AM

I/P AM WAVE= O/P WAVE=

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DEPARTMENT

OF




ON

GENERATION OF FREQUENCY MODULATED WAVE

USING IC 8038


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DEPARTMENT

OFELECTRONICS AND COMMUNICATION ENGINEERING



ON

DESIGN AND IMPLEMENTATION OF 2ND

AND 4TH

ORDER LP BUTTERWORTH FILTERS


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AIM: Design and Implementation of 2nd and 4th order LP Butterworth Filters

APPARATUS REQUIRED:

1.

Breadboard with components of desired values(IC 741-2No’s, Resistors and Capacitors)

2. RC Oscillator (1 – No)

3. DC Dual transistor power supply (0-35V)

4. CRO

OTHER ACCESSORIES:

Connecting wires and probes.

THEORY:

Butter Worth filter is one of the most commonly used practical filters that

approximate the ideal response. The key characteristics of Butter Worth filter is that it

has flat pass band as well as stop band. For this reason it is sometimes called flat

filter. An approximation for an ideal low pass filter is

Avs=1/Pn(s)…………………………..(i)

Pn(s) is a polynomial in variable(s) with zeros in left hand plane.

DESIGN RULE: The typical second order B.F. transfer function is of the form.

Av(s) = 1 . ……………………..(ii)

Av (0) (s/ω0) 2+2K(s/ ω0)+1

Where ω0 2лf 0 is the high frequency 3dB point.

First order filter

Av(s) = 1 ………………...…………..(iii)

Av (0) (s/ω0)+1.

First order and second order filter section have been shown in figure.

Av=V0/Vi= R 1 + R1’/R 1 ………………………………….(iv)

AV (S)= Av (0). (1/RC) 2 ……………..(v)

S2=(3-Av(0)/RC)s+ (1/RC)2

From the above equation ω0=1/RC, 2K=3-AV(0) or AV(0)=3-2K.

Normalized Butter Polynomial

n Factors of polynomial

1 (s+1)

2 s2+1.414s+1

3 (s+1)(s2+s+1)

4

(s2

+0.765s +1)(s2

+ 1.848s +1)

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PROCEDURE:


2.

Connect the power supply to the circuit at pin no. 4 and 7 of IC 741.

3. Vary the frequency of RC Oscillator.

4.

Measure the output voltage at pin no. 6 on CRO for different frequenciesand calculate gain in dB.

OBSEVATIONS AND CALCULATIONS:

Sl. No. FREQUENCY Log10f Amplitude

Peak to peak

Vout (V)

A=Vout

Vin

Gain in dB

20 log10A

RESULT:

PRECAUTIONS:

2.

All the connections should be perfect.



4. DC supply should not exceed 12V.

REFERENCES:

1. Pamphlet to be supplied.

2.

Op-Amps and Linear Integrated Circuits by Ramakant A. Gayakwad

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U1

741

3

2

4

7

6

51

9.1kohm

9.1kohm

9.1kohm

9.1kohm

2200pF2200pF

U2

741

3

2

4

7

6

519.1kohm2.2kohm

2200pF2200pF

-12V

+12V+12V

-12V

Vin

Vout

9.1kohm 9.1kohm

CKT DIAGRAM FOR SECOND AND FOURTH ORDER LOW PASS

BUTTER WORTH FILTER

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DEPARTMENT




ON

DESIGN OF AMPLITUDE MODULATION AND

DEMODULATION SYSTEM USING COMMSIM


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AIM: Design of Amplitude modulation and demodulation system using Commsim.

THEORY:

Amplitude Modulation (AM) is defined as a process of Modulation in which the

Amplitude of the carrier wave c(t)is varied about a mean value, linearly with the base

band signal m(t). It may be described as a function of time in the form

S(t) = Ac (1+ Ka m(t) ) cos (2 ∏ f c t)

Where, Ac = Amplitude of carrier wave c(t)

f c = Frequency of carrier wave c(t)

Ka = Amplitude sensitivity

m(t) = Base band Signal

Fig. : AM waveform

Figure shows that the envelope of signal S(t) has the same shape as base band

signal m(t) provided two requirements are satisfied .

1. The amplitude of Ka m(t) is always less than unity.

2. The carrier frequency fc is much grater than the highest frequencycomponent

W of the message signal m(t).

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Fig : Superheterdyne Am Receiver

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RESULT:

CONCLUSION:

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DEPARTMENT




ON

DESIGN OF FREQUENCY MODULATION AND

DEMODULATION SYSTEM USING COMMSIM


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AIM : Design of Amplitude modulation and demodulation system using Commsim.

THEORY:

Frequency modulation uses the information signal, Vm(t) to vary the carrier frequency

within some small range about its original value. Here are the three signals in

mathematical form:

Information: Vm(t)

Carrier: Vc(t) = Vco sin ( 2 f c t +

FM: VFM (t) = Vco sin (2 f c + (f/Vmo) Vm (t) t +

We have replaced the carrier frequency term, with a time-varying frequency. We have

also introduced a new term: f, the peak frequency deviation. In this form, you should

be able to see that the carrier frequency term: f c + (f/Vmo) Vm (t) now varies between

the extremes of f c - f and f c + f. The interpretation of f becomes clear: it is the

farthest away from the original frequency that the FM signal can be. Sometimes it is

referred to as the "swing" in the frequency.

We can also define a modulation index for FM, analogous to AM:

= f/f m , where f m is the maximum modulating frequency used.

The simplest interpretation of the modulation index, is as a measure of the peakfrequency deviation, f. In other words, represents a way to express the peak

deviation frequency as a multiple of the maximum modulating frequency, f m, i.e. f =

f m.

Example: suppose in FM radio that the audio signal to be transmitted ranges from 20

to 15,000 Hz (it does). If the FM system used a maximum modulating index, , of 5.0,

then the frequency would "swing" by a maximum of 5 x 15 kHz = 75 kHz above and

below the carrier frequency.

Here is a simple FM signal:

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Here, the carrier is at 30 Hz, and the modulating frequency is 5 Hz. The modulation

index is about 3, making the peak frequency deviation about 15 Hz. That means the

frequency will vary somewhere between 15 and 45 Hz. How fast the cycle is

completed is a function of the modulating frequency.

FM Spectrum

A spectrum represents the relative amounts of different frequency components in any

signal. Its like the display on the graphic-equalizer in your stereo which has leds

showing the relative amounts of bass, midrange and treble. These correspond directly

to increasing frequencies (treble being the high frequency components). It is a well-know fact of mathematics, that any function (signal) can be decomposed into purely

sinusoidal components (with a few pathological exceptions) . In technical terms, the

sines and cosines form a complete set of functions, also known as a basis in the

infinite-dimensional vector space of real-valued functions (gag reflex). Given that any

signal can be thought to be made up of sinusoidal signals, the spectrum then

represents the "recipe card" of how to make the signal from sinusoids. Like: 1 part of

50 Hz and 2 parts of 200 Hz. Pure sinusoids have the simplest spectrum of all, just

one component:

In this example, the carrier has 8 Hz and so the spectrum has a single component with

value 1.0 at 8 Hz

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The FM spectrum is considerably more complicated. The spectrum of a simple FM

signal looks like:

The carrier is now 65 Hz, the modulating signal is a pure 5 Hz tone, and the

modulation index is 2. What we see are multiple side-bands (spikes at other than the

carrier frequency) separated by the modulating frequency, 5 Hz. There are roughly 3

side-bands on either side of the carrier. The shape of the spectrum may be explained

using a simple heterodyne argument: when you mix the three frequencies (f c, f m and

f) together you get the sum and difference frequencies. The largest combination is f c

+ f m + f, and the smallest is f c - f m - f. Since f = f m, the frequency varies ( + 1)

f m above and below the carrier.

A more realistic example is to use an audio spectrum to provide the modulation:

In this example, the information signal varies between 1 and 11 Hz. The carrier is at

65 Hz and the modulation index is 2. The individual side-band spikes are replaced by

a more-or-less continuous spectrum. However, the extent of the side-bands is limited

(approximately) to + 1) f m above and below. Here, that would be 33 Hz above and

below, making the bandwidth about 66 Hz. We see the side-bands extend from 35 to

90 Hz, so out observed bandwidth is 65 Hz.

You may have wondered why we ignored the smooth humps at the extreme ends of

the spectrum. The truth is that they are in fact a by-product of frequency modulation

(there is no random noise in this example). However, they may be safely ignored

because they are have only a minute fraction of the total power.

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RESULT:

CONCLUSION:

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DEPARTMENT

OF




ON

DESIGN OF DSBSC MODULATION AND DEMODULATION

SYSTEM USING COMMSIM


MESRA, RANCHI

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AIM : Design of DSBSC modulation and demodulation system using Commsim.

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

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.

The Carrier wave is completely independent of message signal This means that

transmission of carrier wave represents a waste of power. This points to a

shortcoming of AM, that only fraction of total transmitted power is affected by m(t).

To overcome this we may suppress the carrier component from the modulated wave.

Result in Double sideband Suppressed Carrier (DSBSC) Modulation.

In the double-sideband suppressed-carrier transmission (DSB-SC) modulation, unlike

AM, the wave carrier is not transmitted; thus, a great percentage of power that is

dedicated to it is distributed between the sidebands, which implies an increase of the

cover in DSB-SC, compared to AM, for the same power usedThus by suppressing the

carrier, we obtain a modulated wave that is proportional to the product of the carrier

wave and the base band signal

SPECTRUM

This is basically an amplitude modulation wave without the carrier therefore reducing

power wastage, giving it a 50% efficiency rate.

http://en.wikipedia.org/wiki/Amplitude_modulationhttp://en.wikipedia.org/wiki/Amplitude_modulationhttp://en.wikipedia.org/wiki/Amplitude_modulationhttp://en.wikipedia.org/wiki/Amplitude_modulation

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GENERATION

DSBSC is genereated by a mixer. This consists of an audio source combined with the

frequency carrier.

DEMODULATION

For demodulation the audio frequency and the carrier frequency must be exact

otherwise we get distortion.

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HOW IT WORKS

This is best shown graphically. Below, is a message signal that one may wish to

modulate onto a carrier, consisting of a couple of sinusoidal components.

The carrier, in this case, is a plain 10 kHz sinusoid -- pictured below.

The modulation is performed by multiplication in the time domain, which yields a 10

kHz carrier signal, whose amplitude varies in the same manner as the message signal.

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The name "suppressed carrier" comes about because the carrier signal component is

suppressed -- it does not appear (theoretically) in the output signal. This is apparentwhen the spectra of the output signal is viewed

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DEPARTMENT

OF




ON

DESIGN OF SSBSC MODULATION AND DEMODULATION



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]AIM : Design of SSBSC modulation and demodulation system using Commsim.

THEORY: Single-sideband suppressed-carrier transmission (SSB-SC):

It is a refinement of Amplitude Modulation that more efficiently uses electrical power and bandwidth It is closely related to vestigial sideband modulation (VSB

Amplitude Modulation produces a modulated output signal that has twice the

bandwidth of the original baseband signal. Single-sideband modulation avoids this

bandwidth doubling, and the power wasted on a carrier, at the cost of somewhat

increased device complexity

SIGNAL GENERATION

Bandpass filtering

Consider an amplitude-modulated signal, which will have two frequency-shifted

copies of the modulating signal (the lower one is frequency-inverted) on either side of

the remaining carrier wave. These are known as sidebands.

One method of producing an SSB signal is to remove one of the sidebands via

filtering, leaving only either the upper sideband (USB) or less commonly the lower

sideband (LSB). Most often, the carrier is reduced (suppressed) or removed entirely.

Assuming both sidebands are symmetric, no information is lost in the process. Since

the final RF amplification is now concentrated in a single sideband, the effective

power output is greater than in normal AM (the carrier and redundant sideband

account for well over half of the power output of an AM transmitter). Though SSB

uses substantially less bandwidth and power, it cannot be demodulated by a simple

envelope detector like standard AM.

Hartley modulator

An alternate method of generation known as a Hartley modulator uses phasing to

suppress the unwanted sideband. To generate an SSB signal with this method, two

versions of the original signal are generated which are mutually 90° out of phase.

Each one of these signals is then mixed with carrier waves that are also 90° out of

phase with each other. By either adding or subtracting the resulting signals, a lower orupper sideband signal results.

Throwing the baseband signal 90° out of phase cannot be done simply by delaying it,

as it contains a large range of frequencies. In analog circuits, a phasing network is

used. The method was popular in the days of valve radios, but later gained a bad

reputation due to poorly adjusted commercial implementations. Modulation using this

method is again gaining popularity in the homebrew and DSP fields. This method,

utilizing the Hilbert transform to throw the baseband audio out of phase, can be done

at low cost with digital circuitry.

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Weaver modulator

Another variation, the Weaver modulator, uses only lowpass filters and quadrature

mixers, and is a favored method in digital implementations

In Weaver's method, the band of interest is first translated to be centered at zero,conceptually by modulating a complex exponential exp( jωt ) with frequency in the

middle of the voiceband, but implemented by a quadrature pair of sine and cosine

modulators at that frequency (e.g. 2 kHz). This complex signal or pair of real signals

is then lowpass filtered to remove the undesired sideband that is not centered at zero.

Then, the single-sideband complex signal centered at zero is upconverted to a real

signal, by another pair of quadrature mixers, to the desired center frequency.

MATHEMATICAL HIGHLIGHTS

Let be the baseband waveform to be transmitted. Its Fourier transform, , isHermitian symmetrical about the axis, because is real-valued. Doubl

sidebandmodulation of to a radio transmission frequency, , moves the axis of

symmetry to , and the two sides of each axis are called sidebands.

Let represent the Hilbert transform of . Then

is a useful mathematical concept, called an analytic signal. The Fourier transform ofequals , for , but it has no negative-frequency components. So

it can be modulated to a radio frequency and produce just a single sideband.

The analytic representation of is:

(the equality is Euler'sformula

whose Fourier transform is .

When is modulated (i.e. multiplied) by , all frequency components are

shifted by , so there are still no negative-frequency components. Therefore, the

complex product is an analytic representation of the single sideband signal:

where is the real-valued, single sideband waveform. Therefore:

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And the "out-of-phase carrier waves" mentioned earlier are evident.

Lower sideband

represents the baseband signal's upper sideband, . It is also possible, and

useful, to convey the baseband information using its lower sideband, , which is

a mirror image about f=0 Hz. By a general property of the Fourier transform, that

symmetry means it is the complex conjugate of :

Note that:

The gain of 2 is a result of defining the analytic signal (one sideband) to have the

same total energy as (both sidebands).

As before, the signal is modulated by . The typical is large enough thatthe translated lower sideband (LSB) has no negative-frequency components. Then the

result is another analytic signal, whose real part is the actual transmission.

Note that the sum of the two sideband signals is

which is the classic model of suppressed-carrier double sideband AM.

SSB and VSB can also be regarded mathematically as special cases of analog

quadrature amplitude modulation.

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DEMODULATION

The front end of an SSB receiver is similar to that of an AM or FM receiver,consisting of a superheterodyne RF front end that produces a frequency-shifted

version of the radio frequency (RF) signal within a standard intermediate frequency

(IF) band.

To recover the original signal from the IF SSB signal, the single sideband must be

frequency-shifted down to its original range of baseband frequencies, by using a

product detector which mixes it with the output of a beat frequency oscillator (BFO).

In other words, it is just another stage of heterodyning.

For this to work, the BFO frequency must be accurately adjusted. If the BFO is mis-

adjusted, the output signal will be frequency-shifted, making speech sound strangeand "Donald Duck"-like, or unintelligible.

As an example, consider an IF SSB signal centered at frequency = 45000 Hz. The

baseband frequency it needs to be shifted to is = 2000 Hz. The BFO output

waveform is . When the signal is multiplied by (aka

'heterodyned with') the BFO waveform, it shifts the signal to and to

, which is known as the beat frequency or image frequency. The

objective is to choose an that results in = 2000 Hz. (The

unwanted components at can be removed by a lowpass filter (such as

the human ear).)

Note that there are two choices for : 43000 Hz and 47000 Hz, aka low-side and

high-side injection. With high-side injection, the spectral components that were

distributed around 45000 Hz will be distributed around 2000 Hz in the reverse order,

also known as an inverted spectrum. That is in fact desirable when the IF spectrum is

also inverted, because the BFO inversion restores the proper relationships. One reason

for that is when the IF spectrum is the output of an inverting stage in the receiver.Another reason is when the SSB signal is actually a lower sideband, instead of an

upper sideband. But if both reasons are true, then the IF spectrum in not inverted, and

the non-inverting BFO (43000 Hz) should be used.

If is off by a small amount, then the beat frequency is not exactly , which

can lead to the speech distortion mentioned earlier

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RESULT:

CONCLUSION

RESULT:

CONCLUSION:

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DEPARTMENT

OF




ON

GENERATION OF THE AMPLITUDE MODULATED WAVEAND CALCULATION OF % MODULATION USING

ACL01 KIT & ACL02


MESRA, RANCHI

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AIM: Generation of the Amplitude modulated wave and Calculation of %

Modulation using ACL01 kit & ACL02

APPARATUS REQUIRED:

1.

ANACOM 1/1 kit2. IC power supply (+12V, 200mA and – 12V, 50mA)

3. CRO

OTHER ACCESSORIES:CRO probes and wires.

THEORY:

When a low frequency signal controls the amplitude of high frequency signal,

we get the amplitude-modulated wave. The high frequency signal is known as carrier

and low frequency signal is called the modulating signal.When a carrier is amplitude modulated by a single sine wave the resulting

signal consists of three frequencies:

1.

Original Carrier Frequency

2. Lower Sideband Frequency (f c-f m)

3.

Upper Sideband Frequency (f c+f m)

When one of the above sideband is suppressed it is known as single sideband

modulation. Up to 50% of power can be saved by using this modulation technique.

PROCEDURE:

DSB GENERATION:

1. Connect the 1/1 module to the power supply as shown in the figure.

2. Ensure that the following initial conditions exist on the board.

a)

Audio input select switch in INT position.

b) Mode switch in DSB position.

c)

Output amplifier gain preset in fully clockwise position.

d) Speaker switch in OFF position.

3. Turn ON power to the ANACOM 1/1 board.

4.

Turn the Audio Oscillator block’s amplitude preset to its fully clock wise position.

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5. Turn the Balance preset in the balanced modulator and band pass filter circuit

to its fully clock wise position.

6. Observe the waveform at tp1, tp9 & tp3 on CRO.

7.

Turn the Balanced preset in the balanced modulator & Band pass filter circuitand observe the waveform at tp3 on CRO.

Test pin are tp1, tp9, tp3 and tp13.

SSB GENERATION:

1. Connect the 1/1 module to the power supply as shown in the figure.

2.

Ensure that the following initial conditions exist on the board.

a.

Audio input select switch in INT position.

b.

Mode switch in DSB position.

c.

Output amplifier gain preset in fully clockwise position.

d.

Speaker switch in OFF position.

3. Turn ON power to the ANACOM 1/1 board.

4.

Turn the Audio Oscillator block’s amplitude preset to its fully clock wise

position and observe waveform at tp14 on CRO.

5.

To achieve the single sideband following blocks are used:

a)

BALANCED MODULATOR

b)

CERAMIC BAND-PASS FILTER

c) BALANCED MODULATOR AND BAND-PASSFILTER

CIRCUIT-2

6. Observe the waveform at tp15, tp17 & tp20 on CRO.

RESULT:

PRECAUTIONS:

1. All the connections should be perfect.


reading must be avoided

REFERENCES:

1. Pamphlet to be supplied

2. Electronics communication System by George Kennedy.

3.

Communication System by S. Haykin,IInd

Edition.

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DEPARTMENT

OF




ON

DESIGN OF PAM MODULATION AND DEMODULATION



MESRA, RANCHI

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]AIM : Design of PAM modulation and demodulation system using Commsim.

THEORY:

Pulse-amplitude modulation, acronym PAM, is a form of signal modulation where

the message information is encoded in the amplitude of a series of signal pulses.

Example: A two bit modulator (PAM-4) will take two bits at a time and will map the

signal amplitude to one of four possible levels, for example −3 volts, −1 volt, 1 volt,

and 3 volts.

Demodulation is performed by detecting the amplitude level of the carrier at every

symbol period.

Pulse-amplitude modulation is now rarely used, having been largely superseded by pulse-code modulation, and, more recently, by pulse-position modulation.

Pulse amplitude modulation (PAM) is the transmission of data by varying the

amplitudes (voltage or power levels) of the individual pulses in a regularly timed

sequence of electrical or electromagnetic pulses. The number of possible pulse

amplitudes can be infinite (in the case of analog PAM), but it is usually some power

of two so that the resulting output signal can be digital. For example, in 4-level PAM

there are 22 possible discrete pulse amplitudes; in 8-level PAM there are 23 possible

discrete pulse amplitudes; and in 16-level PAM there are 24 possible discrete pulse

amplitudes.

In some PAM systems, the amplitude of each pulse is directly proportional to the

instantaneous modulating-signal amplitude at the time the pulse occurs. In other PAM

systems, the amplitude of each pulse is inversely proportional to the instantaneous

modulating-signal amplitude at the time the pulse occurs. In still other systems, the

intensity of each pulse depends on some characteristic of the modulating signal other

than its strength, such as its instantaneous frequency or phase.

PAM is only one of several forms of pulse modulation. Other methods include

varying the durations (or widths), the frequencies, the positions, or the intervals of the

individual pulses in a sequence.

Pulse Amplitude Modulation (PAM) is the simplest form of pulse modulation. This

technique transmits data by varying the voltage or power amplitudes of individual

pulses in a timed sequence of electromagnetic pulses. In other words, the data to be

transmitted is encoded in the amplitude of a series of signal pulses. PAM can also be

used for generating additional pulse modulations.

If you look at this from a purely theoretical standpoint, the possible pulse amplitudes

in pulse amplitude modulation can be infinite. This is the case with analog pulseamplitude modulation. A 2 level pulse amplitude modulation causes the resulting

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signal to be digitized while a 4 level pulse amplitude modulation has 22 possible

discrete pulse amplitudes. An 8-level pulse amplitude modulation has 23, and 16-level

pulse amplitude modulation has 24 discrete pulse amplitudes.

Regarding various pulse amplitude modulation, some systems maintain the amplitude

of each pulse directly proportional to the instantaneous modulating-signal amplitudeat the time of pulse occurrence. In other pulse amplitude modulation systems, the

reverse is true - that is, inversely proportional to the instantaneous modulating-signal

amplitude at the time of pulse occurrence. In other pulse amplitude modulation

systems, the amplitude is dependent on additional factors related to the modulating

signal such as the instantaneous frequency and phase, which may be different than its

strength.

However, in practical telecommunication applications, pulse amplitude modulation is

a rare use technology, having been superceded by other techniques such as pulse

position modulation and pulse code modulation. Additionally, a technology called

quadrate amplitude modulation is widely used in telephone modems with a datatransfer rate of more than 300 Kbps.

RESULT:

CONCLUSION:

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DEPARTMENT

OF




ON

GENERATION OF DSBSC MODULATED WAVE USING

ANACOM-1/1 TRAINER KIT


MESRA, RANCHI

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AIM: Generation of DSBSC Modulated wave using Anacom-1/1 Trainer kit

OBJECTIVE:A.

To study the operation of a DSB AM Modulator.

B. To calculate the modulation index of an AM modulated

wave.

A. To study the operation of an DSB AM Modulator.

EQUIPMENT:Modules ACL-01 & ACL-02.

Power supply =/-12V

20MHz Oscilloscope

Connecting Links.

Frequency Counter.

PROCEDURE:1. Refer to the fig.1.14 & Carry out the following connections. Connect OUT

post of SINEWAVE SECTION (ACL-01) to the i/p of Balanced Modulator

(ACL-01) SIG. Post (signal post)

2. Connect output of VCO (ACL-01) OUT post to the input Balance modulator

CAR. post (ACL – 01)

4. Connect the power supply with proper polarity to the kit, while connecting

this, ensure that the power supply is OFF.

5. Switch on the power supply and Carry out the following presetting:

SINEWAVE: OUT post LEVEL about 0.5 Vpp;

FREQ. About 1 KHz

VCO: LEVEL about 1 Vpp; FREQ. About 450KHz, Switch on500KHz.

BALANCED MODULATOR: CARRIER NULL completely

rotated clockwise or counter clockwise, so as “unbalance” the

modulator and to obtain an AM signal with not suppressed carrier

across the output; OUT LEVEL in fully clockwise.

6. Connect the Oscilloscope to the inputs of the modulator post (SIG and

CAR) and detect the modulating signal and the carrier signal (fig.1.15a/b).

7. Move the probe from post SIG to post OUT (output of the modulator),

where signal modulated in amplitude is detected (fig.1.15c). Note that the

modulated signal envelope corresponds to the waveform of the DSB AMmodulating signal.

8. Vary the amplitude of the modulating signal and check the 3 following

conditions: modulation percentage lower than the 100% (fig.1.15c), equal

to the 100% (fig1.15d), superior to 100% (over modulation, fig.1.15e).

9.

Vary the frequency and amplitude of the modulating signal, and check the

corresponding variations of the modulated signal.

10.

Vary the amplitude of the modulating signal and note that the modulated

signal can result saturation or over the modulation.

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B. To calculate the modulation index of an AM modulated wave.

OBJECTIVE: To study modulation index of DSB AM modulated wave.

EQUIPMENTS: Modules ACL-01 & ACL-02.

Power supply =/-12V

20MHz Oscilloscope

Connecting Links.

PROCEDURE:

1. Perform the operation as done in procedure (a) and obtain the AM modulated

wave as shown in fig. (1.16).

2. Using the oscilloscope measure from the waveform. The amplitude B of the

modulation signal at the OUT of the balanced modulator ACL-01. The

amplitude H and h of the modulated signal, and the amplitude C of theenvelope of the modulated signal post OUT of balanced modulator (ACL-01).

3. Calculate the constant k of the modulator, equal to: k=C/B, You find a value a

little over 1.

4. Calculate the amplitude A of the carrier, equal to:

H+h

A=--------------

2

5. Calculate the percentage index of modulation m, equal to:

H-h

m=----------------*100%

H+h

RESULT:

PRECAUTION:

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