G NARAYANAMMA INSTITUTE OF TECHNOLOGY & SCIENCE

(FOR WOMEN) SHAIKPET, HYDERABAD – 500008

ANALOG COMMUNICATION LABORATORY MANUAL

DEPARTMENT OF

ELECTRONICS & COMMUNICATION ENGINEERING MARCH - 2007

G NARAYANAMMA INSTITUTE OF TECHNOLOGY & SCIENCE

(FOR WOMEN) SHAIKPET, HYDERABAD – 500008

GNITS GNITS-D / ECE / LLM / 023( ) / 01 LAB WISE-LABMANUALS DEPARTMENT : ECE

ANALO COMMUNICATION LABORATORY MANUAL

DEPARTMENT OF

ELECTRONICS & COMMUNICATION ENGINEERING MARCH - 2007

AMPLITUDE MODULATION &DEMODULATION

AIM: To study the function of Amplitude Modulation & Demodulation (under modulation, perfect modulation & over modulation) and also to calculated the modulation index. APPARATUS :

1. Amplitude Modulation & Demodulation trainer kit. 2. C.R.O (20MHz) 3. Function generator (1MHz). 4. Connecting cords & probes.

CIRCUIT DIAGRAM:

Amplitude modulation circuit diagram

Demodulation circuit diagram

THEORY:

Amplitude modulation can be produced by a circuit where the output is product of

two input signals. Multiplication produces sum and difference frequencies and thus the side

frequencies of the AM wave. Two general methods exist for achieving this multiplication,

one involves a linear relation between voltage and current in a device and the second uses a

linear device.

A linear form of modulation of modulation causes a current I, of one frequency to

pass through an impedance Z, whose magnitude varies at a second frequency. The voltage

across this varying impedance is then given by E = I sinω1t * z sinω2t

The above equation is the output is a result of multiplication of two frequencies. If

one of them is carrier frequency and the other is the modulating frequency the result is an

AM waveform. The circuit diagram of the amplitude modulation, the carrier is fed to the transistor Q1 of its base. This

produces a collector current in Q1 of carrier frequency. The impedance in the collector circuit of Q1 is decided

in the transistor Q2. Modulating signal is fed to the base Q2 which changes the impedance offered by Q2 at the

modulation frequency output is taken through a transformer coupling. When the modulating is zero Q2 offers a

fixed impedance in the collector circuit of Q2, so that the output is a constant unmodulated carrier. As the

modulating signal is applied to Q2 the impedance changes and the amplitude of carrier at output also changes in

accordance with the equ(5). Thus an amplitude modulated carrier is obtained at the output.

In a communication system a high frequency carrier is modulated by the low frequency signal. The

modulated carrier is transmitted by the transmitter antenna. At the receiver we have to recover the information

back from the modulated carrier. The process of separation of signal from the carrier is called demodulation or

detection. the demodulation circuit diagram is a linear diode detector. In this circuit the linear portion of

dynamic characteristics of diode is used and hence the circuit is a linear detector. It consists of a half wave

rectifier followed by a capacitor input filter. Input to the circuit is an AM wave with a high frequency carrier and

a low frequency envelope corresponding to the signal. The diode cuts-off the negative going portion of the AM

wave. Capacitor ‘C’ charges up to the peak of the carrier cycle through the low resistance rd and then during

negative half cycle tries to discharge through relatively high resistance RL. Capacitor value is so chosen that this

discharge is very small in time between carrier half cycles. Hence the capacitor voltage tends to follow the

envelope of the carrier and the voltage available across RL is simply the modulation envelope superimposed on a

constant level. A dc level in the output comes because the current through diode flows in the form of pulses

occurring at the peak of each carrier cycle.

When the input to detector circuit is a AM waveform then the one of the component in VR cannot be

assumed to be constant all the time. Actually it is constant over a few cycles of carrier in which time it is

assumed that modulating signal being low frequency would not have changed appreciably. Due to this reason

the measurement of detection efficiency can be done on an un modulated carrier because VR would be expected

to be constant.

PROCEDURE:- 1. The circuit should be connected first, only then the power supply should be switched on.

2. Measure the frequency & amplitude (p-p) of the fixed carrier signal present on the kit.

3. Connect the circuit as per the given circuit diagram.

4. Apply fixed frequency carrier signal to carrier input terminals.

5. Apply modulating signal from function generator of 1VP-P of 500Hz.

6. Note down and trace the modulated signal envelop on the CRO screen.

7. Find the modulation index by measuring Vmax and Vmin from the modulated (detected/ traced) envelope.

M=(Vmax –Vmin)/(Vmax+Vmin)

8. Repeat the steps 5,6 & 7 by changing the frequency or/& amplitude of the modulating signal so as to

observe over modulation, under modulating and perfect modulation.

9. For demodulation, apply the modulated signal (A.M) as an input to the demodulator and verify the

demodulated output with respect to the applied modulating signals and their respective outputs.

EXPECTED WAVEFORMS:-

RESULT QUESTIONS 1.Define AM and draw its spectrum? 2.Draw the phases representation of an amplitude modulated wave?

3.Give the significance of modulation index?

4.What are the different degree of modulation?

5.What are the limitations of square law modulator?

6.Compare linear and nonlinear modulators?

7.Compare base modulation and emitter modulation?

8.Explain how AM wave is detected?

9.Define detection process?

10.What are the different types of distortions that occur in an envelop detector? How can they be eliminated?

FREQUENCY MODULATION & DEMODULATION AIM: To study the functioning of frequency modulation & demodulation and to calculate the modulation

index.

APPARATUS: 1.Frequency modulation & demodulation trainer kit.

2. C.R.O (20MHz)

3.Function generator (1MHz).

4.Connecting chords & probes.

CIRCUIT DIAGRAM:

FREQUENCY MODULATION CIRCUIT DIAGRAM:

FREQUENCY DEMODULATION CIRCUIT DIAGRAM:

THE

ORY:

This kit consists of wired circuitry of:

1. AF generator.

2. Regulated power supply

3. Modulator.

4. Demodulator.

1.AF Generator:

This is an op-amp placed wein bridge oscillator. A FET input quad Op-Amp (ICTL084) is used here to

generate low frequency signals of 500 Hz and 5KHz to use as modulating signal. In this experiment, a

switch is provided to change the frequency. Required amplification is provided to avoid loading effect.

2. Regulated power supply:

This consists of bridge rectifier, capacitor filters and three terminal regulators to provide required dc

voltages in the circuit i.e. +15 V, -15 V, +5V .

3. Modulator:

This has been developed using XR-2206 integrated circuit. The IC XR-2206 is a monolithic

Function generator; the output waveforms can be both amplitude and frequency modulated by an external

voltage. Frequency of operation can be selected externally over a range of 0.01 MHz. The circuit is ideally

suited for communications, instrumentations and function generator applications requiring sinusoidal tone,

AM, FM or FSK generation. In this experiment, IC XC-2206 is connected to generate sine wave, which is

used as a carrier signal. The amplitude of carrier signal is 5vPP of 100 KHz frequencies.

4. Demodulator:

This had been developed using LM4565 integrated circuit. The IC LM565 is a general-purpose

phase locked loop containing a stable, highly linear voltage controlled oscillator for low distortion FM

demodulation.

The VCO free running frequency f0 is adjusted to the center frequency of input frequency modulated

signal i.e. carrier frequency which is of 100 KHz. When FM signal is connected to the demodulator input,

the deviation in the input signal (FM signal) frequency which creates a DC error voltage at output of the

phase comparator which is proportional to the change of frequency δf. This error voltage pulls the VCO to

the new point. This error voltage will be the demodulated version of the frequency modulated input signal.

PROCEDURE: 1. Switch on the power supply of the kit (without making any connections).

2. Measure the frequency of the carrier signal at the FM output terminal with input terminals open and plot

the same on graph.

3. Connect the circuit as per the given circuit diagram.

4. Apply the modulating signal of 500HZ with 1Vp-p.

5. Trace the modulated wave on the C.R.O & plot the same on graph.

6. Find the modulation index by measuring minimum and maximum frequency deviations from the carrier

frequency using the CRO.

frequency signal modulating

deviationFrequency maximumfS Mr ==

7. Repeat the steps 5& 6 by changing the amplitude and /or frequency of the modulating Signal.

8. For demodulation apply the modulated signal as an input to demodulator circuit and compare the

demodulated signal with the input modulating signal & also draw the same on the graph.

EXPECTED WAVEFORMS

NOTE: Note down all the input and output wave forms of the signals applied and obtained respectively.

RESULT:

QUESTIONS 1.Define frequency modulation?

2.Mention the advantages of indirect method of FM generation?

3.Define modulation index and frequency deviation of FM?

4.What are the advantages of FM?

5.What is narrow band FM?

6.Compare narrow band FM and wide band FM?

7.Differrntiate FM and AM?

8.How FM wave can be converted into PM wave?

9,State the principle of reactance tube modulator?

10.Draw the circuit of varactor diode modulator?

11.What is the bandwidth of FM system?

12.Want is the function of FM discriminator?

13.How does ratio detector differ from fosterseely discriminator?

14.What is meant by linear detector?

15.What are the drawbacks of slope detector?

BALANCED MODULATOR AIM: To study the following of the Balanced Modulator as a

1. Frequency Doubler

2. DSB-SC Generator.

APPARATUS:

1. Balanced modulator trainer kit 2. C.R.O (20MHz)

3. Connecting cords and probes

4. Function generator (1MHz)

CIRCUIT DIAGRAM:

THEORY: 1. RF Generator:

Colpitts oscillator using FET is used here to generate RF signal of approximately 100 KHz Frequency

to use as carrier signal in this experiment. Adjustments for Amplitude and Frequency are provided in panel for

ease of operation.

2. AF Generator:

Low Frequency signal of approximately 5KHz is generated using OP-AMP based wein bridge

oscillator. IC TL 084 is used as an active component, TL 084 is FET input general purpose quad OP-AMP

integrated circuit. One of the OP-AMP has been used as amplifier to improve signal level. Facility is provided to

change output voltage.

3. Regulated Power Supply:

This consists of bridge rectifier, capacitor filters and three terminal regulators to provide required dc

voltage in the circuit i.e. +12v, -8v @ 150 ma each.

4. Modulator:

The IC MC 1496 is used as Modulator in this experiment. MC 1496 is a monolithic integrated circuit

balanced modulator/Demodulator, is versatile and can be used up to 200 Mhz.

Multiplier:

A balanced modulator is essentially a multiplier. The output of the MC 1496 balanced modulator is

proportional to the product of the two input signals. If you apply the same sinusoidal signal to both inputs of a

ballooned modulator, the output will be the square of the input signal AM-DSB/SC: If you use two sinusoidal

signals with deferent frequencies at the two inputs of a balanced modulator (multiplier) you can produce AM-

DSB/SC modulation. This is generally accomplished using a high- frequency “carrier” sinusoid and a lower

frequency “modulation” waveform (such as an audio signal from microphone). The figure 1.1 is a plot of a

DSB-SC waveform, this figure is the graph of a 100KHz and a 5 KHz sinusoid multiplied together. Figure 1.2

shows the circuit that you will use for this experiment using MC 1496 balanced modulator/demodulator.

PROCEDURE:-

I-Frequency Doubler 1. Connect the circuit as per the given circuit diagram.

2. Switch on the power to the trainer kit.

3. Apply a 5 KHz signal to both RF and AF inputs of 0.1VP-P.

4. Measure the output signal frequency and amplitude by connecting the output to CRO.

5. Repeat the steps 3 and 4 by changing the applied input signal frequency to 100KHZ and

500KHz. And note down the output signals.

NOTE:- Amplitude decreases with increase in the applied input

frequency. II-Generation of DSB-SC

1. For the same circuit apply the modulating signal(AF) frequency in between 1Khz to 5Khz

having 0.4 VP-P and a carrier signal(RF) of 100KHz having

a 0.1 VP-P .

2. Adjust the RF carrier null potentiometer to observe a DSB-SC waveform at

the output terminal on CRO and plot the same.

3. Repeat the above process by varying the amplitude and frequency of AF but RF maintained

constant.

NOTE :- Note down all the waveforms for the applied inputs and their respective outputs.

EXPECTED WAVEFORMS:-

Note: In frequency doubling If the input time period is “T” after frequency doubling the time period

should be halfed.i.e,”T/2”.

RESULT:

QUESTIONS 1.What are the two ways of generating DSB_SC.

2.What are the applications of balanced modulator?

3.What is the advantages of suppressing the carrier?

4.What are the advantages of balanced modulator?

5.What are the advantages of Ring modulator?

6.Write the expression for the output voltage of a balanced modulator?

PRE-EMPHASIS & DE-EMPHASIS

AIM: To study the functioning of Pre-Emphasis and De-Emphasis circuits.

APPARATUS: 1.Pre-emphasis & De-emphasis trainer kits.

2. C.R.O (20MHz )

3. Function generator (1MHz).

4. Patch chords and Probes.

CIRCUIT DIAGRAM:

THEORY:

Frequency modulation is much immune to noise than amplitude modulation and significantly more

immune than phase modulation. A single noise frequency will affect the output of the receiver only if it falls

with in its pass band.

The noise has a greater effect on the higher modulating frequencies than on lower

ones. Thus, if the higher frequencies were artificially boosted at the transmitter and

correspondingly cut at the receiver, improvement in noise immunity could be expected. This

booting of the higher frequencies, in accordance with a pre-arranged curve, is termed pre-

emphasis, and the compensation at the receiver is called de-emphasis.

If the two modulating signals have the same initial amplitude, and one of them is pre-

emphasized to (say) twice this amplitude, whereas the other is unaffected (being at a much

lower frequency) then the receiver will naturally have to de-emphasize the first signal by a

factor of 2, to ensure that both signals have the same amplitude in the output of the receiver.

Before demodulation, I.e. while susceptible to noise interference the emphasized signal had

twice the deviation it would have had without pre-emphasis, and was thus more immune to

noise. Alternatively, it is seen that when this signal is de-emphasized any noise sideband

voltages are de-emphasized with it, and therefore have a correspondingly lower amplitude

than they would have had without emphasis again their effect on the output is reduced. The amount of pre-emphasis in U.S FM broadcasting, and in the sound transmissions accompanying

television, has been standardized at 75 microseconds, whereas a number of other services, notably CCIR and

Australian TV sound transmission, use 50 micro second. The usage of microseconds for defining emphasis is

standard. 75 microseconds de-emphasis corresponds to a frequency response curve that is 3 db down at the

frequency whose time constant is RC is 75 microseconds. This frequency is given by f=1/2ΠRC and it is

therefore 2120 Hz; with 50-microseconds de-emphasis it would have been 3180 Hz. Figure I shows pre

emphasis and de-emphasis curves for a 7 microseconds emphasis, as used in the united states.

If emphasis is applied to amplitude modulation, some improvement will also result,

but it is not as great as in FM because the highest modulating frequencies in AM are no more

affected by noise than any others. Apart from that, it would be difficult to introduce pre-emphasis and de-emphasis in existing AM

services since extensive modifications would be needed, particularly in view of the huge numbers is receivers in

use.

PROCEDURE:

I-PRE-EMPHASIS

1. Connect the circuit as per the circuit diagram

2. Apply a sine wave to the input terminals of 2 VP-P (Vi)

3. By varying the input frequency with fixed amplitude, note down the output amplitude (Vo) with respect

to the input frequency.

4. Calculate the gain using the formula

Gain = 20 log (VO/ VI) db

Where VO = output voltage in volts.

VI = Input voltage in volts.

And plot the frequency response.

II-DE-EMPHASIS

1. Connect the circuit as per circuit diagram.

2. Repeat steps 2,3 & 4 of Pre-Emphasis to de-emphasis also.

EXPECTED WAVEFORMS Gain Gain (-db) (-db)

Frequency(Hz-khz) Frequency(Hz-khz) Fig: Pre-emphasis Fig: De-emphasis

TABULAR COLUMN:-

VI =2v S.No Input Frequency

(50Hz to 20KHz) Out put voltage (Vo) (volts) GAIN

20 log (VO/ VI) db

RESULT:

QUESTIONS

1.What is the need for pre-emphasis?

2.Explain the operation of pre-emphasis circuit?

3.Preemphasis operation is similar to high pass filter explain how?

4.Deemphasis operation is similar to low pass filter justify?

5.What is de-emphasis?

6.Draw the frequency response of a pre-emphasis circuit?

7. Draw the frequency response of a de-emphasis circuit?

8. Give the formula for the cutoff frequency of the pre-emphasis circuit?

9.What is the significance of the 3db down frequency?

CHARACTERISTICS OF MIXER

AIM: To study the functioning of a frequency mixer. APPARATUS:

1. Frequency mixer trainer kit. 2. C.R.O (20MHz) 3. Connecting cords and probes. 4. Function generator (1MHz).

CRICUIT DIAGRAM:

THEORY: To construct frequency mixer. Connect two different inputs signal at Base (IF frequency) and emitter (Local Oscillator) and the collector output is given to low pass filter to get the beat frequency and observe the wave forms.

A frequency mixer is used in very radio and television receiver, it is also used in many other electronic systems. When a sine wave drives a nonlinear circuit, we get harmonics of each sine wave plus new frequencies called the sum and difference frequencies. RELATION TO NONLINEAR DISTORTIONS

Nonlinear distortion causes harmonic and inter-modulation distortion. Any device or circuit with a nonlinear input-output relation results in nonlinear distortion of the signal. In the time domino, this means that the shape of the periodic signal changes as it passes through the nonlinear circuit. In the frequency domain, the result is a change in the spectrum of the signal. If only one input sine wave is present, only harmonic distortion occurs; if two or more input sine waves are involved, both harmonic and inter-modulation distortion occurs. MEDIUM-SIGNAL OPERATION WITH TWO SINE WAVES :

When two input sine waves drive a medium-signal amplifier, something remarkable happens, in addition to harmonics new frequencies appear in the output. To be specific here is what we will prove in this section. When two input sine waves with frequencies fx and fy drive an amplifier in the medium-signal case, the output spectrum contains sinusoidal components with these frequencies. fx and fy : The two input frequencies 2fx and 2fy : The second harmonics of the input frequencies fx + fy : a new frequency equal to the sum of the input frequencies fx - fy : a new frequency equal to the difference of the input frequencies

For instance, if the two input frequencies are 1KHz and 20KHz, the output spectrum contains

sinusoidal frequencies of 1KHz and 20KHz (the two input frequencies), 2KHz and 40KHz (second harmonics), 21KHz (the sum), and 19KHz (the difference). THE BASIC IDEA

Two input sine waves drive a nonlinear circuit. As before, this results in all harmonics and inter-modulation components. The bandpass filter then passes one of the inter-modulation components, usually the difference frequency fx – fy. In term of spectra, the frequency mixer is a circuit that produces an output spectrum with a single line at fx – fy when the input spectrum is a pair of lines at fx and fy.A low – pass filter may be used in place of a bandpass filter, provided that fx – fy is less than fx or fy. For instance, if fx is 2MHz and f is 1.8 MHz, then. Fx – fy = 2 MHz – 1.8MHz = 0.2 MHz

In this case, the difference is lower than either input frequency, so we can use a low-pass filter if we wish(Low-pass filters are usually easier to build than bandpass filters.).But in applications in which fx – fy is between fx and fy, we must use a banpass filter. As an example, if fx = 2MHz and fy = 0.5 MHz, then Fx – fy = 2 MHz – 0.5 MHz = 1.5 MHz

To pass only the difference frequency, we are forced to use a band pass filter. USUAL SIZE OF INPUT SIGNALS

In most applications, one of the input signal to the mixer will be large. This is necessary to ensure nonlinear operation, unless one of the signals is large, we cannot get inter-modulation components. This large input signal is often supplied by an oscillator or signal generator.The other input signal is usually small. By itself, this signal produces only small-signal operation of the mixer. Of ten one of the reasons this signal is small is because it is a weak signal coming from an antenna.

The normal inputs to a mixer, therefore, are:

1. A large signal adequate to produce medium – or large-signal operation of the mixer. 2. A small signal that by itself can produce only small-signal operation.

PROCEDURE:

1.Connect the circuit as per the given circuit diagram.

2. Switch on the power supply of trainer kit.

3.Apply a sine wave at input Fx of 2 VP-P amplitude and 100 KHz frequency.

4.Apply a sine wave at input FY of 2 VP-P amplitude and 100 KHz frequency.

5. Observe the output waveform on the CRO.

6.Repeat the steps 3,4 and 5 by changing the values of Fx once greater than and

less than FY in a steps of 5Khz(in the range 80KHz to 120KHz)

7. Verify the output signal obtained with the theoretical value.

8. Plot the graph for Fx versus F(x-y). NOTE:- Note down the waveform of inputs as well as the respective outputs.

EXPECTED WAVEFORMS:

TABULAR COLOUMN

INPUT INPUT OUTPUT S.NO Fx (KHz) Fy (KHz) F(x-y) (KHz)

1 100 100 2 105 100 3 110 100 4 115 100 5 120 100 6 95 100 7 90 100 8 85 100 9 80 100

RESULT: QUESTIONS: 1.What is the need for a frequency mixer? 2.What is heterodyning? 3.Which filter is used at the o/p of transistor circuit in a frequency mixer? 4.What are the frequency components that appear at the collector of the transistor in the mixer circuit? 5.Why is the transistor operated in the nonlinear region in a frequency mixer?

SINGLE SIDE BAND SYSTEM AIM : To generate SSB using phase method and demodulation of SSB signal using Synchronous detector.

APPARATUS: 1.SSBtrainer kit 2. C.R.O (20MHz)

3. Function Generator (1MHz).

CIRCUIT DIAGRAM:

THEORY:

Single side band signal generation using Phase shift method and demodulation of SSB signal using

Synchronous detector. This exp consists of

1.R.F generator.

2.A.F generator.

3.Two balanced modulators.

4.Synchronous detector 5.Summer

6.Subtractor

1.RF generator:

Colpitts oscillator using FET is used here to generate RF signal of approximately 100KHz frequency to

use as carrier signal in this experiment. Phase shift network is included in the same block to produce another

carrier signal of same frequency with 900 out of phase. An individual controls are provided to vary the output

voltage. Facility is provided to adjust phase of the output signal.

2.AF generator:

This is a sine cosine generator using OP-OMP. IC TL 084 is used as an active component, TL 084 is a

FET input general perpose quad op-amp integrated circuit. A three position switch is provided to select output

frequency . An individual controls are provided to vary the output voltage.AGC control is provided to adjust the

signal shape.

3.Balanced Modulator :

This has been developed using MC 1496 IC, is a monolithic integrated circuit Balanced

modulator/demodulator, is versatile and can be used up to 200MHz. These modulators are used in this

experiment to produce DSB_SC signals. Control is provided to balance the output.

5. Summer and Subtractors:

These circuits are simple summing and subtracting amplifiers using OP-AMP. IC TL084 is used as an

active component, TL 084 is a FET input general purpose quad OP-AMP integrated circuit.

The phase shift method makes use of two balanced modulators and two phase shift networks as shown

in figure. One of the modulators receives the carrier signal shifted by 900 and the modulating signal with 00 (sine

) phase shift, where as the other receives modulating signal shifted by 900 ( cosine ) and the carrier ( RF) signal

with 00 phase shift voltage.

Both modulators produce an output consisting only of sidebands. It will be shown that both upper

sidebands leads the reference voltage by 900, and the other lags it by 900. The two lower side bands are thus out

of phase and when combined in the adder, they cancel each other. The upper side bands are in phase at the adder

and therefore they add together and gives SSB upper side band signal. When they combined in the subtractor,

the upper side bands are canceling because in phase and lower side bands add together and gives SSB lower side

band signal.

PROCEDURE:

SSB MODULATION

1.Connect the circuit as per the given circuit diagram.

2.Switch on the kit and measure the output of regulated power supplies positive and

negative voltages.

3.Observe the outputs of RF generators using CRO .Where one output is 00phase the

another is 900 phase shifted(or) is a sine wave and shifted w.r.t other (or) is a cosine

wave.

4. Adjust the RF output frequency as 100KHz and amplitude as ≥ 0.2 Vp-p

(Potentiometers are provided to vary the output amplitude & frequency).

5. Observe the two outputs of AF generator using CRO.

6. Select the required frequency (2kHz, 4kHz, 6kHz) form the switch positions for

A.F.

7. Adjust the gain of the oscillator by varying the AGC potentiometer and keep the

amplitude of 10Vp-p.

8. Measure and record the above seen signals & their frequencies on CRO.

9. Set the amplitude of R.F signal to 0. 2Vp-p and A.F signal amplitude to 8Vp-p and

connect AF-00 and RF-900 to inputs of balanced modulator A and observe DSB-

SC(A) output on CRO. Connect AF-900 and RF-00 to inputs of balanced modulator

B and observe the DSB-SC (B)out put on CRO and plot the same on graph.

10. To get SSB lower side band signal connect balanced modulator outputs (DSB-SC)

to subtractor and observe the output wave form on CRO and plot the same on

graph.

11. To get SSB upper side band signal, connect the output of balanced modulator

outputs to summer circuit and observe the output waveform on CRO and plot the

same on graph.

12.Calculate theoretical frequency of SSB (LSB & USB) and compare it with

practical value.

USB = RF frequency + AF frequency.

LSB = RF frequency – AF frequency.

EXPECTED WAVE FORMS: -

RESULT: QUESTIONS 1.What are the two ways of generation of SSB wave?

2.What are the features of filter method generation of SSB?

3.What are the adventages of phase shift method of SSB generation?

4.What are the disadvantages of phase shift method of SSB generation?

5.What are the advantages of SSB-SC AM?

6. What are the disadvantages of SSB-SC AM?

7. What are the applications of SSB-SC AM?

PHASE LOCKED LOOP

AIM: To study the characteristics of PLL.

APPARATUS:

1. PLL Trainer Kit

2. C R O (20MHz)

3. Digital Multimeter

PLL BLOCK DIAGRAM:

PLL CIRCUIT DIAGRAM:

THEORY:

Phase Locked Loop is a versatile electronic servo system that compares the phase and frequency of a given

signal with an internally generated reference signal. It is used in various applications like frequency

multiplication, FM detector, AM modulator & De modulator and FSK etc.

Free running frequency (f0):

When there is no input signal applied to pin no:2 of PLL, it is in free running mode and the free running

frequency is determined by the circuit elements Rt and Ct and is given by

F0 = 0.3/(RtCt) where Rt is the timing resistor

Ct is the timing capacitor

Lock range of PLL (fL):

Lock range of PLL is in the range of frequencies in which PLL will remain lock, and this is given by

fL = ± 8f0 /VCC Where f0 is the free running frequency

VCC = VCC –(- VCC)

= 2 VCC

Capture range(fC):

The capture range of PLL is the range of frequencies over which PLL acquires the lock. This is given

by

fC = Π21

C

L

xCxf3106.3

2Π Where fL is the lock range and

CC is filter capacitor

R = 3.6 X 103

PROCEDURE:

Free running frequency:

1. Switch on the trainer and measure the output of the regulated power supplies i.e., +12V and ±5V

2. Observe the output of the square wave generator-using oscilloscope and measure the frequency range.

The frequency range should be around 1KHz to 10KHz.

3. Calculate the free running frequency range of the circuit for different values of timing capacitor and

Rt.

4. Connect 0.1µF capacitor (CC) to the circuit and open the loop by removing short between pin 4 and 5 .

Measure the minimum and maximum free running frequencies obtainable at the output of the PLL (Pin

4)by varying the pot. Compare your results with your calculation from step 3 (theoretical value).

Simultaneously you can observe the output signal using CRO.

Table 1: 1 Free running frequency

Rt value (pot resistance in

Ohms)

Theoretical value

(frequency in KHz)

Practical value

(frequency KHz)

Lock range:

5. Calculate the lock range of the circuit for a 5KHz free running frequency and record in table 1.2.

6. Connect pins 4,5 with the help of springs and adjust potentiometer to get a free running frequency of

5KHz . Connect square wave generator output to the input of PLL circuit. Provide a 5KHz square

signal of 1 Vpp approximately (make this input frequency as close to the Vcc frequency as possible).

7. Observe the input & Output of the PLL.

8. Observe the input and output frequencies while slowly increasing the frequency of the square wave at

the input. For some range output and input are equal (This is known as lock Range and PLL is said to

be in lock with the input signal). Record the frequency at which the PLL breaks lock. (Output

frequency of the PLL will be around VCO frequency and in oscilloscope you will see a jittery waveform

when it breaks lock instead of clean square wave). This frequency is called as upper end of the lock

range and records this as F2.

9. Beginning at 5KHz, slowly decrease the frequency of the input and determine the frequency at which

the PLL breaks lock on the low end record it as F1

10. Find the lock range from F2 – F1 and compare with the theoretical values from step5.

Lock range Table 1.2:

Theoretical Value

(frequency in KHz)

Practical Value

(frequency in KHz)

Capture range:

11. Calculate the capture range of the circuit for a 5KHz free-running frequency (consider filter capacitor

(CC) is 0.1µF).

12. With the oscilloscope and counter still on pin 4, slowly increase the input frequency from minimum

(say 1KHz), Record frequency (as F3) at which the input and output frequencies of the PLL are equal,

this is known as lower end of the capture range.

13. Now keep input frequency at maximum possible (say 10KHz) and slowly reduce and record the

frequency (as F4) at which the input and output frequencies of PLL are equal. This is known as upper

end of the capture range.

14. Find capture range from F4 – F3 and compare it with the theoretical value (from step 11)

15. Repeat the steps from 11 to 14 with CC value 0.2µF

Capture range:

Filter Capacitor (CC) Theoretical value Practical value

0.1µF

0.2µF

Characteristics of PLL :

F1 F3 fo F4 F2 Capture range Lock range RESULT: QUESTIONS

1.What are the applications of PLL?

2.What is a PLL?

3.What is a VCO?

4.Define the lock range of a PLL?

5.Define the capture range of PLL?

6.Give the expression for free running frequency f0 of a PLL?

7.What is meant by the free running frequency of a PLL?

8. Give the formulae for the lock range and capture range of the PLL?

SYNCHRONOUS DETECTOR

AIM :- To generate SSB using phase method and demodulation of SSB signal using Synchronous detector.

APPARATUS:- 1.SSBtrainer kit 2. C.R.O (20MHz)

3. Function Generator (1MHz). CIRCUIT DIAGRAM: -

THEORY Single side band signal generation using Phase shift method and demodulation of SSB signal using

Synchronous detector.This exp consists of

1.R.F generator.

2.A.F generator.

3.Two balanced modulators.

4.Synchronous detector

5.Summer 6.Subtractor

1. RF generator:

Colpitts oscillator using FET is used here to generate RF signal of approximately 100KHz frequency to

use as carrier signal in this experiment. Phase shift network is included in the same block to produce another

carrier signal of same frequency with 900 out of phase. An individual controls are provided to vary the output

voltage. Facility is provided to adjust phase of the output signal.

2. AF generator:

This is a sine cosine generator using OP-OMP. IC TL 084 is used as an active component, TL 084 is a

FET input general purpose quad op-amp integrated circuit. A three position switch is provided to select output

frequency. An individual controls are provided to vary the output voltage. AGC control is provided to adjust the

signal shape.

3. Balanced Modulator :

This has been developed using MC 1496 IC, is a monolithic integrated circuit Balanced

modulator/demodulator, is versatile and can be used up to 200MHz. These modulators are used in this

experiment to produce DSB_SC signals. Control is provided to balance the output.

4. Synchronous detector:

The base band signal m(t) can be uniquely recovered from a DSB-SC signal s(t)

by first multiplying s(t) with a locally generated sine wave carrier and then low pass

filtering the product. It is assumed that the local oscillator signal is exactly coherent or

synchronous, in both frequency and phase with the carrier wave c(t) used in the

balanced modulator to generate s(t). This method of demodulation is known as coherent

detection or synchronous detection. In this unit IC MC 1496 is used as synchronous demodulator. The MC 1496 is a monolithic balanced

modulator/ balanced demodulator, is versatile and can be used up to 200MHz. On board generated carrier is

used as synchronous signal.

5. Summer and subtractors:

These circuits are simple summing and subtracting amplifiers using OP-AMP. IC TL084 is used as an

active component, TL 084 is a FET input

General purpose quad OP-AMP integrated circuit.

The phase shift method makes use of two balanced modulators and two phase shift networks as shown

in figure. One of the modulators receives the carrier signal shifted by 900 and the modulating signal with 00 (sine

) phase shift, where as the other receives modulating signal shifted by 900 ( cosine ) and the carrier ( RF) signal

with 00 phase shift voltage.

Both modulators produce an output consisting only of sidebands. It will be shown that both upper

sidebands leads the reference voltage by 900, and the other lags it by 900. The two lower side bands are thus out

of phase and when combined in the adder, they cancel each other. The upper side bands are in phase at the adder

and therefore they add together and gives SSB upper side band signal. When they combined in the subtractor,

the upper side bands are cancel because in phase and lower side bands add together and gives SSB lower side

band signal.

PROCEDURE:-

SSB MODULATION

1. Connect the circuit as per the given circuit diagram.

2. Switch on the kit and measure the output of regulated power supplies positive and

negative voltages.

3. Observe the outputs of RF generators using CRO.Where one output is 00phase the

another is 900 phase shifted(or) is a sine wave and shifted w.r.t other (or) is a cosine

wave.

4. Adjust the RF output frequency as 100 KHz and amplitude as ≥ 0.2 Vp-p (Potentiometers are provided to

vary the output amplitude & frequency).

5. Observe the two outputs of AF generator using CRO.

6. Select the required frequency (2k, 4k, 6k) form the switch positions for AF.

7. Adjust the gain of the oscillator by varying the AGC potentiometer and keep the

amplitude of 10Vp-p.

8. Measure and record the above seen signals & their frequencies on CRO.

9. Set the amplitude of R.F signal to 0.2Vp-p and A.F signal amplitude to 8Vp-p and

Connect AF-00 and RF-900 to inputs of balanced modulator A and observe DSB-

SC(A) output on CRO. Connect AF-900 and RF-00 to inputs of balanced modulator

B and observe the DSB-SC (B)out put on CRO and plot the same on graph.

10. To get SSB lower side band signal connect balanced modulator outputs (DSB-SC)

to subtractor and observe the output wave form on CRO and plot the same on

graph.

11. To get SSB upper side band signal, connect the output of balanced modulator

outputs to summer circuit and observe the output waveform on CRO and plot the

same on graph.

12. Calculate theoretical frequency of SSB (LSB & USB) and compare it with

practical value.

USB = RF frequency + AF frequency.

LSB = RF frequency – AF frequency.

SSB DEMODULATION 1. Connect the SSB signal from the summer or subtractor at SSB signal input terminal of synchronous

detector.

2. Connect RF signal (00) at RF input terminal of the synchronous detector.

Observe the detector output on CRO and compare it with the modulating signal (AF Signal) and plot the

same on graph.

EXPECTED WAVE FORMS: -

RESULT: QUESTIONS 1.What are the two ways of generation of SSB wave?

2.What are the features of filter method generation of SSB?

3.What are the advantages of phase shift method of SSB generation?

4.What are the disadvantages of phase shift method of SSB generation?

5.What are the advantages of SSB-SC AM?

6. What are the disadvantages of SSB-SC AM?

7. What are the applications of SSB-SC AM?

SSB DETECTION 8.Give the circuit for synchronous detector?

9.What are the uses of synchronous or coherent detector?

10.Give the block diagram of synchronous detector?

11.Why the name synchronous detector?

DIODE DETECTOR CHARECTERISTICS AIM: To perform demodulation of an amplitude modulated signal using

(i) Simple diode detector and (ii) Practical diode detector APPARATUS :

5. Diode detector characteristics trainer kit.

6. C.R.O (20MHz)

7. Function generator (1MHz).

8. Connecting cords & probes.

CIRCUIT DIAGRAM:

THEORY:

Demodulation involves two operations:

(i) Rectification of the modulated wave and

(ii) Elimination of RF components of the rectified modulated wave

Simple Diode Detector

The diode is the most common device used in AM demodulator. Signal (AM modulated signal) is

applied to anode and output is taken from cathode. Diode operates as half wave rectifier and passes only positive

half cycle of the modulated wav e. Further signal is applied to a parallel combination of resistor (Rd) and

capacitor (Cd) which acts as a low pass filter. This LPF allows only low frequency signal to output and it by

passes RF component to the ground.

This simple diode detector has the disadvantage that the output voltage, in addition to being

proportional to the modulating signal, also has a dc component, which represents the average envelope

amplitude (i.e. carrier signal) and a small RF ripple. However these unwanted components are removed in a

practical detector leaving only AF signal.

Practical Diode Detector:

In practical diode detector the cathode terminal of the diode is connected to one end of the secondary of

IF transformer. The other end is grounded. Secondary is tuned with the capacitor C1. The capacitors C2 and C3

are used for RF filtering.

The modulated signal is applied at the input of IF transformer. The voltage applied is negative and

hence the cathode of the diode passes is connected to the IF transformer. So the diode passes both the positive

and negative half cycles. The RF filtering is done by C2 and C3. The output is taken at the volume control.

PROCEDURE:- 10. Connect the trainer kit to mains and switch on the power supply. ( Measure the power supply voltage,

+12V and -12V)

11. Observe outputs of RF and AF signal generator using CRO, note that RF voltage is approximately

300mv p-p of 1MHz frequency and AF voltage is 10V p-p 2KHz frequency.

12. Now connect the modulator output to the simple diode detector input.

13. Observe the AF signal at the output to the simple diode detector at approximately 50% modulation

using CRO.

14. Compare it with the original AF and observe that the detected signal is same as the AF signal applied.

Thus no information is lost in the process of modulation. (Note: Only wave shape and frequency will be

same, amplitude will be attenuated and phase may change)

15. To observe AM wave at different frequencies, connect AF signal from external signal generator to the

input of modulator and observe demodulated wave at different frequencies.

16. Repeat the experiment using practical diode detector circuit.

EXPECTED WAVEFORMS:-

AM Modulated signal

AF output

RESULT QUESTIONS

1. Define the term selectivity and sensitivity of a receiver.

2. What is the purpose of diode in diode detector circuit?

3. What are the disadvantages of simple diode detector circuit?

4. What are the factors influencing the choice of intermediate frequency in receivers?

5. What are the advantages of practical diode detector?

DIGITAL PHASE DETECTOR AIM: - To detect the phase difference between two square wave signals using digital phase detector.

APPARATUS:- 1.Digital phase detector trainer kit 2. Regulated power supplies

3. C.R.O (20MHz)

4. Connecting cords & probes

5. Digital frequency counter or multimeter

CIRCUIT DIAGRAM: -

EX-OR Phase detector connection diagram

EX-OR phase detector logic diagram

NOR gate R-S Flip Flop connection diagram

THEORY The phase detector compares the input frequency and the VCO frequency and generates a dc voltage

that is proportional to the phase detector difference between the two frequencies.

Depending on the analog or digital phase detector used, the PLL is either called an analog or digital

type respectively. For simplicity, the digital phase detectors are used. Examples of digital phase detectors are

Exclusive –OR phase detector

Edge – triggered phase detector

EX-OR phase detector:

The exclusive –OR phase detector that uses an exclusive –OR gates such as CMOS type IC 4070. The

EX-OR phase detector is preferred when both the inputs are square waves. The output of the EX-OR gate is

high only when fin and fout are applied at EX-OR inputs the output is the difference between the two inputs. In

the waveforms shown below fin is lagging fout by some phase shift, the output is the phase difference between

the two signals.

Edge triggered phase detector:

Edge triggered type of phase detector is preferred when both the inputs are pulse waveforms. This edge

triggered type of phase detector is designed using by RS Flip Flop. The RS Flip Flop is formed from a pair of

cross coupled NOR gates using IC such as CD 4001. The RS Flip Flop is triggered that is the output of detector

changes its logic state on the positive (leading edge of the input fin and fout.

PROCEDURE:-

1. Switch on the trainer kit

2. Observe the output of the square wave generator available on the trainer kit using

CRO and measure the range with the help of frequency counter, the frequency

range should be around 2KHz to 13KHz.

3. Calculate the free running range of the VCO output i.e between 4th pin of IC

PLL 565 and ground. For different values of timing resistor Rt, fout is given by

Fout = ttCR

3.0 where Ct: timing capacitor = 0.01 µF, Rt : timing resistor

4. Connect the square wave to the input of IC PLL 565 and short 4th and 5th pin of

PLL. Vary the input frequency of the square wave, when the PLL is locked that is

connected to one input fout EX-OR phase detector. The other input fin of EX-OR

phase detector is the coming from inbuilt of square wave generator.

5. Connect the pulse generator output to the input of IC 565 PLL and short 4th & 5th

pin of PLL. Vary the input frequency of the square wave when the PLL is locked

that is connected to one input of Edge triggered phase detector input i.e. fout. The

other input fin of edge triggered phase detector is the pulse input coming from the

inbuilt pulse generator.

6. The dc output voltage of the exclusive-OR phase detector is a function of the phase

difference between its two inputs fin and fout.

EXPECTED WAVE FORMS: -

RESULT: QUESTIONS

1. What is a phase detector?

2. What are the various types of digital phase detectors?

3. What is the major difference between digital and analog PLLs

4. List the basic building blocks of the discrete PLL.

5. What is the major advantage of a monolithic phase detector over an exclusive OR

and edge triggered phase detector?

FREQUENCY SYNTHESIZER AIM: To study the operation of frequency synthesizer using PLL

APPARATUS:

1. Frequency synthesizer trainer AET -26A

2. Dual trace C.R.O (20MHz)

3. Digital frequency counter or multimeter

4. Patch chords

CIRCUIT DIAGRAM:

(fig.a)

Phase Comparator

Amplifier Low pass filter

V C O

Div. N Network frequency divider

Fin= fout N

fin Fout =N.f in

THEORY:

Phase locked loop:

PLL stands for ‘Phase locked loop’ and it is basically a closed loop frequency control system, which

functioning is based on phase sensitive detection of phase difference between the input and output signals of

controlled oscillator.

Before the input is applied the PLL is in free running state. Once the input frequency is applied the VCO

frequency starts change and phase locked loop is said to be in captured mode. The VCO frequency continues to

change until it equals the input frequency and PLL is then in the phase locked state. When phase locked the loop

tracks any change in the input frequency through its repetitive action.

Frequency synthesizer:

The frequency divider is inserted between the VCO and the phase comparator. Since the output of the

divider is locked to the input frequency fin, VCO is running at multiple of the input frequency. The desired

amount of multiplication can be obtained by selecting a proper divide by N network. Where N is an integer. For

example fout = 5 fin a divide by N=10, 2 network is needed as shown in block diagram. This function performed

by a 4 bit binary counter 7490 configured as a divide by 10, 2 circuit. In this circuit transistor Q1 used as a driver

stage to increase the driving capability of LM565 as shown in fig.b.

To verify the operation of the circuit, we must determine the input frequency range and then adjust the

free running frequency Fout of VCO by means of R1 (between 10th and 8th pin) and C1 (9th pin), so that the output

frequency of the 7490 driver is midway within the predetermined input frequency range. The output of the VCO

now should be 5Fin.

Free running frequency (f0):

Where there is no input signal applied, it is in free running mode.

F0 = 0.3 / (RtCt) where Rt is the timing resistor

Ct is the timing capacitor.

Lock range of PLL (fL)

FL = ± 8f0/VCC where f0 is the free running frequency

= 2VCC

Capture range (fC)

fC = C

L

XCXf3106.3

221 ππ

PROCEDURE:

1. Switch on the trainer ad verify the output of the regulated power supply i.e. ± 5V. These supplies

are internally connected to the circuit so no extra connections are required.

2. Observe output of the square wave generator using oscilloscope and measure the range with the

help of frequency counter, frequency range should be around 1KHz to 10KHz.

3. Calculate the free running frequency range of the circuit (VCO output between 4th pin and ground).

For different values of timing resistor R1 ( to measure Rt switch off the trainer and measure Rt

value using digital multimeter between given test points). And record the frequency values in

tabular 1. Fout = 0.3 / (RtCt) where Rt is the timing resistor and Ct is the timing capacitor = 0.01 µ f.

4. Connect 4th pin of LM 565 (Fout) to the driver stage and 5th pin (Phase comparator) connected to 11th

pin of 7490. Output can be taken at the 11th pin of the 7490. It should be divided by the 10, 2 times of

the fout.

EXPECTED WAVEFORMS Input waveforms

Output waveforms

Fin KHz Fout = N fin KHz Divided by 10, 2

RESULT: QUESTIONS:

1. What are the applications of PLL?

2. What is PLL?

3. Define Lock range of a PLL.

4. What is a VCO?

5. What are the applications of frequency synthesizer?

6. What is meant by the free running frequency of PLL?

7 What is the operation of a frequency synthesizer?

8. Which block is mainly used in frequency synthesizer