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The Islamia University of BahawalpurUniversity College of Engineering and Technology

Department of Electronics engineering

ES-324 A&D CommunicationLAB EXPERIMENT NO.01Name: --------------------------- Roll No. --------------------------Lab instructer:________________________

DSB-SC Modulation & Demodulation using MATLAB

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

In the double-sideband suppressed-carrier transmission (DSB-SC) modulation,unlike AM, the wave carrier is not transmitted; thus, a great percentage of powerthat is dedicated to it is distributed between the sidebands, which implies anincrease of the cover in DSB-SC, compared to AM, for the same power used.

DSB-SC transmission is a special case of Double-sideband reduced carriertransmission.

Matlab code for modulation:

ts=1.e-4; t=-0.04:ts:0.04; % defining input signal Ta=0.01; x1=sinc((2.*t)./Ta); x2=sinc((2*t)./Ta-1); x3=sinc((2.*t)./Ta+1); x=2*x1+x2+x3; % performing fourier transform lfft=length(t); lfft=2^ceil(log2(lfft)); X=fftshift(fft(x,lfft)); fx=(-lfft/2:lfft/2-1)/(lfft*ts); % modulation m=x.*cos(2*pi*500*t); %fourier transform
http://en.wikipedia.org/wiki/Transmission_(telecommunications)http://en.wikipedia.org/wiki/Amplitude_modulationhttp://en.wikipedia.org/wiki/Carrier_wavehttp://en.wikipedia.org/wiki/Carrier_wavehttp://en.wikipedia.org/wiki/Carrier_wavehttp://en.wikipedia.org/wiki/Double-sideband_reduced_carrier_transmissionhttp://en.wikipedia.org/wiki/Double-sideband_reduced_carrier_transmissionhttp://en.wikipedia.org/wiki/Double-sideband_reduced_carrier_transmissionhttp://en.wikipedia.org/wiki/Double-sideband_reduced_carrier_transmissionhttp://en.wikipedia.org/wiki/Carrier_wavehttp://en.wikipedia.org/wiki/Carrier_wavehttp://en.wikipedia.org/wiki/Carrier_wavehttp://en.wikipedia.org/wiki/Amplitude_modulationhttp://en.wikipedia.org/wiki/Transmission_(telecommunications)

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lfft=length(t); lfft=2^ceil(log2(lfft)+1); M=fftshift(fft(m,lfft)); fm=(-lfft/2:lfft/2-1)/(lfft*ts);

figure(1) plot(t,x, '-ko' , ...

'LineWidth' ,2, ... 'MarkerEdgeColor' , 'k' , ... 'MarkerFaceColor' , 'g' , ... 'MarkerSize' ,10);

xlabel( 't' ); ylabel( 'x(t)' ); title( 'x(t)' ); axis([-0.05 0.05 -3 3]); set(gca, 'color' , 'y' )grid on ; figure(2) plot(t,m, '-ko' , ...


xlabel( 't' ); ylabel( ' m(t)' ); title( 'x(t)cos(w_ct)' ); axis([-0.05 0.05 -3 3]); set(gca, 'color' , 'y' ); grid on ; figure(3) plot(fx,abs(X), '-ko' , ...


xlabel( 'f' ); ylabel( 'X(f)' ); axis([-600 600 0 250]); title( 'X(f)' ); set(gca, 'color' , 'y' ) grid on figure(4) plot(fm,abs(M), '-ko' , ...


xlabel( 'f' ); ylabel( 'M(f)' ); axis([-600 600 0 250]); title( ' modulated signal' ); set(gca, 'color' , 'y' ); grid on ;

Result:

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-0.05 -0.04 -0.03 -0.02 -0.01 0 0.01 0.02 0.03 0.04 0.05-3

-2

-1

0

1

2

3

t

x ( t )

x(t)

-0.05 -0.04 -0.03 -0.02 -0.01 0 0.01 0.02 0.03 0.04 0.05-3

-2

-1

0

1

2

3

t

m ( t )

x(t)cos(wct)

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Matlab code for demodulation:

dm=m.*cos(2*pi*500*t); % performong fourier transform DM=fftshift(fft(dm,lfft));

-600 -400 -200 0 200 400 6000

50

100

150

200

250

f

X ( f )

X(f)

-600 -400 -200 0 200 400 6000

50

100

150

200

250

f

M ( f )

modulated signal

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% defining bandwidth b=150; h=fir1(40,[b*ts]); % use ideal LPF of 150Hz bandwidth r=filter(h,1,dm);

R=fftshift(fft(r,lfft)); figure(1); plot(t,dm, '-ko' , ...


xlabel( ' t' ); ylabel( 'dm(t)' ); title( 'x(t)cos^2(wc.t)' ); axis([-0.05 0.05 -3 3]); set(gca, 'color' , 'y' ) grid on figure(2); plot(t,r, '-ko' , ...


xlabel( 't' ); ylabel( 'r(t)' ); title( 'r(t)' ); axis([-0.05 0.05 -3 3]); set(gca, 'color' , 'y' ) grid on figure(3) plot(fm,abs(DM), '-ko' , ...

'LineWidth' ,1, ...

'MarkerEdgeColor' , 'k' , ... 'MarkerFaceColor' , 'g' , ... 'MarkerSize' ,10);

xlabel( 'f' ); ylabel( 'DM(f)' ); title( 'spectrum of x(t)cos^2(wc.t)' ); axis([-1200 1200 0 250]); set(gca, 'color' , 'y' ) grid on figure(4)plot(fm,abs(R), '-ko' , ...


xlabel( 'Hz' ); ylabel( 'R(f)' ); title( 'spectrum of recieved signal' ); axis([-1200 1200 0 250]); grid on set(gca, 'color' , 'y' )

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Result:

-0.05 -0.04 -0.03 -0.02 -0.01 0 0.01 0.02 0.03 0.04 0.05-3

-2

-1

0

1

2

3

t

d m ( t )

x(t)cos 2(wc.t)

-0.05 -0.04 -0.03 -0.02 -0.01 0 0.01 0.02 0.03 0.04 0.05-3

-2

-1

0

1

2

3

t

r ( t )

r(t)

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Observations: It is observed that:

The transmission is done due to high frequency carrier signal. The voice signal resides inside the carrier wave.

Voice signal is safely transmitted to the receiving end by carrier wave. At receiving end, the carrier signal is received in its actual form byeliminating the carrier signal

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To Familiar with Signal Source Module 52-100-A

PERFORMANCE OBJECTIVES

Upon successful completion of this experiment, the students will be able to:

Know to use the Signal Source module. Know that its frequency can be controlled by an input voltage. Be familiar with the dB scale of voltage ratio.

EQUIPMENT REQUIRED

Signal Source (52-100-A) Power Supply (52-200-Q)

Oscilloscope,5 MHZ Frequency Meter, Digital, 1Mhz Graph Paper, Linear Graph paper,3-cycle,logarithmic-linear.

DISCUSSION

In order to communicate information over a distance, some form of modulated carrier signal mustbe used. The layout of signal source module is shown in Figure 1. The heart of the module is anintegrated circuit which is a Voltage-Controlled Oscillator (VCO) producing both triangular and square-wave outputs, although we shall use the square-wave output. You will see later that is adequate for theHigh-frequency signals in our practical experiments.

The frequency of oscillation is determined by resistance and capacitance within the Module, and by acontrol voltage V. The frequency-control voltage V is the sum of three

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Signals A, B and C Signals. A and B are external input having different sensitivities each having acalibrated potentiometer. Signal C is an internal dc voltage, adjustable by a

10- Turn potentiometer to provide manual control of frequency.

The output of the VCO is connected through a variable attenuator to the output sockets

On the right of the module.

Figure 1

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PRELIMINARY PROCEDURE

1.1 Calibration of the Voltage-Controlled Oscillator.

With the power supply switched off, make the connections to the Signal Source Module shown inFigure 2.

On the Signal Source module, make sure that the sockets AX and BX are not connected, turn the

Variable attenuator to 0 dB and the control C to 10 (ie, turn the right-hand and bottom knobs fully

clockwise). Connect you oscilloscope to the ground and 0 dB output terminals of the Signal Source module.

Set the oscilloscope to 1 s\div and the CH 1 to 0.5 V\div. Switch on the power supply. Adjust the oscilloscopes trigger Controls to obtain a stable display.

Figure 2

Now turn the frequency control C. Make a note of what happens. Use the time base of the

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oscilloscope to estimate the range of frequencies available as the frequency Control is moved

between position 0.10 and 10.0 on the scale. Note that as the Control is moved to zero, the

oscillation may possibly stop; that is why the lowest. Frequency was measured at position 0.10. The digital frequency meter will enable you to measure the frequencies more Accurately. Because

the normal 0 dB output may be at a rather low voltage for Some frequency meters, an auxiliary

output of the same frequency is provided; Labeled TTL out. The digital frequency meter is

connected to this. Tabulate your results in table-1.

.

Scale Setting Frequency (kHz)

0.10

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0Table -1

Based upon the results recorded in your table, plot a graph on linear graph paper, of Frequency

against scale setting.

1.2 Use of the External Frequency Control inputs Use the equipment as set up for Practical 1.1 Note that the input terminals Ax and Bx in the Signal Source module

enable the frequency to be changed by applying a voltage to them.

Their sensitivities are adjustable over different ranges by the respectivePotentiometers Ax and Bx.

The socket marked +1V ref, provides a Convenient voltage to apply for testing the Ax and Bx

inputs.

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Set the main frequency control C to give a frequency of 100 kHz, and Then connect the +1V ref

signal to Ax. Insert a wire link in the A signal Path (shown by the dotted line) and observe what

happens as you adjust the A sensitivity control. Make a note of the amount by which the 1V signal changes the frequency.

1 When the sensitivity control is at 0.2 When the sensitivity control is at 1.0.

In addition, determine what frequency would you expect if the control is set to0.5. Calculate your answer, then check it experimentally. The results should be recorded in Table-2. Transfer the +1V ref signal to terminal Bx and take a second, similar set of results.

Sensitivity Control

Setting

Frequency with no

+1V signal(kHz)

Frequency with

+1V signal (kHz)

Frequency Change

(kHz)

Using input A

0

1.0

0.5

Using input B

0

0.1

0.05Table -2

1.3 Calibrating the Attenuator An attenuator is a device for reducing the magnitude of a signal. The unite in

Which attenuation is quoted is the decibel (dB), which is a logarithmic measure

Of the amount of reduction. This is convenient because successive attenuations

Can be added, rather than multiplied.

The Signal Source module contains two attenuators, one variable by the controlKnob marked 0 to -20, the other having an attenuation, which is fixed by whichever Outputsocket, is chosen. If the knob is set to x, and the socket marked y is chosen, the magnitude of the output signal will be at( x+y) dB with respect to a fixed reference Value. Since 0 dB implies a

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multiplier of 1, the reference voltage is obtained at socket 0with the knob is at 0. With the at -8 for example, the output at socket -2 will be 32 dB smaller than that.

With your oscilloscope still connected to the 0 dB output, make sure that the variable attenuator is

still set to 0 dB (fully clockwise). See that sockets Ax and Bx are disconnected. Set the frequency

control C to give approximately 500 kHz (this settings not critical). Adjust the oscilloscope for a stable display and measure the peak voltage from the

Oscilloscope screen. Record your reading in a cope of Table-3.Then adjust the variable attenuatorto _ 3 dB and record the new peak-to-peak voltage In the second row of the table. Continuetaking further readings. To obtain all the values of attenuation in Table-3 You will need to usedthe various output sockets of the fixed attenuator; adjusting the Variable attenuator to make upany additional attenuation needed.

Compare the output voltage from 0 dB socket, when the variable attenuator is set to-12, with the

output from the -6dB socket, with the variable attenuator -6. This should Confirm that dB values

can be added together.

Attenuator

Setting

(dB)

Output Volts

(mV)

(peak-To-peak)

V

V

Log10 {V }

V

20 log10 { V

V

0

-3

-6

-9

-12

-15

-18

-21

-24

-27

-30

-33

-36Table -3

REVIEW QUESTIONS

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1. Which kind of signals can be generated by this module and what is frequency range.________________________________________________________________________________________________________________________________________________

2. Explain the function of Attenuator. Why the attenuators are calibrated in decibels (dB).

________________________________________________________________________________________________________________________________________________

3.

Taking the output voltage at the 0 dB setting as the reference V, calculate the

Ratio between this and every other

Voltage V, ie, V

V

Find log10 (V) then calculate thing as -20log10 (V)

V V

Note that is the same thing as -20log10 (V)

V

20log10 (V) being the output voltage V expressed in dB with reference to V

V

Enter your results in your table (Table 3-1-3), and compare the values in the last

Column with the dB values in the first column. Comment on any discrepancy.

An effective way of showing that the dB is a logarithmic unit is to use logarithmic

Graph paper. Use three-cycle logarithmic-linear paper with axes as shown in

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Figure 3-1-3 to plot the dB values against (V)

V

1.1 SummaryThe signal Source provides a square- wave output whose frequency can be varied over the approximaterang 100 kHz to 1 MHZ.

The frequency can be altered by applying an external voltage signal. Positive voltage

Increase the frequencies.

The output attenuators are calibrated in decibels (dB). The dB is a logarithmic measure

Of signal strength expressed as a ratio. If a particular voltage is taken as a reference,

Then other voltage can be expressed in terms of dB by the formula:

dB value = 20log10 ( V )

V

1.7 Practical Aspects

The choice of a square-wave oscillator for the signal source is primarily made because the circuit issimple and inexpensive to build, and will do all that is needed. There are,

However, very many different kinds of oscillator, which may be chosen to meet any

Given set of requirements.

You will discover in later assignments that sine waves have special properties, and

In particular that a sine wave has only one frequency. It will be shown too that a

Square wave can be regarded as equivalent to a series of sine wave of different

Frequencies, all added together. One sine wave, called the fundamental has the

Same frequencies as the square wave; the other, of higher frequencies, are called

Harmonics. We shall be able to ignore the harmonics, because we shall be using

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Circuits which respond to particular frequencies, and we will choose these to

Respond only to the fundamental.

A high frequency is often required for use as a carrier signal. The choice of the

Frequency range provided is high enough to demonstrate the general properties

Of high-frequency circuits, but much lower than some frequencies which are used.

This is because special care is needed at very high frequencies to avoid problems with

Stray capacitances and long unscreened leads. Even in the 100 kHz to 1 MHZ range

Which will be used, you should make the connection as short as possible and, where

Possible, keep your hands away from the modules and wiring when taking readings.

1.8Typical Results and Answers

1.8.1 Exercise 1.1

Scale Setting Frequency(kHz)

0.10 15.8

1.0 190.8

2.0 347.8

3.0 488.3

4.0 618.4

5.0 741.2

6.0 859.97.0 976.2

8.0 1091.3

9.0 1208.9

10.0 1317.8Table 3-1-1

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If such a graph where made at low frequencies, it would be found to be a straight line,

But over the frequency range used here, it will be found to be noticeably non-linear, due

To the characteristics of the integrated circuit used.Howere, this will not be important

And the graph will be useful as a calibration for use in later assignments.

8.2 Exercise 1.2

Sensitivity Control

Setting

Frequency with no+1V

Signal(kHz)

Frequency with+1V

Signal (kHz)

Frequency Change

(kHz)

Using input A

0 100 100 0

1.0 100 446.5 346.5

0.5 100 252.9(measured)

273.25(calculated)

Using input B

0 100 100 0

0.1 100 137.8 37.8

0.05 100 118.5(measure)

118.9(calculated) Table 3-1-2

1.8.3 Exercise 1.3

Attenuator

Setting

(dB)

Output Volts

(mV)

(peak-to-peak)

V

V

Log10 V

V

20log10 V)

V

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0 700 1.0 0 0 (Ref)

-3 520 1.35 0.13 -2.6

-6 320 2.18 0.34 -6.8

-9 260 2.69 0.43 -8.6

-12 180 3.89 0.59 -11.8

-15 140 5.0 0.70 -14.0

-18 90 7.78 0.89 -17.8

-21 70 10.0 1.00 -20.0

-24 45 15.56 1.19 -23.8

-27 35 20.00 1.30 -26.0

-30 22 31.82 1.50 -30.0

-33 17 41.18 1.62 -32.4

-36 12 58.33 1.77 -35.4Table 3-1-3S

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To Familiar with Tuned Circuit Module 52-100-D


Upon successful completion of this experiment, the students will be able to

That the parallel combination o f inductance and capacitance forms a tuned circuit thatresonates at a particular frequency.

That tuned circuits can be used to respond selectively to signal of particular frequencies. That their selectivity depends on the damping, or energy losses ass ociated with the circuit.

EQUIPMENT REQUIRED

Signal Source (52-100-A)

Tuned Circuit (52-100-D) Power Supply (52-200-Q) Oscilloscope,5 MHZ Plug- In 10K Graph Paper, Linear .

DISCUSSION

A capacitance stores energy when a voltage exists across its terminals. An inductance stores energy when

a current flows in it. We find therefore that when A circuit contains both inductance and capacitance, it

can oscillate, and it tends to Respond in a special way at a particular frequency called the natural

frequency.


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1.4 Damped Oscillations. This first practical does not require the Tuned Circuit 52-100-D to be connected to the Power

Supply.

With the power switched off, connect the Tuned Circuit module, function generator and

oscilloscope as shown in Figure 1.

Set the function generator to provide a square-wave output at 3 kHz. Set the oscilloscope for a time base scale of 5 s per division, with operation externally triggered

from the function generator. The Y sensitivity can be set to 100 mV per division.

Figure 1.

When the oscilloscope has been correctly adjusted, note the waveform. Turn the knob on the Tuned Circuit module to vary the capacitance. Notice that the

Frequency of the oscillation changes.

Use the time base to estimate the maximum and minimum frequencies and record

Them.

Set the frequency knob to a central position. Then estimate from the oscilloscope,The ratio by which each oscillation is smaller than the one before, and record your result.

Plug a 10 k resistor across the Hi and Lo sockets of the Tuned Circuit module using the adaptor provided. Note that the damping is now increased, so that oscillation dies away more quickly.

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1.5 Frequency Response Connect the Signal Source, and Tuned Circuit modules, frequency meter and oscilloscope as

shown in Figure 2.

Figure 2

On the Signal Source, set the attenuator to 0 dB. The connection of the Bx terminal is intendedto give fine control of its frequency. Set the B control to mid-scale, and then adjust the Ccontrol to give a frequency of 455 kHz, as nearly as you can. Check that the Bcontrol then allows the frequency to be varied either side of 455 kHz, or then adjust itaccurately to 455 kHz.

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Set the oscilloscope to free-run with internal synchronisation at a time base scale of 2 s perDivision. Set the Y scale to 50 mV per division.

Rotate the knob on the Tuned Circuit module, watching the oscilloscope. Notice that there is oneSetting for which the output signal becomes a maximum. This is the setting which makes theResonant frequency equal to the signal frequency. The circuit is then said to be tuned to the signalfrequency. Leave the knob at this setting. Do NOT touch it again during the rest of this practical.

We want now to find the frequency response; ie,. To find how the output of the tuned circuitVaries as a function of frequency. To do this, we could measure the different heights of theWaveform on the oscilloscope, but this would be tiresome and not very accurate. A better way isto use the attenuator to adjust the display height always to one easily-checked Value. Anyalteration setting needed to do this must then accurately correspond to a change in the response,measured in dB.

Adjust the attenuator until the peak-to-peak voltage is a convenient value related to thegraticuleLines, say 4 V. A setting of about -20 dB should be about right.

Record the dB setting against the frequency. Then select values of attenuation decreasing in stepsOf 3 dB (approximately, as convenient). For greatest accuracy keep the variable attenuatorsettings as near 0 as possible, making the main adjustments on the height of the oscillogram isBrought back to the reference value.

Record the dB setting and corresponding frequencies on a copy of Table 1.

Attenuation

(db)

Frequencies(kHz)

Low high

Table 1

Finally, set the frequency accurately to give maximum response, noting the dB reading.Then, altering except the signal frequency, find and record the two frequencies for which

the dB figure differs by exactly 3dB from the setting at maximum response.

From the results in Table 1, plot a graph ( on liner graph paper) of the dB valuesAgainst frequency.

Calculate the bandwidth from your results.

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It can be shown that Q, the resonant frequency

Q = f and bandwidth B are related by the formula:

B

f = ()

2

Use the above formula to calculate the value of Q.

1.6 Swept-Frequency Display Make the appropriate connections as indicated in Figure 3. Use a triangle waveform for the auxiliary signal( which is better than a sine wave; you could

experiment to find out why). Its frequency should be about 20 Hz.Now make the following settings.

On the Signal Source:

Set the attenuation to dB.

Set the Ax and Bx controls to zero.

Adjust the frequency control C so that the frequency meter reads about 455 kHz.

On the oscilloscope:

Set the Y -channel for dc-coupling and for a sensitivity of 0.5V/division.

If using Figure 3 -2-10, set the timebase to free-run with a scale setting of 2 ms/division.

If using Figure 3 -2-11, switch to X-Y operation, then adjust the X sensitivity and/or the outputof the auxiliary signal source until the display just sweeps across the width of the screen.

On the Tuned Circuit:

Adjust the tuning of the module to resonance, shown by maximum Y -amplitude on theoscilloscope.

On the Signal Source:

slowly increase the Ax or Bx sensitivity controls and the display should change shape.Adjust the manual frequency control C until the peak amplitude occurs in the middle of the screen.

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Figure 3.

RVIEW QUESTIONS

1 Explain is the effect on the peak response.

2 Explain the frequency-slective behaviour of tuned circuits. ___________________________________________________________________________

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Department of Electronics engineering ES-324 A&D Communication

LAB EXPERIMENT NO.04Name: --------------------------- Roll No. --------------------------Lab instructer:________________________

To Familiar with Electromechanical Filters Module 52-100-D


Upon successful completion of this experiment, the students will be able to

Know various mechanical resonators that can be coupled into electrical circuits. Know how to use a quartz crystal to obtain a very narrow bandwidth of transmission. Be familiar with a typical electromechanical band-pass filter

EQUIPMENT REQUIRED

Signal Source (52-100-A) Tuned Circuit (52-100-D) Power Supply (52-200-Q) Filters (52-100-C) Oscilloscope,5 MHZ Plug- In 620 Graph Paper Linear

DISCUSSION

Some material when subjected to mechanical stress, develop electrical signals and,

Conversely, when subjected to electrical stress they deform mechanically. They are said to be piezo-

electeric (from the Greek word piezon meaning pressure). A piece of such

Material, provided with suitable electrodes, can therefore be coupled to an electrical circuit.

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In this experiment we shall examine a very simple form of filter, using a piece of quartz crystal as a

resonator; this providing a very narrow bandwidth filter. Quartz is a piezo-electric substance which is

very stable and has vary low damping. It therefore provides excellent resonance at a frequency which is

very stable.


1.1 Simple Crystal Filter

Connect the 52-100-A Signal source and 52-100-C Filters modules, the frequency, and

oscilloscope as shown in Figure1. The Y lead to the oscilloscope must be short.

Set the oscilloscope for a time base scale of 2 s per division, free- running with internalsynchronization. The Y sensitivity can be set to 50mV per division.

Adjust the frequency of the signal source to 455KHz .This must be done very carefully, starting

with the B control knob in its central position; using the C knob to get as close as possible before

finally returning to the B knob for fine adjustment.

Now watch then oscilloscope and very slowly and carefully alter the fine adjustment. You should

find that there is very narrow range of adjustment over which the oscilloscope shows a wave form

of about 2 V peak to peak amplitude.

If this does not happen, try again more slowly. If that does not work, re-check that your range of fine control is centered on 455 KHz and then set the frequency meter so that you can read

changes in frequency of 10Hz or less.

Measure the frequency at which this resonance occurs.Compare it with the nominal value of 455

KHz.

Estimate the bandwidth at 3 db down and hence calculate the Q of the crystal, as:

Q = f

B

Where B is the bandwidth and f is the resonant frequency.

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Fig. 1

1.2 Anti- Resonance This practical will need the 52-100-D Tuned Circuit module to be tuned to 455 kHz. Be careful

not to alter the frequency of the signal source. You can set the tuned circuit using your results of

Lab. 2. Alternatively, connect its primary terminals temporarily to the signal source and

secondary to the oscilloscope and tune for maximum response.

Connect the equipment as shown in Figure 2. Set the oscilloscope timebase to 500 ms/division, or as nearly as the oscilloscope permits. Check

the voltage of the timebase output. If it is much more than 2 V peak-to peak, it may be necessary

to reduce it by an external attenuator before applying it to the Bx terminal. The peak-to peak

voltage, multiplied by the B control setting, should be about 0.02 V.

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Fig.2

Set the variable capacitor of the Filters m odule to min. Then, very slowly and carefully use the

fine frequency control AX on the Signal Source module, and if necessary, the coarse control C, to

adjust the signal frequency until you can see the amplitude of the waveform rise sharply to a peak

in the centre of the screen.

The sharp peak is due to the series resonance of the crystal. On one3 side of it you should see a

notch in the response; the response passes through a minimum at a frequency slightly different

from the peak frequency

The minimum in the response is sometimes called an anti-resonance, to distinguish it from the

resonance, which C forms a parallel tuned circuit with the inductive reactance of L and C in

series.

1.3 Ceramic Filter1.3.1 Frequency Response of a Ceramic Filter

Connect the Signal Source and Filters modules, and Y1 channel of the oscilloscope as shown in

Figure3.

There may now be a comparatively large signal displayed. Reduce the Y sensitivity to

0.2V/division, if necessary, to get it within the screen height. Set the output of the sweep

oscillator to 10 Hz.

Now on the Signal Source module, increase the setting of control Bx. Depending on which circuit

you are using, it may be necessary also to adjust control Ax and C. You should obtain a display

more or less like Figure 4.

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Sketch the shape of the frequency response. Mark on your sketch the peak-to peak voltage

averaged over the ripples in the pass-band response.

Fig.3

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Fig.4

RVIEW QUESTIONS

1. Find the amplitude of the response at 8 kHz either side of the centre frequency. Note that it willbe necessary in dB relative to the pass-band response.

_____________________________________________________________________

2. In which direction the frequency of anti-resonance move initially and why?.

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Department of Electronics engineering ES-324 A&D Communication

LAB EXPERIMENT NO.08Name: --------------------------- Roll No. --------------------------Lab instructor:________________________

Introduction to spectrum analyzer

Theory: A spectrum analyzer measures the magnitude of an input signal versus frequencywithin the full frequency range of the instrument. The primary use is to measure the power of thespectrum of known and unknown signals. The input signal a spectrum analyzer measuresis electrical, however, spectral compositions of other signals, such as acoustic pressure wavesand optical light waves, can be considered through the use of an appropriate transducer.

By analyzing the spectra of electrical signals,dominant frequency, power, distortion, harmonics, bandwidth, and other spectral components of a signal can be observed that are not easily detectable in time domain waveforms. Theseparameters are useful in the characterization of electronic devices, such as wireless transmitters.

The display of a spectrum analyzer has frequency on the horizontal axis and the amplitudedisplayed on the vertical axis. To the casual observer, a spectrum analyzer looks likean oscilloscope and, in fact, some lab instruments can function either as an oscilloscope or aspectrum analyzer.
http://en.wikipedia.org/wiki/Electricityhttp://en.wikipedia.org/wiki/Frequency_spectrumhttp://en.wikipedia.org/wiki/Acousticshttp://en.wikipedia.org/wiki/Opticshttp://en.wikipedia.org/wiki/Transducerhttp://en.wikipedia.org/wiki/Frequency_spectrumhttp://en.wikipedia.org/wiki/Electricityhttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Electric_Powerhttp://en.wikipedia.org/wiki/Distortionhttp://en.wikipedia.org/wiki/Harmonicshttp://en.wikipedia.org/wiki/Bandwidth_(signal_processing)http://en.wikipedia.org/wiki/Frequency_spectrumhttp://en.wikipedia.org/wiki/Time_domainhttp://en.wikipedia.org/wiki/Waveformhttp://en.wikipedia.org/wiki/Wirelesshttp://en.wikipedia.org/wiki/Oscilloscopehttp://en.wikipedia.org/wiki/Oscilloscopehttp://en.wikipedia.org/wiki/Wirelesshttp://en.wikipedia.org/wiki/Waveformhttp://en.wikipedia.org/wiki/Time_domainhttp://en.wikipedia.org/wiki/Frequency_spectrumhttp://en.wikipedia.org/wiki/Bandwidth_(signal_processing)http://en.wikipedia.org/wiki/Harmonicshttp://en.wikipedia.org/wiki/Distortionhttp://en.wikipedia.org/wiki/Electric_Powerhttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Electricityhttp://en.wikipedia.org/wiki/Frequency_spectrumhttp://en.wikipedia.org/wiki/Transducerhttp://en.wikipedia.org/wiki/Opticshttp://en.wikipedia.org/wiki/Acousticshttp://en.wikipedia.org/wiki/Frequency_spectrumhttp://en.wikipedia.org/wiki/Electricity

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General features & description:

Frequency Range: 9kHz~2.7GHz Input Range: -100dBm~+20dBm Average Noise Floor of -130dBm/Hz Power Measurements: ACPR / OCBW /CH Split Window: Simultaneous Measurements in Two Separate Frequency Spans. Resolution Bandwidth: 3 kHz, 30 kHz, 300 kHz and 4 MHz 100 Trace/State Memories with Date/Time stamp Battery Operation (optional) Only 10 Pounds (4.5 kg)

Function of major keys:

Span: select the spam function. Span is used to scan the entire frequency range.

Frequency: it is used to select centre, start & stop frequency.

Peak search: It will automatically find the peak signal & show the frequency & amplitude.

Amplitude: it selects the amplitude relative functions.

Marker: it selects the marker relative functions.

Scroll key: it changes the setting in fine steps.

RF input: N type connector for RF measurement input.

Editing keys: include number, unit, minus sign, back space and enter key

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