BTEC406 LAB Analog Communication Systems - Sri …srisukhmani.edu.in/wp-content/uploads/2014/04/acs.pdfBTEC406 LAB Analog Communication Systems 1. Generation of DSB & DSB-SC AM signal

BTEC406 LAB Analog Communication Systems

1. Generation of DSB & DSB-SC AM signal using balanced

modulator & determine modulation Index &detection of DSB using

Diode detector.

2. Generation of SSB AM signal & detection of SSB signal using

product detector.

3. To generate a FM Signal using Varactor & reactance modulation.

4. Detection of FM Signal using PLL & foster seelay & resonant

detector.

5. To Study Super heterodyne AM receiver and measurement of

receiver parameters viz. sensitivity, selectivity& fidelity.

6. To study the circuit of PWM & PPM modulator & Demodulator

7. Study of Frequency Division Multiplexing / Demultiplexing with

sinusoidal & audio inputs Using DSBSC.

8. Generation & study of Analog TDM at least 4 channels.

9. Sampling Theorem & Reconstruction of Signal from its samples

using Natural Sampling, Flat Top Sampling & Sample & Hold

Circuits & effect of duty cycle.

10. To draw & study Polar plots & polarization of Helical, Ground plane,

Yagiuda & dipole Antenna & calculate Antenna gain, Antenna beam

width, Element current & Front-back ratio of antenna.

11. To study Antenna matching using stubline.

12. To study a transmission line attenuation & frequency characteristics.

SRI SUKHMANI INSTITUTE OF ENGINEERING & TECHNOLOGY DERABASSI

DEPARTMENT: ELECTRONICS AND COMMUNICATION ENGINEERING

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ANALOG COMMUNICATION

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BTEC -406 SEMESTER:-

4th(ECE Branch)

EXPERIMENT-1

AIM:-Generation of DSB-SC signal using balanced modulator.

APPARATUS:-Balanced modulator kit, CRO, function generator.

THEORY:-

As shown in circuit diagram, the 1496 has one differential amplifier consists

of Q5-Q6 during a dual differential amplifier .Composed transistor Q1-Q2 and

Q3-Q4.As seen from the circuit the pair Q5-Q6 is voltage to current convertor,

which produces proportional current from modulating s/g and Q1-Q4 are

acting as current switches. The main points are given below:-

a. When no carrier is present and no information s/g is applied at Q5

input, a steady current flows through the Q5 to Q1-Q2 pair and Q6 to

Q3-Q4 pair. Since current source is present at both Q5-Q6 emitters, the

complete circuit is balanced and –Vo=+Vo(dc)

b. When carrier is presented and no information s/g at the input. The

output of Q2 and Q3 is out of phase and equal in magnitude and output

of Q3-Q4 are diff. amplifier. The output of Q1-Q3 and Q3-Q4 are

summed at –Vo and +Vo points. Because of opposite polarity s/g, the

sum at both output is zero, hence no output s/g is present.

c. When carrier and information s/g are both present at the input, then

the output current in Q6 has reverse of



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Q5.Since it is also a amplifier. It has current in balance at the emitter of Q1-

Q2 and Q3-Q4 pair. In this case, the output of Q3-Q4 is higher than that of Q1-

Q2. At summing point, opposite polarity s/g are cancelled out and only

information s/g is obtained.

PROCEDURE:-

1. Make the connections as shown in circuit diagram.

2. Switch ON power supply and give the information s/g and carrier s/g

to the kit of DSB-SC balanced modulator.

3. Note the amplitude and frequency of modulating s/g as well as of the

modulated output signal from the CRO.

OBSERVATION TABLE:-

OUTPUT WAVEFORMS:-

S.No

.

V f Vmax Vmin ma=Vmax*Vmi

n/

Vmax+Vmin

%

Mod.

1.

2.

3.

4.

PRECAUTIONS:-

1. Connections should be tight.

2. Reading should be taken carefully and accurately.

RESULT:- The DSB-SC signal is generated using balanced modulator with ma=100%

EXPERIMENT NO-2

AIM:-Generation of SSB AM signal & detection using product detector.

APPARATUS:- SSB generation kit, connecting leads.

BLOCK DIAGRAM:-

THEORY:-

THE NEED AND GENERATION OF SSB:-

As we know the DSB modulation and its disadvantages, the situation

improved in DSB-SC modulation. But there is still wasteful power, since in

DSB-SC both sidebands are transmitted, while they has similar information.

To recure the problem another modulation technique is employed called

„Single Sideband (actual trasmit) or SSB‟, The spectrum of DSB-SC is again

plotted with speech frequencies ranging 0.3-3.4khz.



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To obtain SSB signal in first stage DSB-SC modulation is performed. The

obtained sideband signal is passed through a appropriate filter and again

mixed with higher frequency to form final signal for transmitter amplifier.

The choice of passing LSB or USB play major role and must be defined.

Fig….The spectra of sidebands at transmitter output

From the fig. Above we not that the passing LSB results in similar

transmitting frequency as was USB before mixing. It is known that lower

the transmitter freq higher the power required to transmit it far away, If

USB is pass out the problem is get solved this is why upper sideband is

selected

10khz at an attenuation rate of 6dB capacitor are employed to tune the filters

at resonant and several are to obtain rate -30dB

Fig .The Input and output signal of SSB

DEMODULATION OF SSB, THE SYNCHRONOUS

DETECTOR:-

The demodulation can‟t be performed by simple envelope detector, since

there is no envelope. In similar way there is no carrier component. To

demodulated SSB signal another type of detection used called synchronous

detection or the system as product demodulator.

In basic from a product demodulator looks like mixer state of transistor radio

receiver. The basic difference is that the output of such receiver is in form of

another high frequency signal called intermediate frequency, whether in

demodulation case it is low frequency called low frequency beat. There is

lack of synchronousm is modulator carrier and demodulator oscillator in

these circuit. To improve the system performance, crystal controlled

oscillator are used. In our board demodulation is carried out by another chip

(LM 1496 L),

a. When no signal is present: In this case theory of DSB-SC may be

applied since there is no information signal. The result is no

presentation of local oscillator frequency due to phase cancellation

at output.

b. Before the describing the operation of demodulation, when the

signal is present at the input of Q5, let us know that the signal of

SSB is still a continuous changing signal as information of

demodulation signal amplitude and its frequency which may

cancelled as repetition of changing amplitude, through a its appear a

constant band of frequency of basic frequency, The signal is present

at the base of Q5 its dynamic impedance varies accordance with

input signal information, since input signal has input about

repetition(frequency) and its amplitude equal to modulating signal

amplitude. The amplified signal obtained at Q5 collector is get

mixed with the local oscillator frequency current. several

frequencies with their respective amplitude are amplified by Q2,

since there is possibility of 2nd

,3rd

or Nth multiplication.

PROCEDURE:-

1. Switch „ON‟ the instrument using ON/OFF switch.

2. Connect the oscilloscope channel „A‟ across carrier oscillator socket

& ground socket and observe the wave shape.

3. Now connect the „A‟ channel across modulating signal output &

ground socket and observe the different frequency signal with

variation of set frequency knob .

4.Connect the circuit as shown in fig.

5.Now connect oscilloscope channel „B‟ across DSB-SC output and

adjust DSB to obtain nearly perfect signal‟

6.Now connect the oscilloscope channel „B‟ across SSB output and

measure the frequency find out which side band is obtain after filteration.

7.Now change the modulation signal and observe that output is decrease

and some band ripple is observe. Measure SSB output amplitude peak to

peak for each modulating frequency.

PRECAUTION:-

1. Connection should be tight.

2. Readings should be taken properly.

RESULT:-SSB signal is generated and demodulated.

EXPERIMENT NO-3

AIM:-To Generate a FM signal using Varactor & Reactance modulation.

APPARATUS:-FM generation kit, Connecting wires.

THEORY:-

(I)Varactor modulation:-

The variation in capacitance from part of the tuned circuit that is used to

generate the FM signal to be transmitted. Have a look at the Varactor

modulation as shown given below.

We can see the tuned circuit which sets the operation frequency of the

oscillator and the varactor which is effectively is parallel with the tuned

circuit. Two other component which may not be immediately obvious are C1

and L1.C1 is a d.c blocking capacitor to provide d.c isolation b/w the

oscillator and the collector of the transmitter L1 is an RF choke which allows

the information signal through to the varactor but block the RF signal.

The operation of the varactor modulation is:-



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1. The information signal is applied to the base of the input transistor

and appear amplifier and inverted at the collector.

2. This allow the frequency pass through RF choke and is a applied

across varactor diode.

3. The varactor diode change its capacitance is sympathy with the

information signal and therefore changes to the total value of the

capacitance in the tuned circuit.

4. The changing value of capacitance causes the oscillation frequency to

increase & decrease under the control of information signal.

Before we start of the varactor/reactance modulation technique we

shell study a simple VCO circuit.

Simply connect the output to the socket labeled VCO modulation in

and observe the FM modulated waveform on the oscilloscope at the

VCO modulation out terminal. Keep the amplitude of audio output to

approx 4v p-p and frequency 2Khz approx observe a stable FM

modulated waveform on CRO. This should look like as under similar

waveforms as shown below,

Now disconnect the audio amplifier‟s output from modulation IN and

connect it to audio IN, keep the reactance/vibrator switch in varactor

position. Observe the output of mixer/amplifier circuit keep the

oscilloscope in X 10 position now observe the full waveform by

shifting the X position.

The resemblance b/w the output of VCO and varactor modulator are

same.

The frequency modulation in VCO was more because the frequency

difference/w the carrier and the modulating signal was very less. But

in real life application reactance and varactor modulating techniques

are used which utilizes high frequency carrier and you will not

observe signal.

PROCEDURE:-

1. Ensure that the following initial condition exist on ME 770‟s

All switched faults off.

Amplitude pot(in mixer amplifier block)in fully clockwise

direction.

VOC switch(in phase locked loop detector block)in OFF

position.

2. Make a connection as shown in figure.

3. Switch ON the power.

4. Turn the audio oscillator blocks amplitude port its fully clockwise

position and the examine the blocks output t.p.1 on the oscilloscope.

This is audio frequency sine wave which will be used as a modulation

signal note that the sine wave‟s frequency can be adjusted from about

300 Hz to approximately 3.4 Khz by adjusted the audio oscillator

frequency port.

5. Connect the output socket of the audio oscillator block to the audio

input socket of the modulation circuit block.

6. Set the varactor/reactance switch to the varactor position. This switch

select the varactor modulation also disables the reactance modulator to

prevent any interference b/w two circuits.

7. Put the varactor modulator‟s carrier frequency port in its midway

position, and then examine TP 34.Note that it is sine wave of

approximately 1.2vp-p centered on 0 v.

8. The amplitude of FM carrier is adjustable by means of mixer/amplifier

block‟s amplitude port from the zero to its hot level. Try turning this

port slowly anticlockwise, and note the amplitude of the FM signal

can be reduced to zero. Return the amplitude port to its fully

clockwise position.

9. Try varying the carrier frequency port and observe the effect.

10. Also see the effect of varying the amplitude and frequency port in

the audio oscillator block.

11. Turn the carrier frequency port in the varactor modulator block slowly

clockwise and note that in addition to the carrier frequency increase

there is decrease in the amount of frequency deviation that is present.

12. Return the carrier frequency port to its middle position and monitor

the audio input and FM output triggering the oscilloscope on the audio

input signal. Turn the audio oscillator amplitude port through its range

of adjustment and note the amplitude of FM output signal does not

change.

(II)Reactance Modulation:-

In below diagram the capacitor C and resistor R and the two

components used for the phase shifting, and together with the

transistor, from the VCC. This VCC is actually in parallel with the

tuned circuit.

The operation of Reactance Modulation is:-

1. The oscillator and the tuned circuit provide the un-modulated

carrier freq. and this freq. is present on the collector of

transistor.

2. The capacitor and the resistor provide the 90 degree phase shift

b/w collector voltage current.

3. The changing information s/g being applied to the base has the

same effect as changing the bias voltage applied to the

transistor and, this would have the effect of increasing and

decreasing the value of the capacitance.

4. As the capacitance is effectively in parallel with the tuned

circuit the variation in value will cause the frequency of

resonance to charge and hence the carrier frequency will be

varied in sympathy with the information s/g input.

PROCEDURE:-

1. The first six steps are same as that of Varactor Modulation,

2. The output s/g from the reactance modulator block appear at

TP13,before being buffered and amplified by the amplifier block. At

TP13 the capacitive loading affect may slightly affect the modulator‟s

output frequency.

3. In order to avoid this problem we will monitor the buffered FM output

s/g from the amplifier block.

4. Put the Reactance Modulator‟s pot in its midway position then examine

TP34.

5. The amplitude of FM carrier is adjustable by means of the amplifier

block‟s amplitude pot, from zero to its present level. Try turning this pot

slowly anticlockwise, and note that the amplitude of the FM s/g can be

reduced to zero.

6. The frequency of the FM s/g should be approximately 455khz at the

moment. This carrier frequency can be varied from 453khz to 460khz

by adjusting the carrier frequency in the reactance modulator block.

7. This step is same as that of 6th

step of Varactor Modulation.

8. Monitor the audio input(TP6) and FM output(TP34) triggering the

oscilloscope on the audio input s/g. Turn the audio oscillator‟s

amplitude pot throughout its range of adjustment and note that the

amplitude of the FM output s/g does not change.

RESULT:-The FM signal is generated using Varactor and Reactance

Modulation.

PRECAUTION:-

1.Connection should be tight.

2.Readings should be taken properly.

EXPERIMENT-4

AIM:- To study frequency demodulation using detuned resonant circuit

detector, phase lock loop, foster seeley detector.

APPARATUS:- frequency demodulation kit, cro, connecting lead.

THEORY:-

An frequency receiver is a very similar to an AM receiver. The most

significant change is that the demodulation must now extract the

information signal from a frequency rather than amplitude modulation

wave. The basic requirement of frequency demodulation is therefore

to convert frequency changes into change in voltage, with a minimum

amount of distortion.

DETUNED RESONANCE CIRCUIT:-

This is the simplest form of frequency demodulation. It work but it does

have a few drawback. A parallel tuned circuit deliberately detuned so that

the carrier occurs approx half way up the left hand slope of the response. We

can see that the amplitude of output signal will increase.



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Decrease as the input frequency changes. For example , if the frequency of

the incoming signal were increase, the operating point would move toward

the right on diagram. This will cause an increase in the amplitude of output

signal. A fm signal at the output it is really that simple.

PHASE LOCK LOOP DETECTOR:-

This Is another demodulator that employs a phase comparator circuit. It is a

very good demodulator and has the advantage that is available as a self

contained integrated circuit so there is no setting up required. You plug it in

and it work for . for this reason, it is often used is commercially broad cast

receiver. It has very low level distortion.

The overall action of the circuit may at sem rather pointer. There is voltage

controlled oscillator. The d.c voltage from the outpur of the LPF controls the

frequency of the oscillator. Now this voltage keeps0scillator running at the

same frequency as original as D.C voltage level that from the demodulator s/g

. the frequency response is highly linear.

FOSTER SEELEY DETECTOR:-

The last two demodulator to be considered employ the phase shift often

accompanies a change in frequency in an A.C circuit.

At first glance it look rather complicated but it become simpler if we

consider it at time. If the input frequency increase above it un

modulated value the phasor of would fall below 90 degree due to the

parallel tuned circuit become increase capacitive. The phasor

representing V1 and V2 would move clockwise. This would result in

large no of total voltage being applied across D2. Since the capacitor c1

would be charged to higher voltage. The final output voltage from the

circuit would be +Ve voltage.

4.RATIO DETECTOR:-

There are few modification that have provided a much improved protection

form noise. Diode D1 has been reversed bias so that the polarity of the

voltage across C2.

When the carrier is modulated, the voltage across C1 and C2 are equal and

additive the audio output C2 or R2, capacitor C6 is large electrolytic

capacitor. In fact it just act as a power supply or battery. The important thing

to note is keep the total voltage of C1+C2 at a constant value.

PROCEDURE:-

1. FOR DETUNED RESONANT CIRCUIT:-

Make the connection shown in figure.

Switch ON the power supply

Initially, we will use the varactor modulator to generate our FM

signal

To select the varator modulator put the reactance/varator switch in

varactor position

The audio oscillator output signal is now being used by VM to FM

a 445khz carrier sine wave

The LPF amplifier block strongly alternate the high frequency

ripple component at output and block D.C .

2.PHASE LOCKED LOOP DECETOR:-

Make the connection shown in figure.

Turned ON power to METIO module.

Now monitor the audio signal to VM block together with the

output from PLLd, triggering the oscilloscope in TP14

The LPF/amplifier bloks strongly alternate the high freq. ripple

component at the detector output and also bloks D.C

Adjust the audio oscillator block‟s amplitude and freboost and

compare the original audio signal with the final demodulator

signal.

2. FOR RATIO DETECTOR:-

Make the connection shown in figure

Turned ON power of module.

Now monitor the input signal to the VM block together with the

ratio output from the ratio detector block triggering the oscillator

on TP 14 . The signal at TP 53 should be connection two main

component.

The LPF/amplifier block removed the D.C offset voltage at the

detector output. Strongly attenuates any residual high freq. ripple

may be present.

Monitor the audio input to the VM and the output of the LPF and

adjust the gain point until the amplifier the modulated output

wave form.

Adjust the audio oscillator blocks amplitude and frequency

component and compare the original signal with the demodulated

signal.

3. FOR FOSTER SEELEY DETECTOR:-

Make the connection shown in figure

Turned ON power of module.

We will use the VM to generate FM signal since this is more

linear of the two modulators as fact as its freq. /voltage

characteristic is.

Now monitor audio input signal to the VM block together with the

foster seeley /ratio detector block triggering the oscilloscope on

TP 14.

PRECAUTION:-

Connection should be tight.

Readings must be taken carefully.

RESULT:- Frequency demodulated s/g is generated using detuned resonant

circuit detector, phase lock loop, foster seeley detector.

]

EXPERIMENT-6

AIM:-To generate the pulse width & Pulse position modulated and

demodulated signals

APPARATUS-: 1. Pulse width modulation and Demodulation Trainer. 2. CRO 3. BNC probes and Connecting Wires

THEORY:-

PWM:-In PWM, the samples of the message signal are used to vary the

duration of the individual pulses. Width may be varied by varying the

time of occurrence of leading edge, the trailing edge or both the edges of

the pulse in accordance with modulating wave. It is also called Pulse

Duration Modulation.

PPM:-In Pulse Position Modulation, both the pulse amplitude and pulse duration are held constant but the position of the pulse is varied in proportional to the sampled values of the message signal. Pulse time modulation is a class of signaling technique that encodes the sample values of an analog signal on to the time axis of a digital signal and it is analogous to angle modulation techniques. The two main types PTM are PWM and PPM. In PPM the analog sample value determines the position of a narrow pulse relative to the clocking time. In PPM rise time of pulse decides the channel bandwidth. It has low noise interference



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PROCEDURE:-

FOR PWM:-

1 . Switch on pulse width modulation and Demodulation trainer . 2 . Connect the Clk O/P to the clk I/P terminal of PWM

modulation. 3 . Connect the AF O/P to AF I/P terminal

of PWM modulation. 4 . Observe the PWM O/P at pin 3 of 555 IC on CRO.

5. By varying frequency and amplitude of the modulating signal, observe

the corresponding change in the width of the output pulses. 6 . During demodulation, connect the PWM O/P of PWM modulation to the

PWM I/P of PWM demodulation. 7 . Observe the demodulated output at AF O/P of PWM demodulation on

CRO.

FOR PPM:-

1. Switch on PPM modulator and demodulator

trainer.

2. 2 . Connect the Clk O/P to the Pin 2 of 555

IC. 3 . Connect the AF O/P to the pin 5 of 555 IC. 4 . Observe the PPM O/P at pin 3 of second IC 555 on CRO. 5 . Connect the PPM O/P to the PPM I/P of PPM

demodulation. 6. Observe the demodulated O/P on

CRO.

OBSERVATION:

S.No Control Voltage(V) o/p pulse width (msec)

Expected Wave forms for PWM:

Expected Waveforms for PPM:

Observations:

Modulating Time Period (ms) Total Time

Signal Pulse Width Pulse Width Period(ms)

Amplitude ON (ms) OFF

(Vp-p) (ms)

PRECAUTIONS:-

1. Trace waveform carefully.

2. Connection should be tight and clean.

RESULT:-

EXPERIMENT-7

AIM:-To study of frequency division multiplexing / demultiplexing with

sinusoidal and audio input using DSB-SC.

APPARATUS:-Frequency division Multiplexing/ Demultiplexing kit,

connecting wires.

THEORY:-

Multiplexing means sending of number of separate s/g together over the same

number of wire simultaneously without interference.

(I)FDM:-In FDM system the transmission bandwidth is divided b/w various use as

shown in below figure:



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Here each channel is associated with a carrier frequency which is integral or

multiple with other carrier frequency, being modulated by information. The

bandwidth of these channel is restricted to some designed frequency slot adjacent

to previous channel. To save the power DSB-SC is used.

IN below figuretwo channels FDM system is shown. The balanced modulator

produced SC-DSB output, Now taking it the output frequency summed as FDM

signal as shown below:

Taking the highest frequency 0.4-4khz, there is gap b/w the USB for f1 and LSB of

f2, sufficient to reject overlapping of sidebands. Hence in demultiplex teo band

pass filter are required with their certer frequency at f1 &f2.

(II)FDD:-To demultiplex, complex FDM s/g band pass filter are used. The ideal

filter pass out only its characteristic frequencies hence it is easy to recover the

original modulated s/g.But in practical filters, due to slanting slopes unnecessary

co-channel s/g are also pass out cause to produce ripple at demodulated output.

The product demodulators are used to demodulate the information obtained from

demultiplexed s/g. The heterodyne frequency called carrier has same frequency as

in modulator. The demodulated output which is difference of modulating USB or

LSB has, high frequency ripples whic h are cut off by LPF.

PROCEDURE:-

(I)For Multiplexing:

1. Connect the circuit as shown in figure.

2. Switch ON the power supply of kit.

3. Connect oscilloscope channel-A with carrier-A and channel-B with carrier-B

and observe the carrier waveform which is used in FDM.

4. Now connect the oscilloscope channel-A with modulating s/g-A output &

channel-B with modulating s/g-B output and observe the signals as shown

5. Keep modulating s/g-A amplitude at 1Vpp & trigger oscilloscope with this

signal.

6. Keep modulating s/g-B amplitude eat minimum position.

7. Connect oscilloscope channel-A with TP2 socket and observe the SC-DSB

signal are shown.

8. Now increase the amplitude of modulating s/g-B and observe the SC-DSB

s/g by connecting oscilloscope channel-B at the TP1.

9. Now connect the oscilloscope channel-A adder output i.e. FDM signal

output .

10.Now by increase the amplitude of modulating s/g-A and B and observe the

s/g at output. Note that the carrier A & B are integral of main OSC

frequency, which are modulated and added to form FDM signal.

(II)For Demultiplexing:

1. Connect the circuit as shown in figure.

2. Now set the 1v to peak amplitude of modulating s/g-A & B with help of

oscilloscope.

3. Now connect the oscilloscope channel-A with TP3 and channel-B with TP4

and observe the band pass filter for each signal.

4. To extract the modulating s/g it is passed through product demodulator.

5. Now connect the oscilloscope channel-A with TP5 & channel-B with TP6

and observe the putput of demodulator circuit i.e. the signal contains high

frequency ripples as shown below:

PRECAUTIONS:-


2. Reading should be taken properly.

RESULT:-

EXPERIMENT-8 AIM:- Generation & study of Analog TDM at least 4 channels. APPARATUS:-ST 2103 Trainer Kit, CRO and connecting leads . THEORY:-

FUNCTION GENERATOR:- The block provide analog signal to be used as analog input for the 2103 board although external signal can be ‘inputted’ the synchronization of these on board signal with sampling signal eliminated the oscilloscope triggering problems. The analog input are amplitude adjustable two sine ware generator marked 1KHz and 2KHz representing the signal frequency are to be used in fast mode operation. For slow mode operation two D.C. level DC1, DC2 of adjustable amplitude can be used as input signal to board. TRANSMITTER TIMING LOGIC:-

The transmitter timing logic is responsible for timing control of various activities as all operation are of vital importance. The mode switch can be switched to select either FAST or SLOW Mode of Operation. FAST mode is used to get the impression of real time operation of board. The sampling frequency is in case is 480KHz per channel. In SLOW mode, the sampling freq is 1.953 Hz/channel. Control signal and data flow or LEDs The Tx clock output of this block is the System Clock. A LED has been provided at this output to view ON/OFF (high/low) state of the Clock. In fast mode, LED cannot follow Fast Signal and therefore looks continuously illuminated. However the intensity of the LED, depend on the mark Ratio of O/P Signal. The Tx Clock Signal is connected to Rx Clock socked in ST2104 Receiver trainer in Mode1. The Socket marked Tx to its stand for transmitter time interval ‘O’ and is used to identify the first time interval of timing sequence. The O/P is a logic ‘O’ at other time interval.



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It is used to establish synchronization is Mode 1 is selected. In this mode it is connected to Rx. To socked in ST2104 Receiver trainer A LED has been provided to view the signal in slow mode. Sampling unit:- This unit convert the analog Input Signal to the PAM Signal and then multiplex them in time domain. The sampling of two channel CHO & CH1 can be observed with LED marked CHO sampled in fast mode, CH1 samples in slow mode. A/D CONVERTOR BLOCK:- In this block the time division Multiplexed analog PAM Signal are digitally coded. The operation of this unit is controlled by signal from transmitter timing logic block named SC which indicated Start of Conversion(SC). The signal can be visually observed by LED illumination is slow mode. The EC signal is output of A/D Converter Circuit indicating END OF CONVERSION. The PCM word is then clocked into latched drives which drive LEDs indicating the bit status as output word. PARALLEL TO SERIES CONVERTOR (Shift Register):- The O/P from A/D Converter is in parallel format which must be converted into a serial format prior to transmission through cable etc. This process is called parallel to Serial Convertor. It is performed by two 4-bit Shift Register. The S/L Signal is output from the transmitter timing block and indicate where the data is being loaded or shifter in Shift Register. Output Logic Block:- The block ensures that the Shift PCM data from two analog input channel and output from the Sync. Code generator are routed through the output of STZ103. Transmitter trainer at the correct cycle in the block so as the let the data settle down due to spurious transmission before transmitted. The final O/P marked ‘PCMOUTAT’ is thus the coded version of the analog Input along with Sync. Code multiplexed in time domain and delayed of half clock cycle. Each new data bit appear at the PCM output socket at the centre of each time interval according to the table PROCEDURE:-

1. Switch on the power supply.

2. Connect CRO with kit and switch on.

3. First we apply dc at I/P Channel CH0 and CH1.

4. Switch the transmitter timing logic in fast mode.

5. Take the wave shape of output on CR0.

6. Switch the transmitter timing logic in slow mode.

7. Take the wave shape of O/P from on CR0.

8. We apply ac of 1KHz at Input Channel.

9. Switch transmitter timing logic first in fast and then in slow mode..

10.We observe the O/P signal on CR0 screen by switch on the

transmitter timing signal logic first in fast and in slow mode.

11.At last we apply two different frequency as signal at two different

channel and observe the O/P signal shape at CR0 by switch

transmitter logic in fast and slow mode.

RESULT:-:- by sing two channel, we have studied about the time-diversion multiplexing.

PRECAUTIONS:-


2. Reading should be taken properly.

EXPERIMENT-9

AIM:- To study of sampling theorem & reconstruction of signal from its samples

using natural sampling, flat top sampling & samples & hold circuit & effect

of duty cycle.

APPARATUS:- Sample and hold circuit bit, CRO, connecting wires.

CIRCUIT DIAGRAM:-



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THEORY:-

The sample and hold circuit is designed to study the sampling of an analog time

varying single. The loads had inbuilt sin wave single source which is synchronised

with pulse generator which generator four different frequency single. The duty

factor of pulse can be for 0.1 or 0.5 by means of miniature toggle switch. Two hold

capacitors are provided to observe drop rate on sampling times. The sampling is

done by a sample and hold amplifier chip type LM398K. The disruption of the load

control and socket are:-

1.POWER ON:- It is a miniature toggle switch meant for power ON/OFF.

2.SINGLE GENERATOR:- 1 KHZ sine wave generated by direct synthesis

which is synchronised with the pulse generator rate of facilitate to observe wave

form in steady state. In amplitude control is provided to bring its O/P amp. From

zero to maximum Level.

3.CRO TRIGGER:- Pair of socket is provided to synchronise cathode ray

oscilloscope for standby or steady waveform. The CRO should be externally

triggered while using this facility. The amplitude is 4vpp square wave.

4.PULSE GENERATOR:- The pulse generator is composed of digital circuiting

has for preselect frequency and circuit single W/C and he obtained at sample pulse

O/P socket. The spot frequencies are skeletal by sample frequency selector and the

duty factor is controlled between 0.1-0.5 by D.F. switch.

5.C(SWITCH)SELECT:- Another miniature toggle select two different value of

hold capacitor C.

6.SAMPLE AND HOLD AMPLIFIEER:-Type LM398 unit its internal work

diagram is printed upon the panel. The analog is directly connected with sample

pulse O/P in turn should be connected with sample frequencies or trigger out

socket for low frequencies sampling.

SAMPLING THEROM:- If pulse modulation system, the no. of discrete steps of

an information time signal x(t) can be completely represented in its sample from

and recovered lock from sample from if sampling frequency fs≥2fm. Where fm is

the maximum frequency of continuous signal x(t).

The sampling thermo puts limit on the minimum value of sampling frequency fs. It

is define as nyquist rate.

PROCEDURE:-

1. Take the sample and hold circuit kit.

2. Connect the CRO and connect it at CRO trigger switch.

3. Now connect the sample the sample pulse sample with I/P socket.

4. Now take O/P occur O/P terminal with help of CRO.

5. Now observe the waveform of natural PAM and flat top PAM.

6. By selecting the capacitor switch, we obtain natural PAM [for 1C=0.001

µF] and flat top for [1C=0.001µF].

WAVE FORMS:-

PRECAUTIONS:-



RESULT:- Descried waveform is obtained.

EXPERIMENT NO-10(A)

AIM:- STUDY OF FOLDED DIPOLE ANTENNAS.

APPARATUS:-

a) Dipole antenna X 2, Folded dipole antenna.

b) ATS 10 instrument.

c) Antenna transmitter Tripod and Receiver Stepper tripod with connecting

cables, Measuring tape.

PROCEDURE:-

1. Connect the Dipole Antenna to the tripod and set the attenuator high for high

RF output. Set the length of the antenna to ƛ /2-5% or 24 cm end to end

.Keep the antenna in horizontal direction.

2. Now connect another dipole antenna to the stepper pod and set the receiver

to 600 MHz .Set the attenuator to low. Adjust the dipole for resonance at 60

MHz.

3. Set the distance between the antennas to be around 1m.Remove any stray

object from around the antennas, especially in the line of sight. Avoid any

unnecessary movement while taking the readings.

4. Now rotate the dipole antenna around its axis in steps of 5 degrees. Take the

level readings and note down.

5. Note the maximum reading out of the whole set of readings. This will form

the 0dB reference reading. Now subtract all the readings from this reference



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readings and note down. Now use this new set of readings for drawing a

plot.

6. Plot the readings on a pole or Cartesian plane with log/linear scales on the

graph papers provided at the back of the manual.

7. This plot with both the dipoles in horizontal plane shall form an Azimuth

plot.

8. Now without disturbing the setup - rotate the dipole antenna at receiver

from horizontal to vertical plane.

9. And rotate the dipole antenna around its axis in steps of 5 degrees. Take the

level readings of receiver at each step and note down.

10. Plot the readings also on a poler or Cartesian plane with log/linear scales on

the graph papers provided at the back of the manual.

11. This plot shall constitute the Elevation plot of the dipole antenna.

12. Now repeat the procedure for a folded dipole as well.

PRECAUTIONS:-



RESULT:-

sEXPERIMENT NO-10(B)

AIM:-STUDY OF GROUND PLANE WITH REFLECTOR & DIRECTOR.

APPARATUS:- a) Sipole antenna X 2.

b) ATS 10 instrument.

c) Antenna transmitter Tripod and Receiver Stepper tripod with connecting

cables, Measuring tape.

d) Directional coupler, adapter.

PROCEDURE:-

1. Connect the dipole antenna to the tripod and set the attenuator to high.

Adjust dipole for resonance at 600 MHz.

2. Now connect a yagi antenna to the stepper tripod and set the receiver

to 600 MHz. Set the attenuator to low.Set the length of the antenna

according to figure below. Keep the antenna in horizontal direction.

3. Set the distance between the antennas to be around 1m. Remove any

stray abject from around the antennas, especially in the line of sight.

Avoid any unnecessary movement while taking the reading.

4. Now rotate the yagi antenna around its axis in steps of 5 degrees. Take

the level readings of receiver at each step and note down.

5. Note the maximum reading out of the whole set of readings. This will

form the 0Db reference reading. Now use this new set of readings for

drawing a plot.



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6. Plot the readings on a polar or Cartesian plane with log/linear scales

on the graph papers provided at the back of the manual.

7. This plot with both the dipole & Yagi in horizontal plane shall form

an Azimuth plot or azimuth pattern.

8. Now without disturbing the setup – rotate the yagi antenna at receiver

from horizontal to vertical plane. Also rotate the dipole antenna to

vertical plane at the other end.

9. Now rotate the yagi antenna around its axis iin steps of 5 degrees.

Take the level readings of receiver at each step and note down.

10. Plot the reading also on a polar or Cartesian plane with log/linear

scales on the graph papers provided at the back of the manual.

11. This plot shall constitute the Elevation plot or zenith pattern of the

Yagi antenna.

12. Repeat the procedure for a 4el/3el yagi. Observe the difference in

patterns.

PRECAUTIONS:-



RESULT:-

EXPERIMENT-12

AIM:-Transmission line trainer has been designs to study the simulated L.C.R.

transmission line & to find out the value of frequency & impedance experiment

from the graph.

APPARATUS:- Transmission line trainer kit.

THEORY:-

Basic principles of transmission line:-

Transmission lines are means of conveying signals or power from one point to

another from such a broad definition, any system of wires can be consider as

forming one or more transmission line. However ,if the properties of these lines

must be taken into account, the lines might as well be arranged in some simple

,constant pattern. Thus all practical transmission lines are RRnged in some uniform

pattern, this simplifies calculations, reduces costs and increases convenience.

Types of transmission line:-

One of the simplest forms of a transmission line is the open-wire line or the twisted

pair. Since the two conductor of this type of line have same relationship with

respect to ground, it is a balanced line. But this type of line has very poor shielding

properties and has a tendency to radiate. Coaxial lines are the more popular of the

two in RF communication. A coaxial line consists of a central conductor and an

outer conductor with the outer conductor reffered to as shield normally grounded.



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Equivalent circuit representation of a transmission line:-

Since each conductor has a certain length and diameter, it must have resistance and

inductance, since there are two wires close to each other, there must be capacitance

between them finally, the wires are separated by a medium called the dielectric,

which cannot be perfect in its insulation.

Losses in transmission line:-

The three major sources of losses in RF transmission line are:

1. Copper losses

2. Dielectric losses

3. Radiation losses

Characteristic impedance of a transmission line:-

Characteristics impedance of a transmission line is its input impedance if

it was infinitely long .Refer to the transmission line equivalent circuit of

figure. it can be proved with simple mathematics that the characteristics

impedance of this line is given by:

Z=[ (R+JwL)÷(G+JwC)]½

Where,

R=Distributed resistance per unit length

L=Distributed inductance per unit length

G=Distributed shunt conductance per unit length

C=Distributed capacitance per unit length

In a lossless transmission line R=0,G=0

Therefore,

Characteristics impedance=(L/C)½

The input impedance of a transmission line terminated in its characteristics

impedance is equal to its characteristics impedance only.

PROCEDURE:-

Open circuit line:-

1. Close all the switches from S1 to S10 and leave the line open to the receiving

end.

2. Set the frequency of AF oscillator at 1000 or 1200c/s at the o/p f voltages at

2.5V.

3. Measure the voltage by using digital multimeter at receiving and of each “T”

section.

4. Plot the voltage obtained each section.

5. Repeat the next amplitude say 3V with sine wave.

Short circuit line:-

1. Short circuit the line at the receiving end.

2. Close all the switches from S1 to S10 and leave the line short all the receiving

end.

3. Set the frequency of AF oscillator at 1000 to 1200c/s at the output of voltages at

2.5V.

4. Measure the voltage by using digital multimeter at receiving and if each “T”

section.

5. Plot the voltage obtained against each section in the previous graph.

6. Attenuation constant per section.

7. Now remove short circuit from receiving end and open all switches S1 to S10.

8. Keep frequency of AF oscillators at 1200c/s and output voltage at 1V.

9. First determine the voltage at the receiving end of 1st section close switch S1

and note the output voltage at the receiving end of nd section keeping input

constant, repeat for all section.

PRECAUTIONS:-

1. AF oscillator or function generator should be use in which the impedance

should be low or below to 100ohms.

2. Input audio signal should be kept constant with the prescribed amplitude,

while measuring the voltage at each “T” section.

3. Hence plot the graph by getting the readings properly.

4. Values of components are:

R=15Ohms each

C=0.01µF each

L=165µF each

5.Error in values of R,L & C components are ±2%.

RESULT:-

Documents

BTEC406 LAB Analog Communication Systems - Sri …srisukhmani.edu.in/wp-content/uploads/2014/04/acs.pdfBTEC406 LAB Analog Communication Systems 1. Generation of DSB & DSB-SC AM signal