Welcome

to

Incharge:- Prof. M. Salim Beg

Co-Incharge:- Prof. Ekram Khan

M. Hadi Ali Khan

This Laboratory is equipped with the latest and advanced Infrastructure and provides facilities for conducting Experiments in the field of Signal Processing,

Analog and Digital Communication, Radio and Television, Microwaves and Satellite Communication, Antennas and Radar Systems.

Research Facilities are also available in the field of Wireless Blue-tooth technology, Digital Mobile Technology, Software Defined Radio, Wireless Sensor Networks and in the multimedia technology catering to the present need of the nation. under the guidance of Foreign qualified staff members of international repute.To know more about this Laboratory, visit the website of the lab. at this URL:-

http://hadi202002.tripod.com/lab.htmlM. Hadi Ali Khan

Cources Offerred

Established in the year 1977, The laboratory is presently offering the following courses for B.Tech Class:-

• EL 392 :- Communication Lab. – I

• EL 394 :- Communication Lab. – II

• EL 493 :- Communication Lab. – III

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EL 392 :- Communication Lab. – I

This is the first Laboratory Course offered to B.Tech students at their III year level.

This Laboratory course will enable the students to understand the nature of signals, Communication Channels Schemes of Analog modulation & Demodulation, they study in their theory courses, by way of performing interesting experiments.

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Staff Associated with this Course

Dr. Omar Farooq (Course In-Charge)

Prof. Z. A. Abbasi

Dr. A. A. Moinuddin

Er. M. Hadi Ali Khan

Let us begin with the Introduction to Various Communication Systems

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What is a Communication System ?

Any set of Equipments used for sending and receiving information may be called a Communication System.

The Information may be Speech, music, Images, videos, Text and Graphics or any Scientific Data.

The System used for the Transmission and Reception of the above information is referred to as A Communication System.

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Examples of Various Communication Systems

Information Comm. System used Technique used

Speech and Music Land-Line & Mobile Phones, Radio AM, FM & TDM,

GMSK

Text and Graphics Telex and Fax FSK & PSK

Videos CCTV, MATV and Cable TVs AM, FM

Scientific Data Telemetry systems such as EEG, ECG, EMG & Radar systems,

FSK, PWM, TDM etc

Computer Communication Wi-Fi and Wi-Max OFDM (BPSK,

QPSK, QAM)

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Techniques of Transmission

TDM

Analog Modulation

Digital Modulation

AM FM ASKFSKPSK

PCMDM

Modulation

PAMPPMPWM

PM QAM

FDM/OFDM

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What is Modulation ?When it is required to transmit an information signal to a largedistance, an additional HF signal is used whose parameters are controlled by the information signal.

In the terminology of Communication Engg., the information signal is referred to as message or modulating signal, usually designated by m(t), and the additional HF signal is referred to as “Carrier Signal”, usually designated by c(t). The resultant signal is called as “Modulated signal” and is usually designated by f(t).

The technique or process, in which, certain parameter of carriersignal is made to vary in accordance with the instantaneous magnitude of the modulating signal, is called the “Modulation”.

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Types of Modulation• AM:- Amplitude of c(t) is varied in accordance

with the instantanious magnitude of the m(t).

• FM:- Frequency of c(t) is varied in accordance with the instantanious magnitude of the m(t).

• PM:- Phase of c(t) is varied in accordance with the instantanious magnitude of the m(t).

Note that m(t) is taken to be a low-frequency sinusoidal signal whereas c(t) is a high-frequency sinusoidal signal.

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Waveform of AM Signal

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Modulation Index of an AM Signal

m = 25 %M. Hadi Ali Khan

Parameters for the complete Specification of AM Signal

An AM signal is completely specified by the following four parameters:-

A = AM Level in volts p-p

fm = frequency of the message signal in KHz

fc = frequency of the carrier signal in MHz

m = modulation index in %

If the AM signal is generated by using two signal generators, the above parameters can be adjusted by the respective amplitude and frequency controls of the two signal generators.

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Students must do good practice of adjusting these parameters to the required values, asthey will need to do so in many experiments (Envelope detector & Radio Receiver)

List of Experiments (8 experiments)

1. Harmonic Analysis of Square wave

2. Amplitude Modulation & Demodulation

3. Frequency Modulation & Demodulation

4. Study of Transmission Lines Characteristics using E15i kit

5. Study of Demodulation Characteristics of Envelope Detector

6. Modulation Characteristics of Pulse Width Modulator (PWM)

7. Sampling and Re-construction of signals

8. Sensitivity Characteristics of AM Radio Receiver

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Experiment No. 1

Object:-

Generate a Symmetrical Square wave and determine its first six harmonic contentsusing Sigma Harmonic Analyzer kit model COM-118

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Experimental SetupReference:- Relevant Experiment Sheet given in the Lab. Manual

Output-1

Output-2

Amplitude of harmonic

CRO Screen

Symmetrical Square wave

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Experiment no. 2 (AM)OBJECT:- Plot modulation Characteristics of A. M. (a curve between % -modulation index versus amplitude of modulating signal in volts)

AF Signal Gen.

AmplitudeModulator

1 MHz Carrier Gen.

AF Sine-wave

m(t)

AM Signal

Out

c(t)

1 MHz Sine-wave

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AM Kit model AET - 14

Reference:- Relevant Experiment Sheet given in the Lab. Manual

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Experiment no. 3 (FM)OBJECT:-a) Generate three FM signals of different modulation indices taking square wave as a modulating signal, using FM Kit model CS-1204. Calculate the modulation index in each case.(b) Using sine-wave as a modulating signal, generate an FM signal and demodulate it to recover the original modulating signal.

The modulation index of FM wave = (max. freq. deviation) / fm

Maximum frequency deviation = (fmax - fmin) ,

Where fmax is the maximum value of the carrier-frequency corresponding to

higher (positive)-value of sq-wave amplitude and fmin is the minimum value of the carrier-frequency corresponding to lower (negative)-value of sq-wave amplitude.

fm is the frequency of the message signal (square-wave)

Reference:- Relevant Experiment Sheet given in the Lab. Manual

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Wave shape of FM Signal

For taking observations on the kit, use square-wave as a modulating signal

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FM Kit model CS-1204

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Experiment no. 4 (Transmission Lines)

Object:-

(a)Determine the velocity of propagation of HF pulses through the given Transmission line. Calculate the inductance per meter (L) and the capacitance per meter length (C) of the given line.

(b) Trace the reflections observed at the other end of the givenline terminated onto the following loads.:-

(i) Resistive Load (R = 0 Ω, R = 50 Ω , R = 100 Ω )(ii) Inductive Load (any one)(iii) Capacitive Load (any one)

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Transmission Lines

Trn lines cables)

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Experimental Setup for measuring the velocity of propagation

Transmission Lines Kit model E15i

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Measure the velocity of propagation of HF Pulses traveling through the Transmission Line

td = time taken by the pulses in traveling the entire length (l) of the line

Reference:- Relevant Experiment Sheet given in the Lab. ManualM. Hadi Ali Khan

Reflections due to Different Load Terminations

When a load (capacitive or inductive or resistive) is connected to the other end of the transmission line, different shapes of the reflected pulses are observed on the CRO screen.

Trace the reflections observed due to different load terminations on three tracing papers by tracing the reflected pulses by dotted line & marking its name, and the transmitted pulse by continuous line.

Reference:- Relevant Experiment Sheet given in the Lab. Manual

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Experiment no. 5 (Envelope Detector)It is used for the demodulation of AM signal available at the output of final IF amplifier in an AM Radio receiver.

Therefore the signal required at the input of the Envelope Detector should be an AM signal having carrier frequency in the IF range = (450 KHz to 470 KHz), and modulation index around 33 %.

This AM signal is required to be generated by using two signal generators, as discussed earlier.

OBJECT:-(a) Determine the typical values of the parameters of the AM signal

properly detected by the given Envelop Detector Circuit.

(b) Determine its Detection Characteristics (maximum value of m at a constant fm & maximum value of fm at constant m).

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Experimental SetupAM

m(t)

M. Hadi Ali KhanIt can be shown that maximum fm = 5.8(m-2 – 1)1/2

Wave shapes

The message signal should be recovered without any distortion from the AM input

Measure maximum value of m for fixed fm and Maximum value of fmfor fixed m, beyond which the detector’s output gets distorted

Reference:- Relevant Experiment Sheet given in the Lab. ManualM. Hadi Ali Khan

Experiment No. 6 (PWM)

OBJECT: - Generate a PWM signal and plot its modulation characteristics (pulse-width versus DC volts input) using variable DC voltage as a modulating signal.

In pulse-width modulation, a high frequency train of pulses is used as a carrier, and its width is made to vary in accordance with the instantaneous magnitude of the message signal.

For this experiment, take variable DC voltage as a modulating signal (0.2 V to 2.6 V) and a train of pulses obtained from a pulse generator (A = 1 to 4 KHz; D = 25 %, typically) as a carrier signal, measure & record pulse-duration corresponding to input DC voltage; plot a curve between them.

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PWM Kit used in this Experiment

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PWM Circuit used in the kit

This is the ckt of mono-stable multivibratorused as a PWM.

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PWM Signal-wave shape used in actual practice

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Expt – 7 : Sampling & Re-construction of Signals

OBJECT:-

(a) Trace the samples of a sinusoidal signal obtained using the Sampling Trainer kit Model ST–2101 at any three different sampling frequencies and take observations to verify Sampling Theorem (NyquistCriteria).

(b) Re-construct the sampled signal using 2nd orderand the 4th order Low-Pass filters and trace the wave-shapes of the re-constructed signals.

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Expt – 7 : Sampling & Re-construction of Signals

For sampling. take a simple Sinusoidal signal of frequency fm and sample it at different sampling rates fs and observe the wave shapes of the sampled signals.

Verify the “Sampling Theorem”; that is, fs > 2fm , where fs is the sampling rate and fm is the signal frequency.

Reconstruct the original signal from its samples at different sampling rates and observe the effects of sampling rate and order of the LPF on the reconstructed signal.

Study thoroughly, the experimental kit ST-2101, follow the step-by-step procedure and record the observations as given in the Experiment sheet contained in the Laboratory Manual of EL-392, to complete the experiment.

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The CS-2101 used in the Experiment

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Experimental Setup for Re-construction

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Experiment – 8: Plot the Sensitivity Characteristics of AM Radio Receiver

About AM Radio Receivers

An AM Radio Receiver, also known as a Super-hetrodyne radio receiver (SHRR), or, a DSB receiver, is used to receive the radio programs broadcasted from the radio stations by amplitude modulation technique.

The AM Radio stations broadcast their programs on different frequencies in different frequency-bands for short and long distances, known as “Medium-wave” band and “short-wave band”.

The broadcast is in the form of electromagnetic waves containing AM signals propagating through space in different manners. The carrier frequency of the AM signal is the frequency announced by the radio station, and the audio frequency range for the radio programs transmitted by this technique is kept in the range : 20 Hz to 4 KHz, and the modulation index is kept fixed at 33 %.

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Frequency or meter Bands for Radio broadcast

Medium Wave 530 KHz to 1630 KHZ Ground wave propagation

Short wave 3 MHz to 30 MHz Sky wave propagation

Medium wave broadcast is intended for short distance (up to 200 kilometers) whereas short wave broadcast is intended for long distance (above 1000 kms).

For example, BBC World service programs for south Asia can be received on SW bands (on 17.79 MHz in 16 meter band & on 15.31 MHz in 19 meter band in the day-time & on 5.975 MHz in 49 mtr band in the night).

However, radio programs from Delhi station of All India Radio can be heard on 666 KHz in medium wave band of 450 meters.

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Working of AM Radio Receiver

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Characteristics of AM Radio Receivers

Sensitivity:- It can be defined as the minimum strength of the received signal (voltage or power) at the receiver input capable of causing a standard output.

Selectivity:- It can be defined as the characteristics which determines the extent to which it is capable of differentiating between the desired signal and the signal of other frequencies.

Fidelity:- It can be defined as the degree with which a system accurately reproduces at its output the essential characteristics of signal which is impressed upon its input.

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AM Radio or DSB receiver kit model ST-2202

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Lay out of the Radio Receiver kit model ST-2202

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Generation of Am Signal using Two Signal Generators

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Settings to be made on RF Signal Generator ST-4062

Connect the output of this signal generator directly to CRO and obtain a clear sine wave on the CRO screen by making the following settings on this signal generator:-

1. Function selected : Sine-wave 2. Amplitude adjusted: 100 mVp-p (by selecting 40 dBs Attenuation)3. Frequency set : 1000 KHz (by selecting 2 MHz Frequency range)4. DC Offset : OFF 5. Sweep : OFF

Now connect the previously set output of AF SG to the “MOD IN” of this Signal Generator, and set its Modulation to “AM STD”.

The AM wave will now appear on the CRO screen.

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Settings to be made on the AM Radio Receiver kit, Scientech Model ST-2202

• 1. •

Rx-input Select Switch “SKT” position (Dn) Tuned ckt select Switch: “INT” position (Up)AGC Swith: “OUT” position (Up)BFO Switch: “OFF” position (Dn)Detector Switch: “Diode” position (Up)Speaker Switch: “ON” position (Up)All the 8-fault creating Switches: “OFF” position (Up)RF Amplifier gain preset control: mid-way to get detector’s

output at tp-38M. Hadi Ali Khan

After making all the above settings on Signal Generators and the Receiver kit, turn-ON the Receiver kit and connect the previously adjusted AM signal to the Rx-Input of the Receiver kit.

Now, rotate finely the tuning dial of the Receiver kit to receive the input AM signal, When the AM signal will be properly received (after tuning the receiver to the carrier frequency of the AM signal), an audio tone will be heard from the speaker.

The state of best tuning may be ensured by loudest sound of the tone from the speaker, and the largest amplitude of the received signal on the CRO screen.

Check the receiver output at either the Detector’s output at tp-38, or at AF amplifier’s output at tp-39 on the CRO screen.

The Detector’s output at tp-38 will be a sinusoidal signal of the order of 10 mV p-pwhereas the AF amplifier’s output at tp-39 will be a sinusoidal signal of the order of 2.0 Vp-p.

Any of the above receiver output, may be recorded in the observations against the carrier freq value, for the purpose of plotting Sensitivity or Selectivity characteristics of the radio receiver. For details, refer to Experiment Sheet / Lab. Manual

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Determination of the Sensitivity CharacteristicsGenerate an AM signal using two oscillators and adjust its parameters to the following values:-

A = AM Level in volts p-p = around 50 mv

fm = frequency of the message signal in KHz = 800 KHz

fc = frequency of the carrier signal (variable) (from 800 KHz to 1500 KHz)

m = modulation index in % = 33 %

Connect it to Rx input and observe the detector’s output (or at amplifier.so/p on CRO.

Take observations on tuned freq of 800, 900, 1000, 1100 KHz, ---- so on.

Plot a curve between detector’s output (mv) vs tuned freq.

For step-by-step procedure & other settings to be made on the kit, refer to the “Work-Book” of the kit or to Experiment sheet & study material on website:-

http://mhakhan.tripod.com/lab.htmlM. Hadi Ali Khan

This completes the presentation

Produced & presented by

B.Sc(Engg.), Ex-MIEEE(USA), MIETE(India)

Department of Electronics Engineering, AMU, Aligarh

M. Hadi Ali Khan

Website:-http://mhakhan.tripod.com/lab.html