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EE370 Communications Engineering

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1. f S o CS a S S a Creating the vector for the frequency axis f length t 2 length t 2 1 length t ts Plotting all FT on one sheet in a 2x2 matrix format figure 2 subplot 221 plot f M subplot 222 plot f G subplot 223 plot f Y subplot 224 plot f Z Discussion Define the time interval This is usually the first step in any simulation There are three parameters to define the beginning of the interval the step size the end of the interval The beginning and end of the Kousa amp Muqaibel Exp 2 Simulation of Communication Systems Using MATLAB EE370 COMMUNICATIONS ENGINEERING LAB MANUAL interval are intuitive for periodic signals you want to cover 3 5 periods for non periodic signals you usually want to cover the non zero part of the signal The selection of the step size is crucial for the accuracy of the simulation You need enough sample points to represent the signal Usually the step size is taken to be of the order of one hundredth of the smallest period in the program Or the sampling frequency f 1 ts should be 100 times the frequency of the signal In our example since we are having c t of frequency 1000 Hz we selected f 100000 or ts 0 00001 Define the functions m t and c t This is a straightforward step The function abs stands for while pi z Note that the signals m and c are now vectors of the same size as t Perform t
2. Laboratory 4 EE370 COMMUNICATIONS ENGINEERING LAB MANUAL Be logical and systematic First look for obvious errors that are easy to fix Is your measuring device correctly set and connected Are you looking at the proper scale Is the power supply set for the correct voltage Is the signal generator correctly set and connected And so on Next check for obvious misconnections or broken connections at least in simple circuits As you work through your circuit use your lab sheet to record tests and changes that you make as you go along don t rely on your memory for what you have tried Identify some test points in the system at which you know what the signal should be and work your way backwards from the output through the test points until you find a good signal Now you have a section of the system to focus your efforts on Here is where a little thought about laying out your board before connecting it up will pay off if your system looks like a jungle it is going to be very hard to troubleshoot but if it is well organized and if the wires are short it is going to make your job a lot easier Final remark if you do discover a bad module or wire do not just throw it back in the box Tell your instructor or the lab technician about it Neatness When you have finished for the day return all modules to their proper storage bins return all test leads and probes to their storage racks return all equipment to its correct loc
3. 1 Feed the output of CHANNEL 2 to the TUNABLE LPF Toggle the switch to NORM and set the gain to maximum 2 Observe the spectrum of the signal before and after the filter on the same view but separate the two plots right click gt gt choose auto arrange 3 Start from the highest possible cutoff frequency full clockwise and go down Comment on what you see on the spectrum analyzer and what you hear from the headphone Part IV Frequency Translation modulation The spectrum of the signal may be translated on the frequency axis by multiplying the signal with a sinusoid modulation property 1 Connect the output of CHANNEL 1 of the SPEECH module to one input of the MULTIPLIER module 2 Connect the external signal generator to the other input of the MULTIPLIER Set the toggle switch of the MULTIPLIER to DC 3 Make the arrangements on the picoscope to observe the signal before and after the multiplier simultaneously 4 Start from the lowest frequency of the signal generator and increase it gradually Observe the spectrum and listen to the voice before and after the MULTIPLIER Comment on what you see and hear 5 Take a snapshot of the translated spectrum when the signal from the external generator is set to 5 kHz Kousa amp Muqaibel Exp 4 Speech Signals EE370 COMMUNICATIONS ENGINEERING LABMANUAL Post Lab Work Using MATLAB e Record a speech message for 5 seconds use wavrecord commana e Play th
4. ANALOG OUTPUT anatos output BEGINNING OF SEQUENCE SYNCH RESET X SEQUENCE ANALOG CLOCK TTL OUTPUT CLOCK Y SEQUENCE SYNC TL CLOCK outrur FRONT PANEL BLOCK DIAGRAM LINE ENCODER and LINE DEODER Modules In a digital transmission system line encoding is the final digital processing performed on the signal before it is connected to the analog channel although there may be simultaneous bandlimiting and wave shaping Thus in TIMS the LINE CODE ENCODER accepts a TTL input and produce an output that is suitable for transmission via an analog channel The TIMS LINE CODE DECODER decodes it back to the binary TTL format The LINE CODE ENCODER serves as a source of the system bit clock It is driven by a master clock M CLK at 8 3 kHz from the TIMS MASTER SIGNALS module The LINE CODE ENCODER module divides M CLK by a factor of four in order to derive some necessary internal timing signals at a rate of 2 083 kHz B CLK The latter becomes a convenient source for use as the system bit clock The reason we are using a slower clock clock 4 is that the encoder requires some cycles to provide the proper output and hence the data should arrive at a slower rate Because the LINE CODE DECODER has some processing to do it introduces a time delay To allow for this it provides a re timed clock STROBE if required by any further digital processing circuits eg for decoding or error counting modules For a TTL input signal
5. Part IV Effect of Frequency Mismatch Of course no one is interested in making frequency mismatch intentionally But in real life you cannot borrow the carrier from the transmitter Otherwise you could have borrowed the message itself and saved all the hassle of communication One will do his best to reproduce a carrier at the same frequency used at the transmitter but they cannot be 100 identical In this part we use a different source to generate the carrier for the demodulator circuit 1 Generate an independent 9 kHz signal for the receiver circuit For that you can use the Voltage Controlled Oscillator VCO module VCO module has many applications to come later in the course For now we will use it to generate a sinusoidal signal Make sure that the on board switch is set to Kousa amp Muqaibel Exp 5 DSBSC Modulation amp Demodulation EE370 COMMUNICATIONS ENGINEERING LAB MANUAL VCO mode Use the FREQUENCY COUNTER to measure the frequency Make sure nothing is connected to the TTL input of the counter 2 Observe simultaneously the original signal and the recovered signal in time and frequency Describe the effect of frequency mismatch 3 Try to eliminate the frequency mismatch by fine tuning either oscillator 4 Replace the 2 kHz message with a speech signal Increase and decrease the frequency mismatch and describe the effect on the sound quality Post Lab Work 1 You noticed that there is a wide r
6. Sketch the input output characteristics of the quantizer This is a staircase plot with the input voltage on the x axis and the output level labeled as a binary sequence on the y axis 9 Connect the corners of the stair steps with the best fit Is the curve linear Part III Non Linear Quantization Set the toggle switch to 4 bit companding and repeat steps 5 9 of Part II Were you able to observe all 16 levels Why Part IV Time Varying Messages Set the toggle switch to 7 BIT LINEAR Connect the AUDIO OSCILLATOR output to V of the PCM ENCODER Observe the PCM DATA output over consecutive frames How it is different from the DC input case Post Lab Work Write a MATLAB code to implement uniform quantization The quantizer should accept a sampled signal and generate the quantized one The dynamic range of the quantizer is V to V The number of bits should be controllable Demonstrate your program by two examples Kousa amp Muqaibel Exp 9 PCM ENCODING EE370 COMMUNICATIONS ENGINEERING LAB MANUAL Exp 10 PCM Decoding Objective The objectives of this experiment are to e implement PCM decoding and understand its operation e appreciate the importance of data structure and synchronization e evaluate the effect of companding Introduction In the previous experiment the PCM encoder was examined To complete the picture the PCM decoder will be investigated in this experiment Upon reception of a PCM sequ
7. amplitudes closer than those for large amplitudes in a logarithmic proportion At the decoder the reverse action is performed to restore the original amplitude distribution Companding is particularly advantageous when the message has high peak to average amplitude characteristic as in speech signals The following modules will be used PCM ENCODER and AUDIO OSCILLATOR PCM ENCODER Module of TIMS In TIMS A D conversion is performed by the PCM ENCODER module Figure 1 The input to the PCM ENCODER is an analog message The sampling rate of the module is defined by but not equal to the CLK input which sets a limit on the maximum allowable message bandwidth according to Nyquist Sampling Theorem The dynamic range of the quantizer is Kousa amp Muqaibel Exp 9 PCM ENCODING EE370 COMMUNICATIONS ENGINEERING designed for the range 2 0 volts therefore the input message amplitude must be held within this range The technical details of the module are described in the TIMS Advanced Modules User Manual We go briefly over each of the input and output connections which will be used in this experiment e DIGITISING SCHEME SELECT a three position toggle switch which selects the 4 bit or 7 bit linear encoding scheme or the 4 bit companding scheme e FS frame synchronization a signal indicating the end of each data frame e Vn the analog signal to be encoded e PCM DATA the output data stream e CLK aTTLinput serv
8. In this experiment we implemented the basic operations on sinusoids The experiment was smooth and all results were as expected This is my first time to see and quantify the noise of the electrical and electronic circuit had a little difficulty in working on the picoscope but hopefully with time will be better Kousa amp Muqaibel Appendix B Sample Report 58
9. PCM DECODER 1 Plug in the PCM DECODER module Connect the decoder with the encoder 2 Use the front panel toggle switch to match the transmitter encoding scheme 3 Clock the PCM DECODER by the same clock of the encoder 4 Borrow the frame synchronization signal FS from the transmitter by connecting it to the frame synchronization input FS of the receiver and check that the FS SELECT toggle switch is set to EXT FS 5 Connect CH A1 to the input to the PCM ENCOER module 6 Connect CH B1 to the sample and hold output Vout of the PCM DECODER 7 Ensure that both channels of the oscilloscope are set to accept DC to calibrate the ground of both channels to the zero level Fix the voltage axis to view 5 V to 5 V Part II Quantization Effects The effect of number of quantization levels will be investigated with the help of a DC message Slowly vary the DC output from the VARIABLE DC module back and forth over its complete range Notice that as the input to the encoder moves continuously the output from the decoder moves in discrete jumps Explain this behavior Reset the coding scheme on both modules to 7 bit Sweep the input DC signal over the complete range as before Notice the granularity in the output is almost unnoticeable compared with the 4 bit case Comment Kousa amp Muqaibel Exp 10 PCM Decoding EE370 COMMUNICATIONS ENGINEERING LAB MANUAL Part III Signal Recovery It was not possible when exa
10. a transition between any two bits Is the phase continuous Why How does that affect the bandwidth Set the VARIABLE DC to zero What type of modulated signal is generated Why 6 How can you use the above system to generate PSK Kousa amp Muqaibel Exp 12 Digital Modulation FSK EE370 COMMUNICATIONS ENGINEERING LAB MANUAL Appendix A LABORATORY REGULATIONS AND SAFETY RULES The following Regulations and Safety Rules must be observed in all concerned laboratory locations 10 11 12 13 14 15 16 It is the duty of all concerned parties who use any electrical laboratory to take all reasonable steps to safeguard the HEALTH and SAFETY of themselves and all other users and visitors Be sure that all equipment is properly working before using them for laboratory exercises Any defective equipment must be reported immediately to the Lab Instructors or Lab Technical Staff Students are allowed to use only the equipment provided in the experiment manual or equipment used for senior project laboratory Power supply terminals connected to any circuit are only energized with the presence of the Instructor or Lab Staff Students should keep a safe distance from the circuit breakers electric circuits or any moving parts during the experiment Avoid any part of your body to be connected to the energized circuit and ground Switch off the equipment and disconnect the power supplies from the circuit before lea
11. demodulated signal Is it perfectly recovered 5 Feed the demodulated signal to the HEADHPHONE AMPLIFIER module and plot the signal at the output of the module Remember that this module has a built in LPF Is the recovery better Why Now we want to examine if the level of improvement achieved in step 5 compared to step 4 is significant to a speech signal 6 Replace the single tone message by a speech signal 7 Listen to the signal with and without the LPF of the HEADPHONE AMPLIFIER module use the toggle switch of the LPF SELECT Do you notice any difference in quality What is the lesson learned Part II QAM Modulation and Demodulation Set up the block diagram of QAM modulator and demodulator as shown in Figure 1 1 Use the QUADRATURE UTILITIES module two multipliers and one adder for the modulator part of the system Use the upper multiplier to modulate message 1 and the lower multiplier to modulate message 2 according to the following steps e Message 1 is fed from CHANNEL 1 of SPEECH module e Message 2 is fed from CHANNEL 2 of SPEECH module e Prepare a carrier of 9 kHz sinusoid using the AUDIO OSCILLATOR e Use the in phase component of the oscillator coswt as the carrier to message 1 and the quad phase component sinat as the carrier to message 2 2 To demodulate the signal use the MULTIPLIER module followed by the HEADPHONE AMPLIFIER e One input of the multiplier should come from the modulated signal e Fo
12. if network is available to reproduce them later in the report The lab sheets for the 12 experiments are collected in one booklet separate from this document A set of Laboratory Regulations and Safety Rules are attached in Appendix A All students have to observe them carefully MATLAB will be frequently invoked as part of the post lab work mainly in the form of designing a simulation counterpart for the experimental work Such exercise will improve the student programming skills and acquaint him with the most frequently encountered functions and techniques for simulating communication systems It is the sole responsibility of the student to learn the basics of MATLAB Every student should submit a report on each experiment The report must be self contained and can be read independent from the lab manual All axes in all graphs should be clearly labeled If there is more than one trace in the plot they should be clearly labeled A sample report is attached in Appendix B Troubleshooting Things will not always go as expected this is the nature of the learning process While testing a communication block if the output signal is not what you expect don t just try things at random i e replacing wires rotating knobs and toggling switches hoping to get lucky Rather think before you do anything If you do so you will avoid wasting time going down dead end streets Kousa amp Muqaibel Introduction to Communication Engineering
13. of the envelope detector to the HEADPHONE AMPLIFIER Apply a speech signal to the FM modulator VCO and listen to the demodulated signal Tune the VCO carrier frequency slightly around the 85 kHz until you get the best output BPF modules may have slightly different characteristics Get the approval of your instructor for this step Post Lab Work 1 Show mathematically the operation of the frequency discriminator 2 Comment on the pros and cons of the two demodulation techniques covered in this experiment Kousa amp Muqaibel Exp 8 FM Demodulation EE370 COMMUNICATIONS ENGINEERING LABMANUAL 3 Use the FM signal generated in the LAST experiment post lab work and write a MATLAB code to demodulate the signal Plot the transmitted and recovered signal and note down your observations Useful MATLAB Function fmdemod command available from the Communication Toolbox Kousa amp Muqaibel Exp 8 FM Demodulation 6370 COMMUNICATIONS ENGINEERING ABMANUAL This page is intentionally blank All Experiments start with odd pages for double sided printing Kousa amp Muqaibel Exp 8 FM Demodulation EE370 COMMUNICATIONS ENGINEERING LAB MANUAL Exp 9 PCM ENCODING Objectives e Recognize the various processes of PCM encoding e Realize the structure of the PCM stream e Understand the operation of linear and non linear quantizers Introduction Pulse Code Modulation PCM is a method of conv
14. the signal The horizontal axis represents the frequency whereas the vertical axis represents the magnitude Because of the large variation of the magnitude spectrum the vertical axis is usually set to dB scale Note that Xas 20 log X For example if Aag is 40 dB below Bag then B A 100 The decibel symbol is often qualified with a suffix that indicates which reference quantity has been used For example dBm indicates that the reference quantity 0 dBm is one milliwatt while dBu indicates that the reference quantity 0 dBu is one microwatt When observing the signal spectrum on the spectrum analyzer you will notice a lot of noise all over the frequency axis This is due to the circuit components However the noise level is extremely low in the range of 60 dB or even less compared to the signal level i e one thousands of the signal level it can therefore be neglected You have many options to plot the results you see on the picoscope One option is to save the data in mat or csv In this case you can import the data to MATLAB or MS Excel and reproduce the plot You may alternatively save the plot directly as gif You can download a fully functioning demo version of PICOSCOPE PICOSCOPE 3204 from the following site http www picotech html software html In this experiment we will introduce the fixed modules in addition to the ADDER plug in module 1 The name of this module is not intuitive We will instead r
15. CATIONS ENGINEERING LAB MANUAL To conduct the experiment the following modules are needed TUNABLE LPF AUDIO OSCILLATOR TWIN PULSE GENERATOR 100 kHz CHANNEL FILTER Part I Verification of Fourier Transform Properties 1 Select and connect the proper modules to implement the following block diagram x t y t o gt cos 27 f t OLO 2 Draw the equivalent Modules and show their interconnection 2 Using the frequency counter set the AUDIO OSCILLATOR module to produce a 5 kHz sinusoidal signal and connect it to the system as x t Set y t as a sinusoidal signal of frequency 2 kHz from the MASTER SIGNALS module Set f in the above block to 100 kHz Set g to zero full counter clockwise and G to maximum A 00 Obtain the plot of m t from both the spectrum analyzer and the scope and compare with your theoretical expectations Comment on the noise level and harmonics 7 Vary the frequency of x t and observe the impact on both frequency and time domain Describe what you observe in light of the time scaling property 8 Re adjust the frequency of x t to 5 kHz and increase g gradually Observe the change in m t on the spectrum analyzer and the oscilloscope When g is maximum obtain plots of m t waveform and spectrum What is the property we are trying to prove 9 Plot the waveform and the spectrum of z t 10 Zoom the spectrum of z t around 100 kHz and observe its contents 11 Compare the spectrum of m t an
16. DRATURE UTILITIES and a TUNABLE LPF to demodulate the DSBSC generated in Part I 2 Observe the signal in time and frequency domains before and after the LPF simultaneously Is the spectrum before the filter what you expected Explain 3 Vary the cutoff frequency of the LPF and find the range of acceptable values for best recovery of the message Note You can measure the 3 dB cutoff frequency of the LPF by connecting the TTL output of the filter to the TTL input of FREQUENCY COUNTER and divide the reading by 100 While taking the measurement make sure nothing is connected to the analog input of the counter 4 Plot in time and frequency the best recovered signal you can obtain 5 Increase the cutoff frequency of the LPF beyond the range of good recovery What happens to the recovered signal Why Part III Effect of Phase Mismatch In this part we use the PHASE SHIFTER module to introduce a phase error between the carrier at the transmitter and the carrier at the receiver 1 Set the cutoff frequency of the LPF in the demodulation circuit to any value in the good range for recovery 2 Instead of borrowing the carrier from the transmitter feed the carrier of the transmitter to the PHASE SHIFTER module and take the output to the multiplier of the demodulator circuit 3 Observe the original message signal and the recovered signal simultaneously in time domain Vary the phase shift and describe the effect on the recovered signal
17. Either one can be physical stand alone equipment or soft PC based The connection to physical display devices is provided by coaxial cords whereas the connection to the soft devices is provided through USB connection already connected from the back panel The application that runs the soft oscilloscope and spectrum analyzer in our lab is called picoscope and can be started from the shortcut on the PC The DISPLAY INTERFACE module can take up to 4 signals on channels A1 A2 B1 and B2 but allows 2 of them one from A and one from B to be viewed simultaneously The channels can be selected by means of two mechanical switches on the front panel of the module If the displayed signal seems to be sliding left and right or changing too fast then the oscilloscope has to be triggered Triggering is some form of synchronization that provides a reference point for a periodic waveform Without triggering each sweep starts from a different instant of the period resulting in unstable display It is important to consider which of the many signals present will be used to trigger the oscilloscope Use a periodic signal with the longest period from among the displayed signals or use an external signal if needed External triggering is connected to Channel E of the DISPLAY INTERAFCE module You have been exposed to the oscilloscope before but the spectrum analyzer may be new to you The spectrum analyzer is a device that displays the frequency composition of
18. King Fahd University of Petroleum amp Minerals Electrical Engineering Department EE370 Communications Engineering LAB Manual Dr Maan A Kousa amp Dr Ali H Muqaibel January 2011 version 1 1 TutorTIMS FreeWare V1 0 Disabled functions enabled in full featured TutorTIMS Only available to institutions htt Awww webtims com tutontimsinfo html mfa instruments Pty Ltd All rights reserved Version 1 0 EE370 COMMUNICATIONS ENGINEERING LAB MANUAL Contents INTRODUCTION TO COMMUNICATION ENGINEERING I LABORATORY cceccscscceccsceccsceccecscceccecs 3 EXP 1 GETTING FAMILIAR WITH THE LABORATORY EQUIPMENT csccsscssscsccsscssscsscescnssceecesceeseues 7 EXP 2 SIMULATION OF COMMUNICATION SYSTEMS USING MATLAB ccccccccscecececececcccccccecececes 11 EXP 3 REPRESENTATION OF SIGNALS amp SYSTEMS cccsccscscceccsceccecccceccsceccecccceccsceccescccecceseccecccceceucs 15 EXP 4 SPEECH SIGNALS vesisscicccisecccccacccccccecestccccsvecedeiavedadcadecsedessecscicasetededssesiedesedcdeavesssdosdered eseceseses 19 EXP 5 DSBSC MODULATION amp DEMODULATION ccccccscscceccsceccecccceccsceccecccceccscecceccsceccesecceccccecacs 23 EXP G AM AND QAM ciisccscccssicescoscdsscecevscesscasccecvsssedesetenacesnbons secesessceoccavecsscsacedeevees Soesi aessaad oaaae 27 EXP 7 FM MODULA TION rra e E EEEE EEEE EET EEA SiE 31 EXP 8 FM DEMODULATION cccecececcccccccccececcccccccccccccececac
19. S 301 C System Unit The modules are simple electronic circuits which serve as basic communications building blocks Each module fixed or plug in has a specific function functions fall into three categories 1 Signal Generation oscillators variable DC etc 2 Signal Processing multipliers filters etc 3 Signal Measurement frequency counter PC based instrument inputs Kousa amp Muqaibel Exp 1 Getting Familiar with the Laboratory Equipment EE370 COMMUNICATIONS ENGINEERING LAB MANUAL Some of those modules are classified as basic modules while others are advanced modules The fixed modules are all basic They include BUFFER AMPLIFIERS FREQUENCY AND EVENT COUNTER HEADPHONE AMPLIFIER MASTER SIGNALS TRUNK PANEL VARIABLE DC and PC BASED INSTRUMENT INPUT The list of available plug in modules is shown in the table below Module i Type Module Tye ADDER Basic _ 13 VOLTAGE CONTROL OSCILLATOR 2 Basic MULTIPLIER Basic_ 15 QUADRATURE UTILITIES Advanced umiumes Basic 19 PCMENCODER Advanced TUNEABLELOW PASS FILTER 1 Basic 20 PCMDECODER Advanced TUNEABLE LOW PASS FILTER 2 Basic 21 BIT CLOCK GENERATOR Advanced TWIN PULSE GENERATOR Basic 22 SPEECH MODULE Advanced A data sheet for each module describing its input s output s configurable parameters and function can be found in the User Manuals Basic and Advanced available in the lab bench drawers A soft copy
20. VARIABLE DC from 2 V to 2 V in steps of 0 5 V and measure the output frequency You may use the ow p measurement facility in picoscope to measure the DC value Fill in the first row in the table in the Lab Sheet 6 With the variable DC on its minimum value set the GAIN control sensitivity of the VCO to about 60 make sure that you do not overload the VCO the LED should not light up Redo step 5 and fill the other row in the table 7 Plot the output frequency versus the input voltage for each setting e Which of the above settings results in a more linear performance in the given range of Vin e Determine the linear range for the second case 60 setting e Using the table only estimate the frequency of the VCO when the DC input is 1 75 V for both settings Which setting results in easier interpolation Why Part II Setting the Frequency Deviation The frequency deviation is equal to the product of Vinmax and GAIN Our objective is to design the GAIN that yields frequency deviation of 10 kHz for an input signal of 4 volts peak to peak This can be done as follows Set a DC voltage of 2 V as input to VCO Set the GAIN control fully anti clockwise and the output frequency to 100 kHz Advance the GAIN control until the frequency changes by 10 kHz Change to VARIABLE DC to 2V and confirm that the deviation is about 10 kHz in the other direction Record the measured frequency PSN eS Kousa amp Muqaibel Exp 7 FM Mod
21. ange for the design of the LPF cutoff in order to recover the demodulated signal Is there a particular value you prefer Why 2 You have seen that constant phase mismatch results in no shape distortion of the signal only magnitude reduction Prove this mathematically 3 If the phase mismatch was not constant but time varying how would it affect the sound 4 Implement DSBSC modulation and demodulation perfectly coherent in MATLAB for the signal and carrier frequencies used in the experiment Submit the m file plot of modulated signal and recovered signal in time and frequency What is the difference between spectra plots in MATLAB simulation and the ones observed on the picoscope Kousa amp Mugqaibel Exp 5 DSBSC Modulation amp Demodulation EE370 COMMUNICATIONS ENGINEERING LABMANUAL This page is intentionally blank All Experiments start with odd pages for double sided printing Kousa amp Muqaibel Exp 5 DSBSC Modulation amp Demodulation EE370 COMMUNICATIONS ENGINEERING LAB MANUAL Exp 6 AM and QAM Objectives e Demonstrate the modulation and demodulation process of AM signals e Implement the modulation and demodulation of Quadrature Amplitude Modulation QAM e Examine the sensitivity of QAM to phase errors Introduction AM is the term given to Double Side Band with Carrier modulation The main advantage of AM over DSBSC is the simplicity of the demodulator circuit the envelope detect
22. at ID 200XXXX EE 370 5X Date 22 August 20XX Experiment 3 Basic Operations on Sinusoids Objectives 1 Perform basic operations on sinusoids in the lab 2 Demonstrate time and frequency domain representations of signals 3 Realize practical limitations Lab Work and Results Part I The Sum of Two Sinusoids The following block diagram was implemented in the lab Signal 1 Oscilloscope amp Spectrum Analyzer Signal 2 Figure 1 Block Diagram of Sinusoids Addition Plots ae ARAA AA AAA i VA AAA AR AA AAD AA AANA l AN R M ad a a A A A E A E D VTA AL AA AT AAAA AAAA TA AAAA AAA TAIRI WAP A AE Aaa WV i yy UYI iV ue Vy yy A Yu Y vy VV Y VV VV VV VY VY ily Ha Aral a AN Na Malthe Res eee ewe ee Ss V V j V lt Faas MM Yai We VAY aks are aa MTT wy VTA Ney T u KANINI UR A A AA AT i MH NH IN i WH Iil h i VII UNA TN t D VV Phaaeaeae li Jag 1 y Vos i SEAAADARRAEARORAARARARDRO ROOD ASR ORORORAEAL wT wt Wall aA Vwi Sa M Vid A Sal wi EU WR COONEY S Py eS eo E rT A t A f l n z i j f i alla tla lin dia dia dia dda dia dia tla tla tla fadia dba dha tte tte A LEVEL Bee ae T ESETET eee es d IN s AN l i a b Figure 2 a Waveform and b Spectrum of the sum of 2 kHz and 3 KHz sinusoid Kousa amp Muqaibel Appendix B Sample Report EE370 COMMUNICATIONS ENGINEERING Discussion and Comments Answers to ques
23. ation and clean up the lab station If appropriate switch off the unneeded equipments We hope you an enjoyable learning experience Kousa amp Muqaibel Introduction to Communication Engineering Laboratory 6370 COMMUNICATIONS ENGINEERING ABMANUAL This page is intentionally blank All Experiments start with odd pages for double sided printing Kousa amp Muqaibel Introduction to Communication Engineering Laboratory ze EE370 COMMUNICATIONS ENGINEERING Exp 1 Getting Familiar with the Laboratory Equipment Objectives e Learn the various components and conventions of the lab equipment from TIMS e Use the data sheets to learn about the operation parameters and limitations of system modules e Explore the features and capabilities of the PC based oscilloscope and spectrum analyzer e Perform basic modeling using TIMS TIMS Overview Throughout the course we will be using the laboratory equipment 301C PC based from TIMS to complement and demonstrate the theoretical part of the course We will devote this experiment to introduce the equipment and get familiar with its usages TIMS is a telecommunications modeling system that models block diagrams representing telecommunications systems Physically TIMS is a dual rack system the upper rack accepts up to 12 plug in cards or modules the lower rack houses a number of fixed modules as well as the system power supply Figure 1 TIM
24. ation FSK EE370 COMMUNICATIONS ENGINEERING LAB MANUAL SEQUENCE MASTER SIGHALS GENERATOR 100kHz sin 100kHz cos 100kHz TTL sample TIL CPFSK message sin o C control sine out Figure 4 CPFSK generation Part II General Method of FSK Generation A general method of FSK generation with higher degree of freedom is shown in Figure 5 SEQUENCE FSK out fram VARIABLE DC 2kHz message from MASTER SIGNALS Figure 5 General Method of FSK Generation 1 Connect the circuit in Figure 5 o fi is 2 kHz obtained from the MASTER SIGNALS modules of is tunable and obtained from VCO Make sure that the on board switch SW2 is set to VCO mode Also set the toggle switch to LO fs the bit rate of the message is determined by the AUDIO OSCILLATOR The SEQUENCE GENERATOR produces a TTL 0 5V sequence of rate f DC shift of around 2 5V is needed to adjust the TTL level to V in order to generate FSK Set the DC source to full counter clockwise about 2 5V The system generates two carriers at f and f The DUAL ANALGO SWITCH will alternate between the two according to the message sequences 2 Vary f How does that affect the waveform and the spectrum of the modulated signal 3 Set f to minimum then to maximum Which setting generates a better modulated signal Why Kousa amp Muqaibel Exp 12 Digital Modulation FSK EE370 COMMUNICATIONS ENGINEERING LABMANUAL 4 Zoom in to
25. ations of your equipment Introduction This document contains the laboratory experiments to accompany the course EE 370 Communications Engineering offered by Electrical Engineering Department KFUPM The document contains twelve experiments four on basic and general background four on analog modulation and four on digital modulation The four basic experiments cover introduction to the laboratory equipment simulation of communication systems using MATLAB time and frequency domain representation of signals and processing of speech signals The analog modulation part covers the generation and detection of Double Side Band Suppressed Carrier DSBSC modulation Double Side Band With Carrier also known as AM modulation Quadrature Amplitude Modulation QAM and Frequency Modulation The digital modulation experiments include PCM encoding and decoding line codes and digital carrier modulation ASK and FSK Each experiment whenever applicable contains the following sections Objectives where the expected achievements by the end of the experiment are stated Introduction where the theory of the subject is reviewed The introduction is kept brief assuming the student has covered the material in detail in class or can refer to his textbook for further reading System Modules where the main new modules to be used in the experiment are described Lab Work leading the student on how to run the experiment The lab work is or
26. cceccccccccccecececececcccccccccucececececacacacaecececes 35 EXP 9 PCM ENCODING iveiedcssicicccccccdsscccscccacccccdeccccacasscdesceeccscocscscscacdsasscecsesedescdedcscaccoassescesadasescessesnaeds 39 EXP 10 PCM DECO DIN G raa r a aa aaraa aa aeaa raaa a E S a ros a siera i oaa io iSS ieii 43 EXP 11 LINE CODING r raar a aa a E a a e r SE Kaa VN NEIN 47 EXP 12 DIGITAL MODULATION FSK ssssssssossssssscosscsssscsssssssosesssssosecsscsssscssossssossosesssssssecsscsosssssosss 51 APPENDIX A LABORATORY REGULATIONS AND SAFETY RULES cccccccscscececcccccccccscecscececcccccccces 55 APPENDIX B SAMPLE REPORT cccccccccccccsccccccccccccccscccccecececcccccccccscscscececcccccccccscccecececcccccccsescscece 56 Kousa amp Muqaibel Contents EE370 COMMUNICATIONS ENGINEERING LAB At Introduction to Communication Engineering I Laboratory Purpose of Communication Engineering I Laboratory The goals of the communication laboratory are 1 to allow you to perform experiments that demonstrate the theory of signals and communication systems that are discussed in course 2 to introduce you to some of the electronic blocks that make up communication systems which may not be discussed in the lecture course because of time limitations and 3 to familiarize you with proper laboratory procedure including precise record keeping logical troubleshooting safety and learning about the capabilities and limit
27. d z t and comment on the modulation property Part II Filtering of Periodic Signals In this part we verify the Fourier Series representation of periodic signals and examine the effect of filtering on the signal s shape and spectrum Tunable LPF 1 Apply a square wave signal with frequency of 2 kHz to the TUNABLE LPF module Set the TUNE and GAIN knobs on the module to maximum full clockwise and set the toggle switch to WIDE Observe the input and the out of the filter in both time and frequency domain Are they similar Why Kousa amp Muqaibel Exp 3 Representation of Signals amp Systems EE370 COMMUNICATIONS ENGINEERING LAB MANUAL 2 Turn the TUNE knob to minimum full counter clockwise Observing the output gradually increase the cutoff frequency to allow one harmonic then two harmonics then three and so on 3 Obtain time and frequency plots for three cases one harmonic two harmonics max filter bandwidth Adjust the axes to zoom in the important data and get clear plots 4 Explain the effect of the filter cutoff frequency on the output waveform Part III System Identification Systems in general are characterized by their impulse responses or transfer functions An impulse is a non realizable function However it can be approximated from a train of square pulses by making the pulse width as narrow as possible and the period as large as possible This technique will be used to characterize differe
28. e e No DC component this allows AC coupling capacitor or transformer between stages as in telephone lines e Spectrum shaping this is important in telephone line applications for example where the transfer characteristic has heavy attenuation below 300 Hz e Synchronization where bit clock recovery can be simplified e Error detection capabilities It should be possible to detect some patterns of errors System Modules To complete the experiment the following modules are needed SEQUENCE GENERATOR LINE CODE ENCODER and LINE CODE DECODER SEQUENCE GENERATOR Using a common external clock signal the SEQUENCE GENERATOR produces two independent pseudorandom sequences X and Y In this experiment we need only one output The SEQUENCE GENERATOR will be clocked by B CLK from the LINER ENCODER module A SYNC output is provided which is coincident with the start of the sequences The synch out from the SEQUENCE GENERATOR can be used to trigger the oscilloscope The sequences may be stopped and restarted at any time via front panel controls Sequences X and Y are available as either standard TTL or analog level output The SEQUENCE GENERATOR is a basic module and you can read more about it in TIMS 301 User Manual The module and its block diagram are shown in the figure below Kousa amp Muqaibel Exp 11 Line Coding EE370 COMMUNICATIONS ENGINEERING LAB MANUAL SEQUENCE GENERATOR RESET PUSH BUTTON TTL LEVEL RESET
29. e message to confirm the recording use wavplay command You can use the pause and disp command to help you control beginning of recording e Calculate and plot the spectrum of the message e Translate the spectrum by 5 kHz e Plot the translated spectrum e Submit the m file and the plots Kousa amp Muqaibel Exp 4 Speech Signals EE370 COMMUNICATIONS ENGINEERING LAB MANUAL Exp 5 DSBSC Modulation amp Demodulation Objectives By the end of this experiment the student should be able to e demonstrate the modulation and demodulation process of DSBSC e realize the real life difficulties and challenges in designing coherent demodulators e examine the implications of the lack of perfect coherence on the recovered signal and distinguish the different forms of distortion Introduction Double Side Band Suppress Carrier DSBSC is one type of Amplitude Modulation The modulation process is straightforward the message is multiplied by a high frequency carrier The modulated signal occupies double the bandwidth of the baseband signal Recovering the message signal from the demodulated signal is performed coherently That is the demodulated signal is multiplied by a high frequency sinusoid in perfect synchronization in phase and frequency with the incoming carrier This requirement poses a challenge on the design of the demodulator circuit as it would then require a part for carrier recovery Failing to accomplish
30. e relation f length t 2 length t 2 1 length t ts Plotting We leave this step to the student to explore Use the help command to read about plot subplot figure legend xlabel ylabel title and axis commands Lab Work 1 Create and run the m file above and produce Figure 1 and 2 2 Change m t to 2 sin 2m 1000t and c t to cos 27 10 t and the cutoff frequency of the filter to 2 kHz Redo part 1 Post Lab Work 1 Include the m file and the figures for the work you did in the lab in your report 2 Using MATLAB add the signals m t exp 100 t and c t cos 2m 10 t then separate them by means of filtering only LPF and BPF Provide the m file and a plot of the sum in time and frequency and of each of the recovered signals in time and frequency Kousa amp Muqaibel Exp 2 Simulation of Communication Systems Using MATLAB EE370 COMMUNICATIONS ENGINEERING LAB MANUAL Exp 3 Representation of Signals amp Systems Objective By the end of this experiment the student should be able to e verify experimentally the relation between frequency and time domain representation of signals e observe some of none idealities related to noise floor and harmonics e measure the transfer function of a given system filter using narrow pulses Introduction A signal is a function that symbolizes a physical variable of interest Signals can be represented in time or frequency domains Remember this is
31. een the two modes Though an external signal can be used for demonstrating the PCM operation the PCM encoder is equipped with test periodic signals SYNC MESSAGE of frequencies which are fraction of the clock rate These signals are synchronized with the clock and therefore Kousa amp Muqaibel Exp 10 PCM Decoding EE370 COMMUNICATIONS ENGINEERING LAB MANUAL provide improved triggering The frequency of these signals can be set from a dip switch SW2 on the board of the PCM ENCODER Note that these signals are not pure sinusoids You can read more about the PCM DECODER module in the TIMS Advanced Modules User Manual Lab work This experiment consists of four parts In part I we set up the PCM encoder and decoder In parts II to IV we examine quantization signal recovery and companding respectively Part I System Setup The PCM Encoder 1 Set up the PCM ENCODER for a clock rate of 8 3kHz and coding scheme 4 bit LINEAR 2 Choose a large negative DC for the message from the VARIABLE DC module 3 Connect the output of the PCM ENCODER to CH A1 of the oscilloscope and confirm that the corresponding codeword is 0000 so only the embedded alternating 0 and 1 bits for remote FS in the LSB position should be seen They should be 1920us apart Verify by measurement and calculation 4 Verify the operation of the PCM encoder by varying the DC source like you did in the previous experiment The
32. efer to it as DISPLAY INTERFACE module Kousa amp Muqaibel Exp 1 Getting Familiar with the Laboratory Equipment EE370 COMMUNICATIONS ENGINEERING LAB MANUAL Lab Work 1 Read the data sheet of the ADDER in the TIMS Manuals Basic Modules Which of the following equations can be implemented using the ADDER and which cannot Write your answers in the Lab Sheet 2 cos 2m 2x106t 1 5 cos 2m 2x105t 1 3 cos 2m 2x104t x t 0 5 sin 2m 2x103t 2 5 cos 2m 2x104t x t 10 5 sin 2m 2x103t 1 3 cos 2m 2x104t x t 0 5 sin 2m 2x103t 2 Use the FREQUENCY COUNTER module to verify the frequencies of the following four signals from the MASTER SIGNALS 100 kHz sine 8 3 kHz Clock 2 kHz TTL and 2 kHz sinusoid Note down the values Warning The FREQUENCY COUNETR module accepts TTL and analog inputs ONLY ONE OF THEM SHOULD BE CONNECTED AT A TIME otherwise you may get erroneous measurement 3 Connect the previous four signals of the MASTER SIGNALS module to the four inputs of the DISPLAY INTERFACE Use the switches to display them on the oscilloscope picoscope Measure the amplitude of each signal and note them down in the Lab Sheet 4 Use the VARIABLE DC BUFFER AMPLIFIERS and ADDER modules to generate the signal 3cos 27x2x10 t 6 V Draw the modules and show the connections Let your instructor verify the waveform 5 Observe and plot the spectra of each of the four signals of the MASTER SIGNALS module a Do the
33. ence the PCM decoder 1 extracts a frame synchronization signal FS from the data itself from the embedded alternate ones and zeros in the LSB position or uses an FS signal borrowed from the transmitter 2 extracts the binary number which is the coded and quantized amplitude of the sample 3 identifies the quantization level which this number represents generates a voltage proportional to this amplitude level 5 presents this voltage to the output Vout The voltage appears at Vout for the duration of the sampling period A Note that it is not possible to recover a distortionless message from these samples They are flat top rather than natural samples The decoder itself has introduced no distortion of the received signal but the signal from the PCM encoder is already an inexact version of the signal at the input of the encoder Message reconstruction can be improved by low pass filtering To complete the experiment the following modules are needed PCM DECODER PCM ENCODER SPEECH MODULE TUNABLE LPF PCM Modules In this experiment we will use the PCM ENCODER and DECODER modules The decoder is driven by an external clock borrowed from and so synchronized to that of the encoder Frame synchronization may be achieved either by extracting the FS signal from the embedded information in the received data or by borrowing it externally from the encoder A toggle switch FS SELECT in the PCM DECODER allows switching betw
34. er so that they can be easily compared and plot them 6 What is the frame duration Bit duration Codeword duration 7 What is the sampling rate of the PCM ENCODER Is it appropriate to sample a speech signal Why Part II Quantizing levels for 4 bit linear encoding 1 Set the toggle switch to 4 BIT LINEAR Though standard PCM uses 7 bits selecting the 4 bit encoding scheme will reduce the number of quantization levels to be examined to 16 only Kousa amp Muqaibel Exp 9 PCM ENCODING EE370 COMMUNICATIONS ENGINEERING LAB MANUAL 2 Feed a DC voltage level from the VARIABLE DC module to Vin of the PCM ENCODER Turn the knob of the variable DC voltage to the least negative value full counterclockwise 3 Display on the oscilloscope both the FS signal and the PCM DATA output Describe the binary sequence of the PCM DATA for three consecutive frames Give reasons for such sequence 4 Vary the DC voltage slowly back and forth over its complete range and note how the data pattern changes in discrete jumps 5 Adjust Vn to its maximum negative value Record the DC voltage You should be getting all zeros for the 4 bit binary number for this DC setting 6 Gradually increase the amplitude of the DC input signal until you notice a change to the PCM output Record the binary sequence of the new digital word and the input amplitude at which the change occurred 7 Continue this process over the full range of the DC supply
35. erting an analog signal into a digital signal A D conversion This is achieved by a PCM encoder via three operations in sequence sampling quantization and coding A step by step description of the operations of a standard PCM encoder is as follows The encoder is driven by a TTL clock The input analog message is sampled periodically The sample rate is determined by the external clock and the number of bits per frame fs CLK n 1 3 Each sample amplitude is compared with a finite set of amplitude levels called quantization levels These are distributed within the range V volts 4 Each sample is assigned a digital binary codeword representing the number associated with the quantizing level which is closest to the sample amplitude The number of bits n in the digital codeword and the number of quantizing levels L are related by the equation L 2 5 The codeword is assembled into a time frame together with other bits as may be required In many commercial systems a single extra bit is added in the least significant bit position This is alternately a O or a 1 These bits are used by subsequent decoders for frame synchronization The frame is transmitted serially A typical operation that takes place when performing A D conversion of speech signals is companding Companding stands for signal compression at the encoder and expansion at the decoder In the encoder compression makes the quantizing levels for small input
36. es as the MASTER CLOCK for the module Clock rate of this module must be 10 kHz or less manufacture limitation For this experiment we will use the 8 333 kHz TTL signal from the MASTER SIGNALS module PCM ENCODER Tow CONTROL TDM SLAVE on TDM MASTER INPUT OUTPUT BUE MASTER SYNCHRONISED DIGITISING MESSAGE SCHEME SELECT 0 FRAME SYNC OUTPUT Bete O SERIAL PCM DATA FRONT PANEL Figure 1 The front panel of the PCM ENCODER Each binary word is arranged in a time frame The time frame contains eight slots of equal length and is eight clock periods long The slots from first to last are numbered 7 through 0 These slots contain the bits of a binary word The least significant bit LSB is contained in slot 0 See Figure 2 ek JU UU UU UU UU UU UU UU UU UU e pm TT TTT TT LET TTT TT PTT TT tty Fs E E BIT 765432 1076543210765432 10 Figure 2 PCM ENCODER timing frame Kousa amp Muqaibel Exp 9 PCM ENCODING 40 EE370 COMMUNICATIONS ENGINEERING LAB MANUAL The LSB consists of alternating ones and zeros These are placed embedded in the frame by the encoder itself and cannot be modified by the user They are used by subsequent decoders to determine the location of each frame in the data stream and its length The remaining seven slots are available for the bits of the binary codeword Thus the system is capable of a resolution of a maximum of seven bits 128 levels This resolution for purposes of expe
37. g As we go on with the experiment the sound will become sharp and loud and you may not feel comfortable to hear it Therefore keep the headphone aside but near enough to hear the sounds Kousa amp Muqaibel Exp 4 Speech Signals EE370 COMMUNICATIONS ENGINEERING LAB MANUAL 4 Increase the frequency of the input gradually Note the change in the sound Record the range lowest frequency and highest frequency over which you can hear the sound 5 Let your partner do the same Who of you has a wider hearing range Part II Spectrum of Speech Signals 1 Put the switch of CHANNEL 1 of SPEECH module to RECORD Speak clearly to the microphone for few seconds Speak continuously and avoid silence periods as much as possible Put the switch to PLAY position 2 Observe the spectrum of the signal on the spectrum analyzer Estimate the bandwidth Estimate the noise floor and consider the spectrum above the noise floor Save a representative snapshot and plot it 3 Now we want to record a continuous sound with high pitches something like whistle or sharp ring tone from your mobile Prepare something and have it ready 4 Start the high pitch sound then switch CHANNEL 2 to RECORD for few seconds before you switch back to PLAY 5 Observe the spectrum of the signal on the spectrum analyzer How is the spectrum different from that of CHANNEL 1 Save a representative snapshot and plot it Part III Filtering the Speech Signal
38. ganized in parts in order to have a clear and integrated structure of the work Kousa amp Muqaibel Introduction to Communication Engineering Laboratory EE370 COMMUNICATIONS ENGINEERING LAB MANUAL Post Lab Work extra questions and tasks for the student to carry after the lab and include in the lab report General Laboratory Procedure While there is no specific document to be submitted at the beginning of the Lab unless your instructor advises you otherwise you are expected to read the experiment fully before you come to the laboratory Interestingly you can even try parts of the experiment at home Here is a list of programs that will equip you with a virtual lab at your home Tool Function Link TutorTIMS Virtual Lab Modules etc http www webtims com Picoscope Oscilloscope amp Spectrum http www picotech com download html Analyzer Matlab Simulation Tool http www mathworks com In addition to the experiment write up a Lab Sheet has been prepared for every experiment The Lab Sheet is a working document designed to help students record all lab activities measurements observations answers to questions in the lab manual The student must have his instructor sign the sheet before he leaves The material in the sheet shall be utilized in writing the report Plots from the PC based oscilloscope and spectrum analyzer may be saved on a storage media or student file box
39. he multiplication This is also a straightforward step However note the dot after m Why this is necessary here What would happen if you remove the dot Perform full wave rectification This is again a straightforward step provided you recognize that full wave rectification is mathematically equivalent to taking the absolute value Create the LPF This operation is frequently encountered in simulating communication systems A LPF is defined by one parameter the cutoff frequency A filter in MATLAB is represented by its transfer function The transfer function is in general in the form of the division of two polynomials The filter is completely defined by the coefficients of the polynomial at the numerator and the polynomial at the denominator These are the vectors a and b respectively in the program There are many realizations for designing filters One common realization is Butterworth which is the one used here hence the function name butter The butter function has two arguments The first argument is the order of the filter The larger the order the sharper the filter closer to ideal but more processing is required For most of our applications an order of 3 5 should be sufficient The second argument is a coefficient related to the cutoff frequency Without going into the details of the derivation to design a LPF filter of cutoff frequency W the argument should be set to 2 W ts where ts is the time step size of the pr
40. ike to verify our results in Part IV Soectrum Analysis and Bandwidth Estimation using MATLAB 1 Use MATLAB to generate an FM signal y t let the message signal be x t 2 cos 2000 2m t Use a carrier frequency of f 100 kHz and design the sensitivity factor to get a frequency deviation of 10 kHz Hint use the fmmod command available from the Communication Toolbox 2 Plot x t and y t Plot the magnitude spectrum for y t Change the message frequency to 4 kHz observe the spectrum and quantify the effect on the bandwidth 5 Change the frequency deviation to 15 kHz keep message frequency at 2 kHz observe the spectrum and quantify the effect on the bandwidth 6 Compare Simulation results with the experimental ones Kousa amp Muqaibel Exp 7 FM Modulation 6370 COMMUNICATIONS ENGINEERING ABMANUAL This page is intentionally blank All Experiments start with odd pages for double sided printing Kousa amp Muqaibel Exp 7 FM Modulation EE370 COMMUNICATIONS ENGINEERING LAB MANUAL Exp 8 FM Demodulation Objective There are two main objectives for this experiment e toimplement the phase locked loop PLL for FM demodulation e to implement frequency discriminator method for demodulating FM Introduction The block diagram of a phase locked loop PLL is shown in Figure 1 The principle of operation is simple Suppose there is an unmodulated carrier at the input If the VCO was tuned precisel
41. is also available on all laboratory computers desktop All TIMS modules conform to the following conventions e Signal interconnections are made via front panel sockets e Sockets on the left hand side are for module inputs e Sockets on the right hand side are for module outputs e Yellow sockets are for analog signals e Red sockets are for digital signals e Analog signals are held near the level of 4V p p e Digital signals are TTL level O to 5 V e The green socket is the system Ground e Any plug in module may be placed in any of the 12 positions of the upper rack e All modules use the back plane bus to obtain power supply e The modules can be plugged in or removed without turning off the power It is important to note that e The plug in modules are not firmly locked in the rack and need to be held in position while interconnecting leads are removed e When removing the leads hold them from their solid heads and DO NOT PULL them from the flexible segment in order not to damage the wires e There are 22 plug in modules Make sure you leave them in sequence in the storage shelves Kousa amp Muqaibel Exp 1 Getting Familiar with the Laboratory Equipment 8 EE370 COMMUNICATIONS ENGINEERING LAB MANUAL Oscilloscope and Spectrum Analyzer TIMS is equipped with a fixed module PC BASED INSTRUMENT INPUTS that provides interface with display devices namely oscilloscope and spectrum analyzer
42. ished your message set the switch to the PLAY position The recorded content will automatically repeat upon switching to PLAY Note that the length of the recorded message will only be the length of time the switch was in the RECORD position A third non recordable channel LIVE is also provided where the sound at the MICrophone is continuously output as an electrical signal A pair of headphones is provided to allow the user to listen to the recorded messages by patching any one of the SPEECH module s outputs to the HEADPHONE AMPLIFIER in the TIMS System Unit WARNING DO not put the headphone on if you are not having sound yet A sudden high volume sound may harm your inner ear Lab Work This experiment consists of four parts We start by measuring the audible range of our hearing system Then in part Il we record few different voice signals and observe the variations in their spectra In part III we examine the effect of filtering on the sound quality Finally we listen to the effect of slight frequency translation or modulation Part I Audible Range of our Hearing System 1 Set an external power supply to sinusoidal signal of frequency 10 Hz and peak value 2 V 2 Connect the signal to the input of the HEADPHONE AMPLIFIER module Make sure you connect the ground of the external signal generator to the ground of TIMS 3 On the HEADPHONE AMPLIFER keep the gain knob to a low setting and set the LPF SELECT to OUT i e no filterin
43. it The block diagram of Figure 1 illustrates the operation of an FSK generator oscillator 1 f4 FSK oscillator 2 f f f binary message fs bitrate fs lt lt f Figure 1 an FSK transmitter In principle the three frequencies fi f2 and fsare independent In practice this is often not so there are certain advantages in having them related in some way eg as submultiples Oscillator 1 and 2 can be taken from the same source say a VCO whose frequency is changed by the message leading to a continuous phase output CPFSK This is illustrated in Figure 2 which shows a VCO as the source of f and fz and the corresponding CPFSK output waveform SEQUENCE GENERATOR BIT FSK o _ Ba Pe an i V wt m b time gt J iil Figure 2 CPFSK generation and output waveform To complete this experiment the following modules are needed ADDER AUDIO OSCILLATOR DUAL ANALOG SWITCH SEQUENCE GENERATOR and VCO Kousa amp Muqaibel Exp 12 Digital Modulation FSK gt 1 EE370 COMMUNICATIONS ENGINEERING LAB MANUAL System Modules VCO as FSK generator The VCO module was used before for FM generation It can also be sued for FSK generation In this case it must be switched to the FSK mode using the on board switch SW2 A 5V DC to the DATA input of the VCO module allows the setting of f with RV8 while a OV allows the setting of f2 using RV7 These frequencies wil
44. l be in the audio range with the front panel switch set to LO or near 100 kHz when set to HI The two other front panel controls have no influence in this FSK mode See the TIMS User Manual for details of FSK mode for the VCO DUAL ANALOG SWITCH Two identical analog switches are controlled by digital TTL level signals The outputs of the two switches are added internally and presented at the output of the module See Figure 3 DUAL ANALOG SWITCH ANALOG INPUT 1 N1 N1 TTL CONTROL FOR INPUT 1 CONTROL 1 CONTROL 1 CONTROL 2 TTL CONTROL FOR INPUT 2 IN2 CONTROL 2 ANALOG INPUT 2 OUTPUT IN2 OUT FRONT PANEL AIL OUTPUT BLOCK DIAGRAM Figure 3 DUAL ANALOG Switch Module and Block Diagram Lab Work This experiment has two parts The former examines the generation of a continuous phase frequency shift keyed FSK signal while the latter demonstrates a general FSK modulator with higher degree of freedom Part I Continuous Phase FSK CPFSK 1 Set up the circuit for CPFSK modulation as shown in Figure 4 Make sure that the on board switch is set to FSK Set the toggle switch to LO 2 Plot the data sequence and the FSK modulated signal for a duration of 5 to 8 bits Is the phase at the bit transition continuous 3 Plot the spectrum of the Continuous Phase FSK CPFSK Find f and f2 Set the toggle switch to HIGH and find f and f Kousa amp Muqaibel Exp 12 Digital Modul
45. ment on the type of distortion in the output signal Part IV Companding In this part a speech signal is used to demonstrate the effect of companding 1 2 Record your own message using a SPEECH MODULE when you speech include some silence to be able to evaluate the background noise and play it Keep the PCM ENCODER and DECODER at 7 bit LINEAR At the receiver side use the headphone to judge the quality of the PCM audio signal Make sure that the signal amplitude is not high in order not to hurt your ears Examine the effect of companding by switching both the encoder and decoder to 4 bit COMPAND Comment on the quality of the decoder signal compared to 4 bit LINEAR Examine all the possible combinations of quantizer settings at the encoder and decoder in terms of quality recoverable non recoverable loud low with reference gt Note if no external source is available the SYNC MESSAGE of the PCM ENCODER can be used after setting its peak to peak voltage between 2 and 2 using a BUFFER AMPLIFIER The frequency of the SYNCH MESSAGE is determined by the SW2 on board Dip switches on board SW2 set left hand toggle UP right hand toggle DOWN use 65 Hz Kousa amp Muqaibel Exp 10 PCM Decoding EE370 COMMUNICATIONS ENGINEERING to the case of 4 bit LINEAR in both modules First guess the output and then verify your guess experimentally Post Lab Work e When testing the overall PCM encoding decoding system
46. mining the PCM ENCODER in the previous experiment to see the sample and hold waveform within the encoder But assuming perfect decoding it is available at the output of the decoder Connect an external triangular signal of amplitude 4 V peak to peak Adjust the frequency to 20 Hz Do not forget to connect the ground of the source to the GND of TIMS Set the Encoder DECODER to 4 bit LINEAR Slow down the oscilloscope sweep speed to 10 ms div Observe the decoder output signal Plot both the input to the PCM ENCODER and the output of the PCM DECODER Measure the delay between the input and the output How many samples are taken in one period of the input signal Using the Picoscope gt tools gt math channels gt A B obtain a plot of the error output input Explain how the delay affects the error Change the coding scheme from 4 bit to 7 bit Redo step 7 Message reconstruction may be improved using careful low pass filtering 10 11 Connect the output of the PCM DECODER to a TUNABLE LPF Now observe the original signal input to the PCM ENCODER together with the output of the filter and start adjusting the cutoff frequency Using the FREQUENCY COUNTER find the cutoff frequency of the TUNABLE LPF for best possible recovery Recall that the cutoff frequency frequency counter readying 100 Plot the input and output waveforms Adjust the cutoff frequency of the TUNABLE LPF to 50Hz then 500Hz Plot the waveforms and com
47. nt filters 1 Use a TWIN PULSE GENERATOR module and clock it at 2 kHz using the AUDIO OSCILLATOR module TTL output Observe the output from Q1 on the scope and adjust the pulse width to minimum Connect the pulse train Q1 to the input of the TUNABLE LPF Adjust the cutoff frequency of the TUNABLE LPF to a mid value Plot the impulse response and the spectrum of the signal at the output of TUNABLE LPF 4 Vary the cutoff frequency of the TUNABLE FILTER and verify that the envelope of the output spectrum approximates the transfer function of the filter Get your instructor approval Why the spectrum consists of spectral lines and not a continuous curve What controls the spacing between the spectral lines Test your hypothesis 5 Use the above approximate transfer function measurement method to discover the filter characteristics of the 100 kHz CHANNEL FILTER module Obtain the transfer function for the three settings 1 2 3 What is the type of the filter in each case Estimate the 3dB bandwidth of the filters Use the horizontal markers of the picoscope to trap the 3 dB drop then the vertical markers to measure the bandwidth Post Lab Work Use MATLAB to plot and compare the transfer function of 1 Butterworth LPF of cutoff frequency 1 kHz and order 1 3 5 2 Butterworth BPF of cutoff frequencies 5 kHz and 8 kHz order 1 3 5 You can generate an impulse using the function rectpuls t W You can make W as narrow as time
48. objective of visualizing the frequency change In real signals the frequency deviation is very small compared to the carrier Kousa amp Muqaibel Exp 7 FM Modulation EE370 COMMUNICATIONS ENGINEERING LAB MANUAL Lab Work This experiment has four parts The first part studies sensitivity and the range of linear operation of the voltage controlled oscillator VCO In preparation for FM generation in the third part part Il addresses designing the frequency deviation ratio for the modulator Spectrum analysis and bandwidth estimation will be the subject of the last part The following modules are needed to complete the experiment AUDIO OSCILLATOR VCO Part I Sensitivity and Linearity of VCO The output frequency of the VCO varies with the input voltage V The amount of variation Hz volt can be controlled by the deviation sensitivity GAIN Before generating an FM waveform it is required to set the deviation sensitivity to a value that ensures linearity of the VCO over the whole range of message amplitudes Plug in the VCO and make sure that the on board switch SW2 is set to VCO Use the front panel fo control to set the output frequency sin wt close to 100 kHz Connect the VARIABLE DC voltage to the input Vin of the VCO The deviation sensitivity can be set with the front panel GAIN control Set this to about 25 of its fully clockwise 25 ad rotation See the figure for approximate setting 5 Vary the
49. od of generating an FM signal is by the use of a voltage controlled oscillator VCO The frequency of such an oscillator can be varied by the magnitude of an input control voltage The block diagram of VCO FM generator is shown in Figure 1 a Figure 1 b shows a snap shot of an FM signal together with the message from which it was derived Note particularly that there are no amplitude variations the envelope of an FM waveform is a constant For the VCO to work as a frequency modulator it has to manifest a linear relation between the magnitude of the input signal and the output oscillation Large signal amplitude may take the system out of its linear range of operation Therefore a careful design of the deviation sensitivity of the VCO is required to ensure linear operation over the full range of input signal amplitudes Unlike Amplitude modulation the bandwidth of FM signals is not determined by the message bandwidth only but also by message maximum amplitude and deviation sensitivity The product of the last two factors yields frequency deviation The bandwidth of FM signal can be approximated by Carson s rule Bandwidth of FM signal 2 x message bandwidth frequency deviation vco VAMP N nt AN iS TINNEAS a AA Yh message y vv N s Ne ki oN b a bi fo Sa tt i oe a Figure 1 FM by VCO a and resulting output b In this figure the frequency deviation is comparable to the carrier for the
50. ogram For more details about the command butter type gt gt help butter in the MATLAB prompt How many arguments would a BPF require What are they Kousa amp Muqaibel Exp 2 Simulation of Communication Systems Using MATLAB EE370 COMMUNICATIONS ENGINEERING LAB MANUAL Get the output after the filter In the previous step we have only created the filter To apply the filter to a given signal we use the function filter This function has three parameters the coefficients of the filter a and b and the vector to be filtered Note that although we think of the filter operation in frequency domain the filter function operates on a time domain vector The output should as well be taken as a time domain vector Finding the FT of the signals The Fourier Transform of signals can be found in MATLAB using the function fft It can be used with a single argument which is the time domain vector The fft function yields only the positive side of the spectrum To get the double sided spectrum augment fft by fftshift Finally if you are only interested in the amplitude spectrum augment all by the function abs The resulting frequency domain vector will have the same size as the size of the input time domain vector Creating the vector for the frequency axis To plot the frequency spectrum as a function of frequency you need to create the frequency axis The available range of frequencies depends on ts and is given by th
51. only representation The two representations are related by Fourier Transformation In this experiment we are going to examine some Fourier Transform properties namely Property Time Frequency Fourier transform of sinusoids T 5 w Wo lw Wg waren wile rato Fill in the missing blocks in the table See Lab Sheet A system on the other hand is a combination and interconnection of several components to perform a desired task Systems can be characterized by their impulse responses in time domain or transfer functions in frequency domain For a subclass of systems the linear systems the impulse response or transfer function provides a very convenient and straightforward relation between the input and out of the system One type of system that is frequently encountered in communications is the filter A filter is a frequency selective device that allows a certain frequency band to pass with high gain and blocks other bands Depending on which band it passes a filter can be classified as low pass LPF band pass BPF or high pass HPF Lab Work There are three parts in this experiment In part I we verify some of Fourier transform properties In the second part we study the effect of filtering on periodic signals The last part is devoted to identify unknown systems by measuring their impulse response and transfer function Kousa amp Muqaibel Exp 3 Representation of Signals amp Systems EE370 COMMUNI
52. or For that to work the message signal has to be always positive Therefore the message is DC shifted before modulation This gives rise to the model s t m t A cos 27f t 1 For the envelope of s t to be a true representation of m t A gt m where m is the max negative value of the message The ratio m A defines the modulation index which varies from Oto 1 The demodulation of AM signal can be achieved by a simple circuit of a diode a resistor and a capacitor The simplicity of the demodulator is the main attraction of AM modulation However this is done at the cost of less power efficiency In terms of bandwidth AM requires the same band for transmission as DSBSC Quadrature Amplitude Modulation on the other hand allows for twice the bandwidth efficiency of DSBSC or AM In this scheme two messages are modulated with carries that have the same frequency but at quadrature to each other i e have a phase shift of 90 The two modulated signals are added and transmitted over the same channel It is easy to show that each of the messages can be perfectly recovered with coherent demodulation at the receiver The whole system is summarized in Figure 1 Such a scheme however is very sensitive to phase errors Any error will result in one message leaking to the other The following plug in modules will be needed to run this experiment AUDIO OSCILLATOR ADDER MULTIPLIER QUADRATURE UTILITIES PHASE SHIFTER and UTILITIES K
53. orials can be found on the EE 370 course lab website If you need help on how to start working on MATLAB we advise you to read Matlab Primer available in the internet Our focus in this session will be on using MATLAB for simulating communication systems Instead of going in the traditional approach of explaining items individually we will work through one complete example and introduce the application as we go Case Study Write a MATLAB program to simulate the following system z t g t Full Wave y t Low Pass Filter m t B 1 kHz Rectifier c t where m t exp 100 t c t cos 2m 10 t m File Define the time interval ts 0 00001 t 0 1 ts 0 1 Define the functions m t and c t m exp 100 abs t c cos 2 pi 1000 t Kousa amp Muqaibel Exp 2 Simulation of Communication Systems Using MATLAB EE370 COMMUNICATIONS ENGINEERING LAB MANUAL Performe the multiplication g m c Perform full wave rectification y abs g Create the filter cutoff 1000 a b butter 5 2 cutoff ts Get the output after the filter z filter a b y Plot the input and output on the same graph figure 1 plot t m t z legend Input Signal Output Signal xlabel time ylabel amplitude title Case Study Finding the FT of the signals M abs G abs Y abs Z abs fftshift fftshift fftshift fftshift fft m fft g fft y fft z
54. ousa amp Muqaibel Exp 6 AM and QAM EE370 COMMUNICATIONS ENGINEERING IN PHASE modulator branch gt LPF m IN PHASE demodulator branch QUADRATURE demodulator branch QUADRATURE modulator branch Figure 1 QAM Modulator Demodulator Lab Work This experiment consists of three parts In Part we generate and demodulate an AM signal using single tone message as well as a real speech signal In part Il we implement a QAM modulator and demodulator In part Ill we study the effect of phase error on the operation of QAM Part I AM Modulation and Demodulation 1 Generate an AM signal where e The message is sinusoid f 2 kHz from the MASTER SIGNALS module e The carrier has a frequency of 100 kHz from the MASTER SIGNALS e Modulation index 0 75 e Peak value of modulated signal 2 V Tune the DC VARIABLE and the gains of the ADDER G and g until you get the desired settings Make sure the MULTIPLIER coupling is set to DC Hint modulation index A B A B 2 where A and B as shown in the figure below fl Annan Nt Ain tll ee tj i i IRAAN Figure 2 Designing modulation index Kousa amp Muqaibel Exp 6 AM and QAM EE370 COMMUNICATIONS ENGINEERING LAB MANUAL 2 Plot the waveform and the spectrum of the AM signal 3 Demodulate the signal using the envelope detector DIODE LPF circuit on the UTILITIES module 4 Plot the
55. perfect synchronization will result in phase mismatch or frequency mismatch leading to some form of distortion in the recovered signal Multiplying the modulated signal with a local carrier will produce a baseband signal as well as a signal modulated at double the carrier frequency Therefore a LPF is needed at the far end of the demodulator to recover the baseband signal The following plug in modules will be needed to run this experiment AUDIO OSCILLATOR QUADRATURE UTILITIES TUNABLE LPF PHASE SHIFTER and VCO Lab Work This experiment consists of four parts In Part we generate the DSBSC signal using single tone message signal In Part Il we demodulate the signal assuming perfect synchronization of incoming and local carriers We also examine the effect of improper filtering In part III and IV we examine the effect of phase and frequency mismatch respectively Part I Generation of DSBSC 1 Sketch the module diagram to generate DSBSC 2 Generate a DSBSC signal where e The message is sinusoid f 2 kHz from the MASTER SIGNALS module e The carrier has a frequency of 9 kHz use the AUDIO OSCILLATOR e Use one multiplier from the QUADRATURE UTILITIES module Kousa amp Muqaibel Exp 5 DSBSC Modulation amp Demodulation EE370 COMMUNICATIONS ENGINEERING LAB MANUAL 3 Plot the spectrum of the DSBSC signal Part II DSBSC Demodulation 1 Borrow the same carrier of Part and use the second multiplier of QUA
56. r sounds over a much wider frequency range than the ones we produce These sounds are called audible signals A healthy human being can hear frequencies up to 15 20 kHz This is another proof that we are created to hear more than we talk The following plug in modules will be needed for this experiment SPEECH TUNABLE LPF MULTIPLIER in addition to external signal generator The SPEECH MODULE The SPEECH module allows speech and audio signals to be recorded and replayed Three independent channels are provided CHANNEL 1 CHANNEL 2 and LIVE The module includes a built in microphone An EXTernal input is also provided for recording externally generated signals The module front panel looks like that in Figure 1 Kousa amp Muqaibel Exp 4 Speech Signals EE370 COMMUNICATIONS ENGINEERING LAB MANUAL f H LE jo CH1 RECORD PLAY PETO CONTROL CHI CH1 OUTPUT Aav r cHa O cH2 ouTPuT sa LIVE una OUTPUT a LIVE HPF S CONTROL aut F LIVE LPF c R aT IN CONTROL CH2 RECORD PLAY CONTROL MICROPHONE MIC EXTERNAL INPUT FRONT PANEL Figure 1 Speech Module Channels 1 and 2 can each record up to 32 seconds of speech from the common MICrophone input To record speech or other sounds on either channel set the front panel switch to RECORD and speak clearly into the microphone The length of your message may vary from a few seconds up to 32 seconds As soon as you have fin
57. r the other input connect the in phase component of the carrier Can you hear message 1 clearly e Connect the quad phase carrier Can you hear message 2 clearly e Ask you instructor to check your system and sign the lab sheet Part III Effect of Phase Error on QAM 1 Feed the carrier of message 2 through PHASE SHIFTER module before connecting it to the modulator circuit 2 Vary the phase shift and keep listening while demodulating message 1 What do you notice Kousa amp Muqaibel Exp 6 AM and QAM EE370 COMMUNICATIONS ENGINEERING LABMANUAL 3 Vary the phase shift and keep listening while demodulating message 2 What do you notice Post Lab Work 1 Prove Equation 2 2 Show mathematically that when the carries are not perfectly in quadrature with each other the two messages leak in one another at the demodulator output 3 Implement Part of the experiment AM Modulation and Demodulation in MATLAB Submit the m file and the plots of modulated signal and recovered signal in time and frequency Kousa amp Muqaibel Exp 6 AM and QAM EE370 COMMUNICATIONS ENGINEERING LAB MANUAL Exp 7 FM Modulation Objective The objectives of this experiment are to e generate FM signals using VCO e understand the modulator sensitivity and linear range of operation e examine the factors affecting the shape of the spectrum and the bandwidth of FM signals Introduction A simple and direct meth
58. riment can be reduced to four bits by front panel toggle switch The 4 bit mode uses only five of the available eight slots one for the embedded frame synchronization bits and the remaining four for the binary codeword in slots 4 3 2 and 1 See Figure 3 7 bit mode b7 be bs b4 b3 b gt b bo 4 bit mode 0 0 0 Da b3 b2 b bo Code word gt 5 F R A M E gt Figure 3 Frame structure for 4 bit and 7 bit words Lab Work The experiment consists of four parts In Part we set up the module and observe the time frame structure In Part Il we identify the quantization levels by examining PCM of a DC input using 4 bit linear quantizer A DC input ensures completely stable oscilloscope displays and enables easy identification of the quantizing levels In Part Ill we switch to 4 bit companding mode and observe the difference in quantizer behavior to the linear mode Finally in Part IV we consider a more meaningful input an AC signal Part I PCM Frame Structure Plug in the PCM ENCODER into the TIMS shelf Patch the 8 333 kHz TTL CLOCK from the MASTER SIGNALS module to the CLK input of the PCM ENCODER 3 On one of the oscilloscope channels display the frame synchronization signal FS Adjust the sweep speed to show three frame markers These mark the end of each frame 4 On the second oscilloscope channel display the CLK signal 5 Place the two waveform on the top of each oth
59. save the spectra of the following two line codes NRZ L and Bi L Manchester Based on the spectra of the two codes compare them in terms of DC content and first null bandwidth How is this BW related to the time domain waveform Part II Line Decoding 1 Connect the LINE DECODER module and make sure it is clocked with the clock received from the LINE ENCODER B CLK 2 Connect any of the outputs of the LINE ENCODER module to the corresponding input of the LINE DECODER module Press RESET on both modules 3 Observe the generated sequence at the output of the SEQUENE GENERATOR together with the recovered sequence at the output of the LINE CODE DECODER on the two channels of the oscilloscope Are the two waveforms identical 4 Plot the two waveforms and measure the introduced delay Part III Signal Inversion Test Some Line codes are differential in nature and are insensitive to the signal inversion This feature is important for many communication systems as the signal can get inverted during transmission for example opposite connection of wires or inverting amplifiers results in an inverted signal To check the sensitivity of the specific line code to signal inversion 1 Select a particular code and verify that the message is successfully decoded Insert a BUFFER AMPLIFIER which is an inverting amplifier in the transmission path Adjust the GAIN of the BUFFER AMPLIFIER Note that the LINE CODE DECODER requires for successf
60. second is used for the PLL demodulator Lab Work Part I FM Demodulation Using PLL Reconstruct the FM modulator as in the previous experiment FM Modulation Let the message be 2 kHz from the AUDIO OSCILLATOR the carrier 100 kHz from VCO and the modulator VCO GAIN about 25 Model the PLL demodulator illustrated in Figure 1 For the filter use RC LPF provided in the UTILITIES Module In the MULTIPLIER module set the toggle switch to AC Draw the corresponding module diagram Set the VCO in the demodulator to 100 kHz Set the GAIN control to mid range position Connect the output of the modulator to the input of the demodulator The PLL may or may not lock on to the incoming FM signal Tune the GAIN and if necessary the center frequency of the PLL VCO until you obtain lock Examine the output of the PLL VCO and compare it with the original message Replace the message from the AUDIO OSCILLATOR by a speech signal and make sure that you can hear the recorded message correctly Study the effect of varying the frequency fo and GAIN of the PLL VCO on the quality of the received speech Part II Frequency Discriminator 1 2 4 Set the VCO to generate an FM signal with carrier frequency 85 kHz and GAIN around 25 Connect the FM signal to the BPF Use the 100 kHz CHANNEL FILTER MODULE set CHANNEL SELECT to 3 Perform envelope detection by connecting the BPF output to the DIODE LPF in the UTILITIES module Connect the output
61. spectra plots coincide with your expectations Explain b How far is the noise level below the signal level 6 Using a 2 kHz sinusoidal signal on one channel and 8 33 kHz digital signal on the other channel familiarize yourself with the picoscope by exploring the following features Feature Switch between oscilloscope and frequency analyzer on the same view Display one or both channels on the same view window Separate the two channels on the same view so that they are non overlapping do it manually and auto Change the setting of the axes Take a snap shot or continuous scan Zoom in a specific segment of the graph Display measurements of DC value frequency period Use horizontal and vertical markers Set the oscilloscope on external triggering Create time view and spectrum view and save them Kousa amp Muqaibel Exp 1 Getting Familiar with the Laboratory Equipment 10 EE370 COMMUNICATIONS ENGINEERING LAB MANUAL Exp 2 Simulation of Communication systems Using MATLAB Objectives The main objective of this session is to learn the basic tools and concepts for simulating communication systems using MATLAB Introduction MATLAB is a user friendly widely used software for numerical computations MATLAB is vector oriented that is it mainly deals with vectors or matrices It is assumed that you have used MATLAB before and you can do simple operations as well as create and run m files Some useful tut
62. step size ts in order to get an excellent approximation of an impulse Kousa amp Muqaibel Exp 3 Representation of Signals amp Systems EE370 COMMUNICATIONS ENGINEERING LABMANUAL This page is intentionally blank All Experiments start with odd pages for double sided printing Kousa amp Muqaibel Exp 3 Representation of Signals amp Systems EE370 COMMUNICATIONS ENGINEERING LAB MANUAL Exp 4 Speech Signals Objectives e Understand the features and characteristics of speech signals e Get acquainted with the SPEECH module from TIMS e Perform simple processes on speech signals filtering frequency translation and examine their effect on the sound Introduction Speech is the most frequently encountered message in communication systems Throughout the lab work we will use a real speech message whenever appropriate In order to be prepared we devote this experiment to study the basic characteristics of speech signals and get acquainted with the SPEECH module of TIMS We generate speech or voice in general by virtue of the vibration of our vocal cords The sounds we produce are composed of many harmonics or pitches Typically the significant part of human voice occupies the range from 300 Hz 3 kHz This can be seen from the spectrum of the voice signal The low end of the spectrum represents the low pitch sounds while the high end of the spectrum represents the high or sharp pitches We can hea
63. the following output formats are available from the LINE CODE ENCODER NRZ L NRZ M UNI RZ BIP RZ RZ AMI Bi L Manchester DICODE NRZ Rather than defining each of the previous codes you will find what they mean experimentally Resetting the LINE CODE ENCODER and the LINE CODE DECODER is recommended every time after the clock is connected or interrupted You can read more about the LINE ENCODER and LINE DECODER Modules in the Advanced Modules Manuals Lab Work This experiment has three parts The first part takes you through defining the available line codes and observing their spectra The second part verifies the overall operation of the line encoding decoding system Differential encoding and signal inversion test are examined in part Ill Kousa amp Muqaibel Exp 11 Line Coding 48 EE370 COMMUNICATIONS ENGINEERING LAB MANUAL Part I Line Codes Definitions and Spectra 1 Plug in the LINE CODE ENCODER module and clock it with 8 3 kHz from MASTER SIGNALS 2 Plug in the SEQUENCE GENERATOR module and clock it with B CLK 2 083 kHz clock provided from the LINE ENCODER 3 Connect the generated TTL sequence X to the LINE ENCODER module input data 4 Using two channels display the generated sequence X and the selected line code Adjust the scope setting to display few bits about 10 bits 5 Observe the different line codes on the scope Explain what each code does the law of transformation 6 Observe and
64. tions posed in the lab manual and or Lab Sheets 1 The sum is period with period 1 msec 2 The noise level in the spectrum plot is 40 dB 3 The sinusoids appeared in the spectrum as spikes at 2 and 3 kHz ee Part II The Product of Two Sinusoids The following block diagram was implemented in the lab Signal 1 Oscilloscope amp Spectrum Analyzer Signal 2 Figure 3 Block Diagram of Sinusoids Multiplier Plots Place Waveform Here Place Spectrum Here Figure 4 a Waveform and b Spectrum of the product of 2 kHz and 3 KHz sinusoid Discussion and Comments Answers to questions posed in the lab manual and or Lab Sheets 1 The product is period with period 1 3 msec 2 The noise level in the spectrum plot is 40 dB No change to Part 3 The product appeared in the spectrum as spikes at 1 and 5 kHz 4 aces Kousa amp Muqaibel Appendix B Sample Report EE370 COMMUNICATIONS ENGINEERING Post Lab Work Answer to Questions in the manual Q1 If the difference is used instead of sum How does that affect the spectrum Why Answer There will be no change to the magnitude spectrum This is because Q2 Write a MATLAB file to do the sum of two sinusoids Evaluate the spectrum of the sum Answer Name ID t 1 0 01 1 x sin 2 pi 2000 t y sin 2 pi 300 t Z X Y Z abs fft fftshift z figure 1 Plot 2 figure 2 plot f Z Conclusion
65. ul decoding an input signal of amplitude near 2 volt PP 4 Patch the inverting amplifier in and out to find out if the code is sensitive to signal inversion or not If there is no change to the message output then the code is insensitive to polarity reversals 5 Using the above test identify the codes that are insensitive to channel inversion Kousa amp Muqaibel Exp 11 Line Coding EE370 COMMUNICATIONS ENGINEERING LABMANUAL Post Lab Work 1 Based on your experimental understanding of the law of transformation of the line codes complete the figure below 2 Comment on the DC component synchronization capability and error detection capability of each code input DATA 0 1 0 1 0 O 4 4 4 0 0 4 0 5V Tt a a eo DICODE NRZ Kousa amp Muqaibel Exp 11 Line Coding EE370 COMMUNICATIONS ENGINEERING LAB MANUAL Exp 12 Digital Modulation FSK Objective By the end of this experiment the student should be able to e modulate binary digital signals using FSK e understand the design issue related to choosing the frequencies in the FSK signal e differentiate continuous phase FSK CPFSK from general FSK e realize ASK and PSK as special cases of FSK Introduction Digital modulation techniques include amplitude shift keying ASK frequency shift keying FSK and phase shift keying PSK In this experiment we will concentrate on FSK The other techniques can be related to
66. ulation EE370 COMMUNICATIONS ENGINEERING LAB MANUAL Part III FM Generation 1 Replace the DC voltage source with the output from an AUDIO OSCILLATOR The frequency deviation will now be about 10 kHz since the AUDIO OSCILLATOR output is about 2 volt peak Why the frequency counter is still at 100 kHz 2 Observe the generated FM on the oscilloscope Adjust the range and zoom in to optimize the view Try 20 ps div 3 Vary the frequency of the AUDIO AOSCILLATOR Explain the change in the modulated signal 4 Vary the GAIN of VCO Explain the change in the modulated signal Part IV Spectrum Analysis and Bandwidth Estimation Many interesting observations can be made regarding the FM spectrum 1 Fix the message frequency from the AUDIO OSCILLATOR to 2 kHz and the VCO gain to about 25 Plot the spectrum zooming in the frequency range 40 180 kHz 2 Vary the message frequency and describe the impact on the spectrum of the FM signal Plot the spectrum of the FM signal at the minimum and maximum frequencies of the AUDIO OSCILLATOR 3 Reset the frequency of the message to 2 kHz and vary the deviation ratio by varying the GAIN in the VCO Describe the effect on the spectrum of the FM signal make sure you do not overload the VCO Plot the spectrum at the minimum value and maximum GAIN setting before overload 4 Explain the obtained spectra in light of Carson s Rule for bandwidth estimation Post Lab Work We would l
67. ving the laboratory Observe cleanliness and proper laboratory housekeeping of the equipment and other related accessories Wear proper clothes and safety gloves or goggles required in working areas that involves fabrications of printed circuit boards chemicals process control system antenna communication equipment and laser facility laboratories Double check your circuit connections specifically in handling electrical power machines AC motors and generators before switching ON the power supply Make sure that the last connection to be made in your circuit is the power supply and first thing to be disconnected is also the power supply Equipment should not be removed transferred to any location without permission from the laboratory staff Software installation in any computer laboratory is not allowed without the permission from the Laboratory Staff Computer games are strictly prohibited in the computer laboratory Students are not allowed to use any equipment without proper orientation and actual hands on equipment operation Smoking and drinking in the laboratory are not permitted All these rules and regulations are necessary precaution in Electrical Laboratory to safeguard the students laboratory staff the equipment and other laboratory users Kousa amp Muqaibel Appendix A LABORATORY REGULATIONS AND SAFETY RULES EE370 COMMUNICATIONS ENGINEERING LABMANUAL Appendix B Sample Report Name Smart amp Ne
68. we examined a DC signal with both 4 bit and 7 bit linear quantizers Part II Describe the behavior if 4 bit nonlinear compand was used e Using MATLAB consider a sinusoidal signal with amplitude of V and frequency 1 kHz sampled at 100 kHz With the help of the Quantizer you designed in the post lab work of the previous experiment plot the quantized output in two cases 4 bit and 8 bit quantizers Compare the input with the output and plot the error in the two cases Comment Kousa amp Muqaibel Exp 10 PCM Decoding EE370 COMMUNICATIONS ENGINEERING LAB MANUAL Exp 11 Line Coding Objective The objectives of this experiment are to e get familiar with definitions and properties of commonly used line codes e evaluate the spectrum content for different line codes e demonstrate the advantage of differential encoding through signal inversion test e measure the delay associated with practical digital systems Introduction Digital data can be transmitted by various Line codes Line codes are waveform patterns of voltage or current used to represent the 1s and Os Each line code has its advantages and disadvantages Among other desirable properties a line code is preferred to have the following e Bandwidth efficiency the possibility of transmitting at a higher rate than other schemes over the same bandwidth e Power efficiency For a given bandwidth and quality the transmitted power should be as small as possibl
69. y to the frequency of the incoming carrier wa then the instantaneous output would be a DC voltage of magnitude depending on the phase difference between the output of the VCO and the incoming carrier Now suppose the that the incoming carrier started to drift slowly in frequency Depending upon which way it drifts the output voltage will vary accordingly If the incoming carrier is frequency modulated by a message the output of the PLL will follow the message message out Figure 1 the PLL FM can be demodulated as well by using a differentiator or a frequency discriminator Frequency discrimination can be achieved by applying the FM signal to the linear part transition region of a BPF as depicted in Figure 2 The output of the discriminator is both FM and AM modulated The message can be recovered by applying the discriminator output to an envelope detector followed by LPF The BPF of the 100 kHz CHANNEL FILTERS module has close to linear pattern in the band 80 90 kHz Ho x x bee eee meee o4 lt I i i I 1 A i 1 i 1 i t 7 2 saf de n eee eee ee Figure 2 Band Pass Filter as a frequency discriminator Kousa amp Muqaibel Exp 8 FM Demodulation EE370 COMMUNICATIONS ENGINEERING LAB MANUAL The following modules are needed to complete the experiment AUDIO OSCILLATOR ADDER MULTIPLIER UTILITIES 100 kHz CHANNEL FILTERS VCO 2 modules one for the modulator and the

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