COMMUNICATIONS 1 - Lakehead University
Contents
1. FRAME SYNCHRONIZING Purse cy START UP CLOCK INTERNAL i iis prosrannerR quet Fig 1 COMMUNICATIONS 1 Experiment No 5 2133 PCM PCM SYSTEM JC oce war Control IN R R 77 contral Cock i E 2 ICU ANALOG IN De 991505 Tex 4 acis kn mer d gt Tronsmit 5 9 yee n vec y x i L x 2 Tb dt 18 CLK Dr 2 c m X pijp VO Myr T en WES p Exe H i bem m 2773 Fig 2 COMMUNICATIONS 1 33 Experiment No 5 2133 PCM FRAME SYNCHRONIZING PULSE GENERATOR CLK ys n Spach Blas Fig 3 COMMUNICATIONS 1 34 Experiment No 5 2133 PCM TIME SLOT PROGRAMMER 75 CLK 5 tem IN 5 3 2 2 gt V 5Y 3 Fs Fig 4 COMMUNICATIONS 1 Experiment No 5 2133 PCM TP3020 TP3020 1 TP3021 TP3021 1 Monolithic CODECs General Description The TP3020 and TP3021 are monolithic PCM CODECs im plemented with double poly CMOS technology The TP3020 is intended for p law applications and contains logic for p law signaling insertion and extraction The TP3021 is intend ed for A law applications Each device contains separate D A and A D circuitry all necessary sample and hold capacitors a precis2. gois High when BaD REC quus dom tmn wand PS Gite Mentor snender clock bed oast fo pert aue sive WAR PGM Geen ped o 222 7473 buy qperete si 1 538 Mite 14 44 19 Andes dene 2048 We Ch Ry asenple and bobi gengiier ds 1908 wher and of tis arcade sit 20 BS am oye guise iaengily comming at ar 6 tie Dis it narrat idle vitta undi t 94 Fay tue ey umor CLE egies urit signing E C Ger cook Set Ist pulse Genes caning period pisce of krosi significent Gant of POM duis pur to Qr Seton 22 BSN ihe eae q tains 2 ef GLK fa TST eod dag Sess abt MN QU HS 36 COMMUNICATIONS 1 Experiment No 5 2133 Functional Description POWER UP Upon application of power internal circuitry initializes the CODEC and places it into the power down mode No se quencing of 5V or 5V is required In the power down mode all non essential circuits are deactivated the TRI STATE PCM data output Dy is placed i
3. 8 The power amplifiers can be ule no required by connecting the power aeie input xe 5 the nagadive power Veg isa reduces the ter power coneump en by oparorik ee POWER DOWN CONTROL A power down mode is also provided A logic 1 power down command applied on the pin 13 will reduce the total filter power consumption to less than 1 mW Connect to for normal operation FREQUENCY DIVIDER AND SELECT LOGIC CIRCUIT This circuit divides the external clock frequency down to the switching frequency of the low pass and high pass switched capacitor filters The divider also contains a TTL CMOS in terface circuit which converts the external TTL clock level to the CMOS logic level required for the divider logic This in terface circuit can also be directly driven by CMOS logic A frequency select circuit is provided to allow the filter to oper ate with 2 048 MHz 1 544 MHz or 1 536 MHz clock frequen cies By connecting the frequency select pin CLKO pin 14 to 2 048 MHz clock input frequency is selected Digi tal ground selects 1 544 MHz and Vgg selects 1 536 MHz Applications Information GAIN ADJUST Figure 2 shows the signal path interconnections between the TP3040 TP3040A and the TP3020 signal channel CO DEC The transmit RC coupling components have been chosen both for minimum passband droop and to present the correct impedance to the CODEC dur
4. press File press lt Save gt press lt Screen gt change destination press Tab choose filename using soft keys press Tab choose drive press lt Select gt A should be highlighted press lt Select gt press Enter The file is now saved on A as a bit map gif file and can be imported into a word processor For example to import into WORD Click Insert click Object click Create from file click Browse open drive A choose file click OK click OK size and move to desired spot
5. 1 6 Experiment No 1 2133 Attenuator DESIGN OF A RESISTIVE ATTENUATOR Objective To design and test a T type or 7t type attenuator which gives an insertion loss as required by the lab instructor while maintaining 500 matching at input and output Theory A purely resistive circuit used to lower signal levels between a source and a load is called an attenuator pad It does not introduce any phase shift The pad usually also provides input and output matching If low loss impedance matching is required matching circuits containing only reactive components are used See Reference 1 class text Chapter 1 2 for discussion of insertion loss attenuators and matching pads Figure 1 Assuming Rs and the system being matched the insertion loss is given by InsertionLoss 20log a IN eq 1 Experiment Equipment DC Power Supply 2 500 resistors 49 90 1 BNC banana adapter Function Generator 1 prefab attenuator 1 cable DMM with manual 1 breadboard 1 Yellow grabber cable COMMUNICATIONS 1 7 Experiment No 1 2133 Attenuator Design of the Attenuator The lab technologist will specify the type T or Pi and the desired insertion loss Calculate the resistor values to build a symmetrical attenuator with input and output impedances of 50Q see class text Fig 1 2 2 and 1 2 3 respectively Choose single resistors with nominal resistances closest to the calculated values and c
6. 2x the amplitude displayed by the generator since it represents an impedance almost equivalent to open circuit However this is of no consequence in this case because we dealing with ratios of amplitudes Press Shift Recall Menu display shows A MOD MENU Press display 1 AM SHAPE Press gt display 2 AM SOURCE Press 0 display EXT INT Press gt display EXT Press Enter Press Shift AM display AM EXT i e now the generator will be AM modulated by the external input only MODULATING SIGNAL SET UP the function generator providing the modulation signal set f 10 kHz A 2Ve Using a BNC T adapter connect this signal to the external input at the rear of the carrier HP generator labeled AM Modulation as well as to CH2 of the oscilloscope An external amplitude of 5V p provides 100 modulation The actual amplitude of the signal applied to the modulator circuit of the carrier is of course much smaller and can only be found from the oscilloscope waveform displays Onthe HP scope press Autoscale adjust the time base for a convenient display If the display can t be made stable trigger the other channel or press Run Stop SPECTRUM ANALYZER SET UP Set Frequency to the carrier frequency and Span to 50 kHz On Amplitude change Scale Type from Log to Lin Press Ref Level and adjust the carrier amplitude until the peak of the carrier just reaches
7. a PC board and self contained except for a power supply and measuring equipment The actual system consists mainly of two ICs a CODEC COder DECoder and an IC containing filters Both are designed by the manufacturer to work together as a unit One set handles both the transmission coding as well as the reception decoding The analog signal enters the board at Ay and passes through a filter via a switch into the CODEC The switch allows a DC voltage also provided on the board to enter the CODEC instead of the analog signal The CODEC samples the incoming signal at a rate of 8 kHz assigns an 8 bit digital number to the sampled level and shifts this number out COMMUNICATIONS 1 25 Experiment No 5 2133 PCM to be transmitted In our case the signal is looped right back The signal received at the received digital bit stream is decoded by the CODEC resulting in a sort of stepped waveform the steps corresponding to the received pulse sequence This waveform is passed through a filter to smoothen out the steps and now representing the original signal is finally available at Aour The CODEC may be used in multiplexed systems Each CODEC can handle one out of 32 available channels of 8 bits each The 32 channels times 8 bits each make up one frame A frame synchronizing pulse derived from the system clock marks the start of a new frame As mentioned above one digital word is 8 bits long As mentioned above on
8. short BNC cables Spectrum Analyzer HP 4411 Spectrum Analyzer Generator Oscilloscope Carrier fe Ch1 Ch2 Notations and formulas used Carrier frequency fc Modulating frequency fu Frequency deviation Af Modulation Index B Bandwidth Bem COMMUNICATIONS 1 20 Experiment No 4 2133 FM Modulation Index Af Eq 4 1 fu Bandwidth By fy Eq 4 2 Eq 4 2 is known as Carson s Rule The occupied bandwidth is usually considered using the side frequencies larger than 1 of the unmodulated carrier as a guideline FM Spectrum Set the function generator up as follows carrier frequency fc 100 kHz carrier amplitude 200 mVp p select Shift FM modulating signal frequency fu 10 kHz max deviation Af 5kHz Observe the resulting waveform on the oscilloscope try time base 20us It is not all that informative but at least gives an impression what a frequency modulated signal looks like However we are more interested in the frequency spectrum Thus the spectrum analyzer is the instrument exclusively used for our measurements in this experiment A Amplitude level measurements On the Spectrum analyzer set Frequency lt center frequency gt to fc Span to a suitable range Amplitude to lt Lin gt On the generator press Shift FM to switch the modulation off The scope now shows the unmodulated carrier On the spectrum analyzer press lt Ref Level gt and adjust the ca
9. the frequency to approx 300 Hz adjust the trigger and Hold Off to get a stable display The waveform can now readily be observed and reminds the observer of a staircase shape This shows clearly how the CODEC now performs the reverse procedure of quantizing assigning a discrete voltage level to each particular 8 bit number or sequence Connect the other probe to Aou TP7 The original signal is reconstructed showing a fairly clean sine wave after passing trough the filter and also some amplification with regard to the input signal Change the frequency back to the previous value 3 FS Puls Connect CH1 probe to the Frame Synchronizing pulse TP3 Adjust V div to see the pulse and expand the time base so that the pulse is approximately 1 division in length Connect CH2 probe to the transmitted PCM You will see then a particular pattern on the scope screen consisting of an upper trace 1 level and a lower trace 0 level You may have to adjust V div to observe this properly Turning the intensity fully clockwise you can also distinguish clearly a set of 8 bits representing a binary number related to voltage level at the sampling moment Of course since the sine wave level changes continuously the eye is unable to follow this at a 8 kHz rate and perceives to see all 8 bits at the same time Temporarily connect CH2 probe to the system clock TP10 and compare the clock period to a the width of the FS pulse TP3 and b the
10. the measurements as in a 1 a 3 Set the amplitude of the modulating generator to 3Vp p and change the modulating signal to a triangular wave repeat the measurements as in a 1 a 4 Set the amplitude of the modulating generator to 4Vp p and change the modulating signal to a ramp wave repeat the measurements as in a 1 a 5 Set the amplitude of the modulating generator to 5Vp p and change the modulating signal back to a sine wave If over modulation occurs lower the amplitude so that 100 modulation is achieved i e the upper and lower envelopes just touch repeat the measurements as in a 1 b Trapezoidal Method On the oscilloscope clear all cursors switch Ch2 on and adjust the scale to observe the modulating signal To see the trapezoidal display Onthe HP scope exchange CH1 and CH2 connections press Autoscale Main Delayed then XY b 1 For the same conditions as stated in a 1 use eq 8 3 2 class text to find m The size of the trapezoidal display can be changed for better viewing by varying the vertical deflection of Ch1 and Ch2 Make sketches as above b 2 through b 5 Repeat this measurement under the same conditions as given in a 2 through a 5 When finished go back to the amplitude time display Onthe HP scope clear cursors press Main Delayed then Main Change time base for convenient display and if necessary adjust the trigger edge A1 Section Two Amplitude Frequency Represe
11. 33 Waveform Analysis B Square Wave Now on the function generator switch to square wave LINEAR MEASUREMENT The set up is the same as for the sine wave Now b 1 On the spectrum analyzer read and record the amplitudes of the fundamental and the harmonics up to the 9th harmonic For this measurement you may like to use the Peak Search function Press Peak Search then Next Right etc Some analyzers have only Search printed on the button but the function is the same dB MEASUREMENT Normally spectrum analyzer measurements are NOT done using a linear display as shown above but rather using a logarithmic scale to increase the dynamic range Amplitudes are displayed in dBm this is a power measurement displayed in dB with reference to 1mW and the differences between amplitudes power levels can be read directly in To get familiar with this type of measurement we repeat the experiment using the dB display Press Marker and Off to clear all markers from the screen Press Amplitude and change from Lin to Log Amplitudes are now displayed in dBm If not already there press Ref Level and move the peak of the fundamental or 1st harmonic to the top graticule line by turning the knob The fundamental is now the reference against which all other harmonics are measured Since we know by now from the linear measurements of the square wave spectrum that only odd harmonics exist move the marker us
12. 400 Hz by anideal band pass filter You apply a square wave of 400 Hz and1V amplitude to the input At the output of this filter what would a the signal waveform approximately look like time domain Sketch b the spectrum look like frequency domain Sketch Conclusions Comment on your results COMMUNICATIONS 1 14 Experiment No 3 2133 AM AMPLITUDE MODULATION AM Objective To investigate the characteristics of an amplitude modulated wave and to compare the results with theory Theory See reference No 1 class text chapter 8 and in particular sections 8 1 8 5 Experiment Equipment 2 Function Generators HP 33120A HP and other 2 BNC T adapters Oscilloscope HP 54645D 2 short BNC cables Spectrum Analyzer HP E4411B 2 med BNC cables Basic Set up The HP function generator is used to set up the carrier wave A second generator provides the modulating signal and externally modulates the carrier wave Generator Signal fm Generator Carrier fe Oscilloscope Ch1 Ch2 Spectrum Analyzer In The Oscilloscope provides an amplitude time display time domain while the Spectrum Analyzer provides an amplitude frequency display frequency domain COMMUNICATIONS 1 15 Experiment No 3 2133 AM CARRIER SET UP Connect the HP function generator providing the carrier to channel 1 of the oscilloscope Set the carrier to f 300 kHz A 200 mV Note The scope shows
13. ENT c 3 Measure the spectrum similar as done for the square wave log display up to the 10th harmonic COMMUNICATIONS 1 13 Experiment No 2 2133 Waveform Analysis Analysis 1 For both waveforms compute the amplitudes of the fundamental and the harmonic frequency components in the linear mode Do the same for the log dB mode but this time find the amplitude of the higher harmonics with reference to the fundamental i e setting the fundamental to 0 dB and for the other harmonics find the difference to the fundamental in dB Show at least one sample calculation for each waveform Don t forget the dc component Present both the measured and the computed data in tables for comparison Sketch the frequency spectrum for both waveforms on graph paper to scale linear amplitude of each frequency component vs frequency for the number of harmonics measured Use single lines to represent the frequency components Questions 4 When you did the measurements for the Square Wave using the Log scale the display most likely indicated the presence of harmonics not only at the odd frequency locations but also at the locations of the even harmonics though at a much lower level What could be the cause of that and is this acceptable Consider the power level of these even harmonics shown by the analyzer and also compare with the linear display Consider a common telephone channel with the bandwidth limited from 300 Hz to 3
14. Engineering 2133 COMMUNICATIONS 1 Laboratory Manual Jason Servais El Eng Technologist Manfred Klein Eng Technologist 2008 Department of Electrical Engineering Lakehead University Thunder Bay ON Revised Fall 2008 COMMUNICATIONS 1 Content Policy and Rules for Laboratory Exercises Exp 1 Design of a Resistive Attenuator Exp 2 Periodic Waveform Analysis Exp 3 Amplitude Modulation AM Exp 4 Frequency Modulation FM Exp 5 Pulse Code Modulation PCM Appendix A References 1 Electronic Communications Class text Dennis Roddy and John Coolen Prentice Hall 4th ed 24 43 Lakehead University Department of Electrical Engineering POLICY AND RULES FOR LABORATORY EXERCISES e No Food No Beverages allowed in the laboratory room e Keep clothes bags etc OFF the benches with equipment on them Be On Time Being late is annoying to your lab partners and if the experiment has progressed too far you may not be credited with doing the experiment e Safety precautions must be observed at all times to prevent electric shock damage to instruments etc COME PREPARED BOTH THE WRITTEN LAB REPORTS AND LAB PERFORMANCE INCL ATTITUDE PUNCTUALITY PREPAREDNESS WILL BE CONSIDERED FOR THE FINAL LAB MARK Lab Exercises General The maximum number of students in a lab work group is indicated on the sign up sheet Should students leave a work group for whatever reason such that only one stu
15. Expanding the time base again you can see that the MSB the first bit counting from the left starts with the falling edge of the FS pulse Assign slot 32 Now you can observe that the LSB the 8th bit counting from the left ends with the falling edge of the FS pulse 6 Companding To enhance the S Nratio of a small signal on the transmission channel a process of COMpressing the signal before transmission and exPANDING it upon reception is frequently being used the combination of both thus called COMPANDING Instead of dividing the range from 2V to 2V into 256 equal steps for the A D conversion the range is divided into segments with progressively smaller voltage increments from 2 V towards 0 Volts In our experiment we will have a close look at the compression part We could include the expansion part too but it will be omitted here due to time limitations in the lab Assign time slot no 1 Move the shorting bridge from to Ext DC In Vary the DC voltage and note the binary sequence according to the following table These are the minimum number of measurements taking more readings will provide improved results See table 5 1 to collect the data The resulting curve is somewhat idealized but provides a good perception of the principles involved COMMUNICATIONS 1 29 Experiment No 5 2133 PCM Table 5 1 Binary Sequence Decimal Equivalent to the 8 bit sequence i lt 0 127 gt 0 255 10001011 d Analysi
16. If the encode Hime siot has not ean updated the POM dats wil be during the provinualy easigned slot which may now be assigned to CODEC FIXED TIME SLOY RODE are several ways in which the 020 7 3021 may tha fixed time sot mode The first and method kave CLR disconnected ar te aonmeet CLA Voc in ia eiluation Og at a When De goes iow both encode and decode siot set to one on the second subsequent rama ayo pues Tine siot carmesponds to ag CL or Bes one from ime nominat leading edge of FS F ga seecectively As in me xot axsignment made tha Dy output Inisiitad Tor oos additione fame niter tio clout in powered up A logical 1 6n De powers CODES down on the second subsequent FSy pula A second fied tiae slot method ie to aparate conti Placing n 1 on Dg vll then cause the ssie contrat register to fit up with ones With 81 and equal to 1 CODE wii pevwar dewn Piasta a 90 on Do will cause the serial control regint fo us with zeroes sakry dne Pint one bath the encoder and end poseering up the device koponan sikuoni wih Que method of operelon is that tre dang mensch of Dy most occur at cyclen cf CLK ener ta FS if thig restniction fe mal Tot lowed it is possible tha
17. Marker and lt Delta gt This sets the carrier reference to 0 dBm and allows the difference of the amplitudes of the side frequencies to the amplitude of the unmodulated carrier conveniently to be recorded in dB The Peak Search or Search function may be useful too Switch FM on again and for the same number of side frequencies as seen on the linear display or seen on the Bessel s table record the levels of the sinusoidal spectrum components with reference to the unmodulated carrier i e the difference in dB b 1 Do these measurements under the same modulation conditions as done in a 1 b 2 Repeat the measurements with the same modulation conditions as in a 2 b 3 Repeat the measurements with the same modulation conditions as in a 3 C Deviation As on the oscilloscope the deviation of a carrier is not readily observed on the spectrum analyzer switch to linear display under realistic modulation conditions For the purpose of demonstration only set up conditions as follows 100 kHz 20 1 Hz 100 mHz Af 10 2 span 100 kHz Switch the FM modulation off Note the position of the carrier Switch the FM modulation on again Make notes of what is happening Change fy to 0 2 Hz then to 0 3 Hz Make notes of observations Change Af to 20 kHz then to 30 kHz Make notes of observations D Bandwidth We now have a look at the bandwidth occupied by the spectrum We set up a carrier and modulate it with variou
18. R OWN words to present your report concise clear and clean As pointed out above copying etc will be considered as plagiarism and will be severely punished by reducing marks in severe cases served with an as mentioned above the provider lender of the original work included e notes sheets containing the raw data taken by each student during the experiment to be initialized by the attending technologist before leaving the lab and attached to the written report Reports with the raw data missing are subject to a deduction of one full mark 10 The student is encouraged to develop and use his her own personal style for writing and presenting his her report However standard procedures in industry and research laboratories require certain information to be documented Therefore adhere fairly loosely to a general format like the following Title page Please make an exception here Pages stapled no folders plastic covers etc Course number Experiment number Experiment Title Name Lab partners Date of performance Abstract Statement of objective of the experiment one or two sentences Concise and pertinent outline of the theory underlying the experiment max one page Experiment and Analysis If the experiment consists of two or more parts keep the experimental and analysis sections together the reader of your report does not want to continuously flip pages back and forth to look for data etc Brief ou
19. TRI STATE output from the encoder tor if fitted for use with pin compatible During the encoder time slot the PCM code for the DECs Ensures gain compatibility previous sample of is shifted out most signifi 3 Wy potio the The wi be sant hit frst an rising adge of CL eee ee Ce Tess sot output hae TT y nn E edes and dijo wn dites lada aul hee Gian ee signals iy tals sin 2 Cun b io ANDE wih other Tie etie it qnt R Veg Power bag time aes Pi aCe CL decoder cheek biper webs to in he in and peers 2t Ua gub on tn aperado ite wl changed due repay tna 14 1544 Mi er ing 6 qubeoquant code signing Some or vant 3046 Moy be uitis CLR dr E Aj S piter ELK 2 Fon berea ane pulos Nombaty at doxder Gem PORE b inte Og ddr vale ds a one seek fot test the edge of wile s 0 pues eon at n rasis signating et
20. ame rate or 76 5 for a 2 048 MHz system with an 8 kHz frame rate Again for some applica tions the frame rate could be increased to reduce this delay TYPICAL APPLICATION A typical application of the TP3020 TP3021 used in con junction with the TP3040 PCM filter is shown The values of resistor R1 and DC blocking capacitor C1 are non critical The capacitor value should exceed 0 1 pF R1 should not exceed 160 and the product R1 X C1 should exceed 4 rms 0 1 pf power supply bypass capacitors should be used and placed as close to the device as possible Typical Application t DEB nn war mis Tiro soar desman anid ia QU ute Co tov Giunings o Qvo candied qase i me Aa opt pani AGREE MO AQ ate ABC DEAN ARMEN UN eiit bit in st cnn 0 mn 1 Tho THRONO TPR Sogl mot SES o qal et 38 COMMUNICATIONS 1 39 Experiment No 5 2133 PCM TP3040 TP3040 1 TP3040A TP3040A 1 PCM Monolithic Filter General Description Features The TP3040 TP3040 1 TP3040A TP3040A 1 filter is Exceeds all 03 04 and CCITT specifications monolithic circuit containing both transmit and receive filters 5V 5V power supplies specifically designed for PCM CODEC filtering applications m Low power consumption in 8 kHz sampled systems 45 mW 0 d8m0 into 6000 The filter is manufactured using microCMOS tech
21. arrier set to 0 dB as the reference i e the difference in dB Log display between side frequencies and carrier Show a sample calculation and sketch the spectrum 6 Section Three From the recorded data find carrier frequency fc modulating signal frequency fy modulating index m bandwidth Conclusions Comment on differences advantages and disadvantages of the amplitude time and the trapezoidal method Questions 1 To control an AM radio station s signals which type of measuring method amplitude time or trapezoidal would you use to monitor m and why 2 If an amplitude modulated carrier of amplitude 1V is set at 1 MHz and the function generator supplying the modulating signal would be swept with a sinusoidal signal over a range of 2 kHz to 20 kHz and m 60 what would a the linear spectrum look like sketch with amplitude to scale b the bandwidth be COMMUNICATIONS 1 19 Experiment No 4 2133 FM FREQUENCY MODULATION FM Objective To study some aspects of frequency modulation Background Compared to amplitude modulation frequency modulation provides enhanced noise performance i e a better signal to noise ratio at the expense of increased bandwidth Together with amplitude modulation FM is one of the classic modulation techniques Theory See Reference No 1 class text Chapter 10 sections 10 1 10 5 Experiment Equipment Function Generator HP 33120A BNC T adapter Oscilloscope HP 54645D 2
22. at setting a 0 in this circuit is to set the switch to ON IC 15 Fig 4 If not already in place set the jumper shunts to and Not Signalling COMMUNICATIONS 1 26 Experiment No 5 2133 PCM Apply a sine wave approximately 2 kHz to the BNC input with an amplitude of 350m Vp p measured at TP2 remember the scope probes are 10x This provides a signal of approx 2 Vp p applied to the CODEC input 2 Signal path trough the system To get an overlook of the whole system follow a signal applied to the input through the whole system until received and re constructed at the output Connect CH1 probe to An TP1 Trigger the oscilloscope CH1 and adjust the time base to observe the incoming signal Connect the CH2 probe to TP2 showing the signal after the filter It is unchanged except for the amplitude since the filter provides some amplification This analog signal enters now the CODEC Unfortunately nothing can bee seen of the intermediate steps applied to the signal by the CODEC quantization pulse amplitude modulation etc until the PCM pulse train appears at the output at The output looks somewhat strange but we will have a closer look at that shortly Feeding this signal back into the receiver part of the CODEC the output of the CODEC shows the decoded signal at TP6 The waveform on the oscilloscope may not look like much of the original signal yet On the function generator change
23. at you did about the matching problem sketch 4 Using the resistor values you noted from the unknown attenuator pad calculate the I L and compare with your measurement Questions 5 For the attenuator you designed show that the resistance seen by the source looking forward into the pad is actually 50Q and the resistance seen by the load looking back into the pad is also 500 i e in and output are matched as intended 6 If the 50Q resistor used to match the DC supply to the attenuator input were not provided could the output input voltage ratio still appear to be correct If so would the measurement be correct considering the conditions stated above at the beginning of the experiment objective Prove your findings 7 Comment on Questions 5 and 6 8 Looking at the results of the AC test are any of the measurements at 10 kHz 100 kHz and 1 MHz off the expected value by more than 10 If so would you have an explanation Is there anything to be learned from this Conclusions Comment on your experiment COMMUNICATIONS 1 9 Experiment No 2 2133 Waveform Analysis PERIODIC WAVEFORM ANALYSIS Objective To measure the Frequency Spectra for various periodic voltage time functions and to compare measured results with theory Theory See Reference No 1 Class text Chapters 2 1 2 9 Study in particular eqs 2 7 1 2 9 1 2 9 2 2 9 3 2 9 4 and the associated diagrams The oscilloscope is by far th
24. bed inis die BR of the POM debis graan A receive signaling frame is hecated ir a fashion by widening the Fig plies to two er more of OLE Dering a mosko signaling frame tha lat POM bi shited ki is a and appears Hag ouat ia quacuted or power ia TS from the dedos Since the bit of the POM is fost during elgenting frames the decoder Inter mais the es a way bateen O and a I Thee wilrinines the noise end datation due 1n Qvo dicus 37 COMMUNICATIONS 1 Experiment No 5 2133 ENCODING DELAY The encoding process begins at the start of the encode time slot and is concluded no later than 17 time slots later In normal applications this PCM data is not shifted out until the next time slot 125 5 later resulting in an encoding delay of 125 uS In some applications it is possible to oper ate the CODEC at a higher frame rate to reduce this delay With a 2 048 MHz clock the FS rate could be increased to 15 kHz reducing the delay from 125 pS to 67 pS DECODING DELAY The decoding process begins immediately after the end of the decoder time slot The output of the decoder sampie and hold amplifier is updated 28 CLKg cycles later PCM The decoding delay is therefore approximately 28 clock cy cles plus one half of a frame time or 81 pS for a 1 544 MHz system with an 8 kHz fr
25. dent remains in a group this student may join another team provided there is still room in that team without exceeding the above maximum number Missed Lab Exercises It is mandatory to perform all lab exercises according to course requirements Failure to perform one or more lab exercises results in a grade of F for the course When a student misses a lab exercise for whatever reason he she must notify the instructor as soon as possible If the reasons given for the absence are satisfactory to the instructor a make up opportunity may be arranged There may be a chance to let the student join another team to perform the missed lab provided this does not then exceed the max number of students in that group If it is not possible to accommodate this then a final make up date will be arranged to take place within one week after the end of classes Should the student fail to attend this appointment he she will be required to provide sufficient proof of inability to attend medical certificate air ticket etc to avoid the F grade The onus of proof lies entirely with the student The student then must immediately make another appointment with the lab instructor The lab report in such a case is due within one week after performance else the F stands Lab Reports General It is mandatory that all lab reports must be submitted on time as specified by the lab instructor Plagiarism Plagiarism will not be tolerated and may result in a grade
26. ds Logic 1 oput voltus power down oandien An Fiw nel pulls ie provided witht the CLK input clock fraquensy tuc 2048 Voc 3844 1598 He Van iienaa s provided Analog ground gli analog sipnala ere tm tis pin Met onnaneotud GRE Thi cet of the tenant titer stage 40 COMMUNICATIONS 1 Experiment No 5 2133 Functional Description The TP3040 TP3040A monolithic filter contains four main sections Transmit Filter Receive Filter Receive Filter Pow er Amplifier and Frequency Divider Select Logic Figure 1 A brief description of the circuit operation for each section is provided below TRANSMIT FILTER The input stage of the transmit filter is a CMOS operational amplifier which provides an input resistance of greater than 10 MQ a voltage gain of greater than 5 000 low power consumption less than 3 mW high power supply rejection and is capable of driving a 10 load in parallel with up to 25 pF The inputs and output of the amplifier are accessible for added flexibility Non inverting mode inverting mode or ditferential amplifier mode operation can be implemented with external resistors It can also be connected to provide a gain of up to 20 dB without degrading the overall filter per formance The input stage is followed by a prefilter which is a two pole RC active low pass fil
27. e and the load resistance form a voltage divider the measured output voltage of the function generator will vary with load resistance value and accuracy Thus for example if the function generator s output is measured with no load connected the output will be approximately twice the displayed amplitude Vgen instead Voan Repeat the measurement at 10 kHz 100 kHz and 1 MHz If your measurements don t come out as expected you might want to consider a look at the specifications in the DMM s User Manual 500 Vcen 500 Vicad Figure 2 COMMUNICATIONS 1 8 Experiment No 1 2133 Attenuator Unknown attenuator Re adjust the frequency to 1 kHz Note the number of the ready made attenuator provided by the lab technologist Also record the type T or x and the resistor values Measure the insertion loss using the same method as in the AC Test If there is any matching required do so Make a complete sketch of your measuring circuit Analysis 1 Using the chosen resistor values of your attenuator design re calculate the new actual insertion loss 2a For the DC test compare the measured to this actual Insertion Loss 2b Show how you matched the dc power supply and the DMM to the pad s input and output respectively sketch and state your reasoning Show at which points of the complete circuit you measured and 3a For the AC test compare the measured to the actual Insertion Loss as in 2a 3b Again show wh
28. e most common used instrument to analyze signals in the time domain i e representation of signal amplitude versus time However the analysis of signals in the frequency domain i e the representation of signal amplitude versus frequency requires the use of a group of instruments called analyzers the most versatile of this group being the Spectrum Analyzer In this experiment we will use the spectrum analyzer to find the harmonics of the investigated waveforms The oscilloscope serves only to observe the proper waveform selection but is not used to make measurements Experiment Equipment Function Generator HP 33120A BNC banana adapter Oscilloscope Fluke PM 3370B or HP 54645D BNC to BNC adapter Spectrum Analyzer HP E4411B BNC T adapter DMM Fluke 45 1 BNC cable short 50Q resistor 1 BNC cable long For students not familiar with the instruments the following notation may help with the use of the instruments Function Keys Labeled Keys lt Menu Keys gt Unlabeled Soft Keys Oscilloscope Waveform Waveform Spectrum Generator Analyzer Waveform Set up Measurement Set up Generator COMMUNICATIONS 1 10 Experiment No 2 2133 Waveform Analysis A Sine Wave We start out with the most straight forward waveform to get acquainted with the spectrum analyzer LINEAR MEASUREMENT Set the Function Generator to Sine Frequ 100 kHz Amp 200 To set up the desired waveform properly we need to pay atten
29. e of 32 channels called time slots in the specs can be assigned to one CODEC see the table in the attached codec spec sheet Each CODEC has to be programmed to assign a time slot for its channel and in which mode the CODEC is to be operated in this slot i e to encode decode do both or to be powered down A programmer circuit designed for this purpose is integrated on the board The desired time slot and mode is set with a multi switch Pressing the time slot programmer pulse TS push button switch sends control clock pulses and an 8 bit series of control data pulses to the CODEC initiating the assignment The whole process is controlled by the frame synchronizing pulse FS occurring at an 8 kHz rate Procedure Equipment PC board Power Supply Oscilloscope DMM Function Generator Use the 10x probes with the oscilloscope at all times Make notes and sketches of your observations throughout the experiment This is important since it will help to clarify the various concepts encountered in the experiment which simulates a telephone link as it is used today 1 Set Up The CODEC handles transmitting AND receiving at the same time We use this feature by feeding our transmitted PCM right back to be received again This allows an easy comparison of the outgoing and the received signal Therefore set the mini switches to assign the time slot mode to Encoder and Decoder 0 0 and to time slot 1 0 Note th
30. hing requirements Assuming that we still have the square set up from the previous experiment adjust the Amplitude to 350mVpp and Offset to 175 mV dc The oscilloscope should display the bottom of the square wave to be on the GND level Now change the duty cycle to set the pulse waveform Shift Duty set to 20 Enter This waveform has a dc spectral component which too has to be measured For this you use the DMM Observing the oscilloscope and the DMM check whether the displays show exactly what you expect them to show If you are satisfied go ahead with your measurements If you are not satisfied think what could be wrong and what could be done to remedy the problem Remember the function generator s output characteristics Once everything is all right c 1 record the dc component Then remove all present connections and connect the function generator directly to the spectrum analyzer Set the spectrum analyzer up similar as in part A with the Start frequency at 0 Hz and the Stop frequency at 1 MHz The frequency scale now reads from 0 Hz to 1 MHz with 100 kHz div LINEAR MEASUREMENT c 2 Measure the spectrum similar as done for the square wave linear display up to the 10th harmonic The analyzer s Peak Search function may not mark very small components smaller than about half a division To get a measurement for these use the knob to move the marker or estimate directly from the screen dB MEASUREM
31. ing sampling Optimum noise and distortion performance will be obtained from the TP3040 TP3040A filter when operated with sys tem posk cvedoad volepas of 20537 t at VFO and YEO When t a POM CODEC with a volue miskis this range funrfor gain or ethers be BOARD LAYOUT Cera be taken layout to power supply sd geuri nome Analog ground ONDA af esch fer should ba connected to digi ground NCO af singe Further pavan tn auch titer eral CODEC ia recommended Ground loops be avoided ted between GNOA end GNDO end between the GNOA 41 COMMUNICATIONS 1 42 Experiment No 5 2133 PCM Typical Performance Characteristics Transmit Filter Stage Receive Filter Stage mL DOTI 10 LII We I ld 3 LLLI a SEP ONDA EET a tn Be fie go o Bes irs edge tn dies 2 COR T ka Qo amp seed Oe to 34141 and ceca ig wil recht prs WLS aoe 9800 74 BIURET COMMUNICATIONS 1 43 2133 APPENDIX A Appendix A Saving screen display of the Spectrum Analyzer bitmap Once the display is on the screen either from an input waveform or loaded from the internal hard drive
32. ing the Peak Search Next Pk right gt routine to the frequency location of the 3rd harmonic The difference of the power level indicated now to the level measured for the fundamental shows how much the power level of the 3rd harmonic is below the level of the fundamental spectral component The difference is measured in dB b 2 Using the approach just described measure the power levels of the fundamental and the harmonics up to the 9th Incidentally a more convenient way of measuring the above is to set the fundamental as 0 dBm reference and read the harmonic s power levels directly To do this press Peak Search the marker jumps to the highest peak Then press Marker and Delta This sets the level of the marker at the fundamental at 0 dB and using the Peak Search Next Pk right routine allows to quite easily read the levels of the other harmonics directly with reference to the fundamental Note the Delta function also sets the frequency of the fundamental to Zero ignore since this is obviously not the case If you would like to save the screen display of the analyzer on disk see Appendix A COMMUNICATIONS 1 12 Experiment No 2 2133 Waveform Analysis C Pulse Train Wave Disconnect the spectrum analyzer and press the green Preset button The spectrum analyzer switches back to its default values The set up is the same as for the previous measurements Again pay attention to the generator s output matc
33. ion voltage reference and internal auto zero circuit A serial control port allows an external controller to individually assign the PCM input and output ports to one of up to 32 time slots or to place the CODEC into a power down mode Alternately the TP3020 TP3021 may be operated in a fixed time slot mode Both devices are intended to be used with the TP3040 monolithic PCM filter which provides the input anti aliasing function for the encoder and smoothes the output of the decoder and corrects for the sin x x distortion introduced by the decoder sample and hold output Simplified Block Diagram Features Low operation power 45 mW typical m Low standby power 1 mW typical 5V operation TTL compatible digital interface m Time slot assignment or alternate fixed time slot modes W Internal precision reference Internal sample and hold capacitors Internal auto zero circuit TP3020 p law coding with signaling capabilities TP3021 A law coding Synchronous or asynchronous operation 35 COMMUNICATIONS 1 Experiment No 5 2133 PCM Connection Diagrams TUH 5538 3 TU H 5538 4 Top View Top View Order Number TP3020J or TP3020J 1 Order Number TP3021J or TP3021J 1 See NS Package Number J24A See NS Package Number J22A Description of Pin Functions Symbol Function Symbol Function 1 Internally connected to GNDA NC Unused 2 5 2 Connects to an external sample hold capaci nt Dx Serial PCM
34. n the high impedance state and the receive signaling output of the TP3020 SlGg is reset to logical zero Once in the power down mode the method of activating the TP3020 TP3021 depends on the chosen mode of operation time slot assignment or fixed time slot TIME SLOT ASSIGNMENT MODE The time slot assignment mode of operation is selected by maintaining CLKc in a normally low state The state of the CODEC is updated by pulsing CLKc eight times within a period of 125 5 or less The falling edge of each clock pulse shifts the data on the Dc input into the CODEC The first two control bits determine if the subsequent control bits B3 B8 are to specify the time slot for the encoder B1 0 the decoder B2 0 or both B1 and 2 0 or if the CO DEC is to be placed into the power down mode B1 and B2 1 The desired action will take place upon the occur rence of the second frame sync pulse following the first pulse of CLKc Assigning a time slot to either the encoder or decoder will automatically power up the entire CODEC cir cuit The Dx output and Dg input however will be inhibited for one additional frame to allow the analog circuitry time to stabilize If separate time slots are to be assigned to the encoder and the decoder the encoder time slot should be assigned first This is necessary because up to four frames are required to assign both time slots separately but only three frames are necessary to activate the Dx output
35. nology 30 mW power amps disabled and switched capacitor integrators are used to simulate gy Power down mode 0 5 mW classical LC ladder filters which exhibit low component sen 20 48 gain adjust range No external anti aliasing components TRANSMIT FILTER STAGE m Sin x x correction in receive filter The transmit filter is a fifth order elliptic low pass filter in m 50 60 Hz rejection in transmit filter series with a fourth order Chebyshev high pass filter It pro TTL and CMOS compatible logic vides a flat response in the passband and rejection of sig All inputs protected against static discharge due to nals below 200 Hz and above 3 4 kHz handling RECEIVE FILTER STAGE The receive filter is a fifth order elliptic low pass filter de signed to reconstruct the voice signal from the decoded de multiplexed signal which as a result of the sampling pro cess is a stair step signal having the inherent sin x x fre quency response The receive filter approximates the func tion required to compensate for the degraded frequency re sponse and restore the flat passband response Block Diagram Re PRIOR p LL COMMUNICATIONS 1 Experiment No 5 2133 1E m Connection Diagram Dual In Line Package VFX View Order Number TP3040J TP3040AJ or TP3040J 1 or TP3040AJ 1 See NS Package J16A Description of Pin Functi
36. ntation Frequency Domain Make adequate sketches throughout the experiment Now concentrate on the Spectrum Analyzer Begin with the Lin display What you see there now is the amplitude spectrum for a sinusoidally modulated carrier wave as shown in Fig 8 5 1 class text Set Span back to 100 kHz and the modulating generator to the sine wave form The following measurements are for sine wave only COMMUNICATIONS 1 17 Experiment No 3 2133 AM Remove the modulation disconnect the modulating generator and observe the carrier on the screen re adjust the peak of the carrier to the top graticule line if necessary turning the knob slowly and waiting a second or two until the analyzer has caught up with the new level Now the carrier can be considered normalized to 1 scaled to 10 divisions 1 Re connect the modulating signal and set it to 2Vp p Record the amplitude of the side frequencies in terms of or divisions of the unmodulated carrier c 2 Set the modulating signal to 3 5Vp p and repeat the measurement as in c 1 c 3 Set the modulating signal to 5Vp p and repeat the measurement as in c 1 c 4 Change display from Lin 100 The carrier should be at the top graticule line For the same conditions as in c 1 through c 3 measure and note the amplitude level of the sidebands relative to the carrier in dB How Remember Experiment No 2 Section Three Application Record the inventory number on the top f
37. of F for the course Any material taken from sources like books manuals web sites magazines etc must be clearly referenced as a footnote or under a bibliography A re write of a report will be granted only under exceptional circumstances Missed Lab exercises In some courses group lab reports may be allowed by the lab instructor The group s composition is also determined by the lab instructor If a student fails to perform a lab exercise with his group he she will have to write his her own individual lab report Late Submission The submission schedule due date will be made known by the attending lab instructor Late submission results in a deduction of 0 5 marks per day out of 10 full marks No or Partial Submission A final date for submission will be clearly indicated on the sign up sheet and or announced by the lab instructor If after that date not all lab reports have been submitted the student will receive a grade of F for the course The deduction of marks for late submission still applies Format 5 e The report must be typed Graphs may be produced by computer provided the software is suited for that use i e grid proper scaling and correct labelling can be achieved and the plot is smooth If a graph is used to extract data or to provide some precise information show precisely how the information is obtained here it may be better to draw it on graph paper by hand usually is faster too e For your report use YOU
38. ons Funetion The norinverting input ze tha wane fier VPd Theinvarins input to the fter BS The us d for sdkewtmenis of the ranoni Biter VPaO The lew power ter ouput This ean drive the receive of an electronic hy bri PWR The inp tm the fter power PWRO The nondnverting cudnt of the receive Bier pow ampik The onn creelly iteriaes PHARO The inverting quiput of the Bier power Thie can be used with PEPO difarendasy tranatonmer hybrid The power sugely pi Regonvmanded Vos The positiva power The recommend od ia SV The the moaive stega vFRO 5 8 2 GU 15 GNDA Ib vege Plastic Lead Chip Carrier t o lt x 5 o E E 2 31 2 i 19 18 PON TP3040V 16 CLK 15 1 4 8 gt gt TL H 6660 4 Order Number TP3040V or TP3040AV or TP3040V 1 or TP3040AV 1 See NS Package V20A Funet Agta ground input pus Ad digital red er ncod to this in Mester rout clock Input frequency can be g fected wa 2048 Mir 1 544 Mir 1 538 MHZ Ths input pi used to power down Que TP3040A ule kis perio
39. onstruct the pad DC Test Set the DC Power Supply to 2V and apply directly to the input of the attenuator Measure the output and compute the insertion loss Is the result what you expected The attenuator was designed with an input impedance of 500 and an output impedance of the same value The internal resistance of the power supply however is considerably less than 50Q and the input resistance of the DMM considerably more than that Thus the power supply and the DMM need to be matched to the attenuator pad Do the matching and again measure the voltage at the attenuator input and attenuator output Adjust the power supply voltage if necessary to keep the voltage at the attenuator input at 2V Compute the insertion loss AC Test Disconnect the DC power supply Set the Function Generator to a sine wave 2Vays 1 kHz output use the DMM to measure all voltage levels Measure the insertion loss applying similar techniques as above With regard to the matching consider the following a the generator has an output impedance of 500 b the following excerpt from the function generator s User s Manual The HP 33120A generator has a fixed output source resistance of 50Q see Fig 2 During calibration output amplitudes are calibrated for both the open circuit voltage no load and the terminated output voltage loaded The terminated output amplitude is calibrated for an exact 500 load Since the function generator s output resistanc
40. ront edge of spectrum analyzer EA xx Disconnect the input cable to the spectrum analyzer Press Preset to put the analyzer in its default condition Press File then Load then Trace Drive C should be highlighted Turn knob to highlight the filename In our case the desired filename for 2nd year students is AM2 for 3rd year students AMS Hecord the filename you used Press Enter From the display record a 1 center frequency 2 span d 3 positions frequencies of the lower and upper side frequency d 4 scale type Lin or Log d 5 with the carrier set to reference top line record the amplitudes of the side frequencies with reference to the carrier Analysis 1 Collect all data in a suitable form in a clearly arranged table 2 Section One part a amplitude time method Using eq 8 3 1 class text find the modulating index m for the given modulating conditions a 1 to a 5 Show how you did that sketches sample calculation COMMUNICATIONS 1 18 Experiment No 3 2133 AM 3 Section One part b trapezoidal method Using eq 8 3 2 class text find m for the given modulating conditions b 1 to b 5 Show how you did that sketches sample calculation 4 Section Two Using eq 8 5 1 class text find m for the given modulating conditions c 1 to c 3 Lin display Show a sample calculation and sketch the spectrum 5 Section Two Show the relation of the side frequencies to the carrier with the c
41. rrier peak to the top graticule reference line This corresponds to the amplitude of the unmodulated carrier s spectrum being normalized to 1 over 10 vertical divisions a 1 With Af still set to 5 kHz switch the modulation on again and record the amplitudes of the sinusoidal spectrum components of the modulated carrier and the side frequencies with the normalized carrier as reference In practical terms measure the divisions a side frequency with an amplitude of for example 3 divisions equals 0 3 x the carrier amplitude It is sufficient to record only the significant side frequencies Consider significant side frequencies as those with an amplitude of 1 or more of the unmodulated carrier amplitude Record the positions of the side frequencies on the frequency scale with regard to the carrier that is the distance of the side frequencies to the carrier frequency a 2 Change the deviation to Af 24 kHz Repeat the above measurements you may want to change Span to a more convenient value to accommodate all significant side frequencies COMMUNICATIONS 1 21 Experiment No 4 2133 FM a 3 Change the deviation to Af 40 kHz Repeat the above measurements again changing Span if necessary B Power level measurements On the spectrum analyzer Amplitude menu switch from lt Lin gt to lt Log gt Switch FM off again and verify that the unmodulated carrier aligns to the top graticule line as the reference level Press
42. s 1 Describe and sketch the steps of a signal passing through the system from input signal to transmitted signal from received signal to output 2 Compare and sketch the relationship between clock pulses FS pulse and PCM signal sequence 3 Sketch a full frame showing the 32 channel organization with respect to the FS pulse COMMUNICATIONS 1 30 Experiment No 5 2133 PCM 4 Using your data from procedure no 6 plot Decimal Equivalent ordinate vs Voc abscissa on graph paper Note the flip of the binary sequence and the decimal equivalent at 0 Volts That means you need to adjust your ordinate scaling to accommodate a smooth transition The shape of the graph is the result of compressing in our case according to a signal processing scheme called u law When the signal is reversed it undergoes a similar decompressing process restoring the original form Conclusions Comment on your experiment Questions 1 What is the purpose of the input filter 2 What is the purpose of the output filter 3 To show the bit sequence for the companding part we changed from an AC to a DC signal Why was this necessary 4 Demonstrating on your graph of the compression process and in your own words attempt a short interpretation of the purpose and effect of this feature COMMUNICATIONS 1 31 Experiment No 5 2133 PCM PC BOARD LAYOUT A Our TIME SLor PROCRAHMHIAIG PULSE
43. s modulating signal frequencies while keeping the deviation constant Take all Markers Off Set 500 kHz amplitude 200 mVee Af 75kHz Center frequency to fc Span to 200 kHz Amplitude to lt Lin gt Ref level to 10 mV COMMUNICATIONS 1 22 Experiment No 4 2133 FM d 1 Set fy 100 Hz Measure the approximate bandwidth Easiest way to do this Press BW Avg change Resolution Bandwidth from Auto to Man Then turn knob to set resolution bandwidth to 1 kHz Press Marker Span Pair then set to Span Turning the knob symmetrically moves two markers and the frequency difference bandwidth can be read directly off the screen d 2 Set fu 1 kHz Repeat the above measurement d 3 Set fy 10 kHz Repeat the above measurement Change Span if necessary E Application Record the inventory number on the top front edge of the spectrum analyzer EA xx Disconnect the signal input from the spectrum analyzer Load a file Press Preset to put the analyzer into the default state Press File and Load then Trace Drive C should be highlighted If not change to C with Select function Turn knob to select the filename In this case the desired filename for 2nd year students is FM2 and for 3rd year students Record the filename you used Then press Enter The file should be loaded and the screen should show some spectrum Record carrier and side frequency amplitude levels and
44. st the time base to display the FS pulse with a width of one division Connect Ch2 probe to PCM TP4 Turn the DC control on the board you now see the 8 bits taking values of 0 or 1 depending on the DC voltage level Since with this time base setting 1 bit is approximately 1 division wide it is easy to read the 8 bit sequence The falling edge of the FS pulse marks the beginning of the first bit the MSB the LSB is the one at the right end 5 Time Slot The 8 bit sequence represents the first of 32 time slots 2 channels available Other time slots may be assigned using the table provided in the spec sheet of the CODEC making it possible to run 32 CODECs or 32 lines at one time Multiplexing See the table on the CODEC spec sheet Decrease the time base until you can see one complete frame i e two FS pulses The 8 bit sequence or number is now squashed together bit still quite distinguishable and representing time slot 1 Set the mini switch Ba to 1 i e to Off COMMUNICATIONS 1 28 Experiment No 5 2133 PCM Pressing the TS button initiates the assignment of the new time slot On the screen you see the 8 bit sequence move to the right into the second time slot Setting 1 B 0 and pressing TS moves the 8 bit number further right to the third time slot Setting 1 1 assigns time slot no 4 and so on Setting Ba to 1 assigns the 32nd time slot Assign time slot 1
45. t on the frame prior to power down the encoder could be assigned to an incorrect time slot 9 1 3 7 15 or 31 resulting in possible PCM bus conflict SERIAL CONTROL PORT When the TP3020 TP3021 is operated in the time slot as signment mode or the fixed time slot mode with continuous clock the data on Dc is shifted into the serial control regis ter bit 1 first In the time slot assignment mode depending on B1 and B2 the data the RCV or XMT time slot regis ters is updated at the second FSg or FSx pulse after the first pulse or the CODEC is powered down In the continuous clock fixed time slot mode the CODEC is pow ered up or down at every second FSg or FS x pulse The control register data is interpreted as follows Assign time slot to encoder and decoder Assign time slot to encoder Assign time slot to decoder the power down 3 Toug 8 are sored Note that oth porah tine siet 2asignments if fa possible th Yow dint which does not Tita can be veelui to disabis on encoder or decoder without pasering down the CODEC The TP3990 COOEC contsina cirauiby 1o und extract aignating internation ter the POM data The tremit signaling sme in signifie ty widening the PSy pales from ane of io fue or more cycles When this cours the dete present on tee Big Input et the sigh clock mules of the seconde siot inmer
46. ter designed to attenuate high fre quency noise before the input signal enters the switched ca pacitor high pass and low pass filters A high pass filter is provided to reject 200 Hz or lower noise which may exist in the signal path The low pass portion of the switched capacitor filter provides stopband attenuation which exceeds the D3 and 04 Specifications as well as the CCITT G712 recommendations The output stage of the transmit filter the postfilter is also a AG active Ke pans finer whieh elavwates cick Goquency at isasi 40 08 The quipu of tee rent qut copeble of Giving 23 2 peek io pesi signal 10 load in panio with ue to 25 28 RECEIVE FUTTER The epu siege of he ter which is tequency treat may bo presari on the receive Ingut A ewitehed opadan ow mews tar the arch fy provide the ascessary pessband Sainees alophend and sin x v gain correction witch is stenitar the the tow nese stage clock Gaquency nola qnd provides rer kepedanos of diig en sub crak POWER AKPUMERS power amplifiers sis gho merdead te to rane farmer coupled Ine two are the of the nieve postier qain seting mizon
47. the spectrum component s frequency locations i e the complete spectrum assume the unmodulated carrier level was set to the top graticule line as reference Record also center frequency and span Bessel s table Mod Index Carrier Side Frequencies Un modulated Jo J J J carrier amplitude 1 0 0 01 0 03 0 01 0 06 0 13 0 05 0 02 0 28 0 13 0 05 0 02 Negative values are of mathematical interest only For the modulation always use the absolute value of course COMMUNICATIONS 1 23 Experiment No 4 2133 FM Analysis Part A For the modulating conditions given a 1 through a 3 find the modulating index from the Bessel s table From the Bessel Functions table which lists the amplitude coefficients of the modulated carrier and the side frequencies with regard to a normalized carrier find the theoretical amplitude levels corresponding to your measurements Neatly tabulate the experimental together with the theoretical data for convenient comparison Part B Similarly to part A show the results in terms of dB Part C Interpret your observations Part D For the given modulating conditions compute the bandwidth of the occupied spectrum using Carson s Rule Compare your experimental data with the computed data With regard to part D how closely do the measured bandwidth and the bandwidth given by Carson s Rule correlate What conclusion would you draw from these results with regard
48. the top graticule reference line Thus the carrier is now normalized to 1 or 10 divisions Section One Amplitude Time Representation Time Domain We first ignore the spectrum analyzer and concentrate on the oscilloscope to investigate the two common methods to find the modulation index m a Amplitude Time Method b Trapezoidal Method Make adequate sketches throughout the experiment a Amplitude Time Method Move the channel 2 position so that the trace of the modulating signal lies on top of the AM envelope Press A2 then switch Vernier lt gt Now trace 2 can be adjusted in small increments and you can verify that the modulation signal trace corresponds exactly to the AM envelope trace Then switch channel 2 OFF Find the modulating index for the following conditions COMMUNICATIONS 1 16 Experiment No 3 2133 AM a 1 Set the amplitude of the modulating generator to 1 sinusoidal waveform record the amplitude of the carrier in Ve e from the scope display by temporarily disconnecting the modulation signal if the display is unstable change trigger to channel 1 by pressing Edge and lt A1 gt record the amplitude of the modulating signal in Vp p from the scope display not from the modulating generator display make sketches of the waveforms indicating your measurements a 2 Set the amplitude of the modulating generator to 2Vp p and change the modulating signal to a square wave repeat
49. tion to the generator s output matching requirements remember Exp 1 Fig 2 a 1 Connect the signal to the oscilloscope Does it correspond to what the function generator s display indicates Record a 2 Connect the signal to the DMM Measure on the DC range and on the AC range Do these measured data correspond to the generator s display Record dB MEASUREMENT Connect the signal to the Spectrum Analyzer Set the Spectrum Analyzer as follows Frequency Start frequency 0 kHz press 0 on numeric pad then lt kHz gt Stop frequency 1 MHz Span Should read 1MHz i e horizontal base is 100 kHz division Amplitude Ref Level 100 mV press 100 on numeric pad then lt mV gt Scale Type Lin The bottom scale now reads frequency from 0 Hz to 1 MHz i e 100 kHz div The left vertical scale now reads from the Ref level 100mV on the top to 0 V at the bottom i e 10mV division a 3 Close to the left end of the frequency scale at f 100 kHz the analyzer shows the amplitude of the fundamental or 1st harmonic frequency component Measure this amplitude Note the spectrum analyzer input impedance is 500 the spectrum analyzer displays the RMS value Check the amplitude of this frequency component does it correspond to the value you expect to see Is it correct Record Compare with the function generator s output display Does everything make sense Note COMMUNICATIONS 1 11 Experiment No 2 21
50. tline of the method of investigation whatever is applicable Procedure Measurement techniques Schematic diagrams Equipment identification Data tables Observations relevant to the experiment and the results Arrange experimental data and do the necessary calculations if applicable at least a sample calculation to prepare for analysis Theoretical calculations at least sample calculation Comparison of experimental results with theory preferably in form of tables graphs Probable causes and magnitude of errors Conclusion Summary Review questions Raw data notes attached to report and initialized by the attending lab technologist GOOD PRESENTATION IS OF THE UTMOST IMPORT ANCE AS IS CORRECT ENGLISH AND GRAMMAR EXPECT 20 OF YOUR LAB MARK ASSIGNED TO THIS AREA GENERAL INFORMATION EQUIPMENT If equipment needs to be signed out contact one of the technologists The person signing it out is responsible for it Your marks will be held back until all equipment books data manuals tools etc are returned i e your graduation might depend upon it Signed out equipment has to be returned to the same technologist from whom you signed it out Assure your name is then removed from his sign out list No equipment may be removed from any of the laboratories without explicit permission As you see this is very important TAKE LABS VERY SERIOUSLY Lakehead University Electrical Engineering Department July 2007 COMMUNICATIONS
51. to the validity of Carson s Rule Consider the same variation of fm as in part D applied to an AM signal How does it affect the bandwidth here compared to FM Part E From your recorded data find fc fm Af and p Conclusions Comment on the experiment and your results COMMUNICATIONS 1 24 Experiment No 5 2133 PCM PULSE CODE MODULATION PCM Objective To investigate aspects of quantization synchronization companding and multiplexing processes in a PCM system Background To make use of the many advantages of transmitting digital signals over transmitting analog signals speed precision security etc a number of schemes are available to modulate a pulse train with the desired information The most important of these methods is Pulse Code Modulation where an analog signal is sampled and translated into a binary signal consisting of strings of a fixed number of On or Off states Theory See Reference No 1 class text Chapter 11 1 11 3 sections about quantization compression and receiver For more detailed information regarding this particular circuit see the the following outline schematics and the attached extract from the manufacturer s data book Experiment System Description Read the description and details presented in the specification sheets and study the circuits The board layout on Fig 1 should help you find your way through the experiment Condensed Outline The system is provided on
52. width of one bit of the Signal TP4 COMMUNICATIONS 1 27 Experiment No 5 2133 PCM Since the FS pulse synchronizes the whole system time wise this pulse lends itself as the best trigger source for most measurements on the scope 4 PCM Signal Under procedure No 3 it has been observed that the PCM signal consists of an 8 bit sequence for a certain voltage level but because of the time varying nature of the applied sine wave the value of any single bit 1 or 0 cannot be observed If we want to have a closer look at the PCM signal we therefore need to find some special arrangement to slow things down To see the PCM sequence for a particular voltage level would require the continuous sampling of the same level thus encoding the same 8 bit word or number every time This can be done using a little trick by applying a variable DC source as the input signal Then the sampled signal level can be left constant or be changed in any desired interval or step and the O or 1 value of each bit of the 8 bit number sequence representing this level can be observed on the screen Set all mini switches B to 0 i e assign time slot 1 Change the jumper from An to EXT DC IN The DC voltage level can be monitored on the voltmeter and should cover the same range as the peak peak AC signal that is 2Vpc Like the AC signal before the DC voltage is now applied to the CODEC input Trigger on CH1 FS pulse Adju
Download Pdf Manuals
Related Search