Lab 3 Manual- Signal Analysis in Frequency Domain

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Lab 3 School of Engineering Technology and Applied Science (SETAS) Information and Communication Engineering Technology (ICET) CBER 702: Communication Networks Lab 3: Signal Analysis in Frequency Domain *By signing above, you attest that you have contributed to this submission and confirm that all work you have contributed to this submission is your own work. Any suspicion of copying or plagiarism in this work will result in an investigation of Academic Misconduct and may result in a “0” on the work, Lab 3: Signal Analysis in Frequency Domain 1 Name Student ID Signature*

Lab 3 Learning Objectives Upon completion of this lab, students will reliably demonstrate the ability to:  Set up and operate the Spectrum Analyzer  Analyze different signals in Frequency Domain Equipment Required 1. A computer with Multisim installed 2. Within Multisim use : Agilent Function Generators: Spectrum Analyzer: https://zone.ni.com/reference/en-XX/help/375482B-01/multisim/usingspectrumanalyzer/ https://www.youtube.com/watch?v=WnKK11UEvVE Overview Spectral analysis gives information about a signal by decomposing it into sine waves of different frequencies. Spectrum analyzer is the instrument used for studying signals in the frequency domain. If a perfect sinusoidal signal (i.e. no distortion) is injected into the input of a spectrum analyzer, one vertical line would be seen at the precise frequency (f o ) of the signal, as shown in Figure 3.1. Figure 3.1 Spectral line of a perfect sinusoidal signal However, signal generators provide real signals which are not perfect. There is always some distortion, which causes much smaller lines to appear at the multiples of the fundamental frequency, as shown in Figure 3.2. A non-sinusoidal signal, such as a triangle wave or square wave, also produces more than one line. The signals to be used throughout these exercises are imperfect; lines caused by distortion may appear on the screen. 2

Lab 3 Figure 3.2 Spectral lines of an imperfect sinusoidal signal Now, if two sinusoidal signals are injected, assuming perfect signals of frequency f 1 and f 2 with equal amplitudes, the analyzer will show a spectrum consisting of two lines, one at each frequency f 1 and f 2 , as shown in Figure 3.3. Figure 3.3 Spectral lines of two sinusoidal signals The distance between each line depends on the FREQUENCY SPAN selected on the Spectrum Analyzer and the horizontal division on the screen corresponds to frequency. For each frequency span, the 3

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Lab 3 analyzer contains a bandpass filter, which governs the spectral resolution of the analyzer. The analyzer can distinguish between signals with frequency differences larger than the bandpass of the filter. Signals with a similar frequency differences than the bandpass can’t be separated; the resulting spectrum display will show only one line even if there are several as shown in Figure 3.4. As the filter is shifted along the frequency axis, the frequency components f 1 , f 2 , f 3 , become indistinct. The line at f4 remains distinct, since the frequency difference with the nearest frequency f3 is larger than the filter bandwidth. Table 3.1 shows the approximate resolution for each frequency span. Figure 3.4 Spectrum Analyzer resolution Note: The approximate resolution also depends on the level of each frequency; this means that a weak frequency component could be masked by a much stronger neighboring frequency. Table 3.1 Approximate resolution of the Spectrum Analyzer Procedure 4

Lab 3 1. Setup the modules as shown in figure 3.5 and power up the equipment. Figure 3.5 Suggested Module Arrangement 2. Setup the equipment for Sinusoidal waveform with the following adjustments On the Function Generator FUNCTION : OUTPUT FREQUENCY : 20 kHz OUTPUT LEVEL : 0.7 Vrms (1 Vpeak) On the Spectrum Analyzer: FREQUENCY SPAN : 50 kHz/V 3. Obtain a spectrum similar to Figure 3.6 Figure 3.6 Spectrum of 20 kHz {Take screenshot #1 and paste in the designated space in the Lab Worksheet} 4. Now setup the equipment for Sinusoidal waveform with the following adjustments 5

Lab 3 On the Function Generator FUNCTION : OUTPUT FREQUENCY : 40 kHz OUTPUT LEVEL : 0.7 Vrms (1 Vpeak) On the Spectrum Analyzer: FREQUENCY SPAN : 50 kHz/V 5. Obtain a spectrum similar to Figure 3.7 Figure 3.7 Spectrum of 40 kHz {Take screenshot #2 and paste in the designated space in the Lab Worksheet} 6. Now setup the equipment as shown in Figure 3.8. Figure 3.8 Suggested Module Arrangement 6

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Lab 3 7. Obtain a spectrum similar to Figure 3.9 Figure 3.9 Spectrum of 20 kHz and 40 kHz signal {Take screenshot #3 and paste in the designated space in the Lab Worksheet} 8. Set the FREQUENCY SPAN to all the values as shown below. For each setting, count the number of divisions separating the two lines. Fill in Table 3.2. I. {Take screenshot #4 for Frequency span 1 M and paste in the Lab Worksheet} II. {Take screenshot #5 for Frequency span 50 K and paste in the Lab Worksheet} III. {Take screenshot #6 for Frequency span 2K and paste in the Lab Worksheet} IV. {Fill up the table in the Lab Worksheet} Table 3.2 FREQUENCY SPAN (Hz/V) Start (Hz) Center (Hz) End (Hz) NUMBER OF DIVISIONS 1 M 0 500 K 1 M 200 K 0 100 K 200 K 50 K 0 25 K 50 K 10 K 0 5 K 10 K 2 K 0 1 K 2 K 9. Can you distinguish the two lines now in all frequency span values? If not, why? ( Write the answer in Lab Worksheet) 7