CNET304 Lab 5 FM & FSK Modulation (1)

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Lab 5: FM & FSK Modulation Lab 5: FM & FSK Modulation Prepared by: Dr. Sattar Hussain,  Centennial College, 2020 Name Student ID Signature* Dipesh Giri 301290889 Tapendra Bist 301306360 Milan Bhandari 301280047 *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 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, 1 School of Engineering Technology and Applied Science (SETAS) Information and Computing Engineering Technology (ICET) CNET304 Wireless Technology Course Lead: Dr. Sattar Hussain Section No. 006 Mark Obtained (out of 25) Due Date 22 Feb

Lab 5: FM & FSK Modulation Learning Objectives Upon completion of this lab, students will be able to:  Generate a frequency-modulated signal and display it on an oscilloscope  Analyze the time domain and frequency domain characteristics of a generated FM signal  Vary the frequency deviation and observe its impact on the FM generated signal  Locate the FM spectra sidebands and calculate the modulation index  Calculate the bandwidth of the generated FM signal  Generate an FSK signal and display it on an oscilloscope  Analyze the time domain and frequency domain of a generated FSK signal  Vary the frequency deviation and observe its impact on the FSK generated signal Equipment Required 1. R&S RTB2002B Digital oscilloscope. 2. RSA306B Spectrum Analyzer 2

0.12 Lab 5: FM & FSK Modulation Pre-Lab Assignment [ 2 marks ] A carrier of 49 MHz is frequency-modulated by a 1.5-kHz square wave. The modulation index is 0.25. Sketch the spectrum of the resulting signal. (Assume that only harmonics less than the sixth are passed by the system.) as per the table: The modulation index is 0.25 and the power of carrier P c = 0.98 with one sideband with a power of 0.12. Procedure Important Notes: a. For this lab, some of the parameter values are assigned based on the group number. Such assignment is referred to by the letter x. Always replace the x (whenever it is found) with your group number. b. All screenshots must show the time stamp at the right-bottom corner. All hand sketches must br correctly labeled with horizontal and vertical scales or values. c. Note: You are required to print your name and your lab partner name on every single screenshot submitted within this lab using the Annotation tools of the RTB2004B Oscilloscope. 1. To start, click the [Preset] key to reset the instrument to the scope mode and default state. 2. Click the [ Gen ] key on the front panel to open the " Function Generator " menu, where you can create various waveforms. 3. Generate FM signal with a sinewave carrier signal of f C = 9x.0 kHz, amplitude V C = 0.5 Vpp, modulated by sinewave modulating signal with f m = 5 kHz. Set the deviation frequency f d to 50 kHz . Adjust the Oscilloscope parameters as follow: Output 1 Function Sine 3 0.98 P c Sideband

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Lab 5: FM & FSK Modulation Frequency (Carrier Frequency) 9x.0 kHz Amplitude 500 mVpp Offset 0 V Noise 0% Modulation 1 Modulation Type FM Function Sine Frequency (Modulating Frequency) 5 kHz Deviation 50 kHz 4. Make the following adjustment and set up for CH1 of the oscilloscope: 4 Coupling DC Vertical Scale 100 mV Time Scale 50 µs

Lab 5: FM & FSK Modulation 5. You may need to synchronize the oscilloscope with the internal triggering level if the AM signal is not stable or clear. To do that, move the trigger level (TL) Marker up or down until you obtain the signal shown in the screenshot below. You may also press the [ Single ] key to freeze the Oscilloscope display and get a single shot. Remember to unfreeze the display for the next reading by clicking the [ Run/Stop ] key. 6. [ 2 mark ] Sketch or print and paste a screenshot for the Oscilloscope display below. 5

Lab 5: FM & FSK Modulation 7. Set the Deviation back to 50 kHz and click [ FFT ] key. Adjust the FFT screen as follow ( make sure your screen is in unfreeze mode ): 6 Start Frequency 0 Hz Stop Frequency 200 kHz Span 200 kHz RBW 1 kHz Source C1 FFT Window Flat Top Vertical Scale dBm

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Lab 5: FM & FSK Modulation 8. Click the [ Cursor ] key and choose V-Marker for Type and Spectrum for Source. Use the Next Peak/Prev. Peak to select a peak in the spectrum. Two vertical cursors will appear. You can use any one of them. 9. Locate the marker on the peak of the carrier frequency. Observe the sidebands to the right and the left of the carrier frequency. 10. Record in Table 1 below the power in dB of the carrier and the power of all visible sidebands to the right of the carrier spectra line. Exclude the sidebands at the far right that has power less than 1% of the carrier power, i.e. all the sidebands with power less than P C ( dB )− 20 dB . For example, if your carrier power, P C =-20 dB, discard the sidebands with power less than - 40 dB. Expand the table as needed. Carrier/ Sidebands Carrier 1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th …. Frequency (kHz) 91.087 95.9 100.9 7 106.1 0 110.9 8 115.9 9 126.0 130. 89 135. 89 141. 14 146.0 3 Power (dBm) -14.26 - 29.28 - 13.96 - 26.74 - 15.28 - 14.72 - 15.38 - 12.0 6 - 12.8 - 15.7 2 - 20.32 [ 4 marks ] Table 1 11. Calculate the modulation index using the formula m f = f d f m . Find the number of sideband corresponding to this modulation index from the Table given in the Appendix on the last page. Record your results in Table 2. 12. Measure the FM signal bandwidth. To do so, locate one cursor at the left-hand end of the spectra where the spectra line is equal to or above 1% of the carrier power. Similarly, locate the second cursor at the right-hand end where the spectra line is equal to or above 1% of the carrier power. Observe and read  f at the bottom of the Oscilloscope display. This is the FM bandwidth. Record the result in Table 2 . 7

Lab 5: FM & FSK Modulation 13. Calculate the FM signal bandwidth BW FM = 2 ×f m × N , where N is the modulating of the sidebands from the Appendix table. Record the result in Table 2 . [ 4 marks ] Table 2 Modulation index m f 10 Number of calculated sidebands (From the Appendix Table) 14 Number of visible sidebands (From table 1) 10 Measured FM Signal Bandwidth (kHz) 110 Calculated FM Signal Bandwidth (kHz) 140 14. [ 2 mark ] Compare the calculated number of sidebands and bandwidth with that obtained from the FM spectrum. Bandwidth is 10 times the calculated number of sidebands. Or Bandwidth = sidebands * modulation index 15. [ 2 mark ] Sketch or print and paste a screenshot for the FFT display below. 8

Lab 5: FM & FSK Modulation 16. Observe the ch deviation to the value that would display only 5-6 side components. Complete Table 3 below. [ 3 marks ] Table 3 Number of visible sidebands 6 Deviation (kHz) 5 Modulation index (calculated) 1 Number of sidebands (From Appendix Table) 3 FSK Modulation 1. Click the [ Gen ] key and generate an FSK signal by adjusting the following parameters: Output 1 Function Sine Frequency (Carrier Frequency) 100 kHz Amplitude 500 mVpp 9

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Lab 5: FM & FSK Modulation `Offset 0 V Noise 0% Modulation 1 Modulation Type FSK Hop. frequency 90 kHz FSK Rate 1 kHz 2. [ 2 marks ] Sketch or print and paste the Oscilloscope display below. 10

Lab 5: FM & FSK Modulation 3. [ 2 mark ] Comment on the number of sidebands obtained compared to the FM spectrum. FM Demodulation Close the web browser to close the Remote Front Panel of the Oscilloscope. Locate the Tektronix SignalVu-PC shortcut on the remote desktop. Double click or right-click and then click Run as Administrator. The RSA306B Tektronix Spectrum Analyzer screen will be displayed as shown below. 11

Lab 5: FM & FSK Modulation 1. Click the Presets button. 2. Set the Frequency to 99.1 MHz, the Span to 20.5 MHz, and Res BW to 10 kHz. 3. Set the Ref Lev to -30 dBm. 4. Right-click the screen and then click Marker to peak . 5. Click To Center in the bottom marker setting area. This sets the center frequency of the analyzer to the center of the signal. 6. Click the Audio Demod settings 7. Select FM – 200 kHz as the demodulation. 8. Click Run to start listening to the FM radio signal. 9. Adjust the Audio Gain setting so you can hear the demodulated signal. The sound level is also affected by the setting of the Windows volume control. 10. [ 2 mark ] Discard steps 10 and 11. These steps are for saving an audio file. Instead, copy and paste a screenshot below: 12

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Lab 5: FM & FSK Modulation 11. [ 2 mark ] Have you tuned to any FM station? If yes, list below the frequencies of each station. Note that the FM stations appear as spectra line shine above a noise floor. To listen to new station, click Stop in the Audio Demod , change the Frequency to the broadcasting frequency of the new FM station and click Run . = Yes, we have tuned the FM station. The frequencies are: 104.506875 MHz 106.9925 MHz 13

Lab 5: FM & FSK Modulation Appendix A 14

Lab 5: FM & FSK Modulation FM Modulation index vs. sidebands 15

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