Lab 3.3 ASK and PSK Modulations Zachary Trotter

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Jan 9, 2024

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EET380 Digital Communications Instructor: Michael Blythe Campus: Lab 3.3 ASK and PSK Modulation Student Name(s): Zachary Trotter Click or tap here to enter text.

2 Contents Honor Pledge: .............................................................................................................................................. 2 Abstract ....................................................................................................................................................... 3 Introduction ................................................................................................................................................. 3 Procedures .................................................................................................................................................. 4 Conclusion ................................................................................................................................................. 15 References ................................................................................................................................................. 16 Honor Pledge: I pledge to support the Honor System of ECPI. I will refrain from any form of academic dishonesty or deception, such as cheating or plagiarism. I am aware that as a member of the academic community, it is my responsibility to turn in all suspected violators of the honor code. I understand that any failure on my part to support the Honor System will be turned over to a Judicial Review Board for determination. I will report to the Judicial Review Board hearing if summoned. Date: 12/29/2023 12/29/2023 Zach Trotter

3 Abstract In this lab the student is asked to implement a basic modem for Binary Amplitude Shift Keying, and Binary Phase Shift Keying. Introduction In RF digital modulation, a baseband digital signal modulates a single radio frequency (RF) carrier, which creates two instantaneous related shifts in amplitudes, phase or frequency of the RF carrier. The effects are shown in the following figures. 0 0 .5 1 1 .5 2 2 .5 3 -4 -3 -2 -1 0 1 2 3 4 Amplitude Shift Keying (ASK) As is seen, in ASK, each binary information shifts the amplitude of the RF carrier to one of the two possible amplitudes in its data intervals. 0 0 .5 1 1 .5 2 2 .5 3 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 Phase Shift Keying (PSK) As is seen, in PSK each binary information shifts the phase of the RF carrier to one of the two possible phases in its data intervals. -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 Frequency Shift Keying (FSK) As is seen, in FSK each binary information shifts the frequency of the RF carrier to one of the two possible frequencies for the data intervals. 12/29/2023 Zach Trotter

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4 In this lab, you will implement modulator and demodulator circuits for ASK and PSK. You will use the time domain and frequency domain observations to implement the detector at receiver. You will finish the second part of this lab that is one DPSK and FSK on next session. Procedures Part A-1.Amplitude Shift Keying (ASK) - modulator Procedure: Assemble the following circuit using MultiSIM. If you have difficulties to assemble the circuit, please download the MultiSIM file of ASK_Mod.ms11. This circuit is a simple On-Off keying (OOK) modulator. OOK is a special case of ASK. Experiment A.1 : Run the simulation and look at the spectrum analyzer’s screen. You must have already seen the spectrum of this modulation. Can you name the modulation, which has similar spectrum? Based on the spectrum analyzer, the carrier frequency is displayed prominently in the middle with two proceeding fundamental signals and their harmonics. This is a similar spectrum to the amplitude modulation by the square wave. 12/29/2023 Zach Trotter

5 Do you remember what economical way was used to demodulate that analog modulation? An envelop detector used with a comparator. ………………………………………………………………………………… ………………………………………………………………………………… Task: Place the snapshot of OOK in time and in frequency domain in the following space. 12/29/2023 Zach Trotter

6 Experiment A.2 : Use the probe of the spectrum analyzer to find the center frequency, and the center of the two main side bands. Can you find any connection between your observations, the frequency of the carrier and the frequency of the data? Please briefly include your justifications. f c = 3 kHz, f 1 = 2.9 kHz,f 2 = 3.1 kHz The data and carrier are operating on the same frequency which means they correspond with the modulation. Part A-2.Amplitude Shift Keying (ASK) - detector Procedure: Assemble the following circuit using MultiSIM. If you have difficulties to assemble the circuit, please download the MultiSIM file of ASK_Detect.ms11. 12/29/2023 Zach Trotter

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7 The above circuit shows an ASK modulator along with an envelope detector. The detector is followedby a simple single level comparator which lets eliminate the residual high frequency spectrum and transient response after envelope detection. Experiment A.3 : Run the simulation and look at the oscilloscope’s screen. You can easily compare the original information before ASK modulation and the detected information. Can you make a connection between the original data and the detected data? The original and detected data are operating on the same fundamental frequency of 99.176 Hz and within the same time domain. Task: Place the snapshot of your observation on oscilloscope in here. Please crop the unwanted parts of the figure to get the best presentation. 12/29/2023 Zach Trotter

8 12/29/2023 Zach Trotter

9 Part B-1.Phase Shift Keying (PSK) In this part of the lab, you will implement a binary PSK modulator and then you will demodulate it. To implement the demodulator you will use your knowledge from basic communications circuits and also your observation in frequency domain. Procedure: MultiSIM does not have the implementation of the analog mixer IC LM1496. You also have this option to download the simulation MultiSIM file of PSK_Mod.ms11. 12/29/2023 Zach Trotter

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10 Experiment B.1 : Run the simulation and look at the oscilloscope and the spectrum analyzer’s screen.Describe your observation briefly There is a phase shift occurring every 5us with a phase shift from 0 degrees and at 180 degrees. Both frequencies can be observed on the spectrum analyzer with the carrier being 1.094MHz and the output is 909.091kHz Recall that double sideband modulation (DSB) also has similar spectrum. What was the major issue in detection of DSB? The issue with detection of DSB is the Oscillator and carrier must be operating at the same frequency and phase. 12/29/2023 Zach Trotter

11 Task: Place a proper snapshot of the PSK signal in time and in frequency domain. 12/29/2023 Zach Trotter

12 Experiment B.2 : Can you find the frequency of the carrier and the data signal from the spectrum? Please do. Carrier = 1.094MHz Data = 909.091kHz Experiment B.3 : can you explain the reason of other frequency elements in the spectrum of PSK, based on Fourier analysis that you had in foundations of communications? Based on the Fourier analysis, the other frequencies are representations of the harmonics produced by the modulated signal 12/29/2023 Zach Trotter

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13 Part B-2.PSK detection Procedure: PSK, similar to DSB suffers from carrier inaccuracy at receiver, as it needs coherent detection. To reduce the confusion, instead of the mixer IC 1496, for detection of PSK, we use a simple multiplier that in reality plays the same role as mixer. Download the MultiSIM file of PSK detection. Experiment B.4 : Run the simulation and look at the oscilloscope screen. Describe your observations. There is a 45 degree phase shift occurring between the input and output signals. The filter is between the logic gates and the OP AMP is creating a ripple effect as the capacitor is charging to meet the demands of the input signal. This is causing a delay which is shifting the output signal and it also has a gain of 2.06V. 12/29/2023 Zach Trotter

14 Please include the snapshot of the signal along with your explanation. 12/29/2023 Zach Trotter

15 Experiment B.5 : Based on what you learned in ASK detection, can you explain the reason of using OpAmp at the far-end part of the circuit? This is a closed loop op amp and it is used as a comparator and outputs the difference between the two inputs pins Experiment B.6 : Recall DSB from your basic communications course, what would happen if the carrier frequencies at transmitter and received were different? There will be distortion or there could be quadrature null effect occurring. Experiment B.7 : Recall DSB from your basic communications course, what would happen if the phase of carriers at the transmitter and received were different? The creates an alternated signal to that of the original signal or intelligence signal Conclusion In conclusion, ASK is a form of amplitude modulation using binary symbols related to the number 1 and 0 that represent HIGH and LOW based on the carrier signal. If the signal value represents a 1 then the carrier signal is amplified to carry the intelligence signal but if it is a 0 then it is suppressed, and no transmission occurs. The amplitude is a direct representation of a set of binary digits that are modulated to transmit the signal. As for PSK, the carrier signal is modulated by the represented phase of the intelligence signal. As mentioned with ASK, PSK uses a fixed number of phases that are assigned specific binary digits and are modulated to send the signal. The binary representation is the same as ASK with a 1 and 0 (HIGH and LOW) and as the amplitude is shifted HIGH it cause a phase inversion to happen from LOW to HIGH and when the amplitude shifts back down there is a HIGH to LOW transition cause 12/29/2023 Zach Trotter

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16 another phase inversion References Frenzel, Louis. Principles of Electronic Communication Systems (p. 78-89). McGraw- Hill Higher Education. Kindle Edition. 12/29/2023 Zach Trotter