Labs 5 & 6

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352

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Electrical Engineering

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Jan 9, 2024

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Labs 5 & 6: Amplitude Modulation & Double Side-Band Suppressed Carrier Modulation ECT 352 Chris Nixon November 2 nd , 2023 Professor Katykhin

Objectives: The primary objectives of this lab experiment were to comprehend the principles of Amplitude Modulation, generate and modulate AM signals, and evaluate the modulation index and power of the AM signal. Results: For this experiment, the students used the Emona DATEx to generate a true AM signal by implementing its mathematical model. To construct a message signal, the students added a DC component to a pure sinewave, which was then multiplied by another sinewave of a higher frequency (the carrier). Students examined the AM signal using an oscilloscope and compared it to the original message. Furthermore, rather than a simple sinewave, students used speech to convey their message. Following that, the students altered the amplitude of the message signal and observed how it affected the modulated carrier. In addition, the students saw the effects of modulating the carrier excessively. The students then used an oscilloscope to measure the depth of modulation of the AM signal. Ultimately, the students gathered measurements for various Emona DATEx set-ups throughout both labs 5 and 6, helping them further comprehend the capabilities of the hardware unit, as well as the software component. Analysis: The experiment results show that the DATEx system can create and demodulate AM signals. The DATEx system can measure the modulation index and power of an AM signal. The AM signal's sidebands are positioned at frequencies equal to the sum and difference of the carrier and modulating frequencies. The AM signal's bandwidth is the sum of the carrier frequency and the modulating frequency. The AM signal's envelope is a copy of the modulating signal. The demodulated AM signal is a carbon copy of the modulating signal. Furthermore, the AM signal's sidebands are positioned at frequencies equal to the sum and difference of the carrier and modulating frequencies. The sidebands in lab 5 are located at frequencies of 100 kHz and 90 kHz. The AM signal's bandwidth is the sum of the carrier frequency and the modulating frequency. The bandwidth of the AM signal in lab 5 is 200 kHz. Aside from the data, there were a few issues that the students encountered while working on the labs, such as cables being broken or components of the DATEx board itself being broken. Conclusion: In conclusion, The experiment effectively showed AM modulation principles. The DATEx system can be used to create, demodulate, and measure AM signal parameters. Ultimately, AM signals can be demodulated using a variety of techniques, including a diode detector or a synchronous detector. The students learned that speech and music are transformed into an electrical signal in an amplitude modulation communications system using a device such as a microphone through doing this lab experiment. The message or baseband signal is the name given to this electrical signal. The message signal is then utilized to alter the amplitude of a pure sinewave known as the carrier electronically. The carrier's frequency is frequently substantially higher than the message's frequency. Furthermore, DSBSC, like AM, employs a microphone or other transducer to transform voice and music into an electrical signal known as the message or baseband signal. The message signal is then utilized to alter the amplitude of a pure sinewave known as the carrier electronically. And, as with AM, the carrier frequency is frequently substantially higher than the frequency of the message.

Definitions: AM: Use the modulating signal to modulate the carrier signal and transmit both the carrier and the sidebands. DSBSC: Use the modulating signal to modulate the carrier signal, then suppress the carrier and transmit only the sidebands. Questions: CH. 5 2. What feature of the Multiplier module's output suggests that it's an AM signal? Because the Multiplier module generates a high-frequency AM signal. If the output signal's amplitude varies over time, it could be a type of AM signal. Alternatively, it could be a single baseband analog signal. AM works by multiplying the carrier and message signals. The AM signal is demodulated by sampling it at the carrier frequency. Amplitude modulation (AM) is the process of changing the amplitude of a carrier wave in response to a message or information stream. The output of the multiplexer is the multiplication of the input signal and the carrier signal. If the frequency of the input signal is less than or considerably less than the frequency of the carrier signal, the multiplexer output can be treated as an AM signal. 3. The AM signal is a complex waveform consisting of more than one signal. Is one of the signals a 2Khz sinewave? Yes, one of the signals within an AM signal is typically a 2 kHz sine wave, which is the modulating signal. This modulating signal encodes the information (audio in this case) onto the carrier wave, allowing it to be transmitted and later demodulated to retrieve the original audio signal. 4. For the given inputs to the Multiplier module, how many sinewaves does the AM signal consist of, and what are their frequencies? The AM signal's sidebands are positioned at frequencies equal to the sum and difference of the carrier and modulating frequencies. The sidebands in this experiment are located at frequencies of 100 kHz and 90 kHz. In an AM signal, there are three sinusoids. 5. Why is there still a signal out of the Multiplier module even when you’re not humming (or talking, etc)? Because of the signal's noise and other harmonics. Harmonics are signals that interfere with each other (f, 2f, 3f, etc.). 6. What is the relationship between the message’s amplitude and the amount of the carrier’s modulation?

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The AM signal's envelope is a copy of the modulating signal. Carrier modulation quantity = (Message amplitude) / (Carrier amplitude) 7. What is the problem with the AM signal when it is over-modulated? When the level of modulation surpasses 100%, this is referred to as overmodulation. It is almost always considered a fault state in the sense of this definition. The signal is "off the scale," in layman's words. Overmodulation causes spurious emissions from the modulated carrier as well as distortion of the recovered modulating signal. This signifies that the output waveform's envelope is distorted. 8. What do you think is a carrier’s maximum modulation index without over-modulation? The greatest modulation index of a carrier without overmodulation is 1. CH. 6 1. What feature of the Multiplier module’s output suggests that it’s a DSBSC signal? The absence of a carrier frequency in the frequency spectrum and the presence of two sidebands in the Multiplier module's output indicate that it is a DSBSC signal. 2. The DSBSC signal is a complex waveform consisting of more than one signal. Is one of the signals a 2kHz sinewave? Because the DSBSC signal is the result of the message and carrier signals, it is a complicated waveform composed of several signals. The message signal is typically low in frequency, whereas the carrier signal is high in frequency. As a result, one of the signals could be a 2kHz sinewave. 3. For the given inputs to the Multiplier module, how many sinewaves does the DSBSC signal consist of, and what are their frequencies? An ideal double balanced mixer will provide equal outputs at F(c) + F(m) and F(c) - F(m) for a carrier signal of frequency F(c) and a modulating signal F(m). As a result, the DSBSC signal is made up of three sine waves. 4. Why does this make DSBSC signals better for transmission than AM signals? Because we simply send the information signal message in a DSBSC signal, we save a lot of power and have higher efficiency than an AM signal. 5. Why isn’t there any signal out of the Multiplier module when you’re not humming or talking?

Because of the signal's noise and other harmonics. Harmonics are signals that interfere with each other (f, 2f, 3f, etc.). 6. Based on your observations in Step 25, when the message’s amplitude is varied neither dimensions P or Q are affected. only dimension Q is affected. only dimension P is affected. • both dimensions P and. Q are affected. 7. What is the name of this type of distortion? Amplitude distortion/filtering.

Lab 5 – Amplitude Modulation

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