Week 04.pdf - COMMUNICATION SYSTEMS I Chapter III Dr Cihat \u015eEKER Electrical-Electronics Engineering 2020 Amplitude Modulation Fundamentals Topics

Week 04.pdf - COMMUNICATION SYSTEMS I Chapter III Dr Cihat...

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COMMUNICATION SYSTEMS I Chapter III Dr. Cihat ŞEKER Electrical-Electronics Engineering 2020
Dr. Cihat ŞEKER, KBU, EEE, 2020 2 Topics Covered in Chapter 3 Amplitude Modulation Fundamentals 1. AM Concepts 2. Modulation Index and Percentage of Modulation 3. Sidebands and the Frequency Domain 4. AM Power 5. Single-Sideband Modulation 6. Classification of Radio Emissions
Dr. Cihat ŞEKER, KBU, EEE, 2020 3 AM Concepts In the modulation process, the voice, video, or digital signal modifies another signal called the carrier. In amplitude modulation (AM) the information signal varies the amplitude of the carrier sine wave. The instantaneous value of the carrier amplitude changes in accordance with the amplitude and frequency variations of the modulating signal. An imaginary line called the envelope connects the positive and negative peaks of the carrier waveform. Figure 1. Amplitude modulation. ( a ) The modulating or information signal.
Dr. Cihat ŞEKER, KBU, EEE, 2020 4 AM Concepts Figure 2. Amplitude modulation. ( b ) The modulated carrier.
Dr. Cihat ŞEKER, KBU, EEE, 2020 5 AM Concepts In AM, it is particularly important that the peak value of the modulating signal be less than the peak value of the carrier. V m < V c Distortion occurs when the amplitude of the modulating signal is greater than the amplitude of the carrier. A modulator is a circuit used to produce AM. Amplitude modulators compute the product of the carrier and modulating signals. Figure 3. Amplitude modulator showing input and output signals.
Power Gain or Attenuation dB = 10 log P out / P in Dr. Cihat ŞEKER, KBU, EEE, 2020 6 Modulation Index and Percentage of Modulation The modulation index ( m ) is a value that describes the relationship between the amplitude of the modulating signal and the amplitude of the carrier signal. m = V m / V c This index is also known as the modulating factor or coefficient , or the degree of modulation . Multiplying the modulation index by 100 gives the percentage of modulation. Overmodulation and Distortion: The modulation index should be a number between 0 and 1. If the amplitude of the modulating voltage is higher than the carrier voltage, m will be greater than 1, causing distortion. If the distortion is great enough, the intelligence signal becomes unintelligible. Distortion of voice transmissions produces garbled, harsh, or unnatural sounds in the speaker.

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