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Communication Systems Prof. Chngming Kuo
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Chapter 6 Single Tone Modulation Comparisons (cont.)
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Single-Tone Modulation Comparisons The forms of DSB, SSB, and conventional AM have been introduced in other modules. In this module, the modulation is restricted to a single-tone sinusoidal function and the behavior of the different methods is studied.
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Single-Tone Modulation Comparisons (cont.) Both time and frequency domain forms are reviewed, and power comparisons are made. Results provide certain quantitative criteria for comparing system performance.
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Power Relationships
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AM Single Tone Power Comparisons
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Example 1 A single tone modulated DSB signal has peak voltage of 200 V across 50 . Determine average and peak power levels:
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Example 2 An AM transmitter has a carrier power of 1 kW and the antenna input resistance = 50 . Find values of antenna rms voltage and current with no modulation:
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Example 2 (cont.) An AM transmitter has a carrier power of 1 kW and the antenna input resistance = 50 . Find values of antenna rms voltage and current with no modulation:
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Example 3 For AM transmitter of Example 2, determine for modulation of 50% and 100%, the average power, peak envelope power, and sideband power.
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Example 3: Tabulated Values
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Example 4 50% modulation: For transmitter of Examples 2 and 3, find antenna rms voltage and current for 50% and 100% modulation.
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Example 4 (cont.) 100% modulation:
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Summary With single-tone modulation, DSB peak power is twice the average power. With single-tone modulation, SSB peak and average powers are the same. For complex waveforms, peak power may be much greater. With single-tone modulation, AM average power is 1.5 times carrier power. With single-tone modulation, AM peak power is 4 times carrier power.
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