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Lecture 2: AM Transmission

Lecture 2: AM Transmission. Prof. Park ELC 222 Essex County College. Modulation. Modulation is the process of impressing a low-frequency intelligence signal onto a higher-frequency carrier signal. The low-frequency intelligence signal Intelligence Modulating Signal Information Signal

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Lecture 2: AM Transmission

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  1. Lecture 2: AM Transmission Prof. Park ELC 222 Essex County College ELC 222

  2. Modulation • Modulation is the process of impressing a low-frequency intelligence signal onto a higher-frequency carrier signal. • The low-frequency intelligence signal • Intelligence • Modulating Signal • Information Signal • Audio Signal • The high-frequency carrier signal • Radio-Frequency (RF) Signal • Three Characteristics of Signal • Amplitude • Frequency • Phase ELC 222

  3. AM Fundamentals • Lower-Side Frequency (fc – fi) • Carrier Frequency (fc) • Upper-Side Frequency (fc + fi) ELC 222

  4. Example 2-1 • A1.4 MHz carrier is modulated by a music signal that has frequency components from 20 Hz to 10 kHz. Determine the range of frequencies generated for the upper and lower sidebands. ELC 222

  5. Example 2-2 • Determine the %m for the following conditions for an unmodulated carrier of 80V peak-to-peak (p-p). ELC 222

  6. Example 2-3 • Determine the maximum sideband power if the carrier output is 1 kW and calculate the total maximum transmitted power. ELC 222

  7. Example 2-4 • A 500-W carrier is to be modulated to a 90 percent level. Determine the total transmitted power. ELC 222

  8. Example 2-5 • An AM broadcast station operates at its maximum allowed total output of 50 kW and 95 percent modulation. How much of its transmitted power is intelligence? ELC 222

  9. Example 2-6 • The antena current of an AM transmitter is 12A when unmodulated but increases to 13A when modulated. Calculate %m. ELC 222

  10. Example 2-7 • An intelligence signal is amplified by a 70% efficient amplifier before being combined with a 10-kW carrier to generate the AM signal. If you want to operate at 100% modulation, what is the dc input power to the final intelligence amplifier? ELC 222

  11. Example 2-8 • A transmitter with a 10-kW carrier transmits 11.2 kW when modulated with a single sine wave. Calculate the modulation index. If the carrier is simultaneously modulated with another sine wave at 50% modulation, calculate the total transmitted power. ELC 222

  12. Mathematical Representation of Sine Wave • v = Vp sin(t + ) • Where v = instantaneous value • Vp = peak value •  = angular velocity = 2f •  = phase angle • AM: Amplitude Modulation • FM: Frequency Modulation • PM: Phase Modulation ELC 222

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