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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

Lecture 2: AM Transmission

Prof. Park

ELC 222

Essex County College

ELC 222

modulation
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

am fundamentals
AM Fundamentals
  • Lower-Side Frequency (fc – fi)
  • Carrier Frequency (fc)
  • Upper-Side Frequency (fc + fi)

ELC 222

example 2 1
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.

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

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

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

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example 2 5
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?

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

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example 2 7
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

example 2 8
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

mathematical representation of sine wave
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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