Lecture 2 am transmission
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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

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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.

ELC 222


Example 2 2

Example 2-2

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

ELC 222


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.

ELC 222


Example 2 4

Example 2-4

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

ELC 222


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?

ELC 222


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.

ELC 222


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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