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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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

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AM Fundamentals

Lower-Side Frequency (fc – fi)

Carrier Frequency (fc)

Upper-Side Frequency (fc + fi)

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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

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

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

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

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

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

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?

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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.