Communication Modulation Types - Unit 7

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Questions and Answers

What is the primary reason AM is commonly used in broadcasting?

  • It has a wider frequency range than FM.
  • It is less sensitive to electromagnetic interference.
  • It is easier and cheaper to demodulate. (correct)
  • It allows for higher quality audio transmission.

In an AM transmission, where is the information primarily located?

  • In the modulating signal amplitude.
  • In the frequency of the carrier wave.
  • In the sidebands. (correct)
  • In the carrier frequency.

What is the relationship between the bandwidth of an AM signal and the maximum frequency of the modulating signal?

  • The bandwidth is three times the modulating frequency.
  • The bandwidth is twice the modulating frequency. (correct)
  • The bandwidth is equal to the modulating frequency.
  • The bandwidth is half of the modulating frequency.

What does the modulating index, $ u$, represent in amplitude modulation?

<p>The modulation depth between the carrier amplitude and modulating amplitude. (B)</p> Signup and view all the answers

What type of modulation system does the term Double Sideband Full Carrier (DSBFC) refer to?

<p>A system that transmits all components of the AM signal. (C)</p> Signup and view all the answers

What factors contribute to the total power transmitted in an AM signal?

<p>Carrier power, upper sideband power, and lower sideband power. (D)</p> Signup and view all the answers

In what situations is AM particularly vulnerable to noise?

<p>In environments with significant electromagnetic interference. (B)</p> Signup and view all the answers

What is the role of the crystal oscillator in an AM radio transmitter?

<p>It generates the high frequency carrier wave. (C)</p> Signup and view all the answers

How does the Fourier transform relate to amplitude modulation?

<p>It provides a visual representation of the modulated signal's components. (C)</p> Signup and view all the answers

Which component is responsible for mixing the carrier wave and the audio frequency signal in an AM radio transmitter?

<p>AM modulator (C)</p> Signup and view all the answers

What role does the AF amplifier play in the AM radio transmission process?

<p>It increases the magnitude of energy of the signal. (D)</p> Signup and view all the answers

Which section of an AM radio transmitter is responsible for signal processing before transmission?

<p>Radio Frequency (RF) section (B)</p> Signup and view all the answers

What is the function of the receiving antenna in an AM radio receiver?

<p>To convert the received signal into electrical form. (B)</p> Signup and view all the answers

Which of the following components is NOT part of the AM radio transmitter?

<p>Receiver (D)</p> Signup and view all the answers

What is the primary purpose of the power amplifier in an AM radio transmitter?

<p>To increase the power of the modulated signal before transmission. (A)</p> Signup and view all the answers

Which frequency range does the bandwidth of the modulating signal typically cover?

<p>0 to fm (D)</p> Signup and view all the answers

What is a primary characteristic of VSB modulation?

<p>It simplifies the design process due to relaxed filter requirements. (C)</p> Signup and view all the answers

What is the primary purpose of suppressing the carrier in DSB-SC modulation?

<p>To save power (C)</p> Signup and view all the answers

Which modulation technique is noted for better management of the frequency spectrum?

<p>SSB-SC (B)</p> Signup and view all the answers

What is a key challenge associated with coherent detection in DSB-SC modulation?

<p>Ensuring local oscillator synchronization (A)</p> Signup and view all the answers

What is the advantage of using DSB-SC modulation?

<p>Lower power consumption. (C)</p> Signup and view all the answers

Which type of modulation transmits only a single sideband?

<p>Single Sideband Modulation (C)</p> Signup and view all the answers

What is a significant disadvantage of VSB-SC?

<p>The demodulation system is still complex. (A)</p> Signup and view all the answers

What is the role of an envelope detector in amplitude modulation?

<p>Capturing the envelope of the AM signal (B)</p> Signup and view all the answers

Which application is most suitable for VSB modulation?

<p>Analog TV broadcasting (D)</p> Signup and view all the answers

What is a notable challenge in DSB-SC demodulation?

<p>Maintaining carrier phase synchronisation. (B)</p> Signup and view all the answers

Why is the value of the RC circuit in an envelope detector critical?

<p>It determines the efficiency of demodulation (D)</p> Signup and view all the answers

Which of the following statements about SSB-SC is true?

<p>It has a lower power requirement than VSB-SC. (A)</p> Signup and view all the answers

What advantage does Vestigial Sideband Modulation (VSB) offer?

<p>It allows transmission of a vestige part of a signal (C)</p> Signup and view all the answers

What percentage of bandwidth does VSB-SC typically have compared to SSB-SC?

<p>25% greater (D)</p> Signup and view all the answers

How does single sideband modulation differ from traditional amplitude modulation?

<p>It is more power and bandwidth efficient (B)</p> Signup and view all the answers

What is one of the main drawbacks of using coherent detection in DSB-SC modulation?

<p>Higher complexity and cost for receivers (D)</p> Signup and view all the answers

What is the primary characteristic that changes in amplitude modulation?

<p>Amplitude of the carrier wave (A)</p> Signup and view all the answers

Which modulation technique uses changes in amplitude to transmit information?

<p>Amplitude Modulation (D)</p> Signup and view all the answers

Which type of communication includes methods like Ethernet and twisted-pair?

<p>Baseband Communication (C)</p> Signup and view all the answers

What is one reason for using different carrier frequencies in communication systems?

<p>To facilitate multiplexing (C)</p> Signup and view all the answers

Which modulation technique is an example of digital modulation?

<p>Amplitude Shift Keying (B)</p> Signup and view all the answers

How does increased frequency affect bandwidth?

<p>Increases bandwidth (B)</p> Signup and view all the answers

Which of the following is not a type of modulation mentioned?

<p>Digital Amplitude Modulation (A)</p> Signup and view all the answers

What factor significantly affects the height of an antenna for signal transmission?

<p>Carrier frequency (B)</p> Signup and view all the answers

Which modulation technique is characterized by the use of varying pulse widths?

<p>Pulse Width Modulation (C)</p> Signup and view all the answers

Which type of modulation is not classified under analog modulation?

<p>Pulse Code Modulation (C)</p> Signup and view all the answers

Flashcards

Baseband Communication

Direct transmission of the message signal without using a carrier signal.

Carrier Communication

Transmission of a message signal by modifying characteristics of a high-frequency carrier signal.

Modulation

Variation of a carrier signal's characteristics (amplitude, frequency, or phase) in correspondence with a modulating signal (the message).

Amplitude Modulation (AM)

Modulation technique where the amplitude of the carrier wave varies proportionally to the message signal.

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Analog Modulation

Modulation of continuous signals, including AM, FM, and PM.

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Digital Modulation

Modulation of discrete signals, including ASK, FSK, and PSK.

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ASK

Amplitude Shift Keying: Modulation by changing the amplitude of the carrier.

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FSK

Frequency Shift Keying: Modulation by changing the frequency of the carrier.

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PSK

Phase Shift Keying: Modulation by changing the phase of the carrier.

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Why Modulation is needed?

Modulation is used to increase transmission distance, reduce interference, improve bandwidth efficiency, and enable multiplexing.

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PAM

Pulse Amplitude Modulation: the amplitude of a pulse varies with the amplitude of input signal

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PWM

Pulse Width Modulation: the width of a pulse varies with the amplitude of input signal

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Amplitude Modulation (AM)

A method of transmitting information by varying the amplitude of a high-frequency carrier wave according to the instantaneous amplitude of the modulating signal.

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Modulating Index (µ)

A measure of the extent to which the amplitude of the carrier wave is varied by the modulating signal.

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Double Sideband Full Carrier (DSBFC)

A type of AM modulation where the carrier wave is transmitted and both sidebands are present.

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Sidebands

Frequency components on either side of the carrier frequency in a modulated signal, containing information.

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Carrier Wave

The high-frequency wave whose amplitude is modulated to transmit information in AM.

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AM Signal Bandwidth

Twice the maximum frequency of the modulating signal.

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Demodulation

The process of extracting the original modulating signal from the carrier wave in the receiver.

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Noise Sensitivity

AM signals are vulnerable to interference and noise.

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AM Radio Transmitter

Consists of two sections: Audio Frequency (AF) and Radio Frequency (RF). The AF section generates the signal; the RF section modulates it for transmission.

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AF Section (AM Transmitter)

Generates the audio signal. The signal is amplified and fed to the modulator.

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RF Section (AM Transmitter)

Modulates the carrier wave with the audio signal.

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Carrier Wave

High-frequency wave used to transmit the audio signal.

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Modulator

Combines the carrier wave and audio signal.

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AM Radio Receiver (Antenna)

Collects the radio waves and converts them into electrical signals.

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Amplifier (Receiver)

Increases the strength of the received signal for processing.

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DSB-SC Modulation

A modulation technique where the carrier signal is suppressed, transmitting only the sidebands, saving power.

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Coherent Detection

A method of demodulation requiring perfect phase synchronization between the receiver and transmitter.

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SSB Modulation

Single-sideband modulation uses only one sideband of the signal, making it more bandwidth efficient than AM.

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VSB Modulation

Vestigial sideband modulation technique transmits a signal with a small portion of the other sideband (a vestige) to improve efficiency and reduce distortion.

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AM Demodulation

The process of recovering the original information signal from the modulated AM signal.

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Envelope Detector

A type of demodulator used for AM signals, extracts the envelope of the modulated signal.

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VSB Modulation

A modulation technique that transmits a signal efficiently, used in TV broadcasting. It compromises bandwidth and complexity.

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VSB Bandwidth

Slightly wider than Single Sideband Modulation (SSB).

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DSB-SC Modulation

Double Sideband Suppressed Carrier Modulation; a technique that saves power by removing the carrier wave, but requires a more elaborate receiver.

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DSB-SC Power Saving

Reduces power consumption in modulation by 66% by removing the carrier signal

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DSB-SC Demodulation

Requires a coherent receiver to maintain local oscillator synchronization, making it complex.

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VSB Advantages

Simple to design, transmits low frequencies efficiently, and suitable for TV broadcasts.

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VSB Disadvantages

Demodulation requires a complex receiver.

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DSB-SC Advantages

Low power consumption, and simple modulation system.

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DSB-SC Disadvantages

Complex demodulation and precise receiver synchronization required.

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Study Notes

Modulation Types and Amplitude Modulation

  • Unit 7 covers modulation types and amplitude modulation.
  • The instructor is Professor Thushara Weerawardane.

Outcomes

  • Define different communication types.
  • Differentiate modulation techniques.
  • Discuss amplitude modulation and its applications.
  • Study transmitter and receiver techniques.
  • Analyze various amplitude modulation schemes and their usage.

Types of Communication

  • Baseband Communication: Direct transmission of the message signal. Examples include Ethernet, coaxial cable, twisted-pair, and fiber-optic (broadband) transmission.
  • Carrier Communication: Transmission of a message signal by modulating a carrier wave. This is used for high power transmission.

Baseband Communication Details

  • Baseband signals are transmitted directly.
  • Examples of P2P transmission include Ethernet, coaxial cable, twisted-pair, and fiber-optic (broadband).

Carrier Communication Details

  • Information is sent by changing the characteristics of the carrier wave (amplitude, frequency, phase).
  • A carrier wave is modulated by a message signal to create an amplitude modulated signal.
  • High power transmission is frequently associated with carrier communication.

Modulation

  • Modulation is the process of adjusting a carrier signal's characteristics in relation to the message signal.
  • The carrier wave's amplitude, frequency, or phase can be changed to carry information.
  • The faster the carrier wave can be changed, the more information it can transmit.

Modulation Types

  • Analog Modulation: Continuous variations in the carrier signal's amplitude, frequency, and phase. Included are Amplitude Modulation (AM), Frequency Modulation (FM), and Phase Modulation (PM).
  • Digital Modulation: Discrete, distinct changes in the carrier signal's amplitude, frequency, and phase. Examples include Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK), and Phase Shift Keying (PSK).

Example Modulations Explained

  • Amplitude Modulation (AM): The amplitude of a carrier wave is adjusted in proportion to the message signal.
  • Frequency Modulation (FM): The frequency of a carrier wave is adjusted in proportion to the message signal.
  • Phase Modulation (PM): The phase of a carrier wave is adjusted in proportion to the message signal.
  • Pulse Amplitude Modulation (PAM): The amplitude of a carrier signal is adjusted in proportion to specific pulses, or amplitude, of the message signal.

Why Modulation is Needed

  • To increase antenna height (for different signal frequencies)
  • To reduce interference
  • To use overlapping frequency bands for multiplexing
  • To enhance bandwidth by using high frequencies.

Types of Pulse Modulations

  • PAM: Pulse Amplitude Modulation
  • PWM: Pulse Width Modulation
  • PPM: Pulse Position Modulation
  • PCM: Pulse Code Modulation (including delta modulation and adaptive delta modulation)

Digital Modulation Schemes

  • ASK: Amplitude Shift Keying
  • FSK: Frequency Shift Keying
  • PSK: Phase Shift Keying

Amplitude Modulation Further Details

  • Amplitude Modulation (AM) is used in radio and television broadcasting.
  • AM is easy to demodulate, therefore radio receivers for AM are easier and cheaper to manufacture.
  • However, AM is sensitive to noise and electromagnetic interference

Types of Amplitude Modulation

  • Double sideband with full carrier (DSB-FC),
  • Double sideband-suppressed carrier (DSB-SC)
  • Single sideband (SSB)
  • Vestigial sideband (VSB)

Double Sideband Suppressed Carrier (DSB-SC)

  • A technique where carrier signal is removed for power saving.
  • Coherent detection is used. The greatest challenge is maintaining correct synchronization of the local oscillator

Single Sideband (SSB)

  • Uses fewer transmitters
  • High bandwidth efficiency

Vestigial Sideband (VSB)

  • Is employed in television transmissions, due to the need for low frequency components.

AM Radio Transmitter (Simplified)

  • Consists of two main sections: AF (Audio Frequency) and RF (Radio Frequency).
  • Key components include a microphone, preamplifier, RF oscillator, AM modulator, and power amplifier.

AM Radio Receiver

  • Antenna receives the signal, which is amplified, frequency translated (IF), and detected.
  • An envelope detector is used to capture variations in the received amplitude (EMF)
  • Finally, amplification of the signal and output

Trigonometric Identities

  • Various trigonometric identities, including sin(α + β), sin(α - β), cos(α + β), cos(α - β), tan(α + β), and tan(α - β), have been defined in the lecture.

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