Communication Systems Concepts Quiz

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Questions and Answers

What type of communication is facilitated by radio frequency?

Radar signals and communication.

List one application of infrared (IR) frequency.

LEDs, lasers, and TV remotes are applications of infrared frequency.

Identify one application of medium frequency.

AM broadcasting is an application of medium frequency.

What are two advantages of using a folded dipole antenna?

<p>Higher input impedance and greater bandwidth.</p> Signup and view all the answers

What are the radiation patterns of a resonant dipole antenna with length l=λ?

<p>The radiation pattern is typically a figure-eight shape.</p> Signup and view all the answers

Name a communication device that operates on the principle of telemetry.

<p>Remote controls operate based on telemetry principles.</p> Signup and view all the answers

How does a walkie-talkie facilitate communication compared to a telephone?

<p>Walkie-talkies enable simultaneous communication, while telephones typically require turn-taking.</p> Signup and view all the answers

What is a key feature of FAX devices in communication?

<p>FAX devices allow the transmission of documents over telephone lines.</p> Signup and view all the answers

What are the key functions of a transmitter in an electronic communication system?

<p>The key functions of a transmitter include processing electrical signals, restricting the range of audio frequencies, amplifying the signal, and modulating the message signal onto a carrier wave.</p> Signup and view all the answers

Why is modulation considered a primary function of a transmitter?

<p>Modulation is primary because it superimposes the message signal onto a high-frequency carrier signal, making it suitable for transmission over long distances.</p> Signup and view all the answers

How does frequency limitation impact radio broadcasting?

<p>Frequency limitation helps restrict the audio frequency range to ensure clarity and prevent distortion, typically up to 5 kHz in amplitude modulation radio broadcasts.</p> Signup and view all the answers

In what scenario is signal amplification necessary within a transmitter?

<p>Signal amplification is necessary in long-distance radio communication to strengthen the signal before modulation and transmission.</p> Signup and view all the answers

What two processes, aside from modulation, occur within the transmitter?

<p>The two additional processes are the restriction of audio frequency range and the amplification of the signal.</p> Signup and view all the answers

Why might wire telephony not require extensive processing by a transmitter?

<p>Wire telephony typically requires minimal processing because the signals can be transmitted effectively without significant adjustments.</p> Signup and view all the answers

What is the relationship between the message signal and the carrier signal in modulation?

<p>In modulation, the message signal is superimposed onto the carrier signal, allowing the information to be transmitted over a distance.</p> Signup and view all the answers

How does the processing of a message signal facilitate its transmission?

<p>Processing eases the transmission by optimizing the signal's strength, frequency range, and modulation to ensure clarity over channels.</p> Signup and view all the answers

What is the total power in an AM wave if a 400 W carrier is modulated to a depth of 75%?

<p>The total power in the AM wave is $P_t = P_c(1 + m^2/2)$, where $P_c$ is the carrier power and $m$ is the modulation index. Thus, $P_t = 400(1 + (0.75^2)/2) = 400(1 + 0.140625) = 400(1.140625) = 456.25 W$.</p> Signup and view all the answers

Define atmospheric noise and give an example of its source.

<p>Atmospheric noise, also known as static noise, is caused by natural disturbances such as lightning and thunderstorms. An example source would be lightning strikes.</p> Signup and view all the answers

What are the main characteristics of industrial noise?

<p>Industrial noise originates from mechanical and electrical activities, with sources such as automobiles, aircraft, and electric motors. It can interfere with communication signals.</p> Signup and view all the answers

List two types of extraterrestrial noise and explain their origins.

<p>Two types of extraterrestrial noise are solar noise and cosmic noise. Solar noise comes from solar flares, while cosmic noise originates from distant astronomical sources.</p> Signup and view all the answers

What is shot noise and what causes it?

<p>Shot noise arises in active devices due to the random behavior of charge carriers, such as electrons. It occurs due to the random emission of electrons from cathodes in electron tubes.</p> Signup and view all the answers

Compare simplex and duplex modes of communication.

<p>Simplex communication allows data transmission in one direction only, while duplex communication enables two-way data transmission. Duplex can be either half-duplex or full-duplex.</p> Signup and view all the answers

What role does industrial noise play in communication systems?

<p>Industrial noise interferes with the clarity of signals and can cause disruptions in communication. It originates from various electrical and mechanical processes.</p> Signup and view all the answers

Describe the impact of modulation depth on total power in an AM wave.

<p>The modulation depth affects the amount of additional power contributed by sidebands in an AM wave. Greater modulation depth increases the total power, enhancing signal strength.</p> Signup and view all the answers

Flashcards

Simultaneous Communication

Communication methods where information is transmitted simultaneously to multiple recipients, such as TV and radio broadcasts.

Non-Simultaneous Communication

Communication methods where information is transmitted and received individually between two parties, such as walkie-talkies and telephones.

Telemetry

A device that combines separate parts (like a TV and a remote control) and operates them as one whole.

Folded Dipole Antenna

An antenna with a folded wire element, creating a higher input impedance and wider frequency range.

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Bandwidth

The antenna's ability to receive a range of frequencies while maintaining good performance.

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Input Impedance

The amount of resistance an antenna presents to the incoming signal, affecting the transfer of power from the source to the antenna.

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Radiation Pattern

The graphical representation of how an antenna transmits or receives radio waves in different directions.

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Dipole Antenna Length

The length of a dipole antenna, which affects the frequencies it can efficiently transmit and receive.

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What is noise in communication?

A spurious or undesired disturbance that interferes with the received signal in a communication system.

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Atmospheric Noise

Caused by natural events like lightning discharges and thunderstorms.

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Industrial Noise

Caused by human-made sources like vehicles, machinery, and electrical equipment.

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Extraterrestrial Noise

Originating from outer space, including solar flares and cosmic radiation.

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Internal Noise

Generated within the communication system itself, such as in electronic devices.

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Shot Noise

A type of internal noise caused by the random movement of charge carriers in active devices.

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Simplex Mode

Where communication is only one-way, like a radio broadcast.

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Duplex Mode

Where communication is two-way but only one party can transmit at a time, like walkie-talkies.

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Block Diagram

A block diagram is a simplified representation of a system, showing its main components and their connections.

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Transmitter Function

The transmitter's primary function is to prepare the message signal for transmission.

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Transmitter Signal Processing

The transmitter can restrict the range of audio frequencies, amplify the signal, and modulate the signal onto a carrier wave for transmission.

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Frequency Restriction

In radio broadcasting, the transmitter restricts the signal's frequency range to a specific band, usually up to 5kHz for amplitude modulation (AM) broadcasts.

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Signal Amplification

The transmitter amplifies the signal to increase its strength, enabling it to travel longer distances.

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Transmitter Modulation

Modulation is the process of superimposing the message signal onto a high-frequency carrier wave for transmission. This allows for efficient long-distance transmission.

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Signal Amplification for Long Distance

In long-distance radio communication, signal amplification is crucial to overcome signal attenuation over distance.

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Transmitter's Overall Function

The transmitter's role is to process the message signal to ensure efficient and reliable transmission. This processing includes frequency restriction, amplification, and modulation.

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Study Notes

Important Instructions for Examiners

  • Answers should be assessed by key words, not by exact wording.
  • Model answers and student answers may vary, but understanding should be evaluated.
  • Language errors (grammar, spelling) are not major factors (except in English and Communication Skills).
  • Figures should be assessed for major components; minor variations are acceptable.
  • Numerical problems may have variations due to assumed constants.
  • Examiner judgment on relevant answers based on understanding is acceptable for some questions.
  • Programming language papers may accept equivalent alternate code solutions.

Q1. Attempt Five of the Following

a) Signal to Noise Ratio

  • Signal-to-noise ratio (SNR) is the ratio of a wanted signal's strength to the strength of an unwanted signal or interference.
  • It is also defined as the ratio of signal power to noise power at the same point.
    • SNR = Signal Power / Noise Power

b) Modulation Index in FM

  • Modulation index (m) in FM is the ratio of frequency deviation to modulating frequency.
    • m = Frequency Deviation / Modulating Frequency

c) Carson's Rule for FM Bandwidth

  • Carson's rule estimates the bandwidth of a frequency-modulated (FM) signal.
    • Bandwidth = 2 x (Maximum Frequency Deviation + Maximum Modulating Frequency)

d) Ratio Detector Circuit

  • A ratio detector is a circuit used in frequency modulation (FM) receivers that demodulates the FM signal by detecting the ratio of the two signals, one is strong and the other is a very weak signal.

Q2. Attempt Three of the Following

a) Electronic Communication System Block Diagram

  • A block diagram is a simplified representation of a system. This one illustrates the basic components of an electronic communication system.
    • Information source, transmitter, communication channel, noise, receiver, and destination.

b) FM and AM Receiver IF Values

  • FM radio (intermediary frequency) = 10.7 MHz.
    • Medium wave AM (intermediary frequency) = 455 kHz.

c) Fading in Wave Propagation

  • Fading is a fluctuation in signal strength at a receiver due to interference of signals from different paths.

d) Yagi-Uda Antenna Radiation Pattern

  • Yagi antennas have a directional radiation pattern, illustrated by a diagram.
    • The pattern shows the major lobe, and minor/side lobes.

Q3. Attempt Three of the Following

a) Comparison of Narrowband and Wideband FM

  • Narrowband FM: Modulation index is less than 1, low deviation, low bandwidth, mainly for voice communication.
  • Wideband FM: Modulation index is greater than 1, high deviation, high bandwidth, used for high-fidelity sound quality.
    • Includes details about maximum deviation, frequency range, and applications.

b) AM Signal in Time and Frequency Domains

  • Sketches showing the AM signal in time and frequency domains.
    • Include the carrier component, sidebands, and frequency spectrum characteristics.

c) Reception of High-Frequency Signals at Night

  • High-frequency reception is better at night due to the ionosphere.
    • At night, the upper layers (F1 and F2) of the ionosphere combine, reducing absorption of the signal compared to daytime.

d) Rectangular Microstrip Patch Antenna

  • Rectangular patches are used in microwaves and telecommunications.
    • Circuit components, materials, dimensions, or operating frequency are not specified.

Q4. Attempt Three of the Following

a) Electromagnetic Spectrum

  • Electromagnetic waves propagate through space.
  • The spectrum covers a broad range of frequencies from low-frequency radio waves to high-frequency gamma rays.

b) AM Superheterodyne Receiver Block Diagram

  • A superheterodyne receiver mixes incoming signals with a local oscillator to produce a common intermediary frequency, which is further processed and demodulated.
    • Function of each block of the receiver is described.

Q5. Attempt Two of the Following

a) Mathematical Expression for AM Wave

  • AM wave expressions are derived based on the mathematical functions.
    • An equation to express mathematically the AM wave is provided along with the relevant diagrams.

b) Half-Wave Dipole Antenna

  • Half-wave dipole antennas have a radiation pattern with a directional characteristic.
    • The antenna has a specific radiation pattern in which energy radiates evenly on both sides.

Q6. Attempt Two of the Following

a) Folded Dipole Antenna

  • Advantages: Higher input impedance, greater bandwidth, ease of construction, and cost-effectiveness.

b) Tropospheric Scatter Propagation

  • Tropospheric scatter relies on scattering of the electromagnetic signal off the atmosphere to propagate signals over longer distances. 
    • Path loss and the effects on the use of tropospheric scatter propagation are illustrated.

c) AM Diode Detector

  • A diode detector is used to demodulate AM signals from the radio frequency signals.
    • Included are input and output waveforms.

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Principles of Electronic Communication Model Answer PDF - Winter 2019

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