Data Communications Unit II Quiz

Questions and Answers

What frequency range does the term 'broadcast radio' typically cover?

30 MHz to 1 GHz (correct)

300 Hz to 3 kHz

1 GHz to 300 GHz

3 kHz to 30 MHz

What is a key characteristic of radio waves above 30 MHz?

They are transparent to the ionosphere. (correct)

They are absorbed by the ionosphere.

They can travel beyond the line of sight.

They bounce off walls and obstacles effectively.

What is one advantage of infrared communication compared to microwave transmission?

Infrared does not require licensing for frequency allocation. (correct)

Infrared communication is less reliable in line of sight.

Infrared transceivers can operate at greater distances.

Infrared systems can penetrate walls.

What must be true for infrared transceivers to communicate effectively?

They must be in line of sight or reflected by a surface. Signup and view all the answers

Which of the following best describes a limitation of infrared communication?

Line of sight is necessary for effective communication. Signup and view all the answers

What is the fundamental frequency in the composite signal described?

f Signup and view all the answers

What is the bandwidth of the composite signal?

2f Signup and view all the answers

Which of the following describes a dc component in a signal?

A component of zero frequency Signup and view all the answers

What does a loss of 3 dB indicate in terms of power reduction?

The power is reduced to one-half. Signup and view all the answers

What characterizes a periodic composite signal?

It has frequency components in odd multiples of the fundamental frequency. Signup and view all the answers

Which consideration is NOT one of the three main concerns for a transmission engineer regarding attenuation?

Environmental impact. Signup and view all the answers

How does an increase in bandwidth affect data rate?

Data rate increases when bandwidth increases. Signup and view all the answers

For a signal that includes amplitude components, what does S(f) represent?

The peak amplitude of the constituent frequencies Signup and view all the answers

What effect does frequency variation have on analog signals received?

It introduces distortion. Signup and view all the answers

Which of the following methods can help overcome the distortion caused by delay?

Employing techniques to equalize attenuation. Signup and view all the answers

What happens to the period of the total signal in relation to the fundamental frequency?

It remains the same as that of the fundamental frequency. Signup and view all the answers

Which statement accurately describes a signal's spectrum?

It describes the range of frequencies contained in the signal. Signup and view all the answers

How does the power change when a signal is amplified 10 times?

P2 = 10 P1 Signup and view all the answers

What causes delay distortion in a signal?

Varied speeds of signal components through the medium. Signup and view all the answers

What can be done to ensure a received signal is detectable despite attenuation?

Employ amplifiers or repeaters. Signup and view all the answers

When delay distortion occurs, what happens to the signal components at the receiver?

They exhibit different phases from the sender. Signup and view all the answers

What type of signal do twisted-pair and coaxial cables transport?

Electrical signals Signup and view all the answers

Which of the following characteristics describes twisted-pair cables?

Uses a regular spiral pattern of two insulated wires Signup and view all the answers

What is a common application of twisted-pair cables?

Local area networks in buildings Signup and view all the answers

What is a maximum typical data rate for long-distance applications using twisted pair?

4 Mbps Signup and view all the answers

Why is twisted-pair cable considered the least expensive transmission medium?

It is easier to manufacture and install Signup and view all the answers

What is the primary purpose of having different twist lengths in neighboring pairs of twisted-pair cables?

To reduce crosstalk interference Signup and view all the answers

What constitutes the physical medium in guided media?

The physical path between transmitter and receiver Signup and view all the answers

Which type of guided media transports data as light signals?

Optical fiber Signup and view all the answers

What is the main advantage of graded-index fibers in local area networks?

They reduce travel distance of light by causing it to curve helically. Signup and view all the answers

Which characteristic distinguishes injection laser diodes (ILD) from light-emitting diodes (LED)?

ILDs can sustain greater data rates compared to LEDs. Signup and view all the answers

What is a significant disadvantage of fiber-optic cables?

Maintenance is complex and costs are higher. Signup and view all the answers

What frequency range is typically associated with microwave communications?

1 GHz to 40 GHz Signup and view all the answers

What type of communication is facilitated by unguided media?

Wireless communication using electromagnetic waves. Signup and view all the answers

Which of the following best describes the use of infrared frequencies?

Useful for local point-to-point applications within confined areas. Signup and view all the answers

What is a key factor that affects data transmission in fiber optics?

Scattering due to impurities in the medium. Signup and view all the answers

Which method is typically used for transmission and reception in unguided media?

Antennas Signup and view all the answers

Study Notes

Signal Components and Frequencies

Composite signals consist of sine waves with specific frequencies, expressed as f (amplitude = 1 volt) and 3f (amplitude = 1/3 volt).
The frequency 3f is an integer multiple of f, making f the fundamental frequency.
The period of the composite signal matches the period of the fundamental frequency, calculated as T = 1/f.

Time Domain and Frequency Domain

Each signal has a time domain function S(t) indicating amplitude over time, and a frequency domain function S(f) showing the peak amplitude of frequencies.
The spectrum of a signal represents the range of frequencies it includes, which extends from f to 3f for the composite signal.
Bandwidth is defined as the difference between the highest and lowest frequencies, calculated as 3f - 1f = 2f.

Data Rate and Bandwidth Relationship

A composite signal with a broader frequency range can transmit more data, hence increasing the data rate.
The relationship is straightforward: increased bandwidth leads to a higher data rate.

Power and Attenuation

Power loss is proportional to the square of the voltage, calculated as dB = 20 log10(V2/V1).
A loss of 3 dB indicates a reduction to half the power.
Amplification by 10 times results in a significant gain, affecting transmission quality.

Considerations of Attenuation

Signals must be strong enough to be detected by receivers and remain above noise levels to avoid errors.
Attenuation can vary by frequency, often distorting analog signals due to different signal propagation speeds.
Techniques are available to equalize attenuation across frequency ranges to improve signal integrity.

Delay Distortion

Delay distortion occurs when signal components travel at different speeds, causing phase discrepancies at the receiver.
Variance in delay may alter the composite signal's shape, impacting intelligibility.

Guided Media for Data Transmission

Guided media establishes a physical path for data transfer, including twisted pair, coaxial cable, and optical fiber.
Twisted pair cabling is the most prevalent and cost-effective, used for telephone networks and local area networks.

Twisted Pair Cable Details

Comprises two insulated copper wires in a spiral, typically bundled together for communication.
Commonly supports data rates of 100 Mbps in LANs, with long-distance speeds around 4 Mbps.
Economic and easy to install, but subject to electromagnetic interference.

Optical Fiber Transmission

Optical fiber transports signals as light, utilizing either LEDs or injection laser diodes.
Advantages include higher data rates and lower interference but entails complexity and expense in maintenance.

Unguided or Wireless Transmission Media

Employs electromagnetic waves for transmission without conductors, categorized as wireless communication.
Frequencies from 1 GHz to 40 GHz are ideal for microwave transmissions; lower frequencies (30 MHz to 1 GHz) are designated for radio frequencies.

Applications of Wireless Communication

Radio frequencies provide effective communication, with the ionosphere not affecting transmissions above 30 MHz.
Infrared communication requires direct line-of-sight; it is confined to spaces and does not penetrate walls, enhancing security.

Summary of Key Points

Signal integrity relies on managing amplitude, frequency, and attenuation.
Equalization techniques address distortion due to varying propagation speeds.
The choice of transmission medium influences cost, installation ease, and signal quality.

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Description

Explore the fascinating world of Data Communications in Unit II. This quiz focuses on signal components and their frequency relationships, specifically sine waves and their amplitude characteristics. Test your understanding of these fundamental concepts in communication systems.