Data Communication: Signals and Analysis

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Questions and Answers

What is the lowest frequency of a non-periodic composite signal that has a bandwidth of 200 kHz with a middle frequency of 140 kHz?

100 kHz

60 kHz

40 kHz (correct)

80 kHz

What is the peak amplitude of the non-periodic composite signal in question P3?

10 V

0 V

30 V

20 V (correct)

If the highest frequency of a non-periodic composite signal is 240 kHz, what is the formula used to derive this frequency from the given bandwidth and middle frequency?

Middle frequency - (Bandwidth)

Middle frequency + (Bandwidth / 2) (correct)

Middle frequency + (Bandwidth)

Middle frequency - (Bandwidth / 2)

In a digital signal with nine levels, how many bits are realistically needed per level to ensure an integer result?

4 bits Signup and view all the answers

Which of the following represents a key characteristic of transmission impairment?

Signals degrade after traveling through a medium Signup and view all the answers

Which type of interference primarily affects the integrity of the signal during transmission?

Noise interference Signup and view all the answers

What is the range of frequencies present in the non-periodic composite signal discussed in example P3?

40 kHz to 240 kHz Signup and view all the answers

When a digital signal is represented by more than two levels, what advantage does this offer?

Higher data rates per unit time Signup and view all the answers

What is the definition of bandwidth in the context of a composite signal?

The difference between the highest and lowest frequencies Signup and view all the answers

If a periodic signal comprises sine waves with frequencies of 200 Hz, 400 Hz, and 600 Hz, what is its bandwidth?

400 Hz Signup and view all the answers

What type of frequencies does a non-periodic composite signal have after decomposition?

Continuous frequencies only Signup and view all the answers

In a periodic signal with a bandwidth of 30 Hz and a highest frequency of 90 Hz, what is the lowest frequency?

60 Hz Signup and view all the answers

When decomposing a composite periodic signal, what does Fourier analysis allow us to achieve?

Identify and represent the signal as a sum of simple sine waves Signup and view all the answers

If a composite signal has a bandwidth of 50 Hz and contains frequencies from 150 Hz to 200 Hz, what is the lowest frequency in this signal?

150 Hz Signup and view all the answers

For a composite signal to be considered periodic, what condition must be met regarding its frequency components?

The signal must repeat itself over time Signup and view all the answers

In the context of data communication, what is the crucial benefit of using composite signals over single-frequency sine waves?

They can represent a wider range of data Signup and view all the answers

What does the ratio SNRdB represent?

The ratio of signal power to noise power expressed in decibels Signup and view all the answers

Which type of noise is specifically caused by random motion of electrons in conductors?

Thermal noise Signup and view all the answers

What is the primary cause of distortion in composite signals?

Different propagation speeds of frequency components Signup and view all the answers

How is the power loss in a cable typically defined?

In decibels per kilometer Signup and view all the answers

When calculating signal power at a distance with a loss of -0.3 dB/km, what power would still be present at 5 km starting from 2 mW?

1.85 mW Signup and view all the answers

What is the formula to calculate dBm from power in milliwatts?

dBm = 10 log10 Pm Signup and view all the answers

In practical scenarios, why is achieving ideal SNR conditions unlikely?

Environmental factors introduce unpredictability Signup and view all the answers

Crosstalk noise commonly occurs due to what?

Signal interference between adjacent wires Signup and view all the answers

Study Notes

Data and Signals

Single-frequency sine waves are insufficient for effective data communications.
Composite signals are created from multiple simple sine waves of varying frequencies, amplitudes, and phases.
According to Fourier analysis, any composite signal can be decomposed into these sine wave components.

Composite Signals and Periodicity

Periodic composite signals yield discrete frequencies upon decomposition.
Non-periodic composite signals result in a continuous spectrum of sine waves, covering all frequencies.

Bandwidth and Signal Frequency

Bandwidth is defined as the difference between the highest and lowest frequencies in a composite signal.
Understanding bandwidth is crucial for characterizing both periodic and non-periodic signals.

Mathematical Problems on Bandwidth

Given a periodic signal composed of sine waves at 100, 300, 500, 700, and 900 Hz, the bandwidth can be computed as the difference between 900 Hz and 100 Hz.
For a signal with a 20 Hz bandwidth and highest frequency of 60 Hz, the lowest frequency can be determined by subtracting the bandwidth from the highest frequency.
A non-periodic signal with a bandwidth of 200 kHz centered on 140 kHz will have its extreme frequencies calculated as 40 kHz and 240 kHz.

Digital Signals

Digital signals can represent information as discrete levels; for instance, a binary '1' as positive voltage and '0' as zero voltage.
A digital signal can have more than two levels and encode multiple bits in each signal level.

Mathematical Problems on Digital Signals

For a digital signal with eight levels, three bits are needed to represent each level, allowing for 2^3 = 8 combinations.
For nine levels, while the theoretical representation requires 3.17 bits, realistic encoding necessitates using 4 bits to ensure an integer and power of 2 representation.

Transmission Impairment

Signal quality can degrade due to transmission imperfections, resulting in signal impairment.
Key causes of signal impairment include attenuation, distortion, and noise, where the sent signal differs from what is received.
The power of a signal, measured in dBm, is calculated using the formula dBm = 10 log10 Pm, where Pm is in milliwatts.

Distortion

Distortion alters the form or shape of a signal and predominantly affects composite signals.
Each frequency in a composite signal may have different propagation speeds, leading to varied arrival times at the receiver, resulting in phase discrepancies.

Noise

Types of noise that affect signals include:
- Thermal noise: random fluctuations due to electron movement in wires.
- Induced noise: generated from electrical devices acting as antennas.
- Crosstalk: interference between signals in adjacent wires.
- Impulse noise: sudden disturbances like power surges or lightning.

Signal-to-Noise Ratio (SNR)

SNR is a critical measure representing the strength of a signal relative to background noise, often expressed in decibels as SNRdB.
SNR and SNRdB are calculated by comparing signal power to noise power.
Ideal SNR conditions cannot be fully realized in practical applications; they represent a theoretical benchmark.

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Description

Explore the essential concepts of data communication, focusing on the characteristics of signals and their composition. Understand how composite signals are formed from simple sine waves and the significance of Fourier analysis in this context. This quiz will enhance your knowledge of signal properties and their applications in communications.