Digital Transmission and Analog Conversion

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Questions and Answers

What is the primary purpose of analog-to-digital conversion?

To measure the frequency of an analog signal

To preserve the analog signal's original form

To create a stronger analog signal

To change a continuous signal into a multilevel digital signal (correct)

What does the Nyquist theorem state regarding the sampling rate?

It can be equal to the highest frequency in the signal

It should be less than the highest frequency in the signal

It must be at least 2 times the highest frequency in the signal (correct)

It must be greater than 4 times the highest frequency in the signal

What does quantization specifically refer to in the analog-to-digital conversion process?

Approximating analog sample values with defined digital values (correct)

Sampling a continuous signal at discrete intervals

The process of increasing signal strength

Filtering out high-frequency components from a signal

What role does a low pass filter (LPF) play in an analog signal processing system?

It eliminates high-frequency components to prevent aliasing Signup and view all the answers

How does delta modulation differ from pulse code modulation (PCM)?

Delta modulation measures the change from the previous sample rather than the amplitude of each sample Signup and view all the answers

What is the primary function of a decoder in the context of pulse code modulation?

To decode a pulse-coded signal and reconstruct the original analog signal Signup and view all the answers

Which component is typically used to enhance signal strength and balance signal loss in a transmission channel?

Regenerative repeater Signup and view all the answers

What characteristic differentiates pulse code modulation (PCM) from delta modulation (DM)?

PCM relies on measuring signal amplitude, while DM focuses on signal changes Signup and view all the answers

What is the carrier frequency if the available bandwidth is 100 kHz spanning from 200 to 300 kHz?

250 kHz Signup and view all the answers

What does digital to analog conversion primarily involve?

Altering a characteristic of an analog signal based on digital data. Signup and view all the answers

Which statement about baud rate and bit rate is true?

Baud rate is less than or equal to bit rate in analog transmission. Signup and view all the answers

Which of the following statements is true about the modulation process?

The message signal remains unchanged while the carrier signal changes. Signup and view all the answers

What is the total bandwidth required for Amplitude Modulation (AM)?

BAM = 2B Signup and view all the answers

In Amplitude Shift Keying (ASK), what remains constant while the amplitude changes?

The frequency of the carrier signal. Signup and view all the answers

What distinguishes Binary Amplitude Shift Keying (BASK) from On-Off Keying (OOK)?

OOK represents one bit value with no voltage. Signup and view all the answers

Which of the following is NOT a characteristic of Quadrature Phase Shift Keying (QPSK)?

Incorporates amplitude changes as well. Signup and view all the answers

What is the formula for determining the bandwidth required for Frequency Modulation (FM)?

BFM = 2(1 + β)B Signup and view all the answers

In Frequency Shift Keying (FSK), what happens to the frequency when the digital signal is high?

The frequency increases. Signup and view all the answers

In the context of Amplitude Shift Keying (ASK), what does 'd' represent when using it with a value of 1?

The bit duration. Signup and view all the answers

Which of the following is a type of Phase Shift Keying (PSK)?

Binary Phase Shift Keying (BPSK) Signup and view all the answers

Which modulation technique uses phase shifts but no changes in amplitude or frequency?

Phase Modulation Signup and view all the answers

What characteristic of the carrier signal is altered in Phase Shift Keying (PSK)?

The phase. Signup and view all the answers

In Binary FSK, how does the carrier frequency shift when the binary input signal is Low?

The carrier frequency becomes lower. Signup and view all the answers

Which of the following represents the possible phase reversals in Binary Phase Shift Keying (BPSK)?

0° and 180° Signup and view all the answers

Study Notes

Digital Transmission Overview

Involves converting analog signals into digital formats for transmission.
Ensures integrity of essential content during conversion.

Analog to Digital Conversion (ADC)

Pulse Code Modulation (PCM): Technique that converts analog signals to digital signals; considers each sample's amplitude.
Sampling: Measures the amplitude of a continuous signal at discrete intervals; follows Nyquist theorem: sample rate must be at least twice the highest frequency of the signal.
Quantization: Converts sampled amplitudes into digital values by dividing ranges into levels, assigning center values to each sample interval.

Components of PCM System

Low Pass Filter (LPF): Removes high-frequency components to prevent aliasing in the message signal.
Regenerative Repeater: Enhances signal strength and limits signal loss by regenerating and amplifying the signal.
Decoder: Decodes pulse-coded signals back to the original analog signal, acting similarly to a demodulator.

Delta Modulation

A simpler alternative to PCM that only tracks changes from the previous sample rather than the absolute signal amplitude.

Digital to Analog Conversion

Involves changing properties of an analog signal based on digital data to recreate original signals.

Key Terms

Bit rate: Number of bits transmitted per second.
Baud rate: Number of signal elements transmitted per second; often less than or equal to bit rate in digital data transmission.

Modulation Techniques

Carrier Signal: A signal whose characteristics (amplitude, frequency, phase) are altered to encode information.
Amplitude Shift Keying (ASK): Varies carrier amplitude to represent binary data; uses two voltage levels—one for binary 1 and another for binary 0.
Frequency Shift Keying (FSK): The frequency of the carrier signal changes in relation to binary inputs; high frequency for binary 1 and low for binary 0.
Phase Shift Keying (PSK): Changes the phase of the carrier wave, can be Binary (BPSK) with two phases or Quadrature (QPSK) with four phases.

Analog to Analog Conversion

Can occur via modulation techniques such as amplitude modulation (AM), frequency modulation (FM), and phase modulation (PM).

Bandwidth Considerations

AM Bandwidth: Determined by the audio signal, with the formula BAM = 2B.
FM Bandwidth: Given by BFM = 2(1 + β)B, where β is the modulation index.
PM Bandwidth: Calculated similarly to FM with BPM = 2(1 + β)B.

Example Calculations

If bandwidth is 100 kHz from 200 - 300 kHz, carrier frequency is at 250 kHz; bit rate can be derived under modulation conditions.
For a system using 4 bits per signal in an analog transmission: With 1000 signal elements per second, calculate bit rate based on system specifications.

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Description

Explore the concepts of digital transmission and the process of analog to digital conversion. This quiz covers methods such as pulse code modulation, emphasizing the transformation of analog signals into their digital counterparts. Test your knowledge and understanding of these key concepts in data communications!