chap 3 Data and Signals

Digital data

Discrete data. Example: data stored in computer memory

value of a signal changes

1. changes over a very short span of time --> f is high 2. changes over a long span of time --> f is low

A periodic signals

1. completes a pattern within a measurable time frame 2. the completion of one full pattern is called a cycle

Wavelength properties

1. depend of both the f and the medium 2. property of any type of signal.

Frequency formulas

1. f = 1/T 2. T= 1/f

signal plotting

1. horizontal axis -- time 2. the curve is for analog signal passes through an infinite number of points. 3. the vertical lines of the digital signal, demonstrate the sudden jump that the signal makes from value to value.

Wavelength

1. is another characteristic of a signal traveling through a transmission medium. 2. binds the period or the frequency of a simple sine wave to the propagation speed of the medium 3. is the distance a simple signal can travel in one period.

Measure phase

1. measured in degrees or radians [360° is 2n rad; 1° is 2n/360 rad, and 1 rad is 360/(2n)] 2. A phase shift of 360° corresponds to a shift of a complete period; 3. a phase shift of 180° corresponds to a shift of one-half of a period. 4. a phase shift of 90° corresponds to a shift of one-quarter of a period

Sine wave

1. most fundamental form of a periodic analog signal.

Period vs. Frequency

1. period and frequency are just one characteristic defined in two ways. 2. Period is the inverse of frequency, and frequency is the inverse of period,

Period

1. refers to the amount of time, in seconds, a singal needs to complete 1 cycle. 2. expressed in seconds

Frequency

1. refers to the number of periods in 1 s. 2. expressed in Hertz (Hz), which is cycle per second.

Two Extremes

1. signal does not change at all, it never completes a cycle --> f = 0. 2. signal change instantaneously --> f is infinite and period = 0.

3 parameters of sine wave

1. the peak amplitude 2. the frequency 3. phase

Analog data

A continuous representation of data. Example: sound make by human

simple periodic analog signal

a sine wave, can not be decomposed into simpler signal.

periodic or nonperiodic can be used in

both analog and digital signals

A nonperiodic signal

changes without exhibiting a pattern or cycle that repeats over time.

wavelength in data communication

describe the transmission of light in an optical fiber.

Phase

describes the position of the waveform relative to time O.

An analog signal has

infinitely many levels of intensity over a period of time.

A composite periodic analog signal

is composed of multiple sine waves.

Peak Amplitude

is the absolute value of its highest intensity, proportional to the energy it carries. Example: Electric signal -- volt

A digital signal has

only a limited number of defined values.

data communications

use periodic analogs signals and nonperiodic digital signals.