Phase describes the position of the waveform relative to time 0. If a signal changes instantaneously, its frequency is infinite. If a signal does not change at all, its frequency is zero. Change over a long span of time means low frequency. Change in a short span of time means high frequency. What is its frequency in kilohertz? Example 3.5 Solution First we change 100 ms to seconds, and then we calculate the frequency from the period (1 Hz = 10 −3 kHz).įrequency is the rate of change with respect to time. Example 3.4 Solution From Table 3.1 we find the equivalents of 1 ms (1 ms is 10 −3 s) and 1 s (1 s is 10 6 μs). The period of this sine wave can be determined as follows: Example 3.3Įxpress a period of 100 ms in microseconds. The power we use at home has a frequency of 60 Hz. Noteįigure 3.4 Two signals with the same amplitude and phase, but different frequencies Example 3.2įrequency and period are the inverse of each other. For example, the peak value of an AA battery is normally 1.5 V. The voltage of a battery is a constant this constant value can be considered a sine wave, as we will see later. Example 3.1įigure 3.3 Two signals with the same phase and frequency, but different amplitudes The peak value is equal to 2 ½ × rms value. The signal is squared and then the average amplitude is calculated. This discrepancy is due to the fact that these are root mean square (rms) values. However, it is common knowledge that the voltage of the power in U.S. The power in your house can be represented by a sine wave with a peak amplitude of 155 to 170 V. We discuss a mathematical approach to sine waves in Appendix C. Sine Wave Wavelength Time and Frequency Domain Composite Signals Bandwidth Topics discussed in this section: A composite periodic analog signal is composed of multiple sine waves. A simple periodic analog signal, a sine wave, cannot be decomposed into simpler signals. Noteģ-2 PERIODIC ANALOG SIGNALS Periodic analog signals can be classified as simple or composite. In data communications, we commonly use periodic analog signals and nonperiodic digital signals. Noteįigure 3.1 Comparison of analog and digital signals Analog signals can have an infinite number of values in a range digital signals can have only a limited number of values. Digital data have discrete states and take discrete values. Analog data are continuous and take continuous values. Analog and Digital Data Analog and Digital Signals Periodic and Nonperiodic Signals Topics discussed in this section:ĭata can be analog or digital. The term analog data refers to information that is continuous digital data refers to information that has discrete states. Noteģ-1 ANALOG AND DIGITAL Data can be analog or digital. To be transmitted, data must be transformed to electromagnetic signals. Permission required for reproduction or display. Chapter 3 Data and Signals Copyright © The McGraw-Hill Companies, Inc.
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