7/18 11.2 Cable Transmission of Digital Data When data must be transmitted very long distances (100 mi is not unusual),analog signals tend to be corrupted by the response characteristics of the transmission line and pickup of spurious noise voltages from a number of sources. Under such conditions,it may be desirable to convert the analog signal to some digital form,transmit them in digital form,and then reconvert to analog form if desired. ●Vhy digital?? -The size or precise shape of a pulse in a digital system is not particularly important. -The system operates on the presence or absence of some sort of pulse. -Even rather severe degradation(L.degre'defn,毁坏，恶化)of pulse shape by the transmission medium does not affect the accuracy of a digital system as long as the presence or absence of a pulse can be detected. 8/18 11.3 Fiber-Optic Data Transmission Fiber optics offers wide bandwidths and high data rates while avoiding many of the interference and security constraints associated with traditional electronic communications. -Provides high isolation:glass cable can carry signals to or from instrumentation at high common-mode voltage levels without creating electrical paths between devices. -Immune to electromagnetic interference from sources such as lightning or power switching -Provide good noise rejection -Produce no sparks.11.2 Cable Transmission of Digital Data z When data must be transmitted very long distances (100 mi is not unusual), analog signals tend to be corrupted by the response characteristics of the transmission line and pickup of spurious noise voltages from a number of sources. z Under such conditions, it may be desirable to convert the analog signal to some digital form, transmit them in digital form, and then reconvert to analog form if desired. z Why digital? - The size or precise shape of a pulse in a digital system is not particularly important. - The system operates on the presence or absence of some sort of pulse. - Even rather severe degradation([ˌdeɡrəˈdeɪʃn],毁坏, 恶化) of pulse shape by the transmission medium does not affect the accuracy of a digital system as long as the presence or absence of a pulse can be detected. 7/18 11.3 Fiber-Optic Data Transmission z Fiber optics offers wide bandwidths and high data rates while avoiding many of the interference and security constraints associated with traditional electronic communications. - Provides high isolation: glass cable can carry signals to or from instrumentation at high common-mode voltage levels without creating electrical paths between devices. - Immune to electromagnetic interference from sources such as lightning or power switching - Provide good noise rejection. - Produce no sparks. 8/18