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state. This last analyzer is often called an Events Per Unit Time\EPUT meter though it is usually called a frequency meter when analyzing continuous waveforms (e.g., sinusoidal).

MODULATION: CARRYING' INFORMATION IN A TIME-DEPENDENT FORM

In digital systems, information is usually transmitted in a direct parallel form; that is, there is a direct physical link for each bit of a data word, and each link has to carry only a 1 or a 0 during a word transfer. However, digital information may also be transmitted' serially by using one of the various types of modulation as shown in Figure Time-2. It will be seen that the modulation schemes are of. two basic types. The first type, exemplified in Figures Time-2a and 2d, is characterized by intermittent steplike transitions of the signal between two voltage values. In pulse code modulation, shown in Figure Time-2a, the high voltage values correspond to l's and the low values correspond to 0's. In pulse duration modulation, shown in Figure Time-2d, the information is encoded in the length of the pulse.

 

Fig. Time-2. Various modulation schemes for transmitting digital information.

 

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