Page 1069 - The Mechatronics Handbook

these techniques was heavily influenced by environmental conditions. For instance, smoke signals were not
very effective in windy conditions. In any case, as we will note later, some of the techniques that were in use
centuries ago for conveying information over a distance were similar to the techniques that we currently use.
The only difference is that the implementation of those techniques is exceedingly more sophisticated now
than it was centuries ago.
As the technological progress continued and electronic devices started appearing on the surface, the
field of communication also started making use of the innovative technologies. Alphabets were translated
into their electronic representations so that information could be electronically transmitted. Morse code
was developed for telegraphic exchange of information. Further developments led to the use of the tele-
phone. It is important to note that in earlier days of technological masterpieces, users would go to a
common site where one could send a telegraphic message over a distance or could have a telephonic con-
versation with a person at a remote location. This was a classic example of resource sharing. Of course,
human help was needed to establish a connection with remote sites.
As the benefits of the advances in communication technologies were being harvested, electronic com-
puters were also emerging and making the news. Earlier computers were not only expensive and less reliable,
they were also huge in size. For instance, the computers that used vacuum tubes were of the size of a
large room and used roughly about 10,000 vacuum tubes. These computers would stop working if a
vacuum tube burned out, and the tube would need to be replaced by using a ladder. On average, those
computers would function for a few minutes before another vacuum tube’s replacement was necessary.
A few minutes of computer time was not enough to execute a large computer program. With the advent
of transistors, computers not only became smaller in size and less expensive, but also more reliable. These
aspects of computers resulted in their widespread applications. With the development of personal com-
puters, there is hardly any side of our lives that has not been impacted by the use of computers. The field
of communications is no exception and the use of computers has escalated our communication capabil-
ities to new heights.

38.2 Introduction

Communication of information from one point to another in an efficient and reliable manner has always
been a necessity. A typical communication system consists of the following components as shown in
Fig. 38.1:
• Source that generates or has the information to be transported
• Transmitter that prepares the information for transportation
• Transmission medium that carries the information from one end to the other
• Receiver that receives the information and prepares it for delivering to the receiver
• Destination that takes the information from receiver and utilizes it as necessary
The information can be generated in analog or digital form. Analog information is represented as a
continuous signal that varies smoothly in time. As one speaks in a microphone, an analog voice signal is
generated. Digital information is represented by a signal that stays at some fixed level for some duration of
time followed by a change to another fixed level. A computer works with digital information that has two
levels (binary digital signals). Figure 38.2 shows an example of analog and digital signals. Transmission of

FIGURE 38.1 A typical communication system.

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