.1 Definition A communication system is, simply, any system in which information is transmitted from one physical location-let's call it A-to a second physical location, which we'll call B. I've shown this in Figure 1.1. A simple example of a communication system is one person talking to another person at lunch. Another simple example is one person talking to a second person over the telephone. Figure 1.1 A communication system Chapter One 1.1.2 The Parts of a Communication System Any communication system is made up of three parts, shown in Figure 1.2. First is the transmitter, the part of the communication system that sits at point A. It includes two items: the source of the information, and the technology that sends the information out over the channel. Next is the channel. The channel is the medium (the stuff) that the information travels through in going from point A to point B. An example of a channel is copper wire, or the atmosphere. Finally, there's the receiver, the part of the commu- nication system that sits at point B and gets all the information that the transmitter sends over the channel. We'll spend the rest of this book talking about these three parts and how they work. TRANSMITTER RECEIVER CHANNEL Figure 1.2 Parts of a communication system 1.1.3 An Example of a Communication System Now, let's run through a simple but very important example of a communication system. We'll consider the example of Gretchen talking to Carl about where to go for lunch, as shown in Figure 1.3. Channel (the air) How about Chinese? Windpipe Figure 1.3 Vocal cords Gretchen talking to Carl at lunch HAPPINESS TRANSMITTER IsaCHOICE! Introducing Telecommunications The Transmitter The transmitter, in this case, is made up of parts of Gretchen, namely her vocal cords, windpipe, and mouth. When Gretchen wants to talk, her brain tells her vocal cords (found in her windpipe) to vibrate at between 100 Hz and 10,000 Hz, depending on the sound she's trying to make. (Isn't it cool that, every time you talk, a part of you is shaking a