enth century was the center of the developed world. Communication between the great cities of Europe (e.g., London, Paris, Berlin) controlled commerce. Moving information faster between these centers meant achieving competitive advantage. In 1842, Samuel Morse devised the telegraph code, and introduced an advanced tool for accelerating trade. Almost overnight, people were transmitting messages between Berlin and Paris on the world's first long-haul telegraph system. By the twentieth century, telegraph networks linked all the continents. Huge companies, the first of the global corporations created to operate for a profit across national boundaries, owned and operated those networks. Wires were expensive to place and cable was costly to maintain. Therefore, a wireless transmission method appeared, in the late 1860s, when James Clark Maxwell, a Scot, mathematically proved that electromagnetic waves exist and that they travel at about the speed of light. Twenty years later, a German, Heinrich Hertz, devised an apparatus for detecting and producing electromagnetic waves that demonstrated the validity of Maxwell's theory. We characterize an electromagnetic wave by its frequency, which we commonly diagram as a sine wave (Figure 5-1). We generally portray sine waves as a continuous series of S-shapes placed on their sides. A conceptual base line, (zero crossing point), bisects the 'S.' One full 'S' represents a wave cycle. Each cycle has a positive polarity when the wave rises above the zero crossing point and a negative polarity when it drops below. Hertz's breakthrough was fundamental to electronic communications. For a period after he introduced his scientific work, people commonly referred to electromagnetic waves as Hertzian waves. The frequency of their oscillations was measured in cycles. Later, in the 1960s, the term hertz replaced the word cycles in describing the number of complete cycles that occur in a second. Throughout this book we will use terms such as kHz (in which "K" symbolizes kilo, or thousand) and M