difficult to understand than the other two modulation techniques. Phase is defined Figure 1-16 Frequency modulation Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. First Things First First Things First mathematically as "the fraction of a complete cycle elapsed as measured from a particular reference point." Any questions? OK, Now let's make that definition make sense. Consider the drawing shown in Figure 1-17. The two waves shown in the diagram are exactly 90 degrees "out of phase" of each other, because they do not share a common start point- wave B begins 90 degrees later than wave A. In the same way that we used amplitude and frequency to represent zeroes and ones, we can manipulate the phase of the wave to represent digital data. A few years ago I saw a very graphic (and way too cool) example of how phase modulation can be used in a practical way. I was in Arizona with a film crew, shooting a video for one of my corporate clients. The theme of the video was based on the statement that "if we don't intelli- gently deploy technology, the competition will leave us in the dust." Building on that phrase about dust, we rented a ghost town in Arizona and created a video metaphor around it. In the last scene of the video, a horse-drawn wagon loaded with boxes of technology products disappears into a bloody Arizona sunset, and just before the wagon disappears over the hill, it blasts into the sky on a digital effect that looks like a rocket trail. We loved it. The only problem was that when we got back into the postproduction studio and began to assemble the final show, we discov- ered-to our horror-that the sound of an airplane could be heard Figure 1-17 Phase modulation Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subjec