the wave- form at any given moment; more specifically, it defines the offset of the wave from a reference point. Bandwidth-The range of frequencies (i.e., the difference between the lowest and highest frequencies carried) that make up a signal is called bandwidth. You can manipulate frequency, amplitude, and phase in order to generate a one and a zero. Hence, you can represent digital information over the electromagnetic spectrum, for example, by sending ones at a high frequency and zeros at a low fre- quency. Devices that change the frequency in order to carry information are called frequency-modulated devices. You can also modulate amplitude by sending ones at a high amplitude or voltage and zeros at a low amplitude. A complementary receiv- ing device could then determine whether a one or a zero is being sent. As yet another example, because the phase of the waveform refers to shifting where the signal begins, you could have ones begin at 90 degrees and zeros begin at 270 degrees. The receiving device could discriminate between these two bit states (zero versus one) based on the phase of the wave as compared to a reference wave. Twisted-pair cable, which was the original foundation of the PSTN (telephony) network, has a maximum usable bandwidth of about 1MHz. Coax, on the other The Electromagnetic Spectrum and Bandwidth hand, has greater capacity because it can carry up to a total of 1GHz of frequency spectrum. Within the radio range, microwave is the workhorse of the radio spec- trum. It provides 100GHz to operate with. In comparison, fiber optics operates over a band of more than 200THz (terahertz). As we see increasingly more bandwidth- hungry applications, we'll need to use fiber optics to carry the amount of traffic those applications generate. Of course, it is vital to note that the physical territory ultimately dictates which medium makes the most sense; for example, in a nation like Indonesia, composed of more than 10,000 islands, pulling fiber cable is not practical, SO wireless pre- sents a much more 