5 concerns their interfaces. The mode converter has dual opti- cal interfaces, while the media converter has one electrical interface and one optical interface. However, both types of communications devices are similar in that the primary rationale for their use is to extend transmission distance. Team-Fly® APPENDIX A FREQUENCY VS. WAVELENGTH If we were radio listeners we might be familiar with the fact that there are different ways to indicate where to find a certain station on the radio dial. For example, we could say that a station is operating on 4250 kilo- hertz (kHz), 4.25 megahertz (MHz), or even on 71 meters. And all three ways would be correct! Radio waves are transmitted as a series of cycles, one after the other. The hertz, named in honor of the German physicist Hertz (abbreviated Hz), is equal to one cycle per second (cps). In fact, if you're as old as the author of this book, you might have used the term cps in your high- school physics classes instead of the more modern term Hz. If you were to visit the fuse box or circuit breakers in your home or apartment you might view a label that indicates the specification for the box or circuit breaker. In addition to telling you information about the amperes and voltage, if you reside in North America, you will also note a reference to the electric power being supplied to your home rated at 60 Hz. Electric power is distributed to your residence as alternating current (ac), meaning it goes through a cycle of changing directions of flow. When we say that electric power is 60 Hz, we mean it changes its direc- tion of flow 60 times per second. Radio waves cycle more frequently than electricity, resulting in such waves going through far more cycles per second than electric current. Thus, we need to use bigger units to measure them. One such unit is the kilohertz (kHz), which is equal to 1000 cycles per second. Another com- monly used unit is the megahertz (MHz), which is equal to 1,000,000 cycles per second, or 1000 kHz. The relationship between these units is sh