duce the original speech. In some telephones this receiver is created with the use of microprocessors. The electromagnetic receiver was a central element of Alexander Graham Bell's original telephone patent. Part of the design of the telephone handset that enables you to hear your own voice while talking is called side tone or side noise. The reason for this is to give you some feed- back that the telephone is working. Too much side tone causes an echo. C. The ringer. There is a wide variety in types of ringers. Tele- phones run on DC (direct current) where electrons flow in one direction. The bell or ringer operates on AC (alternating current), which means that electrons are moving in two dif- ferent directions to activate the bell. This AC sent on the local loop (telephone line) is called ring generator (90 to 105 volts AC at 20-Hz). Minus 48 volts DC is always on the line, which is used to operate the telephone after is answered. There is a good analogy for understanding these electri- cal signals. Envision a garden hose. The hose represents the wire. The water is the current. The water pressure is the volt- age (electrical pressure). Stepping on the hose with your foot is equivalent to resistance on an electrical circuit. d. Microprocessors. The microprocessors in electronic tele- phones may replace any of the above internal components and may also add additional capabilities and functions to the telephone, such as speed dialing, etc. Many telephones look the same, but there is wide variation in the capabilities and prices. You can buy a throwaway single- line telephone for less than ten dollars or a multi-line multi-featured telephone to work with a business telephone sys- tem for six hundred dollars. As with many manufactured items, there is variation in the quality of the components that is reflected in the price. The price also tends to be higher on the proprietary 18 is The Telecom Handbook CHAPTER 1 telephones, which work with a specific manufacturer's system, even though they may look the same as those