and their applications in telecommunications. Loss causes the signal power to be dissipated as a signal passes along a wire pair. Power is expressed in watts. For this application, the use of milliwatts may be more practical. If we denominate loss with the notation Ldb, then Lab = 10 log(P1/P2), (2.2) where P1 is the power of the signal where it enters the wire pair, and P2 is the power level of the signal at the distant end of the wire pair. This is the traditional formula defining the decibel in the power domain. See Appendix C. Example 1. Suppose a 10-mW (milliwatt), 1000-Hz signal is launched into a wire pair. At the distant end of the wire pair the signal is measured at 0.2 mW. What is the loss in decibels on the line for this signal? Ldb = 10 g(10/0.2) = 10 log(50) 2 17 dB All logarithms used in this text are to the base 10. Appendix B provides a review of logarithms and their applications. The opposite of loss is gain. An attenuator is a device placed in a circuit to purposely cause loss. An amplifier does just the reverse; that is, it gives a signal gain. An amplifier increases a signal's intensity. We will use the following graphic symbol for an attenuator: We will also use the following symbol for an amplifier: Wire-pair transmission suffers other impairments besides loss. One of these impair- ments is crosstalk. Most of us have heard crosstalk on our telephone line. It appears as another, "foreign" conversation having nothing to do with our telephone call. One basic cause of crosstalk is from other wire pairs sharing the same cable as our line. These other conversations are electrically induced into our line. To mitigate this impairment, physical twists are placed on each wire pair in the cable. Generally there are 2 to 12 twists per foot of wire pair. From this we get the term twisted pair. The following figure shows a 2.5 INTRODUCTION TO TRANSPORTING ELECTRICAL SIGNALS section of twisted pair: Another impairment causes a form of delay distortion on the line, which is cumulative and varies directly wi