s when the input power equals the output power. We can also note that a 0 dB value means that there is no gain or loss at the termination point of a transmission system. Chapter Two Figure 2.11 Impulse noise occurs at random times at Amplitude random frequencies. Frequency TABLE 2.4 Power or S/N Ratio Relationship between Decibels 1.0 1 and Power Mea- surements 1.2 1 1.6 1 2.0 1 2.5 1 3.2 1 4.0 1 5.0 1 6.4 1 8.0 1 10.0 1 20.0 1 40.0 1 80.0 1 100.0 : 1 200.0 : 1 400.0 : 1 800.0 : 1 1000.0 : 1 2000.0 : 1 Understanding Light TABLE 2.4 Power or S/N Ratio (Continued) 4000.0 : 1 8000.0 : 1 10000.0 : 1 100000.0 : 1 A second important value is 3 dB, which is equivalent to a power or S/N ratio of 2:1. Thus, a 3 dB value indicates that the signal value is twice that of the noise. Finally, if you scan Table 2.1 and focus on decibel val- ues in increments of 10, you will note that they correspond to S/N ratios that increase by a power of 10. Thus, a decibel value of 10 is equiv- alent to an S/N ratio of 10, a decibel value of 20 is equivalent to an S/N ratio of 100, and SO on. Metallic Media Transmission Rate Constraints In a copper cable or atmospheric transmission system two key con- straints govern the ability to transmit information at different data transmission rates: the Nyquist relationship and Shannon's law. Nyquist Relationship The Nyquist relationship governs the signaling capability on a channel. In 1928, Harry Nyquist developed the relationship between the bandwidth and the signaling rate (baud) on a channel as B = 2W where B is the baud rate and W is the bandwidth in hertz. BITS VERSUS BAUD Before discussing what the Nyquist relationship means in terms of the maximum achievable signaling rate on a channel, a brief digression into bits and baud rate is warranted. The bit rate, typi- cally presented in terms of bits (of data transmitted) per second (bits/s), Chapter Two represents a measurement of data throughput. In comparison, the baud represents the rate of signal change commonly expressed in terms of hertz. W