hey have functional names, e.g. plastic bag be seen that the arithmetic involved is much simpler, sealer, plastic welder, etc. Their significance is that they especially as gains can also involve inconveniently large use an RF generator which, in terms of safety, needs the numbers, e.g. 69 dB gain=7 943 282. same consideration as any other RF generator. To convert decibel values back to plain ratios we reverse the process: Use of the decibel For 29.03 dB in the earlier example, the ratio is given Whilst most people trained in electrical and electronic antilog (29.03/10) = 102.903 = 800 as in the first engineering will have covered this topic, experience in calculation Introduction to RF and microwave radiation CHAPTER 2.5 Decibels and voltage Table 2.5-5 Table of power (watts) versus decibel value relative to 1 watt. Since power can be expressed as V²/R, then the ratio of two such expressions, where V1 and V2 are the two Watts voltages and R1 and R2 the corresponding resistances, is: (V}R2)/V2 R1 If R1 R2, then the ratio is now: (V1)2/(V2)2 and dB = 10 log (V1)2/(V2)2 0.001 = 20 log V1/V2 This is a very convenient way of handling power in Hence for voltage ratios, the formula for conversion is: calculations. Voltage ratio (dB) = 20 log voltage ratio To convert back to watts power, the process is as before except that the ratio obtained is multiplied by the reference value: Referencing ratios 1000 W = 30 dB W So far we have considered dimensionless quantities where the rules for handling the resultant dB values are To reverse this: those related to the use of logarithms generally. It is possible to reference ratios to any quantity, a common Power (W) = antilog (30/10) X reference value 1 W one being the milliwatt. The usual reference to this = 1000 X 1 (watts) is dBm rather than the expected dBm W. Table 2.5-5 shows some decibel values referenced to 1 watt (dBW) When the reference value is unity, in this case 1 watt, for powers greater and smaller than the reference value. the last multiplication is academic. This