WHAT IS DECIBEL [db]
Various voltage, current and power gains and losses in an electronic
equipment are spoken in terms of decebels. This is an outgrowth from the
telephone field, where the decibel was used as a mathematical
expression, that represented the propery of the human ear to respond to
ratios of sound intensity. Mathematically, the decibel is a logaritmic
ratio, and is used in a relative unit of measurement that originally was
used to express changes in audio power, and the ability of humanear to
recognize these changes. For instance, if an
amplifier produced an output power through its lound speaker of 10
Watts, it would then have to increse its output power 10 times to
100Watts for our ear to detect as much "Loudness" (2 is the logarathm of 100).
Mathematically, we define the decibel as being equal to 10*long to the base 10 of P2/P1, where P@ is always the larger power in watts, and P1 is always the smaller power in watts. The expression "log10" mearely describes the type of logarithms used, generally called common logarithms. Thus, it should be understood that the decibel is only a unit of comparing two levels; it does not give an absolute value for etiher. If we compare two voltages, we say that the decibel gain or loss is equal to 20*log10 of [E2/E1]. This is because P has relationlships of [E2.R and I2R. Hense, currents would be written as 20*log 12/1. For instance, let us assume that the output power of an amplfier is twice the input power. We look up the ratio of 2, and find that it corresponds to 3db. If we have a loss, it is represented as [-db].
Mathematically, we define the decibel as being equal to 10*long to the base 10 of P2/P1, where P@ is always the larger power in watts, and P1 is always the smaller power in watts. The expression "log10" mearely describes the type of logarithms used, generally called common logarithms. Thus, it should be understood that the decibel is only a unit of comparing two levels; it does not give an absolute value for etiher. If we compare two voltages, we say that the decibel gain or loss is equal to 20*log10 of [E2/E1]. This is because P has relationlships of [E2.R and I2R. Hense, currents would be written as 20*log 12/1. For instance, let us assume that the output power of an amplfier is twice the input power. We look up the ratio of 2, and find that it corresponds to 3db. If we have a loss, it is represented as [-db].
