Decibel abbreviation4/16/2023 ![]() Doubling power - another common situation - is a change of 3 dB. You could also figure that out from 20 = 10 x 2, so the dB equivalent is 10 + 3 = 13 dB. For example, from Table 1, a change of 20 is the same as a change of 5 x 4, so a change of 20 in dB is equal to 7 + 6 = 13 dB. A change of 100 (10 2) is a change of 20 (2 x 10) dB a change of 1000 (10 3) is a change of 30 (3 x 10) dB and so forth.Īnother handy thing to remember is that multiplying the ratio by a factor allows you to add the dB equivalent of that factor. Speaking in terms of power, any change by an exponent of 10 is a change in dB of 10 times the exponent. Remembering a simple rule for factors of 10 will come in quite handy, too. Table 1 - Decibel Values for Common Power and Voltage Ratios. Just memorizing the few power dB relationships in Table 1 is easy. You don’t necessarily have to have a calculator at the ready. If you want to compare voltage (or current) levels, you have to account for the relationship between voltage (or current) and power not being linear - doubling voltage (or current) is a quadrupling of power: For example, “This filter attenuates the signal by 20 dB.”) (Somewhat confusingly, it’s common to specify an amount of attenuation as a positive value of dB. If P 2 is less, the value is negative and represents attenuation or loss. If P 2 is larger than P 1, the dB value is positive, such as for amplifier gain. Both quantities themselves must have the same base units, though - watts, for example. The dB is just a number that describes how much bigger or smaller one quantity is compared to the other. Note that the dB has no units because it is a ratio. The dB is a just-perceptible change and more useful as a unit of measurement.” As used in wireless, the decibel is the ratio of two power levels: We use a decibel instead of a whole bel because the bel represents a rather large change in levels. The unit we are really talking about here is the bel (a ratio of sound levels named for Alexander Graham Bell), so a decibel is just 1/10th of a bel. “You have probably recognized deci as the metric prefix that means one-tenth. Learn the decibel (abbreviated as lower-case ‘d’ followed by an upper-case ‘B’ or ‘dB’) and you and your signal will go a long way!įrom the ARRL Ham Radio License Manual’s online math tutorials for beginning hams ( /chpt-2-radio-signal-fundamentals), we introduce the decibel. The “dee-bee” is everywhere in ham radio, and is used for characterizing everything from antenna performance to nano-sized signals. This column covers a number of these measurements and values, and shows you how to use decibels for them. Wireless communication seems to involve many such terms, but many seem to be calculated or expressed in terms of the decibel. Just as confusing are the measurements in this alternate universe. We’ve all experienced the feeling of visiting a group outside of our own background and being completely flummoxed by the rapid-fire jargon being thrown around. » Skip to the Extras Knowing the language of metrics is not optional!
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