4/10/2024 0 Comments Decibel relative scale in negative![]() By the way, we rounded these off so they will be easier to remember, if you need an exact answer, get a calculator! How do you "think" in decibels compared to linear units? Just remember a few key conversions and you will be all set to impress your friends with quick approximations of some heavy multiplication and division (that is, if they are easily impressed). 10 dBm is the same at 10 mW, 20 dBm is the same as 100 mW, 30 dBm is the same as 1000 mW (or one watt). Other, you are comparing one power level to 1 milliwatt. This is simply the same logarithmic calculation but instead of comparing two power levels to each You'll also see the term dBm in the field of microwaves (decibels referenced to milliwatts), or sometimes dBW (decibels referenced to watts). By the way, the decibel is actually a tenth of a Bel, a unit named after (you guessed it) Alexander Graham himself! For example, a ten-dB attenuator has 10 dB loss, while it has -10 dB gain. When you refer to a loss in dB, it is customary to eliminate the negative sign. A negative number of dB indicates loss or reduction in signal strength, while a positive number indicates gain or increase in signal strength. Remember, though, that dB by itself isn't a unit like millimeters or inch, it's all relative. How to "think" in dBĭecibels are very useful for talking about increases (gains) or decreases (losses) without talking about the actual power or voltage levels. You can easily convert from power to voltage and vice-versa if you know the system characteristic impedance (usually 50 ohms). That's because microwave signals are usually measured in milliwatts, not millivolts. The conversion of linear ratios to dB is:īear in mind that in microwaves we are most often referring to power levels, not voltage levels. The beautiful thing about log ratios is that multiplication of "linear" numbers becomes addition, and division becomes subtraction. If you are asking "why are logarithmic ratios convenient?", you are too young to have owned a slide rule. What are they talking about? (if you are a mechanical engineer sitting at a meeting and the topic shifts to "dB", it's probably a good time to get another donut.) A decibel is a convenient logarithmic ratio of two RF power or RF voltage levels (usually input and output levels). Because dB are logarithmic, its a convenient way to compress the universe into a small scale.Ĭheck out Alexander Graham Bell in our Microwave Hall of Fame! Also check out John Napier, he first demonstrated the merits of the logarithmic scale!Įvery time you talk to a microwave engineer it's dB-this and dB-that. Click here to go to our basic concepts of microwaves pageĬlick here to go to our page on power meter measurementsĭecibels (dB) are used in analog electronics.
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