Anything related to the decibel (dB) and similar logarithmic units of measurements (dBm, dBW, etc.).
Anything related to the decibel (dB) and similar logarithmic units of measurements (dBm, dBW, etc.).
See also Wikipedia on decibel.
Questions tagged [decibel]
83 questions
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5 answers
What is the significance of -3 dB?
My oscilloscope has 100 MHz -3dB bandwidth. -3dB is 0.707 units (\$\sqrt{2} / 2\$). What does this mean, why 70.7% attenuation? Is there any particular reason for this attenuation level?
Thomas O
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What does dBm mean?
When working with radios, I've seen the term "dBm". What does this mean?
The wikipedia page gives a table showing the equivalent power in Watts. Is the dBm output just the power level of a transmitter?
How does this differ from signal strength…
Toby Jaffey
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14
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Confusion between Voltage gain & Voltage gain in decibels (dB)
The definition of voltage gain is \$V_{\text{out}}/V_{\text{in}}\$.
However, I read some articles about the gain in decibels, and I have a confusion now.
Here is an article about it: https://en.wikipedia.org/wiki/Gain#Voltage_gain
Here, I understand…
Naetmul
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Why Decibels are used to measure Signal to Noise Ratio?
We just started a communications course in college and we came across SN ratio. The following is an ambiguity I am facing which my professor is unable to resolve:
Signal to Noise Ratio is the ratio of signal power to the noise power. It is often…
iluvthee07
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What does a Bode plot represent and what is a pole and zero of a Bode plot?
I studied Bode plots and the author of my book is somehow relating zeros of transfer functions to Bode plots. What is the relation between zeros or poles of a Bode plot and transfer function? We usually take zeros at \$s=-a\$ (let's say) but how…
Ali Aqdas
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9
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Why do 16 bit systems have a minimum dBFS of -96?
I'm working through the example on this page:
http://chimera.labs.oreilly.com/books/1234000001552/ch03.html
I totally understand why the maximum level of an audio system would be 0 because the log of 1 is 0.
However, I'm confused about the minimum.…
Aptary
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What does it mean for a signal to have an amplitude below 0 dB?
I am a software developer (using high level languages like .NET,C,C++ etc) trying to understand how computers work at a lower level.
I understand that amplitude is always positive because it is calculated by (top-bottom)/2. However, I don't…
w0051977
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What is the meaning of dBi?
When we say, for example, an antenna has spec of 22 dBi;
Does it mean that its power is 22 dB stronger for any point at fixed direction than if it were to emit spherically?
Noob_Guy
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9
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Why 10Log(p1/p2) and 20Log(v1/v2)? Why not just 10Log(x1/x2)?
Based on my very basic current understanding of decibels in electronics, it is said that I should use the db = 10Log(p1/p2) formula if I want to calculate the power ratio in db between two values and the db = 20Log(v1/v2) formula if I want to…
T555
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The unit that is written between parentheses alongside the dB
What is the meaning of the unit that is written between parentheses alongside the dB unit? For example 2 dB (mW) or 2 dB (uW)? What exactly does this unit refer to? Does it refers to the unit of the reference value, the measured value (P2), or both?
John adams
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Is the meaning of a decibel different when applied to voltage vs watts?
If I have an amplifier that provides +3dB, or an attenuator that provides -20dB, then how do I know if that applies to voltage or power?
In other words, if I have a 0dBV signal and I run it though a +3dB amplifier, do I get 3dBV?
Similarly, if I…
Cuadue
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Why do we use dB to represent the difference between two voltages?
For example, the passband of a LC resonant circuit is the differences of frequency at +3db and -3db.
Why do we prefer dB?
Jichao
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5
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How to interpret this type of dBm?
I have encountered a spec of a laser diode given in dBm/nm instead of dBm:
If I want to know the average power between 2065nm and 2075nm, would the integral of that section give the average power in dBm? And what is the purpose of using dBm/nm and…
user1245
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-3dB on filters, just approximated?
I have been told that -3dB is when you get half the power or equivalently the original voltage divided by the square root of 2.
Nonetheless, doing the calculations I get 3.01029dB.
I figure this is because the 3dB value is just the aproximated…
PhoenixPerson
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5
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mW or W when calculating decibels
In my instrumentation class we have been given the following formula to get the power in decibels:
\$10Log(Power(mW)/mW)\$
I'd like to know if taking the power in miliwatts is something widely done or has any importance?
PhoenixPerson
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