Anything related to the decibel (dB) and similar logarithmic units of measurements (dBm, dBW, etc.).

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Decibel vs Decibel milliwatts [duplicate]

What are the differences between Decibel (dB) and Decibel milliwatts (dBm)? I'm most interested in dBm with cell phone signal strength. Please give a detailed explanation. I'm not familiar with the ...
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0answers
34 views

dB Meter with Arduino and AD8307

I am attempting to construct a decibel meter using an electret mic breakout board (shown below) and an AD8307. If necessary I can use just an electret mic, and not the breakout board. I was ...
4
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1answer
292 views

-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 ...
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3answers
186 views

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 ...
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2answers
114 views

I'm confused by the formulas for power gain decibels and voltage gain decibels [duplicate]

I know that my problem with this is some flaw in my logic, I just need someone to point out to me where that flaw is. According to the Wikipedia article, there are different formulas because power ...
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1answer
118 views

Calculating the voltage generated by an 40KHZ Ultrasonic Tranceiver

In particular, this device: http://www.hexamite.com/hx40str.htm ...
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4answers
237 views

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 ...
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8answers
1k views

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 ...
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1answer
185 views

Relationship between FFT in dB and spectrum analyser output in dBm

I am trying to calibrate my RF daughter board in USRP software defined radio. I am trying to measure transmitted power for different frequencies at a certain set gain and transmitter amplitude. When I ...
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4answers
504 views

Confusion between Voltage gain & Voltage gain in decibels (dB)

The definition of the Voltage Gain is \$ V_{out} \over V_{in} \$. However, I read some articles about the gain in decibels, and I have a confusion now. Here is an article about it: ...
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4answers
381 views

Headphones impedance and the SPL

The headphones A has an impedance of 32 Ohms. The headphones B has an impedance of 250 Ohms. Both of the headphones are similar by size. Is it right that the headphones B will play quieter by ...
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5answers
1k views

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 ...
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1answer
80 views

Power and decibels

In one of the examples in a engineering textbook, I noticed that the decibel value for the Power of a transmitter (also known as modulator) was 20DB and this was said to be equivalent to 100W. ...
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3answers
462 views

What do you call the dynamic range of a variable gain amp?

Dynamic range is the ratio of the largest signal a system can process to the noise floor of that system. If the system has variable gain, though, then you could interpret this two ways: Fixed gain ...
6
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4answers
1k views

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?
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3answers
6k views

What is the significance of -3dB?

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?
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5answers
3k views

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 ...