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2answers
75 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 ...
1
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1answer
78 views

Calculating the voltage generated by an 40KHZ Ultrasonic Tranceiver

In particular, this device: http://www.hexamite.com/hx40str.htm ...
5
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4answers
206 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 ...
9
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8answers
955 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 ...
0
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0answers
153 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 ...
6
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4answers
424 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: ...
1
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4answers
321 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 ...
6
votes
5answers
951 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 ...
1
vote
1answer
76 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. ...
3
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3answers
425 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
votes
4answers
938 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?
7
votes
3answers
5k 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?
19
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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 ...