Periodical measurement of an electronical property of a system, most often voltage.
Questions tagged [sampling]
319 questions
59
votes
6 answers
Why are digital oscilloscopes still so expensive?
I'm a beginner in hobby electronics and I am wondering
why digital oscilloscopes are still so expensive?
In times of cheap GHz CPUs, USB 3, ADSL modems, DVB-S receivers, blu-ray players which all of them have remarkable clock frequencies/sampling…
MRalwasser
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36
votes
6 answers
How do digital oscilloscopes achieve such high sample rates?
From the perspective of data capture, how is this achieved? If I wanted to implement a home-made digital device to capture high frequency analogue signals, what are my options? So far, I've only come up with some fairly useless ideas for…
Jodes
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26
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3 answers
Why is the Nyquist data rate lower than the Shannon data rate?
In the book Computer Networks, the author talks about the maximum data rate of a channel. He presents the Nyquist formula :
C = 2H log\$_2\$ V (bits/sec)
And gives an example for a telephone line :
a noiseless 3-kHz channel cannot transmit binary…
subb
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22
votes
3 answers
How is 10G Ethernet physically possible?
10 gigabit Ethernet means that 10 billion bits are transmitted every second, but I don't understand how this is physically possible (let alone 100G Ethernet). The fastest CPUs today only run at ~8GHz, but even if transmission doesn't require a CPU,…
HaLailah HaZeh
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19
votes
5 answers
Why sample at a certain frequency just to immediately downsample it?
I apologize if this question is not well-posed. I'm reading a paper that claims the following:
The magnetometer vectors are sampled at 100 Hz. The detector filters and down samples the vectors down to 10 Hz to remove signal noise and reduce the…
colglaz
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18
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3 answers
Why do digital scopes sample signals at a higher frequency than required by the sampling theorem?
In the quest for a not so expensive PC scope/logic analyzer, I have found a nice little device it looks very well done and I know it will do the job.
However looking at the specifications, I encountered this:
Bandwidth vs Sample Rate
In order to…
LuisF
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18
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3 answers
Why doesn't aliasing of broad band noise 'pile up' in the sample band?
I recently built a simulation to study sampling, the effects of aliasing and the effects of anti-aliasing filters on the sampled signal.
For fundamental frequencies above the sample band it's obvious one sees 'imposters' in the sampled signal. Using…
docscience
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17
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6 answers
Why do oscilloscopes list max bandwidth separate from sample rate?
I would figure that if a scope has a sample rate of 200 MSa/s, it should be able to measure signals up to its Nyquist frequency, 100 MHz. But there are a lot of scopes whose max bandwidth do not match their Nyquist frequency. For instance, the…
fpf3
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17
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3 answers
Exactly what is the role of the zero-order hold in a hybrid analog/digital sampled-data system?
I'll admit, I am asking this question rhetorically. I am curious what answers will come back out of this.
If you choose to answer this, make sure you understand the Shannon-Nyquist sampling theorem well. Particularly reconstruction. Also be…
robert bristow-johnson
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15
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9 answers
When is it required or permitted to sample below Nyquist rate
I have searched past questions and answers on this platform but none answers this question. A prof said it is possible to sample below Nyquist rate under certain conditions.
I will like to know, first, if it is possible to do this, if so, when?
Mikky Mikky
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13
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6 answers
Why does increasing the sampling rate make implementing an anti-aliasing filter easier?
From an answer to a question regarding sampling rate and anti-aliasing filter I read the following:
The closer you get to the theoretical minimum sample rate, the more
difficult the analog filter become to realize practically.
If I'm not…
user1245
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12
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3 answers
What is the "Nyquist" rate for sampling the derivative of a signal?
Background: I'm sampling the current through a capacitor. The signal of interest is the voltage across the capacitor. I will digitally integrate the current measurement to obtain the voltage.
Question: Given that the voltage across the capacitor is…
VIANDERN
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11
votes
8 answers
Maximum sample rate of Arduino Duemilanove?
G'day all!
I have an Arduino Duemilanove hanging around spare at the moment and thought I might try a few audio interfacing projects. I'm just wondering what sort of sampling frequency I can achieve using a single analog input and applying some…
Sketchy Fletchy
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9
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2 answers
Shannon-Nyquist - only for repeating signals?
This was triggered by the comments in this question.
I'm using this definition of the Shannon-Nyquist theorem (form wikipedia):
If a function x(t) contains no
frequencies higher than B hertz, it is completely determined by giving
its ordinates at a…
John B
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8
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3 answers
How to achieve coherent sampling in practice
In the context of measuring a sinusoidal source with an ADC, coherent sampling (i.e. capturing an integer number of periods) allows the use of a rectangular window without spectral leakage.
How does one actually do this in practice?
I am testing a…
DavidG25
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