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Questions tagged [nyquist]

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FOV versus Wavelength

It is well know from Nyquist theorem that, in order to reproduce a signal without aliasing, the acquisition rate must be at least 2 times higher than the maximum frequency of the signal. This gives a ...
35 views

Frequency sampling

How does nyquist sampling theorem works. For example, given a signal with rang 0.5 to 1.5 Hz, why does the fs is 2 Hz?
48 views

Autocorrelating output signal which sampled at rates higher than signalling rate

A bpsk signal(a$_{n}$) with d$_{min}$ = 1, passes through a pulse shaping filter p(t), the resultant pulse shaped signal ($\sum_{n=0}^{k-1} a_{n}p(t-nT_{s})$) passes through an AWGN channel which adds ...
140 views

DAC - Can we create and use frequencies above Fs/2?

I understand how the ADC and Nyquist works. Anything above Fs/2 can be indistinguishable from frequencies inside Fs/2 so we use an alias filter to remove them before sampling. This can also be an ...
• 109
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Methods to determine stability of open-loop systems

Which methods can be used to analyze the stability of open-loop systems only, closed-loop systems only, and both of them? As far as I understand, you can determine the stability of open-loop and ...
• 1
124 views

What's Nyquist frequency in DFT?

I'm currently studying digital signal processing at university but I can't figure out what the Nyquist frequency means in the DFT coefficients, I know what the Nyquist frequency is in the sampling ...
• 103
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How does the sampling rate of a digital filter limit the sampling rate that can be used for replay of filtered signal?

I need a band-limited white noise to characterize a biological sensor that senses mechanical movement. For that, I am generating a Gaussian white noise (MATLAB Communications toolbox) of length 10 ...
1 vote
68 views

68 views

Ratio of aliased to desired energy of a sampled signal

In this article "Sampling: What Nyquist Didn't Say, and What to Do About It" from Wescott, the author shows in Figure 6, the plot of the frequency spectrum of a signal which goes through a ...
36 views

Is there a test/statistic for the reliability of my data given my sampling?

I'm in a situation where I'm sampling blood pressure data over time (unequal sampling) to capture potential peaks. On average, the frequency of circadian blood pressure would be 1. But in reality, ...
43 views

Combining two time series with different cadences (different Nyquist frequencies)...?

If it helps, I want to do perform the below computation in python. Two time-series - 30-min cadence (Nyquist of 24 cycles / day) lasting 27 days, followed by 10-min cadence (Nyquist of 72 cycles / day)...
• 101
1 vote
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modulation transfer function and ground resolved distance

I am trying to understand something in remote sensing but lack a background in science and technology so it is difficult. Hopefully this is a reasonable question to ask. In sensing there are different ...
1 vote
161 views

Sampling a sinusoidal signal smaller than Nyquist rate

If we have a sinusoidal signal at 50 kHz and we sample it by an ADC with a sampling rate of 7 kHz. What would be the output of the ADC? Since the sampling rate is way less than the Nyquist rate (...
• 121
1 vote
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Choice of $N_{terms}$, frequency grid in Lomb-Scargle periodogram

I am completely new to signal processing! Please explain as if speaking to someone who knows nothing more than linear algebra and what a Fourier transform is defined as. I am working with an 8-month ...
43 views

Find constants such that the Nyquist criterion is satisfied [closed]

I have been given the following spectrum, and I want to find a and b such the pulse satisfies the Nyquist criterion, given that the bandwidth of the pulse is 2 kHz and the sampling frequency is 3 kHz. ...
• 21
58 views

How to compute the ifft of a constant value?

I am clearly missing something obvious here because I am trying to do something that ought to be very simple: compute the ifft of a continuous signal. My understanding is that the ifft of a continuous ...
• 296
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Time-interleaved ADCs, Nyquist zones et al

I am trying to decipher some notes on a Time-interleaved Analog-to-Digital Converter with 4 sub-ADCs (the author is unreachable at the moment), but there are few things obscure to me so I was hoping ...
• 103
1 vote
122 views

recreating nyquist regions using FFT python

using python I have sampled a signal and made FFT to see the spectral picture of the time domain signal. the plot bellow shows only 1st and 2nd nyquist zone. I want to expend the spectral image and ...
• 113
283 views

A problem about SQNR, PCM, DPCM, and DM

A baseband analog message signal $x(t)$ with bandwidth 20 kHz, power $10^{-3}$, and $|x(t)| \leq 1$ is waveform encoded and transmitted through a channel of bandwidth 160 kHz. Besides, let the sampled ...
168 views

Question about Nyquist sampling - filtering of high image copies

Suppose I sample an audio signal with a sampling frequency > twice the highest audio frequency. ie, the frequency transform of the sampled signal looks like the image on top here, where there is no ...
• 195
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How do I match a filter to an AWGN channel?

I have the task to find a transition that fulfills the first Nyquist Criterion. After that I am supposed to match that filter to an AWGN channel. For the first part I thought a raised cosine ...
• 3
100 views

LTI Filter for DAC Reconstruction

$\textbf{Question:}$ An analog-to-discrete is designed as, $$x[n] = x_a(nT)$$ In an attempt to recover the analog signal from its samples x[n], a D/A converter is designed as , where $x_1(t)$ is ...
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1 vote
855 views

Why does the bandwidth of a signal need to be half of the sampling rate? [duplicate]

Suppose I perform a DFT on some function with sampling rate of $\frac{1}{\Delta t}$. According to this page, the bandwidth, which is the maximum frequency that can be analyzed when performed the DFT, ...
• 119
2k views

Moving average before downsampling: effect on Nyquist frequency?

First the simple questions: Is there an effect on the Nyquist frequency when I apply a moving average filter on the raw data before I downsample? And what does this do to aliased frequencies? ...
• 163
1 vote
254 views

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Is the slow waveform an alias - and why don't we see other alias'es of different frequencies?

The following figures are data from sampling the DC bus of an inverter for a BLDC/PMSM drive running a speed-loop with FOC. The upper subplots are FFT's of the signal and the lower subplots are of the ...
• 101
95 views

Are there any recommended filter types for passband frequencies near Nyquist?

Is there a recommended filter type for frequency bands near the Nyquist frequency? I have been trying to design complex passband filter with passband $[0.8 ~~1]$ ( where $1$ corresponds to the ...
• 129
314 views

Why are real-world digital images not bandlimited?

In the materials about image resampling, it always mentions that real-world digital images not bandlimited. However no explanation is provided. For example, Sinc resampling in theory provides the ...
• 425
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Having Nyquist bin = aliasing?

Here I motivate the question by deriving FFT upsampling for $N \rightarrow 2N$ with even $N$. One might naively try xup = 2*ifft([xf[:N//2], zeros(N), xf[-N//2:]]), ...
• 9,004
873 views

How is the maximum theoretical data rate of a channel equal to $2B\log_2(V)$ bits/sec.?

According to Andrew S. Tanenbaum (in "Computer Networks", Chap. 2, Section 4 "The Maximum Data Rate of a Channel"), the Nyquist/sampling theorem states that "if an arbitrary ...
294 views

How to choose correctly oversampling ratio?

As many of us have noticed, last two months I am working on GMSK modulation and demodulation design. Before continuing my research, I want to be sure I chose the correct oversampling ratio ( how many ...
• 377
203 views

Reconstructing a signal from a Nyquist plot

I have a system which is like a blackbox which has just one input which could be a sinusoidal wave which is a sum of a range of frequencies, now the problem is that I dont have the time-domain output ...
1 vote
82 views

What does the two following formulas mean?

I am a bit confused between the following two formulas: $$f\le \frac{f_s}{2} \tag{1}$$ and: $$f = \frac{f_s}{N} \tag{2}$$ Now I am given an ACF Plot of a sine/cosine wave and I am asked to find ...
2k views

How do we determine the required sampling rate of a closed loop control system?

Consider the controlled dynamical system $\dot{x}_t = f(x_t, u(t-\tau_{sd}))$, where $0<\tau_{sd}$ denotes the time delay caused by sampling. It is intuitively clear that the time delay caused by ...
• 331
626 views

What is the output signal's frequency when doing operations of two signals?

If I have two continuous time signals x(t) and y(t) of maximum frequencies Ω1, Ω2 respectively. I want to find the sampling frequency used used in continuous-discrete conversion of the following ...
1 vote
124 views

How do I determine the dominant frequency of a signal after sampling?

For example if I have a $10 Hz$ signal and I sample it at $19 Hz$ (less than the Nyquist frequency) how can I determine the dominant frequency of the output and why? If I then apply a lowpass filter, ...