Questions tagged [nyquist]
The nyquist tag has no usage guidance.
228
questions
0
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3answers
24 views
Why Matlab Spectrogram of slow and rarely sampled signal shows high frequencies
I have a signal, which was measured for 14.4 minutes (= 864 seconds). There are 192 measurements, so one measurement was done in every 4.5 seconds, which results in a 0.22 Hz sampling frequency if I ...
5
votes
2answers
204 views
Nyquist frequency isn't working
The situation is that I have a signal with linearly increasing frequency,
$$\text{sin}(2\pi\omega(t)t),$$ where $\omega(t)=a+bt$ for some $a$ and $b$, and we constantly sample at one point per second ...
0
votes
1answer
30 views
Signal to noise ratio (SNR) of a CW signal
I understand the formula SNR = 6.02N+1.76 for a N-bit ADC which quantizes a modulated tone sampled at twice the BW. I am trying to understand what the same equation would be for a unmodulated CW tones ...
0
votes
1answer
52 views
Dealing with normalized cut-off frequencies larger than 1.0
I am trying to create an FIR bandpass filter in python using scipy with the following characteristics:
$$f_{c_{low}} = 310\,Hz$$
$$f_{c_{high}} =600\, Hz$$
giving me a bandwidth of:
$$Bandwidth = f_{...
1
vote
4answers
78 views
DFT after the Nyquist limit
I usually do the DFT using the fft in Matlab. After the Nyquist frequency I don't see any result. Is it possible to perform a dft looking after the Nyquist frequency. I am asking this because I have ...
0
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1answer
40 views
Optimal sampling frequency
I am working with microcontroller's ADC to sample the data. I know that Nyquist criteria tells us that the sampling frequency should be at least twice the highest frequency, but it might involve ...
2
votes
1answer
89 views
Aliasing in Doppler Radar
my book about RADAR says that:
If a Continuous wave radar sends a sine wave at frequency $f_T$ to a moving object (at speed V), a frequency $f_R$ is received. Their difference is called Doppler ...
0
votes
2answers
63 views
How to reconstruct original signal from sampled signal?
My original signal as
f1=2;
f2=5;
fs=100;
Ts=1/fs;
t=0:Ts:1;
xt=cos(2*pi*f1*t)+cos(2*pi*f2*t);
figure
plot(t,xt)
as shown below figure.
and my sampled signal ...
1
vote
2answers
52 views
Nyquist Frequency and Window Length
The Nyquist theorem states that the sampling rate must be twice the highest frequency to be observed. How does the length of the interval play into this relationship?
The main resource that I found ...
1
vote
2answers
1k views
Does the Shannon theorem not apply when the amplitude of a wave is changed faster than half the time period of the wave?
Shannon's version of the sampling theorem states that if a function contains frequencies all strictly less than $B$ hertz, then it is completely determined by giving its ordinates at a series of ...
0
votes
1answer
34 views
Selecting the Nyquist rate for a combination of signals
If several sine waves were combined but each had a separate frequency, for example 10 Hz, 20 Hz and and 30 Hz, what would the required Nyquist rate be for analysis?
From my research, it suggests that ...
1
vote
2answers
68 views
How to deal with “weird” phase plots in bode diagram when designing a controller
I am trying to design a balance controller for a robot. With MATLAB simulink I arrived at the transfer function between the input and the pitch angle for the robot. I have plotted the bode and Nyquist ...
0
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0answers
21 views
Reconstruction of a signal based on non-uniform samples and a well below nyquist sampling rate
I have a set of non-uniform samples that are the following set of data over the course of 1 second:
The rightmost column is in milliseconds, and the first three leftmost columns are each different ...
10
votes
2answers
2k views
Does the Nyquist frequency of the Cochlear nerve impose the fundamental limit on human hearing?
The bandwidth of human hearing by empirical data is $20 \; Hz$ to $20 \; kHz$. A cochlear implant stimulates the auditory or acoustic or Cochlear nerve directly so that the hearing can be improved in ...
0
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2answers
43 views
Wavetable and Nyquist: which size do I need?
I was reading this tutorial by the master earlevel, while trying to build some sort of wavetable.
He says First, let’s back up and figure out how long our tables need to be. Recalling that we need to ...
1
vote
2answers
95 views
Restore real signal from its complex representation if sampled under Nyquist frequency
Assume we have:
real signal: $s(t)$
its analytic representation: $s^+(t) = s(t) + j*H(t)$,
where $H(t)$ - Hilbert transform of $s(t)$
Spectrum of $s^+(t)$ has only positive part, so may be sampled ...
0
votes
0answers
29 views
What is the between spatial frequency of an image and pixel size of the sensor?
In my lecture notes about the sampling of an image I've written that:
Since pixels have a finite dimension the spatial frequency response is attenuated before the "ideal" Nyquist frequency
...
0
votes
1answer
71 views
What should be IQ sample rate at least?
As i read, IQ sample doesn't need nyquist criteria. What is the mathematical representation of this result? Why IQ sample doesn't need nyquist frequency? I know that can be set to nyquist frequency ...
1
vote
1answer
132 views
Aliasing below $f_s/2$
phi = exp(linspace(0, log(511), 1024)) - 1
x = cos(2 * pi * phi)
Above will alias, despite peak instantaneous frequency evaluating to ...
0
votes
0answers
25 views
Interpreting Nyquist Plot for Phase and Gain Margins
I have an open-loop system transfer function given by $G(s) = \frac{K(ABs^2+As+1)(Cs+1)}{s^2A(s(C+D)+1)}$ so I'd expect two poles at the origin and one at $s=\frac{-1}{C+D}$. After using Matlab to ...
2
votes
1answer
41 views
A basic question regarding frequency analysis of an EEG signal
Assume that an EEG signal is sampled at $f_s = 300$ Hz then a 10000-point segment of it is selected, called $x[n]$. The corresponding 10000-point DFT is then computed and called $X[k]$.
Assume further ...
3
votes
1answer
73 views
Sampling pure tone sine waves [closed]
What would happen if I am using the maximum frequency as the sample rate for sampling a pure tone sine wave?
For example, a $10\ \rm kHz$ sampling frequency for a $10\ \rm kHz$ monotone sine wave. ...
1
vote
2answers
209 views
Confused on Pulse Filter Bandwidth and Symbol Rate Relation
***Still need help in 2021 - not fully clear still on Jan 20th ***
I am confused about the relation between Sinc and Rectangle transform pair and how that relates the Bandwidth of Pulses, Bandwidth of ...
0
votes
2answers
589 views
Amplitude modulation vs sampling rate?
As a sampled tone's frequency nears $f_s / 2$, amplitude modulation grows apparent:
("Actual" curve in grey; blue is what we get if taking samples (dots) "at face value"). This is ...
1
vote
1answer
77 views
Sampling Dirac function and a DC signal
Can we sample the Dirac function?
$$ x(t) = \delta(t) $$
Can we sample a DC signal?
$$ x(t) = 1$$
I think that we can't sample $x(t) = 1$ because the Fourier Transform of $x(t) = 1$ is $2\pi \delta(...
3
votes
1answer
129 views
Use of the harris-Moerder Nyquist Pulse Shaping Filter
I became aware today through fred harris' excellent presentation at the DSP Online Conference (https://www.dsponlineconference.com/) of the harris-Moerder pulse shaping filter which was published 15 ...
2
votes
1answer
543 views
Generating digitized white noise: uniform vs normal sampling
Consider the following two ways of generating noise in the time domain for audio applications:
Generate samples from a uniform distribution [-amplitude, +amplitude]...
0
votes
2answers
111 views
Can I sample at Nyquist rate if I know that my samples are taken only at the signal's maxima or minima?
I know that in general the sampling rate, $f_s$, must be greater than twice the highest frequency of the signal, $f$.
If I sample at the Nyquist rate, it can lead to the following:
However, if the ...
-1
votes
1answer
40 views
SDR Dongle, 2MHz Bandwidth related to Fs but bandwidth range 50-2000 MHz
Having a conceptional issue.
If a SDR dongle has a 2MHz signal bandwidth, but that can be anywhere within the range of 50-2000 MHz, why is the bandwidth only 2 MHz.
The clock must be double the ...
1
vote
2answers
347 views
Determine stability of feedback system from open loop transfer function and Nyquist stability criterion gives different results
I'm confused due to the fact that the Nyquist stability criterion and looking at the transfer function doesn't give the same results whether a feedback system is stable or not. When I have the system ...
0
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0answers
43 views
I need help in understanding “Nyquist Criterion” definition
I am researching the split-step parabolic equation and its split step solution as in:
Ozgun, Ozlem & Apaydin, Gokhan & Kuzuoglu, Mustafa & Sevgi, Levent. (2011). PETOOL: MATLAB-based one-...
0
votes
2answers
101 views
Why the Nyquist frequency is 0.5 of Fs, why not 0.55 or 0.65?, brief explanation [duplicate]
This my elaboration of the aliasing issue:
a continuous signal can be represented by factors of :
$e^{(i2{\pi}ft)}$ if we sample this signal then I will get:
$e^{(i2{\pi}fk/N)}$ where $k=0,1,2.., N-1$
...
2
votes
3answers
285 views
aliasing in image processing
I know that aliasing occurs when a signal is subsampled. If the sampling rate is lower than twice the max frequency in a signal, aliasing occurs.
How is it in pictures? as far as I know, a sinc-filter ...
3
votes
1answer
539 views
Sample rates, Samples per Symbol, and Digital Pulse Shaping
Having some confusion about digital pulse shaping for complex baseband (passband) signals. The complex baseband linear modulation equation is
$$s(t)=\sum_{m=-\infty}^{\infty}\text{Re}\{a_m\}h(t-mT)+j\...
0
votes
2answers
86 views
When do we divide by $2\pi$ while solving Nyquist problems?
I slightly lost the tempo in the course for a couple of days, so I apologies for the noob question if seemed so.
Why do we divide by $2\pi$ in Nyquist problems sometimes and sometimes not? I saw there ...
1
vote
5answers
397 views
Positive and negative frequencies in DFT due to frequency folding, or due to negatively indexed frequencies?
When I look for the cause of the mirroring of frequencies in DFT output, I get two types of explanations:
The first one which says the frequencies are mirrored because of the complex exponential ...
0
votes
1answer
42 views
What is an example of using aliasing to your advantage when recovering an input signal?
Suppose you have an arbitrary analog input signal $x_a(t)$ guaranteed to have frequencies within a bandwidth $[f_1,f_2]$ Hz.
Suppose your sampling frequency $F_s$Hz, and sample $x_a(t)$ to produce $...
0
votes
1answer
43 views
Multichannel sampling with aliasing
if i have 2 sensors, sensor1 and sensor2, that sample a signal on complementary points so that sensor2 samples always between sensor1s sampling points. can I achieve the doubled sampling rate with the ...
2
votes
1answer
63 views
Cross Domain Equivalent to Nyquist Sampling Theorem?
In attempting to answer this question by @Oliver here: What characterizies 'causality' for a finite FFT? I have considered the minimum requirement to avoid time domain aliasing in the Discrete ...
1
vote
3answers
116 views
Nyquist Rate of cosine modulated function
Here's my understanding:
$$y(t) = x(t)~ \cos(\Omega_0 t)$$
I take the Fourier transform of y(t) and I get this result:
$$Y(\Omega) = \frac{1}{2}X(\Omega - \Omega_0) + \frac{1}{2}X(\Omega + \...
1
vote
2answers
426 views
Sampling and Reconstruction of digital signal in Matlab
I'm trying to write a program in Matlab that samples (using Nyquist theorem) and recovers signal. However, I cannot write sampling part for sum of 2 signal.
...
0
votes
1answer
96 views
Whats the difference between spatial and temporal resolution?
Iam trying to understand how super-resolution works. But i think i have not understood correctly the difference between the optical resolution (spatial resolution?) and the resolution i know from a ...
-1
votes
1answer
66 views
creating this famous basic nyquist theory photo
Hello i ha built this code
which create a only one replica of the data,
how can i create the whole photo shown bellow of many cycles as shown bellow?
i read in the internet that zero padding could ...
1
vote
3answers
93 views
Upsampling with time offsets
Suppose I have done 4x oversampling for a continuous time signal, but the successive sampling times have a linearly increasing offset. Specifically, the samples with indices {4k; k=0, 1, 2,...} are ...
1
vote
0answers
97 views
Nyquist-Shannon sampling theorem: implications on matching data records?
I have two data records $R_1$ and $R_2$ with sampling periods $T_1$ and $T_2$, where $T_1$ < $T_2$. These records arise from sampling and filtering two signals to remove any noise (including ...
0
votes
3answers
83 views
does aliasing occur always if i sample a vibration in real world applications?
I was reading about the aliasing effect and nyquist. I understand that aliasing effect occurs if the sampling rate is lower than twice the maximum frequency in the signal I want to sample.
So I was ...
0
votes
1answer
136 views
Nyquist theorem vs sampling theorem vs shannon sampling theorem?
Is there any difference between these three?or these are just three names of same theorem?
4
votes
5answers
234 views
Reconstructing/interpolating small regions of a bandlimited signal by taking the fewest possible samples
I have a signal which is bandlimited and can be sampled at arbitrary continuous positions. The value at any position is given by an expensive computation. I need to do some further computation on ...
2
votes
5answers
2k views
A question about sampling rate of cosine signal
Given $$c(t) = \cos(2\pi\cdot 30 \cdot t) $$
If we sample this signal at the Nyquist rate 60 Hz and at a higher rate of 80 Hz, we get the following:
There is no aliasing as $f$ = 30 Hz is less than ...
1
vote
2answers
148 views
anti-alias filter of square pulses
I'm trying to determine whether or not an anti-alias filter is needed for sampling square waves. The goal is to sample square wave pulses from a video detector with an ADC, do some time-domain digital ...
