# Questions tagged [fourier]

Anything related to Fourier series, Fourier transform and similar mathematical tools used to analyze the frequency content of a signal.

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### Instantaneous and active power in an ideal switch powered by real source and squared wave

This is a somewhat theoretical question, but one that has some impact on power theory. The circuit in the figure is composed of a real DC source (with non-negligible internal resistance) and feeds a ...
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### Electric Power in Frequency Domain

Let's consider an impedance Z inside a certain circuit. Let's suppose that we are working with a generic non periodic signal (so it is possible to analyze the circuit with the Fourier Transform). How ...
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### Voltage Measurement through Spectrum Analyzer

I have done some measurements with a Spectrum Analyzer of a square wave of 100kHz and amplitude equal to 1V. The resulting power spectral density is here shown: The highest peaks represent the odd ...
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### Fourier Series of Convolution of Periodic and and Aperiodic Signals?

The impulse response of an LTI system is aperiodic and I pass in a periodic signal. Now I need to find the Fourier series representation of the output. Since Convolution in time domain is ...
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### Using symbolic expression to store and fplot summation (symsum) - truncated Fourier series

I need help to: Create a symbolic expression of a summation; Using fplot, plot this summation for the interval between -1<=t<1 In other words, create a symbolic expression for xN(t) for N= 1,3,...
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### Harmonics in the electric machine

Obtain the fourier series of the waveform of the current i_ {a} (t), considering that its frequency is w_ {0} = 2pi / T. Consider only until the ninth harmonic (Hint: Take advantage of the wave ...
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### Fourier Coefficients

I have no idea how to solve the following exercise, can you help me, please? Find the periodic function whose Fourier coefficients are $$C_{k} = \frac{sin^{2}(\pi k T)}{(\pi k T)^{2}}$$ I think ...
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### Apparent lack of rigor in Phasor domain analysis of steady state AC circuits

so I have encountered a hitch in my understanding of analyzing steady state AC circuits. I have looked everywhere for the answer to my question and I can find nothing. Usually when we analyze ss AC ...
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### Finding a Fourier series of a Burst Fired sine wave having consecutive 2 cycles on & 2 cycles off?

I have been trying to find the solution of the following problem but with no luck. I have a system that generates a waveform of sinusoidal type with the only difference being that this wave has 2 ...
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### Vanishing of Gibbs Phenomenon in MatLab

I was trying to represent a square wave with its Fourier series in Matlab. But as I increased the number of terms in Fourier series expression, the Gibbs phenomenon vanished and the edges of the ...
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### How to determine the transient response of a circuit to causal periodic inputs?

As you know, analyzing a circuit with phasors provides only the steady-state response, and is only useful for sinusoidal signals and DC signals. Fourier series allow us to analyse a circuit with ...
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### If I look at a signal in its frequency domain, are there some guidelines by which I can tell how that signal looks in the time domain?

I was studying the Laplace transform and the Fourier transform, and I can't figure out if there is some intuitive way of finding out how a signal looks in the time domain if we know its frequency ...
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### Spectral lines vs Envelope of PWM wave

On the wiki page of 'Duty Cycle' there is a nice animation that shows the frequency spectrum of PWM wave as its duty cycle is modulated from 0 to 100%. The animation shows the 'spectral lines' as ...
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### Find the exponential Fourier coefficients

I am confused as to what the periodic function, Vin, is! I know the slope is 2/pi, but what about the vertical line? I am also unsure about its relation to Vo.
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### Phase, Frequency and Laplace transform

I have a doubt on the relationship between phase and frequency. We know that the definition of angular frequency is: ω(t) = d($phi$(t) / dt, where $phi$(t) is the istantaneous phase of our ...
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### Filtering a Square Wave into a Sine Wave

I am trying to Filter a +-4V odd inverted square wave into a sine wave. How should I go about doing so? So far I have computed the Fourier series of my particular input signal to be: Which I ...
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### Real time spectrum analyzer and Fourier Transform

I am studying spectrum analyzers and a doubt came to me about real time spectrum analyzers. Suppose you have a signal in the time domain: in order to calculate the Fourier Transform, you need to know ...
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### Phasors and Fourier Transform

I have always been told that for a sinusoidal variable (for instance a voltage signal), the fourier transform coincides with the phasor definition, and this is the reason why the analysis of ...
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### Understanding the Fourier transform

In a current lecture we had a quick visual introduction to the Fourier transform. It was explained that the Fourier transform turns a given wave into an approximative wave that consists out of cosine ...
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### AC signal analysis: Voltage dip (amplitude dip) at time = 0

I'm working on a series RLC problem where the input voltage is a sinusoidal function for all time. The catch is, for t < 0, the sinusoidal function is of greater magnitude than t >= 0. There is no ...
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### Bandwidth of triangular wave for desired linearity

I'm attempting to replicate the Wavetek Model 188 Function Generator with original circuitry. This function generator has a 'VCG (Voltage Controlled Generator)' input which allows the user to apply ...
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### Confused on Fourier Transform. What is amplitude spectrum and phase?

I am learning fourier transform by myself and I am confused on the description below. I can't understand how can I get the second formula by using the Euler formula on the first equation. Why is ...
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### Do square wave exist?

If we send a square waveform through an antenna, will we get square electromagnetic waves with electric and magnetic fields looking like squares? Also, since there is an abrupt/almost jump in ...
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### Impedance calculation from voltage and current (exponential) waveforms

If we want to find the impedance across two terminals (a port) at a frequency $\omega_0$ using the voltage waveform across $v(t)$) and current through ($i(t)$) the terminal, general intuition is ...
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### How does one measure the Fourier components of a signal?

I attended a lecture on ground penetrating radar (GPR). I am used to reflection seismic where the incoming pressure amplitude is measured as a function of time. In GPR, instead the Fourier components ...
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### Using Matlab poctave function under 3 Hz

I would like to get the Fourier transform of my data from 0,5 to 80 Hz at every 1/3 octave. I tried using Matlab poctave function but that one is only working over 3 Hz. My question is there a way ...
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### Frequency division and signal spectrum

I need a mathematical description of what happens to the spectrum of a signal when that signal is processed to divide its frequency. As an example, construct an input signal as the sum of two sine ...
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### Effect of frequency division on a signal's spectrum? [duplicate]

I am constantly on the lookout for effective yet inexpensive means to generate SSB signals. Analog Devices' LTC5598 Direct Quadrature Modulator turns baseband analog I/Q signals into RF from 5MHz to 1....
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### What kind of hardware implements Fourier transform?

I looked around online but I found nothing relevant. It is very difficult for an electronic device to decompose a signal in different frequencies. How this is done at the bare metal level? Any ...
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### ADS harmonic balance discrepancies with sawtooth waveform

I am using ADS for a simulation where I am biasing a diode with a sawtooth waveform. The sawtooth source provided by ADS, and 3 harmonics are specified There are different phase delays across the ...
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### Fourier transform does not produce the correct result

I am trying to calculate the absolute value of a certain sinusoid to see how MATLAB calculates the Fourier Transform by using the freqz() command. Here is my Matlab code ...
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### What exactly does the frequency spectrum represent?

The signals in the image represent a low pass signal and its Hilbert Transform. I know that a plot for a signal's magnitude with reference to frequencies can be found by applying a Fourier Transform. ...
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### Amplitude-Frequency spectrum

I am tasked to find the amplitude of the first harmonic of a square wave. I did a time domain fourier series and plot a frequency spectrum I also did a frequency domain fourier series and plot a ...
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### Fourier series coefficient for sin(wt+theta)

Am trying to find the Fourier series coefficient ck for the following function \begin{equation} x\left(t\right)=\sin\left(wt+\theta \right) \end{equation} Here is my work \begin{equation} c_k=\frac{1}{...
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### Frequency Response Function Estimate via FFT Question

I want to estimate the FRF of a dynamic LTI system given experimental input and output data. I know generally the approach is to use a chirp as an input to make sure enough frequency content is ...
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### Relation between the Fourier transform of Y and X

So, I watched a video from MIT Signals and Systems Open course on youtube, and there is a moment when he substitutes $x(t)e^{jw_ct}$ for y(t), and then: Shouldn't it be just $X(w - w_c)$ ? ...
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### Fourier Series Expansion of the phase current of a three phase full wave bridge rectifier

I am really struggling with this homework problem where I am asked to calculate the harmonic components as a ratio of the first fundamental harmonic of the phase current of a three phase rectifier ...