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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79 views

Bandwidth of a signal

I have found that the convolution of two rect(f) functions (f=frequency) gives a triangular pulse of width 2 centred at 0 Hz. Can anyone tell me what the bandwidth of this pulse is? Is it F or 2F? My ...
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3answers
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.FOUR command doesn't give the required output

This netlist for a full wave rectifier was actually written for PSPICE. When I type the same netlist in LTSpiceXVII, the log file doesn't show the proper output. I have replaced ...
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1answer
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Fourier Series - Double Check Work

I was solving this Fourier series problem from my book, but was not able to find a solution to it to double-check my work. This is the problem: My work: \$T=4+2=6 sec\$ \$C_{n}=(\frac{1}{T})(\int_{t_{...
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5answers
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Does the DC component of any signal also carry information?

Every signal carries some types of information in it. Mathematically we Know from Fourier series that these signals can be represented as a sum of its DC component and all the harmonics of fundamental ...
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Why is a signal that is finite in time domain, infinite in its frequency domain?

Why does every single band-limited signal in frequency have an infinite time domain and vice versa (As it's a symmetric relation, inf in one is finite in the other). I understand how a digital signal ...
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94 views

Inverter Fourier analysis

I have an inverter circuit like below: I will use bipolar control method to produce sine wave. Our teacher said us prove basic harmonic of inverter is equal to multiplying of modulation index and Vd, ...
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0answers
41 views

Finite-duration signal in the time domain, means what exactly in the frequency domain?

I'm trying to understand exactly what restrictions a finite duration time domain signal has on its Fourier transform. I found a helpful table in The Fourier Transform and its Applications by Ronald ...
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55 views

Circuit analysis problem involving Fourier series

Please help me with this problem I can not solve this. It is about Fourier series. It is so hard.
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2answers
93 views

Amplitude Spectral Density from a Fast Fourier Transformation

I want to calculate the Noise-equivalent Power (NEP) of a photodetector. Hereto, I have to measure the Amplitude Spectral Density (ASD) of the detector and divide the result by the Responsivity: The ...
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0answers
92 views

Pulse Doppler radar system simulation using MATLAB

How to code this project in MATLAB I'd tried coding this project (prob. 3-2, third paragraph) in MATLAB through this tutorial : https://www.mathworks.com/help/phased/ug/doppler-shift-and-pulse-doppler-...
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Representation of Fourier transform

I have a problem interpreting 2 different representations of Fourier transform and proving their property. In some texts Fourier transform is represented as : . While in other texts the complex number ...
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4answers
109 views

how to calculate the fourier transform of this input?

I have been trying to find a relation between dominant frequency and the time period 'T'. The input is a digital ramp with an increase of 1mV per step. And each step has a time period 'T'. Will I get ...
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28 views

how to define a relative bandwidth for the signal with the equation K/w^2

I have a straight line with a slope. Thus its fourier transform is K/w^2. I wanted to estimate its relative bandwidth(Wont it be dependent on the slope?[1st question]). If the answer for 1st question ...
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29 views

Relationship between two differently sampled Fourier coefficients

Assume a periodic signal \$s(t)\$ with fundamental period \$T_0\$. If one were to use the period \$kT_0\$ to find the Fourier series coefficients, how would they be related to the standard Fourier ...
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5answers
420 views

What are the applications of the Fourier transform in communications?

I have learned about the Fourier transform, but I do not have a deep understanding of it. I heard that it is used in radios, butI don't know how and why. Can anyone explain it in a very detailed ...
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1answer
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Differences between downsampling and upsampling

Explain why the amplitude of the Fourier transform of a sampled signal changes when downsampling, but not when upsampling.
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Fourier transform of the electrical conductivity function

In this pdf https://studylib.net/doc/18704299/chapter-1 the author writes that the Fourier transform of the current density is: $$ \Delta j_{i}(\mathbf{k}, \omega) \equiv \frac{1}{(2 \pi)^{2}} \iiiint ...
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1answer
71 views

Explanation and Draw of Line Impedance Stabilization Network (LISN)

I am trying to learn about LISN circuits. As far as I see, there are standards for LISN. But the point is everybody is applying standards, I would like to know why these values are chosen or why there ...
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2answers
59 views

The Fourier transform

The Fourier transform is just an operation on certain functions.When the functions are signals, why is it that the variable chosen (w) has to correspond to the frequency of the signal ,when it is just ...
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29 views

partially periodic function and fourier series representation

I am thinking about this for a while but I could not reach a conclusion. If I have a periodic signal let's say a square wave but it is only non-zero for t<100 and t>-100. the function is ...
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1answer
158 views

Converting PDM Data to analog

I have researched about PDM Data and I have seen this sentences on wikipedia: In section of Digital-to-analog conversion "The process of decoding a PDM signal into an analog one is simple: one ...
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1answer
149 views

RC filter impulse response is exponential decaying but inverse Fourier is Sinc function

As we all know that the inverse Fourier transform of a frequency domain unit pulse/rectangular function (which looks like low pass filter) is Sinc function. So, I was under the impression that any low ...
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45 views

can fourier transform be used in circuit design?

If I formulize the input voltage that I am planning to give to a circuit and if I formulize relative output voltage that I expect to see with respect to input voltage, I can take their fourier ...
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1answer
48 views

Labview inverse Fourier transform: Why can't I visualize Gibb's effect (or ringing)?

I am studying electrical engineering and have an assignment which I have been working on for couple weeks, but can't solve. I have a discontinuous function as shown below and applied a FFT on it, ...
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2answers
92 views

How do causality and stability affect the response of a linear time-invariant system?

Suppose that there's a linear time-invariant system with the following transfer function: $$H(s) = \frac{1}{3(s-2)}-\frac{1}{3(s+1)}$$ If the system is causal and stable, I can determine \$h(t)\$ by ...
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1answer
57 views

Phase-shift a Broadband Time-Domain Function

Suppose we have an operator \$A_\phi\$ which phase-shifts a sinusoid by \$\phi\$: $$A_\phi[\cos(\omega t)] = \cos(\omega t + \phi)$$ In phasor domain, \$A_\phi = e^{+j\phi}\$ is a complex constant. I ...
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148 views

Electromagnetic radiation from spark gap

I am an electrical college student. I learned from some papers, sites online, including this forum that lightning discharge or any electrical arc emits wideband radio frequency because the odd integer ...
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1answer
108 views

find current, voltage and power at each branch using fourier series analysis

Question: find current, voltage and power at each branch using fourier series analysis Update - here is my solution attempt:
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1answer
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Using FFT to calculate derivatives of polynomial

I know that there are several posts about FFT and derivatives, but I don't get it. I also tried in mathematics but no answer. The formula is: $$ f(t)→\hat{f}(ξ),f′(t)→2πiξ\hat{f}(ξ) $$ First, I don't ...
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14 views

Integration of PSD (Doppler Spectrum)

The expression for received signal PSD corresponding to a simple cosine wave (frequency fC) being transmitted is given as: \begin{equation} S_r(f) = \mathcal{F}[A_r(\tau)]=\begin{cases} \frac{...
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1answer
67 views

Fourier Transform Time Scaling Property using f (frequency) or w (omega - angular frequency)

The time scaling property for a fourier transform is as follows: My book shows this property in terms of \$f\$; however, my instructor likes to use \$\omega\$. I have also seen this property written ...
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1answer
74 views

Power and Energy Computations in the Frequency Domain

How do you calculate the power and energy of a signal given only the frequency domain form of the signal function? For the purposes of this question, please do not assume that it is possible to find a ...
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2answers
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What is the physical meaning of reactive power in non-sinusoidal steady-state (with harmonics)?

In sinusoidal steady-state (linear loads, no harmonics), I understand what is reactive power \$Q = V_{\text{rms}} I_{\text{rms}} \sin{(\theta)}\$ where \$\theta = \theta_v - \theta_i\$: its absolute ...
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1answer
32 views

Equation for square law circuit modulator

For DSBFC AM (double side band full carrier amplitude modulation ) the message signal m(t) must be multiplied by carrier maybe $$ Ac*cos(\omega_c(t)) $$ (For modulation) This modulation is done in ...
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2answers
278 views

Why is there a low pass filter in a DSBSC demodulator?

In analog communication, DSBSC (double side band suppressed carrier) is way of modulating signal. In this the carrier is simply multiplied with the message signal. At the demodulator, the carrier is ...
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0answers
36 views

Why do sampled signals repeat in the frequency domain?

I do understand it mathematically, that multiplying a signal with a Kronecker(T) is the same as convolving it with Kronecker(1/T) in the frequency domain, and that makes sense. But is there an ...
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1answer
71 views

If interharmonics are defined for periodic signals, aren't interharmonics misleading?

Before explaining my question, I'm going to assume that 1) interharmonics, just like harmonics, are sinusoids; and 2) to analytically represent the interharmonics of a signal, we sum them to the ...
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50 views

Absolute values of fourier transform of noise-charged RLC circuit

I am doing time-domain simulations of currents in a parallel RLC circuit charged by thermal noise. In detail in pseudo-code: ...
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2answers
165 views

When a signal has an interharmonic, is the signal periodic or non-periodic?

I have some questions regarding interharmonics. What I'm going to do is first ask just a few, and then as people answer them I would expand this post or create a new question. Harmonics are sinusoids ...
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1answer
40 views

How to isolate coefficiets from complex fourier series?

I have to find yn/xn ratio. From the circuit analysis i found out transfer function Uout//Uin = . I am having hard time trying to isolate two coefficients of two complex fourier Series. Any help is ...
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2answers
46 views

Validity of superposition when summing powers from each harmonic

In Boylestad's Introductory Circuit Analysis 13th edition page 1176, there's an example about working out the total power dissipated by a circuit fed a nonsinusoidal signal. The signal is decomposed ...
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3answers
42 views

Why do we use a wide-band amplification in order to reproduce a sharp pulse without distortion?

I was reading some content with regards to the Fourier Transform and the uncertainty principle. In the book I was reading that Due to the uncertainty principle, in electronics we use a wide-band ...
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3answers
139 views

Generation of triangular wave from passive networks

I wanted to generate a triangular wave from a pure sine wave using only passive networks (RLC circuit only.) I wanted to realize such a network and at first I thought maybe the Fourier transform (of ...
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2answers
382 views

Low Pass Filter to Isolate DC component

I have a question based on low pass filtering. If I input a signal to this low pass filter, why does the output file have an AC (of very low frequency). The input signal is$$ v_i(t) = 2 + sin(2*pi*...
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1answer
62 views

RC circuit not ideal sampling

I have this circuit and I have to find \$x(t)\$, starting from \$ x_c (t) \$ I know that, at \$t=0\$, the switch is closed, so the capacitor is charged and, at the moment \$ x(n)T_c \$ the switch is ...
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2answers
125 views

Importance of Sine Waves And Maxwell's Equations

Sine waves, by a huge margin, are the most important waveform in electronics - we measure a circuit's frequency response with sine waves and represent all other signals through sine waves, with the ...
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Are there ICs that allow extracting a selected frequency component from a signal? [closed]

In many applications, what you need is just extracting one frequency from a signal (that is, to know its amplitude). I was dreaming about an IC that allows selecting a frequency of interest, perhaps ...
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1answer
244 views

Inverse Fourier transform of a shifted cos

I am preparing for an exam. I found this signal I want to inverse transform using the Fourier transform: The problem is that when I try using the general formula for inverse Fourier transform I get ...
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1answer
79 views

Fourier transform of an integral

I am preparing for an exam. I found this problem : I am trying to use the properties then use a pre-transformed function from the table but I couldn't find one. I saw a solution on web : I think he ...
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2answers
56 views

Fast method to calc th Fourier transform

exist a fast method to calc the Fourier trasform (in both sense, t -> f and f->t)? When I use the table and the properties of the Fourier transform, sometime I have difficult to calc this... Any help ...

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