Questions tagged [spectrum]
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94 questions
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Obtain phase spectrum from frequency/phase modulated signal
I have a homodyne rf setup in which I measure spectra by stepping frequency by frequency. The phase reference resets every time I change the signal frequency, so I can only measure the amplitude, but ...
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How can I use MATLAB to show that the Doppler effect destroys orthogonality of OFDM subcarriers?
I am trying to get a visual representation of how the Doppler effect destroys the orthogonality of the subcarrier and understand this effect.
I plotted three orthogonal subcarriers in MATLAB:
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Strange comb spectrum found during EMI precompliance
During near field testing I encountered this thing I've never seen neither on the wild nor on the book. The board has an STM32F107 with an 8MHz crystal and no ferrites or choke whatsoever (I'm ...
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How can I improve the estimation of the power spectral density (PSD) of a signal from an oscilloscope
I need to obtain the power spectral density (PSD) of a signal measured with an oscilloscope. The signal consists of a sinusoid with a DC component plus noise. I acquired data from the oscilloscope, ...
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On the understanding of signals from an IR detector coupled to a lock in amplifier
I have a CW laser which is modulated by an optical chopper rotating at 1kHz. The modulated CW beam struck a sample holder and the absorption signal is recorder via an Infrared Associates MCT detector. ...
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Spectrum Analyzer problem
I am seeing some strange behavior with my spectrum analyzer. It is a Tektronix RSA306B.
I have put a 50 Ω termination at the input of the spectrum analyzer and I am seeing a lot of spurious ...
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What two laws of harmonics are demonstrated here? [closed]
I clipped the top and bottom of a sine wave at exact reciprocal angles (73.73159173° to 106.2684083° and 253.73159173° to 286.2684083°) to prevent the creation of even (red) harmonics (by being ...
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FFT analysis in LTSpice is giving wrong results during partial execution of time domain simulation (Details in body)
In LTspice, while computing FFT using waveform window (View-> FFT), the results seems to be wrong if FFT is computed after partial execution of simulation ( eg: if simulation is paused in between)...
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Is it possible to to use same frequency band and same frequency blocks for two adjacent/near telecom circles
As shown in the Screen-Shot, TRAI (Telecom Regulatory authority of India) in the pre-auction recommendation manual to DoT(Department of telecommunication) mentions 770 MHz of the spectrum ( 35 MHz for ...
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Would a square waveform (or trapezoidal waveform) have frequency content lower than its fundamental frequency?
I was trying to understand the LC circuit response for the circuit given below.
(Note: fsw indicates the frequency of input square wave as in a buck converter)
As far as I know, for a linear circuit, ...
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Op-amp chopping principle in frequency domain to reduce offset voltage
I am trying to understang the chopping principle used in op-amps with help of this document (page 19 - 20.)
I understand that switch S1 (aka modulator M1) causes modulation with 1/2 duty cycle and it ...
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Confused with parameter definition of spectrometer
Regarding this spectrometer specs, what is meant by "spectral sampling resolution"`? It is give as 2.55 nm. And how is that different from spectral resolution? The term "spectral ...
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Why do we take 50 ohm resistance value for unit conversion in Spectrum View in the oscilloscopes?
While we change the unit in Spectrum View, why is it explicitly mentioned 50 ohm? Why don't we take the resistance value of 1 Mohm into account as well? Though we do have 1 Mohm as one of the ...
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Optical filters: What is the difference between Free Spectral Range (FSR) and the resolution based on (FWHM)
I have a question regarding the Free Spectral Range (FSR) and resolution based on (FWHM) of optical filters like based on Fabry-Perot-Interferometers.
As of now, I always thought of the resolution as ...
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Measuring signal with of nanosecond pulse width with a spectrum analyser?
I'm looking to measure the signal width of electronic signals (device under test, DUT). The problem is that these signals have a quite short pulse width which would require me to use a GHz ...
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What is happening when a signal is acquired at exactly Nyquist frequency?
So I am doing some some simulations with 1V sinusoidal signals, and a 1 second acquisition at sampling frequency of 100 kHz.
Now I am slowly increasing the frequency of the sinusoidal signal. Trying 1 ...
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When multiple cognitive radios transmit simultaneously
Cognitive radio nodes sense the spectrum and start their transmission opportunistically when the spectrum is found to be vacant. The question arises what if two or more nodes find the spectrum to be ...
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Windowing FFT: spectral leakage vs ENOB
I am using Cadence to perform full speed testing of a 4-bit SAR ADC using the FFT and non-coherent sampling.
I've obtained the ENOB and the spectra of the output signal using first the rectangular ...
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Spectrum Sensing
I am trying to find the maximum range of a directional antenna whose beamwidth can be varied. The goal is to understand if a particular (x,y) user lies within the antenna. The distance between the ...
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Why the frequency spectrum of my OFDM output signal has a series of spike?
I'm trying to understand OFDM modulation using Matlab Simulink and I've built the following system
I sent to the input of the OFDM block a frame of 15 samples that comes from the 16-QAM modulator. ...
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Understanding spectral resolution for a spectrometer
I am looking at this Hamamatsu mini-spectrometer, C12880MA.
The specs are,
Spectral response range: 340 to 850
Spectral resolution (FWHM) (typ.): 12 nm
Number of total pixels: 288 pixels
Now the ...
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N Fractional PLL spectrum
I'm studying the different types of N-fractional PLLs based on switching between two or more frequencies to get the desired frequency.
However, I'm facing difficulties to understand how the output ...
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How to find the modulation index of an amplitude modulated signal from the spectrum analyser?
My aim to is compute the modulation index(u) of a amplitude modulated waveform but I only have access to its power spectrum from the spectrum analyser.
I attached an image from the spectrum analyser.
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Does ITU govern both spectrum, and applied power?
I'm really not sure whether EE Stackexchange is the right place to ask. At the same time I'm sure it is the right place to expect a coherent reply.
I am aware of the various bands (C, S, K, X...) that ...
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What could be generating this waveform in an EMC Compliance test?
We are having trouble with a CISPR-11 (EN55011) Radiated Emissions Class B compliance test in one of our solutions. The troubling part of it is basically an industrial motherboard (with a commercial ...
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Red laser that has a higher power output at 400nm than 623nm?
I am doing experiments using a red (623nm) LED. However, when I measured the power output I noticed that it is higher at smaller wavelenghts. I did the measurements using two different power-meters ...
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Spectrum of FM signal?
If a carrier (\$f_c\$) is FM modulated by a single sine wave (\$f_m\$), its spectrum is composed of frequencies at \$f_c + kf_m\$ (\$k \in \mathbb{Z}\$) whose amplitudes are weighted by \$J_n(\beta)\$,...
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What is the irregular signal at the bottom of this "spectrogram"?
I am reading research papers about LoRa, and I have come across the below figure in this one.
The horizontal axis is clearly labeled frequency, but the vertical one isn't. I recognize the chirps in ...
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How can we interpret the negative side of a double-sided frequency spectrum
We know that a frequency spectrum includes both positive and negative frequencies. However, how can we explain the negative frequency physically?
For example, in a wireless communication system, ...
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DAC "aliasing" of harmonics
While reading articles and application notes regarding DACs and their output spectrum, I stumbled across aliasing of higher harmonics to the first Nyquist band.
For example, when generating a single ...
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How to convert dBm to V/m, A/m², and W/m²
Currently I am using a spectrum analyser (SA) Keysight N9020, with an antenna to get readings off the air.
The reading on the SA gives a reading of a unit, dBm.
However, I need to convert dBm to V/m, ...
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Power Spectral Density units
I am trying to compare power spectral density values (obtained from dsp.SpectrumAnalyzer) with PSD values obtained from hardware which has a VSA.
MATLAB's documentation says that " The power spectral ...
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How to model and understand the asymmetry of a parallel RLC circuit spectrum
I'm working with some parallel RCL circuits and I have noted that when I record a power spectrum (so \$\rm{dB}\$ vs \$\rm{Hz}\$) that the spectrum is asymmetric:
As I'm sure you all know if we ...
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Antennas- Spacing between Reflectors & Directors in Wavelengths
I’m building an antenna and I want it to connect to channel 6 on the spectrum allocation chart (2.437 GHz). I’ve calculated the lengths of the reflectors and directors but im just a bit stuck on the ...
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Covid-19: can a UV-C source be improvised from a standard mercury vapor lamp?
I suggest it because the usual professional UV-C sources are in short supply and very costly.
A common 175 W mercury lamp designed for illumination includes the quartz 'lamp' tube itself, inside an ...
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Aperiod vs Period waveform Fourier Transform: How does nature understand which is the case?
Today I reviewed the theory behind the Fourier Transform, and I asked myself a question that I couldn't answer to in the process.
Theory: A periodic waveform has a Fourier series which can be seen ...
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Noise Floor of ADC using PWELCH
While using MATLAB's Pwelch function, I am not able to match the noise floor of the "Modelled" ADC to (Delta)^2/6 {1 sided Spectrum}.
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Infrared Sensor for drug detection [closed]
I saw that there has been a push to make a drug detector that can identify cannabis since it has been legalized. I was looking at mouser.com and found this ir sensor: https://www.mouser.com/...
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What's the reference dB level in a spectrum analyser?
I am using a spectrum analyser to measure the 248kHz buck switching frequency and its harmonics in my board. I have set the frequency range from 200kHz and 1MHz and I am using a near field H-probe.
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How to see Signal frequency and Sampling frequency on the frequency spectrum
If I have a 100 Hz periodic analog signal and let us say it is band limited to 1kHz and I sample it at 3 kHz. If I want to see its frequency spectrum then how to differentiate between the signal ...
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Arduino RGB spectrum problem
Over the last few days I've been working on an anode RGB LED in Arduino, I've tried getting it to do an RGB spectrum but all I would get is just the colors from red to green, then it would get stuck ...
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Doppler spectral power density
In layman terms, why doppler spectral power density has U shape?
Does this mean that frequency components with maximum doppler shift have maximum power?
I am confused with the interpretation of the ...
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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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Calculate power given PSD and bandwidth?
Given the spectral recommendation for an Asymmetric Digital Subscriber Line (ADSL) below, I'd like to calculate the power in Watts that a modem would have to emit for the upstream band. I want to do ...
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Two details about phase noise have been confusing me for a long time. Hope to be resolved
Just like FLOYD M. GARDNER said in the PhaseLock Techniques, 3rd Edition: "In light of that success in spectrum analyzers, a practitioner’s answer to the question above is: The spectrum of phase noise ...
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How does the spectral response of a photodiode change with bias voltage?
Look at this data sheet, in the second page we have a graph for the spectral response.
Now, I have learned that photodiodes must be reverse-biased in order to get a decent signal from them, but then ...
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How do you visualize the frequency spectrum for a digital waveform? [closed]
How does the mathematics of a single or periodic rectangular pulse help us quickly visualize the frequency spectrum for a digital waveform? Develop the ideas behind this.
My professor posed this ...
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non-negative FFT spectrum, subtlety
definations
\$x(t)\$ is a function of time. Physically, it can be voltage, displacement, magnetization and so on. It can be real, complex, vectors or more fancy numbers.
\$C(t)\$ is the auto ...
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Help interpreting strange spectrum
I am sampling a sinusoidal signal with an oscilloscope and viewing its spectrum using the FFT mode. The signal in time domain is this:
and I am getting this spectrum:
The peak above the red line is ...
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Are there any examples on the use of the frequency spectrum between 40 and 42 GHz? [closed]
Since everyone started talking about 5G, I got curious about some parts of the frequency spectrum.
I found out that some operators in the U.S. asked FCC if they could free the range between 40 and 42 ...
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