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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: ...
Anna Koroleva's user avatar
5 votes
2 answers
542 views

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 ...
Lorenzo Marcantonio's user avatar
0 votes
0 answers
26 views

ISO permitted RF emission spectrum for medical devices in hospitals

I've been searching to find the electromagnetic compatibility requirements for medical devices to be used in hospital but cannot find the correct ISO standard. The list here only lists implantable ...
SeanJ's user avatar
  • 919
2 votes
1 answer
123 views

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, ...
wash's user avatar
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1 vote
1 answer
86 views

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. ...
Strelok's user avatar
  • 111
0 votes
2 answers
125 views

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 ...
DRF's user avatar
  • 526
-2 votes
1 answer
110 views

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 ...
Dan Bullard's user avatar
0 votes
0 answers
101 views

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)...
Dynamic_equilibrium's user avatar
0 votes
1 answer
37 views

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 ...
Samdare's user avatar
0 votes
0 answers
63 views

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, ...
Dynamic_equilibrium's user avatar
1 vote
1 answer
105 views

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 ...
MakePlatanGreatAgain's user avatar
0 votes
0 answers
24 views

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 ...
floppy380's user avatar
  • 1,885
0 votes
1 answer
111 views

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 ...
tan45's user avatar
  • 11
1 vote
2 answers
175 views

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 ...
Dakalaom's user avatar
  • 551
7 votes
2 answers
1k views

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 ...
ulix's user avatar
  • 183
0 votes
2 answers
422 views

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 ...
Granger Obliviate's user avatar
0 votes
0 answers
62 views

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 ...
Adnan Ali's user avatar
  • 111
0 votes
1 answer
236 views

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 ...
Granger Obliviate's user avatar
0 votes
0 answers
40 views

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 ...
mukesh 123123's user avatar
0 votes
0 answers
146 views

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. ...
NicoCaldo's user avatar
  • 315
1 vote
2 answers
396 views

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 ...
Beaker's user avatar
  • 11
0 votes
1 answer
66 views

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 ...
Fernando's user avatar
0 votes
1 answer
970 views

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. ...
Electrical_engineer_student's user avatar
0 votes
0 answers
18 views

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 ...
Everyone's user avatar
  • 3,011
6 votes
5 answers
444 views

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 ...
Seelenjäger's user avatar
0 votes
2 answers
113 views

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 ...
Sofia's user avatar
  • 3
1 vote
1 answer
676 views

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)\$,...
Elaws's user avatar
  • 11
0 votes
2 answers
70 views

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 ...
Boba0514's user avatar
1 vote
4 answers
785 views

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, ...
Underdog's user avatar
  • 377
2 votes
2 answers
2k views

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 ...
t_nogic's user avatar
  • 75
3 votes
3 answers
8k views

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, ...
arthur yeo's user avatar
1 vote
1 answer
380 views

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 ...
Saira's user avatar
  • 11
1 vote
1 answer
230 views

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 ...
user27119's user avatar
  • 247
1 vote
1 answer
116 views

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 ...
Neamus's user avatar
  • 281
0 votes
3 answers
221 views

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 ...
user216912's user avatar
1 vote
3 answers
232 views

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 ...
Tripola's user avatar
  • 733
1 vote
1 answer
257 views

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}. ...
Preetham Reddy's user avatar
0 votes
3 answers
152 views

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/...
ChemEng's user avatar
  • 103
1 vote
3 answers
5k views

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. ...
user avatar
0 votes
1 answer
369 views

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 ...
alt-rose's user avatar
  • 1,479
0 votes
1 answer
134 views

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 ...
Lintahlo's user avatar
0 votes
0 answers
45 views

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 ...
Quirik's user avatar
  • 287
1 vote
1 answer
157 views

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 ...
Stefanino's user avatar
  • 616
0 votes
1 answer
1k views

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 ...
Blargian's user avatar
  • 869
3 votes
1 answer
243 views

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 ...
wu yi's user avatar
  • 61
1 vote
1 answer
320 views

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 ...
Fernando Franco Félix's user avatar
0 votes
1 answer
895 views

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 ...
Alex K's user avatar
  • 91
0 votes
0 answers
35 views

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 ...
Jian's user avatar
  • 101
4 votes
3 answers
244 views

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 ...
user171780's user avatar
-1 votes
1 answer
77 views

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 ...
Noldor130884's user avatar