Questions tagged [spectrum]

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16 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 ...
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45 views

spectrum of trapezoid with unequal rise and fall times

What does the spectrum of a trapezoidal waveform look like when the rise and fall times are unequal?
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3answers
121 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 ...
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2answers
67 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 ...
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1answer
84 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)\$,...
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42 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 ...
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4answers
234 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, ...
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167 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 ...
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3answers
1k views

How to convert dBm to V/m, A/m^2 and W/m^2

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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1answer
52 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 ...
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1answer
98 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 ...
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1answer
48 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 ...
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3answers
197 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 ...
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3answers
120 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 ...
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1answer
52 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}. ...
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3answers
99 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/...
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75 views

From noise spectral density to equivalent short circuit input RMS noise

I have an acquisition system that is supposed to be low noise. It acquires from an ADC into a wav file. I read this file and process it with Matlab. Then, being "x" the array with time signal, Fs the ...
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2answers
437 views

What's the reference dB level in spectrum analyser

I am using a Spectrum analyser. Measuring the 248kHz buck switching frequency and its harmonics in my board. I have set the frequency range from 200kHz and 1MHz. Using a near field H-Probe When I ...
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1answer
68 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 ...
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1answer
76 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 ...
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34 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 ...
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1answer
76 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 ...
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1answer
155 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 ...
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1answer
169 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 ...
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1answer
108 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 ...
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1answer
389 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 ...
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30 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 ...
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3answers
150 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 ...
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1answer
52 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 ...
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1answer
82 views

Analog Led Audio Spectrum Analyzer Simulation

I am having a bit of trouble trying to simulate a variation(different frequency ranges/gain for the BP filters) of this project: https://makezine.com/projects/audio-spectrum-analyzer/ I am not too ...
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1answer
49 views

Why averaging in Spectral magnitude domain not in complex domain to estimate spectrum of a process

Consider we need the magnitude spectrum of the signal. Signal is recorded in \$N\$ trials to a certain stimuli. Signal varies from each trial because of noise. So, to estimate the actual magnitude ...
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1answer
366 views

How DC offset affects the spectrum of a single pulse

I know that in the magnitude spectrum of a single square DC pulse (0-8V) the lobes are zero at frequencies $$\frac{1}{t},\frac{2}{t},\frac{3}{t},...etc. $$ where t=pulse duration. If the square ...
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3k views

How to compare brightness of different color LEDs (not RGB)?

I wonder - let's assume one would build some user interface using green, yellow and red or just any other available colored LED (not RGB LED) - what would be the proper (aka best) way to compare the ...
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3answers
839 views

Why do we need the Fourier transforms of sin and cos? [closed]

As we know we perform Fourier transform in case of continuous and "non-periodic" functions, while sin and cosine both function is "periodic" function then why we perform Fourier transform of sin and ...
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5answers
22k views

Full Spectrum LED(400nm~840nm) vs Grow Light LED (RED+BLUE)

I'm planning to buy lights for my planted aquarium tank. After a small research I found that regular lights are not suited for growing plants. Beacuse they need BLUE for Leaf Growth and RED for Stem ...
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178 views

License free frequency spectrum in Australia

What is the license free frequency spectrum in Australia? Is it 433Mhz or 915Mhz Or 868Mhz? I am trying to do some IOT Project using RF (LORA/ZigBee) modules. I thought it was 433Mhz. But some online ...
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167 views

Largest spectrum image sensor and processing its entire spectrum image

I was developing a digital system to process raw images stemming from an image sensor but I would like to deal with "universal" (as possible) spectrum image sensors with no filter. I know that for ...
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3answers
3k views

How Is Intensity of Blue Light Measured?

As a hobby project and to help solve issues getting up early in the morning (specially given that it's winter and the sun isn't up until long after I am) I'm trying to find a bright blue light that I ...
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1answer
96 views

Op Amp adds spectral components to amplified output signal

I'm using this simple circuit to amplify a small signal: simulate this circuit – Schematic created using CircuitLab Input voltage is defined by: ...
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2answers
52 views

Spectral properties of EFM encoding

Data is written to CD/DVD using an encoding called eight-to-fourteen modulation, where each eight bits of data are encoded by fourteen bits on disk. The encoding was designed to give the encoded ...
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1answer
7k views

How to calculate total power from spectrum?

I'm trying to measure total power(dBm) from the following spectrum, the spectrum is 5MHz wide, the peak power from the spectrum is about -40 dBm, I have an array of spectrum points(Power vs Frequency)...
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2answers
180 views

How do I tell if my device qualifies for FCC exemption

According to the FCC: The following devices are subject only to the general conditions of operation in §§15.5 and 15.29 and are exempt from the specific technical standards and other requirements ...
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3answers
344 views

How can I reproduce ambient EM fields inside a Faraday enclosure?

I am part of a research team looking at the possible effects of EM fields on psychological function. The experiment calls for participants to perform a series of tests while inside a Faraday tent that ...
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2answers
85 views

Using CMOS to detect transmittance in sample from LEDs

I am trying to get the transmittance through various liquid samples using specific wavelength LEDs. Originally I was experimenting with photodiodes, but do not seem to be ideal. The target color ...
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0answers
131 views

Speaker designed for ultrasound operation

I've created a transmission protocol in order to transmit information bits between a PC speaker and a smartphone, or between 2 smartphones using ultrasounds. I've implemented a QFSK system which uses ...
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2answers
978 views

RF Transmit Power in an ISM band

I was browsing through some OFCOM Frequency Allocation Tables for use on a small project I'm doing. I require the use of some unlicensed ISM bands in the UK, and found that the lowest unlicensed band ...
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1answer
629 views

Usefulness of VBW in spectrum analyzer

Typically in the block scheme of a spectrum analyzer a video filter, with a bandwidth VBW, is located after the envelope detector and before the screen. As pointed out in this document, the VBW may (...
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2answers
75 views

Spectrum precision of fluorescent lamps

How precise are fluorescent lamps when mass produced? Is their emitted spectrum really identical or is it possible to detect a difference between two random lamps using appropriate filters with photo-...
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1answer
1k views

How to shift signal to baseband using local oscillator frequency?

If the input to a demodulator is a signal having the spectrum shown below, how would I figure out what local oscillator frequency is required to shift the signal to baseband? Is there a formula for ...
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2answers
1k views

How to sketch the spectrum of \$m(t) = \cos(1000)t \times \cos(3000)t\$

I know how to sketch the spectrum of \$m(t) = \cos(1000)t + \cos (3000)t\$ But I stack with that....when it's multiplied? How to sketch the spectrum \$m(t) = \cos(1000)t \times \cos(3000)t\$?