Questions tagged [spectrum]

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98 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
86 views

Aperiod vs Period waveform Fourier Trannsform: 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
36 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
80 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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0answers
24 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
94 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
58 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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0answers
40 views

Need help with choosing the right pre-amplifier for my rural base station design

I am in the process of designing a multi radio base station for a FWA application. The distance from the main base station to the terminating units is a 1 KM. I have 2 sectors and am planning to use ...
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0answers
27 views

How does spectral density of a power signal change when it is multiplied by \$cos(2\pi f_ct)\$?

Suppose we have a power signal \$n(t)\$ whose power- auto-correlation function is: \$R_{n}(\tau)\$ . Now we multiply the signal by a cosine as: \$cos(2\pi f_ct) \cdot n(t)\$, whose auto-correlation is ...
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1answer
62 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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31 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
62 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
50 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
139 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
53 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
277 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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0answers
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
139 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
71 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
46 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
249 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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3answers
2k 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
728 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
20k 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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0answers
139 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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2answers
158 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
2k 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
86 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
41 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
6k 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
153 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
82 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
126 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
795 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
587 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
74 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
894 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
950 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\$?
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1answer
169 views

How to listen to radio communications from a transmitter?

I have two devices communicating at a frequency which I don't know. I want to listen to that communication so that I can replicate one of the devices and fool the other. Basically I want to reverse ...
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2answers
155 views

Find the power spectral density?

I don't understand how the graph of H(w) is used to find the equation for H(150) and H(200.)
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1answer
970 views

Calculating noise power spectrum

I have some signal which I have measured N different times and I want to calculate the noise power spectrum of it. Intuitively to me the way I would do this is simply calculating the power spectrum of ...
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1answer
230 views

Amplitude and phase spectrum

I want to find phase and amplitude spectrum of this signal: Here is what I have done: $$f(t)=\sum_{-\infty}^{+\infty}Fne^{jnwt}, Fn=\frac{1}{T}\int_{0}^{T}f(t)e^{-jnwt}dt=\frac{1}{T}\int_{t1}^{t1+\...
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5answers
11k views

Can I turn Radio waves into light?

Wikipedia says that the frequency of light is 300 THz. I've made a radio waves transmitter that transmits about 100 MHz. If I increase the frequency of the transmitter to 300 THz, will the antenna ...
3
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1answer
413 views

Fourier series of modified sine

I must do this task: Short translate: Picture presents modified sine signal. I must calculate F(k) using Fourier Series, next draw amplitude spectrum and phase spectrum. I have 2 problems: Is this ...
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4answers
21k views

Cool White LED bulbs: Are they “full-spectrum”?

I don't have much knowledge on LED lights and find the technology quite fascinating (yes, I know, it is not that new!) I have read that in order to create "white" light, LEDs actually need to emit ...
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2answers
439 views

Can an oscilloscope add a frequency component to my signal?

I want to check the spectrum of a DDS signal ("pure" sinewave) for undesired frequency components. The way I am doing it is by storing the waveform from a 2GS/s oscilloscope (Agilent DSO81204) and ...
2
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1answer
191 views

How does the energy of non-resolved spectral lines get distributed in an FFT?

For example, if my FFT has a poor resolution of 170Hz (data sequence length is small due to latency constraints) and I am trying to detect a sinusoid in the 150-250 Hz range, will this FFT be good ...
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1answer
113 views

calculating the spectrum of digital modulation methods

I have just started studying the techniques of digital modulation. The book i am reading only has mentioned the psd of bpsk, bfsk , qpsk and msk. I would like to know, how the psd is actually ...