What is Signal: Definition and 988 Discussions

In signal processing, a signal is a function that conveys information about a phenomenon. In electronics and telecommunications, it refers to any time varying voltage, current, or electromagnetic wave that carries information. A signal may also be defined as an observable change in a quality such as quantity.Any quality, such as physical quantity that exhibits variation in space or time can be used as a signal to share messages between observers. According to the IEEE Transactions on Signal Processing, a signal can be audio, video, speech, image, sonar, and radar-related and so on. In another effort to define signal, anything that is only a function of space, such as an image, is excluded from the category of signals. Also, it is stated that a signal may or may not contain any information.
In nature, signals can be actions done by an organism to alert other organisms, ranging from the release of plant chemicals to warn nearby plants of a predator, to sounds or motions made by animals to alert other animals of food. Signaling occurs in all organisms even at cellular levels, with cell signaling. Signaling theory, in evolutionary biology, proposes that a substantial driver for evolution is the ability for animals to communicate with each other by developing ways of signaling. In human engineering, signals are typically provided by a sensor, and often the original form of a signal is converted to another form of energy using a transducer. For example, a microphone converts an acoustic signal to a voltage waveform, and a speaker does the reverse.Information theory serves as the formal study of signals and their content, and the information of a signal is often accompanied by noise. The term "noise" refers to unwanted signal modifications but is often extended to include unwanted signals conflicting with desired signals (crosstalk). The reduction of noise is covered in part under the heading of signal integrity. The separation of desired signals from background noise is the field of signal recovery, one branch of which is estimation theory, a probabilistic approach to suppressing random disturbances.
Engineering disciplines such as electrical engineering have led the way in the design, study, and implementation of systems involving transmission, storage, and manipulation of information. In the latter half of the 20th century, electrical engineering itself separated into several disciplines, specializing in the design and analysis of systems that manipulate physical signals; electronic engineering and computer engineering as examples; while design engineering developed to deal with the functional design of user–machine interfaces.

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  1. M

    A Confused about reflected signal in a bow-tie optical cavity

    Hello! I am building a bow-tie optical cavity, of finesse about 10,000. When I measure the transmitted signal out of the cavity, after aligning it, I see clear peaks, significantly higher than the background and pretty much single mode. I do see 2 other peaks, probably from other modes, but much...
  2. tworitdash

    I Making Sense of Notation Confusion in Statistical Digital Signal Processing

    I started my research in statistical digital signal processing two years ago, so I need to familiarize myself with all the notations people use in probability and statistics. I come from a deterministic science background. I name my variables based on what they mean. A velocity is a v , a...
  3. J

    Wavelength / signal which would pass through concrete and rubble

    Greetings, Please imagine a huge pile of rubble, meters deep. Somewhere inside, there's a device emitting a certain signal. This signal can be picked up by a radar-like device which locates the origin of that signal, with the least interference from the pile of rubble, concrete blocks, metals...
  4. Kami_Munchkins

    Signal Generator assignment, Multisim results confuse me

    TL;DR Summary: Hi, i'm trying to talk about the results, this is a research assignment so i have no support Hello, so here is the circuit. Its a basic signal generator, My issue is in the practical version, the potentiometer effected frequency, but in the simulation this is not the case... I...
  5. Callicious

    Op-amp compensation of cascade fudges audio signal oddly

    Links: LTSpice Pre-amp schematic (resistor values/capacitor values different) Gerber Op-amp Datasheet Hi all; Presently designing pre-amp for my analogue MEMS microphone for bioacoustic recording (ultrasonic, especially.) Don't own an oscilloscope, so relying on spectrograms of audio for...
  6. K

    A Uncertainty on an asymmetry signal

    Hello! I have an experiment in which I measure the counts given some experimental parameters, call them ##E## in order to extract some physics parameter of interest, call it ##X##, so I have ##N(E,X)##. This ##N## (the number of counts) will have a statistical error (which goes like...
  7. Y

    Can I run cable tv signal and on air tv signal in a single coax?

    Hi I currently subscribe to Directv, the signal is from the dish and split into 4 coax to go to 4 different rooms. So each room has a coax output on the wall to hook up to the Directv receiver box. I decided to change to Dish Network. At the same time, I want to install a VHF/UHF digital tv...
  8. U

    I SR vs GR: Logical Necessity of Signal Propagation

    I guess it is safe to say that SR is, mathematically speaking, a framework that correlates discrete events in spacetime by way of a universal constant (the speed of light) so that the "proper distances" that separate them may be determined. I think this means that every conceivable "instant...
  9. O

    Engineering Maximum modulation factor of a two tone signal

    I'm stuck on this because v is a 2 tone signal, so it's not as simple as Am/Ac. The teacher said I will need to differentiate it and equate it to zero, which I thought made sense. Differentiating v gives me: [- mwsin(wt) - mwsin(2w*t)], so there's still unknown variables. I don't know how I'm...
  10. Krion

    B Need help designing a clock with a repeating signal

    Hello! I am in need of a clock expert. Just a disclaimer, I am vastly unfamiliar with much of the inner-workings of clocks and need some help. I have only built a simple Graham Escapement clock, previously. I need to build a clock that triggers a single signal to occur three times at equally...
  11. C

    Exploring Audio Signal Manipulation with Circuits

    I'm just playing around with circuitry, working with manipulation of Audio Signals in active circuits(My guitar, going to build an internal preamplifier). I've been trying to find an answer on this all day with no luck. As eager as I am to see what the effect would be it would be nice to know...
  12. K

    A Error signal when locking a cavity

    Hello! I am trying to lock a laser to a bow-tie cavity. I managed to align the cavity to a certain degree but when I lock it, the error signal looks as below. I do get a significant power enhancement (although about 10 times smaller than expected) and the lock is relatively stable, but the error...
  13. Ahmed1029

    I What Determines the Speed and Clarity of Signals in Wave Physics?

    What exactly is a signal in wave physics? Is any wave considered a signal? Like, consider a superposition of harmonic plane waves, is the signals it carries considered the envelope(that travels at the group velocity) or the individual rippes that travel at a the phase velocity?
  14. N

    Composite signal generation IC in DIFAR Sonobuoys

    Hi all I came to know about an old IC called probably "HE100" which was being used in DIFAR Sonobuoys for generation of composite signal. This IC takes 'Omni', 'Sin and Cosine Dipoles' signals as input and generates composite signals using internally generated 7.5 KHz and 15 KHz carriers. This...
  15. A

    MCNP6 with mpi failed with signal 11 (Segmentation fault)

    I use Python scripts to run mcnp.mpi like And I encountered this bug report The scipts has run normally for a few hours. I extracted the inp file and it can be run normally. I searched on Internet and found it seems to be the problem related to memory, but i checked the log, there's still...
  16. A

    Engineering Small Signal Input Resistance of a BJT amplifier

    The diagram of the BJT amplifier small signal model is below. This is not really a homework question as I am self-learning electronics, but I was advised it may be better placed here than in the technical portion of the forum. Thus I do not have an "attempt" at a solution (which is given as RI...
  17. Twigg

    How is wideband FM implemented on the E4400B signal generator?

    The Agilent E4400B (formerly HP ESG-something) is a <1GHz signal generator. One of its features is that it can take a <10MHz external signal and turn it into frequency modulation on the output carrier signal (like an incredibly wideband VCO). However, the device can also be externally referenced...
  18. K

    A Laser signal input for PDH lock

    Hello! I have a laser with only one input for external signals. Currently I use that to send the error feedback signal when I measure the power transmission from my cavity (not using PDH). If I want to use PDH, I would need to modulate the laser frequency, which means that I need to send to the...
  19. L

    Engineering Adding two signals from different sensors in order to obtain a signal with very high dynamics

    hello I am working on a project concerning a measurement technique which consists of adding two signals from different sensors in order to obtain a signal with very high dynamics. and I would like you to help me because I saw your interventions concerning this system. I don't know yet if this is...
  20. R

    B How best to statistically analyse a PMT signal?

    Hello, I have recently started collecting photomultiplier tube (PMT) tube data, and I'm curious how best to analyse it (attached right). I also have a background capture (attached left). I am looking to get the relative total intensity and any other statistical analysis I could make. Is anyone...
  21. D

    ROC Curve: Background Rejection vs. Signal Efficiency

    Hello forum, I am reading this article on quantum machine learning. At one point in the article (page 7) they plot the ROC curve as background rejection vs. signal efficiency. Researching these concepts (since I did not understand them fully), I read that ROC curves should be plotted as TPR...
  22. A

    WiFi signal strength in Tunnels & Subways.

    As we see the WiFi signal strength is very low as observed in Tunnels, Subways & Undergrounds while we travel in a train or walk. We do not get the wireless network. Can there be any technical solutions for increasing the Wireless signal strength in these areas? Can this be considered a...
  23. M

    Signal Processing: Finding the auto-correlation

    Hi, I am working on the following problem from a textbook, but am getting stuck and am not sure how to proceed. Question: For the system below: v(t) = -cv(t - 1) + e(t) where ## e(t) ## is a zero mean white noise sequence with variance ##\sigma_e ^2## , determine the first two terms in the...
  24. rudransh verma

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    I am reading How computers work and I don’t grasp it. So how is light ultimately get transformed into a beautiful picture on screen in a digital camera? I have got D5200 Nikon. It’s a nice begineers camera.
  25. S

    I Interference of signal photons entangled with idlers

    Consider the following experiment: A photon hits a beam splitter, then a non-linear crystal (nichtlinearer Kristall - sorry, prepared the image in German) on each path that does parametric down conversion, splitting the photon into a signal and an idler. The idlers proceed to two detectors (D1...
  26. hquang001

    Engineering Signal & System CTFT: Find x(t) from X(ω)

    Given the CTFT X(ω): and here are my solution to find CT signal x(t) associated with the given CTFT , but i got stuck at the limit part
  27. B

    I Bias and dark current from a graph of mean signal vs exposure time

    I have a graph of mean signal (per pixel) vs exposure time (sec) for 8 different dark frames. I am being asked to find the bias in ADUs/pixel and the dark current in ADUs/sec/pixel and I am very confused on how I could get it. I know that the average of all of the mean signals is a rough guide...
  28. Jason-Li

    Comp Sci Signal to Noise Ratio Calculation in Decibels: How to Simplify with Decibels

    So pretty confident I understand part (a) however for part (b) I'm not sure if I have carried it out correctly if someone could give me a pointer? (b) 5dBmV Input as a voltage: 5=20Log(V/1mV) V=105/10 V=1.77827941mV Then the noise level is 20dbμV so changing to a voltage: 20=20*Log(V/1μV)...
  29. I

    Signal transfer properties of a spring-suspended platform?

    Ok, the last time I did something with physics, save for simple in-game simulation of gravity, was many moons ago in high school. I certainly did not learn to do this in high school, although two subjects I had there at a basic level, are touched: Waves and Classical mechanics. I have no idea...
  30. Twigg

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    Hi all! Forgive the sloppiness of this post, I'm on the road. Suppose you have a servo loop to stabilize parameter X. The issue is, when you measure X, you introduce some measurement error (let's say its white noise for the sake of argument). The noise causes a potential problem: since the...
  31. JamesBennettBeta

    Engineering Power and RMS Value of a Signal

    I need to calculate the power and RMS value of some equations. The problem is, I found two methods to do that and don't know which is the right method. I have few equations to find the power and RMS value, but here is one equation. $$x( t) \ =\ 7\cos\left( 20t+\frac{\pi }{2}\right),$$ Method...
  32. jack action

    Losing Wifi hotspot when connecting to signal

    New to Wifi. I bought the following wifi network adapter to make my PC a hotspot for my new smart phone to connect to: I could finally make it work by installing the driver from kelebek333 (from the PPA repo). I created a wifi connection with a method similar to this one. (The IPv4 & IPv6...
  33. berkeman

    Thoughts for a low-power 60Hz 120Vrms signal generator please

    For a metrology (power metering) calibration test fixture at work, I'm looking for a low-cost way to generate an isolated 120Vrms (or 240Vrms) sine wave to feed into the high-impedance mesasurement circuitry. The first test fixture used a $40k AC Mains generator instrument driving a 1kW load...
  34. tworitdash

    MATLAB How to change the frequency values inside a time domain signal phase

    The problem I am having is simple. I have a Gaussian spectrum initially. Like this, Process 1: S = m0/sqrt(2*pi*sigma^2) * exp(-(vel_axis - mu).^2/(2*sigma^2)); Here, mu is the mean velocity (frequency) and sigma is the standard deviation. vel_axis is the axis on which I am calculating this...
  35. S

    Mesh hole size calculation for RFID signal blocking

    For a project I am currently facing a problem that I find difficult to solve. I am developing a shielding portal that uses a mesh to blocks UHF RFID signals. I would like to use aluminium mesh due to it being lightweight and its attenuation properties. The frequency of UHF RFID signals in the...
  36. Lord Doppler

    Engineering Voltage Carrier Signal and Voltage Modulating Signal (AM)

    Hello everyone, I'm trying to find the Voltage Carrier Signal and Voltage Modulating Signal from the power spectrum of a AM signal 1) I change the scale dBW to W and I have this: From this I have that Pc (Power of the Carrier signal) is 50 W and I don't know how to continue with the...
  37. Z

    PWM signal generating circuit based on LM393

    This is a PWM signal generating circuit based on LM393. When I was running this LM393 circuit, I found that this circuit only consumes about 10 milliwatts of power at a voltage of 5V. Not only that, this circuit can work normally at 3.3V, 12V and 18V. But later I found that this circuit...
  38. hugo_faurand

    Get electrical signal of a piezoelectric with ultrasound

    Hello everyone ! I'm working on ultrasound probes, and I wanted to measure the electrical signal generated by a piezoelectric device (a transducer). Here is a sketch of the experiment : The goal of the experiment is to compare the electrical signal of the piezoelectric cell and compare it...
  39. M

    Signal Processing: DFT spectrum of sinusoid signals

    Hi, I was recently reading about the discrete Fourier transform and its application to a basic sinusoidal signal. If we know that it has an integer number of cycles in ## N ## samples (and thus no leakage), why would there be two peaks in the spectrum: one at ## m ## and another at ## N - m##...
  40. J

    Calculating Signal to Noise due to thermal noise

    The total noise from other sources and thermal is ##N = N_{other} + N_{thermal}## ##N_{175}/ N_{275} = (N_{other} + \sqrt{2k(175)R\Delta f})/( N_{other} + \sqrt{2k(275)R\Delta f})## I'm not sure how to simplify the expression as ##N_{other} ## is unknown. If I assume ##N_{total} =...
  41. F

    Engineering Sketch the spectrum of the DSB-SC signal

    Here's my work: Could someone please confirm my answer?
  42. PhysicsTest

    Power calculations of AC signal

    The below are the formulas i have seen from the book, but no particular formula for the peak power Instantaneous power ##p(t) = v(t) i(t) W## ->eq1 Average power ##p(t)_{avg} = \frac{\int_{t_0}^{t_0+T} p(t)dt} T W## ->eq2 a. Instantaneous power ##v(t) =A\sin(\omega t)## ->eq3 ##i(t) =...
  43. P

    Engineering Small signal AC modeling for a boost converter with resistive losses

    I've attached my attempts at the solution and the actual question below. I believe the only issue I am having is I don't know how to get rid of "I" in both my final inductor and capacitor equations as the HW states I shouldn't have anything in term of I. I believe I need to put "I" in terms of...
  44. snatchingthepi

    Advice for my first course in Discrete Signal Processing?

    Summary:: I'm about to take my first course in DSP. It is a one term graduate course using the 4th edition of Proakis. I'm about to take my first course in DSP. It is a one term graduate EE course using the 4th edition of Proakis. Does anyone with experience in this have useful advice for such...
  45. hilbert2

    Can Two RF Signal Sources Connected in Parallel Increase Signal Amplitude?

    Suppose I connect two identical signal generators to a dividing coaxial cable with two input ends and one output end. Is the signal amplitude from the output end the same as from one source, is it twice that or something in between? If this should be seen as analogous to two DC voltage sources...
  46. Euan12345

    Using phase difference to find the angle of a signal

    I want to locate an infrared signal using Angle on arrival (AoA), I have elected to use Phase Interferometry to achieve this, I am however struggling to understand how the phase difference (∆ϑ) is found. Can someone explain how I could find this?
  47. F

    Neuron's location and signal exchange with the rest of the body

    Hello, Just checking that my understanding is correct: the nervous system is formed by the central nervous system (CNS), which comprises the brain and the spinal cord, and by the peripheral nervous system (PNS) which bring signals from and to the CNS from and to the rest of the body. Both CNS...
  48. C

    I Gravity: Compounded Space (Time) Signal?

    Disclaimer - I am not an expert by any means so this might be as much about confirming my understanding as an inquiry from the general public... as such, it might be fairly conversational as I attempt to clearly communicate my thoughts and understanding. Please excuse this. If gravity is the...