What is Modulation: Definition and 144 Discussions

In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a separate signal called the modulation signal that typically contains information to be transmitted. For example, the modulation signal might be an audio signal representing sound from a microphone, a video signal representing moving images from a video camera, or a digital signal representing a sequence of binary digits, a bitstream from a computer. The carrier is higher in frequency than the modulation signal. The purpose of modulation is to impress the information on the carrier wave, which is used to carry the information to another location. In radio communication the modulated carrier is transmitted through space as a radio wave to a radio receiver. Another purpose is to transmit multiple channels of information through a single communication medium, using frequency division multiplexing (FDM). For example in cable television which uses FDM, many carrier signals carrying different television channels are transported through a single cable to customers. Since each carrier occupies a different frequency, the channels do not interfere with each other. At the destination end, the carrier signal is demodulated to extract the information bearing modulation signal.
A modulator is a device or circuit that performs modulation. A demodulator (sometimes detector) is a circuit that performs demodulation, the inverse of modulation. A modem (from modulator–demodulator), used in bidirectional communication, can perform both operations. The frequency band occupied by the modulation signal is called the baseband, while the higher frequency band occupied by the modulated carrier is called the passband.
In analog modulation an analog modulation signal is impressed on the carrier. Examples are amplitude modulation (AM) in which the amplitude (strength) of the carrier wave is varied by the modulation signal, and frequency modulation (FM) in which the frequency of the carrier wave is varied by the modulation signal. These were the earliest types of modulation, and are used to transmit an audio signal representing sound, in AM and FM radio broadcasting. More recent systems use digital modulation, which impresses a digital signal consisting of a sequence of binary digits (bits), a bitstream, on the carrier. In frequency shift keying (FSK) modulation, used in computer buses and telemetry, the carrier signal is periodically shifted between two frequencies that represent the two binary digits. In digital baseband modulation (line coding) used to transmit data in serial computer bus cables and wired LAN computer networks such as Ethernet, the voltage on the line is switched between two amplitudes (voltage levels) representing the two binary digits, 0 and 1, and the carrier (clock) frequency is combined with the data. A more complicated digital modulation method that employs multiple carriers, orthogonal frequency division multiplexing (OFDM), is used in WiFi networks, digital radio stations and digital cable television transmission.
In music production, the term modulation has a different meaning: it is the process of gradually changing sound properties in order to reproduce a sense of movement and depth in audio recordings. It involves the use of a source signal (known as a modulator) to control another signal (a carrier) through a variety of sound effects and methods of synthesis. With singers and other vocalists, modulation means to modify characteristics of their voices during a performance, such as loudness or pitch.

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  1. S

    I Gravitational field modulation of a moving mass

    If a mass is moving it has a wavelength - my question is, is the gravitational field of the mass then modulated accordingly ?
  2. 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...
  3. Twigg

    A Imperfectly Phase-Modulated Light / Residual Amplitude Modulation

    I'm trying to understand this paper and others on the same topic. I struggle conceptually with their first equation, which is an expression for an imperfectly phase modulated optical field from an electro-optic phase modulator (EOM) that is contaminated with a little bit of amplitude modulation...
  4. Narayanan KR

    A Different Way to Achieve Electron Velocity Modulation in a Klystron

    Please Notice That the Toroid Coil is Outside the Discharge Tube and yet able to influence electrons moving inside the Tube.
  5. tworitdash

    A Fourier Transform of an exponential function with sine modulation

    I want to know the frequency domain spectrum of an exponential which is modulated with a sine function that is changing with time. The time-domain form is, s(t) = e^{j \frac{4\pi}{\lambda} \mu \frac{\sin(\Omega t)}{\Omega}} Here, \mu , \Omega and \lambda are constants. A quick...
  6. A

    AM, FM modulation, sidebands question

    Hi, I wanted to refresh some knowledge, some years ago @berkeman helped me out with this , thanks. 1) In an AM modulation a fixed frequency carrier wave is amplitude modulated , where the amplitude represents the lower frequency information signal, this modulation of a signal that is amplitude...
  7. F

    Engineering I have some doubts regarding AM Modulation

    3) Suppose, V DSB-SC as follows: Are the following spectrums correct? The carrier frequencies are given as an example.
  8. M

    Frequency Shift Key Modulation: how are the carrier frequencies chosen

    Question: For frequency shift key modulation in the binary case, how are the two carrier frequencies chosen? From online reading, I have seen that the carriers are chosen to be different but also with the goal of minimising bandwidth and without any overlaps of the spectra, etc. However, I...
  9. D

    Space vector modulation, motor control, implementation question

    Hello, I am after some help to try and understand SVM implementation is a micro that controls a motor. As I understand it one of the advantages of using space vector modulation over sinusoidal PWM modulation in motor control is that it can control the phase voltages such that the line-to-line...
  10. lottotlyl

    Engineering Calculate R and C in Envelope Detector Circuit (AM Modulation)

    1. Add impedance in parallel of capacitor and resistor Z_rc = 1/((-wC/j) + 1/R) = (jR)/(j-wRC) 2. Ohm's law for relationship of i_d, Z_rc, and Vo Vo = i_d * (jR)/(j-wRC) Unsure how to do the rest? Thanks.
  11. R

    How Does Amplitude Modulation Work in Radio Transmission?

    Is the carrier wave modulated or in other words "modified" with the information signal? If so how exactly is this done? I can't find or maybe I am looking at the wrong things but I don't understand how this is done. I know that AM is modulated with the amplitude and FM is modulated by the...
  12. J

    Channel length modulation in a MOSFET

    Hi, I'm struggling to understand how channel length modulation takes place in mosfet. The books n internet said that as drain side is positive, there is less potential difference between positive gate and positive drain, while there is more potential difference between positive gate and zero...
  13. DariusP

    Self-phase modulation question (nonlinear optics)

    Okay, so SPM (self-phase modulation) is an effect that happens when an ultrashort pulse travels through a medium and it leads to a change in that pulse's frequency spectrum. It is explained that it occurs because an ultrashort pulse somehow induces a varying change of refractive index and this...
  14. N

    Phase modulation and intermodulation anomaly *Plots inside*

    I have a MATLAB script for modelling a two tone signal (a sum of two sinusoids) going through a non linear transfer function (such as an amplifier). The amplitude of a signal is amplified non linearly, and also the phase is modified depending on the input power of the signal. The two sinusoids...
  15. sherzadakhan

    Visible light communication modulation schemes?

    visible light contains a range of frequencies i.e not of single frequency, then how visible light is used as a carrier in Visible light communication. Further more is it possible to modulate light (in tera HZ frequency range). what modulation scheme is possible and how it is implemented in VLC...
  16. Cocoleia

    DSB-SC Signal from Homework Statement

    Homework Statement I am giving the following signal: and asked to get the DSB-SC signal of this Homework Equations 3. The Attempt at a Solution [/B] So, I know a few things. My prof writes that I would have to multiply my original signal out and then take the Fourier transforms...
  17. U

    Direct Modulation and Photon Lifetime - Laser

    Hello, There is a thing I struggle to understand on laser physics. There is a modulation method called direct modulation for semiconductor lasers where by changing the current we modulate the light which is emitted form the laser cavity. There is a picture below It is stated in...
  18. F

    Optimizing Bandwidth in AM Modulation

    Homework Statement The Attempt at a Solution What should the bandwidth be over here? Confused since there is no mention of carrier frequency.
  19. T

    Does a Variable capacitance switch exist?

    Hi, I want to be able to vary the amount of capacitance in a circuit, ideally I'd like to be able to turn a knob to tap a bank of capacitors, something like the attached picture.Is there some sort of switching or device available that anyone can think of which does this? Cheers
  20. LLT71

    AM vs Beats: Why Do We Need a Carrier Wave?

    not sure if this is dumb question but I was reading something about "beats" and saw some similarities with AM so I got to a conclusion if you have just two waves (same phase) with similar frequencies etc. sin(x)+sin(1.1x) you can maintain AM or...not? if not, why not? if yes than why do we need...
  21. Khaled Kord

    AM Modulation: Understanding Envelopes and Detection

    i just had my first Signals processing Lecture, during AM modulation part my prof said that: V_AM(t) = (V_main(t) + 1) * V_Carrier while V_Carrier = sin (omega * t) 1-is there a proof that we get the envelop of a function by adding one then multiplying by some trig value? 2- what's the...
  22. SSGD

    Microcontroller Pulse Width Modulation to Analog DC Voltage

    What are some effective ways to convert a Pulse Width Modulation from a Microcontroller to a DC Voltage as a function of Pulse Width? 1. Use a low pass filter to remove the unwanted harmonics and leave only the 0th term of the Fourier Series. What produces a better DC Voltage an Active or a...
  23. M

    Amplitude modulation of signals with [suppressed] carrier

    Hello everybody, I'm a little bit confused about two types of amplitude modulation. We distinguish here: Case I : Amplitude Modulation with suppressed carrier (https://en.wikipedia.org/wiki/Double-sideband_suppressed-carrier_transmission): Case II : Amplitude modulation with carrier: Now...
  24. MYMLA

    How Do You Calculate Modulation Index and Sideband Amplitudes in FM Synthesis?

    Homework Statement [/B] A pure tone (sine) carrier signal of 440 Hz is frequency modulated by another sine wave of frequency 440Hz with an amplitude of 1760. (a) For the steady-state portion of the output signal generated by synthesis above, calculate: i) the deviation and ii) the Index of...
  25. Tulio Cesar

    B Amplitude Modulation: Unique Frequency & Bandwidth

    1) I am studying modulation of carrier waves, but I still can't understand something: knowing that in AM the carrier wave has only one frequency and just only its amplitudes vary according to variations in modulating signal amplitudes, why AM carrier waves have bandwidth if the frequency is...
  26. Tulio Cesar

    Understanding the Relationship Between Time and Frequency in Modulation?

    1) I understood how variations in the amplitude of modulating signals are represented in the carrier wave, but I didn't get how frequency variations of the modulating signal are represented, as both AM and FM modulations seem do not care about it. Ex: How to distinguish a high vocal range (high...
  27. P

    How to Calculate Amplitude Modulation Index Without Prefix

    Homework Statement Let's say we have a carrier signal xc(t) = AcCos(ωct) And there is a modulating signal or we can call it the information signal xm(t) = Am Cos(ωmt) and the modulation index is given as 0.8 How to write the modulated signal? It's really confusing as many people give different...
  28. E

    Cross Phase Modulation in Optical Fibers (Fiber Optics)

    Hello everyone. I have been practicing for my exam in fiber optics, and stumbled upon the following question: We have a transmission system with 3 channels, composed of a single mode fiber and a dispersion compensation fiber. Specifications are given for each. We need to calculate the channel's...
  29. onion3000

    Help with understanding modulation in AM, FM and PM radio

    I have a few questions about AM, FM and PM. 1. If FM (or PM) radio modifies the frequency of the signal, how is the signal picked up without having to change the frequency constantly? 2. If PM modulates phase, which modulates frequency, what is the difference between PM and FM? 3. Why is AM...
  30. rude man

    Insights Modulation vs. Beating Confusion - Comments

    rude man submitted a new PF Insights post Modulation vs. Beating Confusion Continue reading the Original PF Insights Post.
  31. B

    Communication systems -- Find the Modulation Depth....

    Homework Statement Hello, the plot in the image shows a modulated signal s(t), with one period of the modulating signal m(t). The mean value of m(t) is equal to zero . Its asked me to find the modulated index, the amplitude of the carrier, the equation of the message(m(t)) and the kind of...
  32. I

    Amplitude modulation and amplifier efficiency

    " A intelligence signal is amplified by a 80% efficient amplifier before being combined with a 12kW carrier to generate the AM signal. if it is desired to operate at 100% modulation, what is the DC input power at the modulator" The choices are a: 12kW b. 7.14kW c.7.5kW d. 15kW my solution...
  33. C

    Armstrong's Modulation Method vs Wideband FM

    Hey guys, quick question. Is the modulation scheme described here (Armstrong's Phase Modulation) simply wide band FM? This Wikipedia article lists the following patent for Ed Armstrong for "Armstrong's Phase Method" and "Wideband FM" 1933 Patent: http://www.google.com/patents/US1941068
  34. J

    What is the Probability of Error in an Adaptive Modulation System?

    Homework Statement 2. Homework Equations The Attempt at a Solution I can't figure out how to get those numbers, I think I have to convert from dB when actually calculating it but I'm unable to get those ones. I have PQPSK = 0.502368 P16QAM = 0.0526855 P64QAM = 0.000004 Pno = 0.4450
  35. Prashasti

    Modulation of waves (Communication Systems)

    Please look at the attachments below. I shall use the word "modulation" instead of "amplitude modulation" since I've been taught about AM only. So, my question is, in the first image (that I've attached), the messenger wave (which is modulated with the high frequency carrier wave) as well as...
  36. Prashasti

    Amplitude Modulation of a wave

    Homework Statement I am utterly confused. When I was reading my textbook , I found something unacceptable. While deriving an expression for a modulated wave, It's been given that "A sinusoidal carrier wave can be represented as c (t) = Ac sin (ωt + Φ) where c (t) is the signal strength of...
  37. RAHIL008

    Why Is Binary Modulation Preferred in Visible Light Communication?

    I read that for VLC, they use toggling the LEDs ON/OFF to represent binaries. Why cannot we modulate the visible light like radio waves.
  38. E

    Doppler effect in modulated signals

    Hello, If been for a while trying to find information about how Doppler effect affects modulated signals. When a transmitter is moving relative to a receiver, the receiver will have a shift in the carrier frequency that will vary as the transmitter gets closer or moves away from the...
  39. U

    Cubic phase modulation of a gaussian beam

    Hi all, I'm reading a paper on light sheet microscopy, i won't go into detail here but they are generating the light sheet by use of an Airy beam. They are using a term i don't understand when describing how the airy beam is generated. Quote "An Airy beam can be generated through the Fourier...
  40. D

    MOSFET Channel length modulation

    In Sedra&Smith's microelectronic circuits they have the following expression for the drain current in a MOSFET in saturation iD = 1/2µpCox(W/L)Vov2(1+VDS/VA)But I don't see how this can be correct. Wikipedia also has another expression, see...
  41. B

    Sub atomic collision and modulation

    when two sub atomic particles collide, being waves as well as particles. at point of collision do they act like radio waves and modulate each other. Are the resultant particle/waves produced by collision equivalent to upper and lower sidebands (as in AM modulation) or bessel functions (as in FM...
  42. O

    Average power in Amplitude Modulation

    Homework Statement how the overall power becomes lesser when one side band is taken away by the bandpass filter and also how it limits the bandwidth of the signal Homework Equations The Attempt at a Solution there is will be the trade off between power and bandwidth. Vdc and Vm...
  43. F

    What causes the capture effect in FM modulation?

    My understanding of the FM capture effect is that if an FM receiver receives two, on frequency signals, it suppresses the weaker one and demodulates the stronger one, given that the difference in signal strength is significant enough. This differs from the case of AM where the two signals are...
  44. K

    Amplitude modulation - why is ωc ωm necessary?

    amplitude modulation -- why is ωc >> ωm necessary? i just want to ask why is ωc >> ωm is necessary for a good amplitude modulation
  45. S

    Good modulation - Why do we need Fp fs?

    Homework Statement Why do we need Fp>>fs for a good modulation, where Fp is the frequency of the Carrier signal and fs the frequency of the originalsignal The Attempt at a Solution If we had Fp≤ fs or less there is no use of modulation, we need a big frequency so waves can go long...
  46. S

    Typical carrier frequency for amplitude modulation

    What is a typical carrier frequency for amplitude modulation? In particular, for amplitude modulation in spectroscopy.
  47. A

    Why cosine wave for phase deviation in phase modulation?

    Phase modulation is a system in which the amplitude of the modulated carrier is kept constant, while its phase and rate of phase change are varied by the modulating signal. By the definition of phase modulation, the amount by which the carrier phase is varied from its unmodulated value, called...
  48. A

    Exploring the Concepts of AM Modulation

    AM amplitude modulation--- Hi everyone, I am learning AM recently, but I have some question that keep troubling me.. 1. We know that AM wave is produced by the multiplication of carrier wave and modulation wave. But why does the equation of AM wave is not a direct multiplication of Vm×Vc...
  49. S

    Single-phase full-bridge inverter with multiple pulse width modulation

    Hey guys. I have been theoretically playing around with a single phase full bridge inverter. What I wanted to do was determine the waveforms for the current going through each of the components (ie. the four diodes and the four thyristors). I assumed all of them were ideal. Since I have no idea...
  50. M

    What Happens When Two Wavelengths Are Modulated at the Same Frequency?

    hi what would happen if i modulated two wavelengths with the same intensity modulation frequency? for example if i had 2.0um light and 1.5um light and modulated them both with the same frequency, would sidebands develop around each wavelength? or would they interfer in a more complicated...