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.
Hi,
I have here an elenco s-1325 analog oscilloscope. I am hacking it into a display unit for one of my projects and have designed two raster scans for the x and y-axis (the oscilloscope is running in x-y mode). I now need to be able to modulate the intensity of the electron beam so as to form...
Homework Statement
A given DSB-LC AM transmitter develops an unmodulated power output of 1kW across a 50 ohm resistive load. When a sinusoidal test tone of 5V is applied to the input of the modulator, it is found that the spectral line for each sideband carrier in the magnitude spectrum is...
In the amplitude modulation equation,
V=(Ec+Ei*coswt)coswt
I don't understand why the instantaneous value of information signal is used. Shouldnt it be peak value as that would give the maximum value (amplitude)?
hi gang,
just a quick clarification please :)
was looking at the Wiki articke on Frequency modulation
http://en.wikipedia.org/wiki/Frequency_modulation
This comment is in the Modulation Index section...
The signal frequency is referring to the applied audio signal doing the...
hello all. If one uses polarization modulation of radio waves does this imply a broad frequency spectrum knowing the carrier frequency and amplitude remain the same only the direction of the electric field is being changed ?
I have read a lot of articles on pulse width modulation and I am none the wiser as to how it generates different voltages by simply varying the pulse width of the waveform. What I read was that if you have a rectangular wave train of some amplitude and change the 'ON' period the "NET" voltage...
Homework Statement
See figure attached.
Homework Equations
The Attempt at a Solution
See pdf attached for my attempt at the solution.
I'm a little confused as to how to draw the phase spectrum for y(t). Would it simply be a line equation of,
-\frac{\pi}{6000}f \pm...
the 2 signals shown are used for modulating ( DSB-SC) a carrier with frequency fc.
Now i need to find the similarities and differences between their time domain representation.
Clearly the both will have same envelope. Now i tried for the difference part but could not find it. One possibility...
In our lab we are to measure speed of light by making a light signal travel through optical fiber. At one end there is the transmitter, which will output the light signal into the fiber, and it will also "modulate" the signal. According to my lab manual, "The reason that the signal is made to...
Hello Everyone!
About Amplitude Modulation, Usually it is seen in the book or web that (e.g. http://www.ni.com/white-paper/3002/en )
'''' The message signal can be represented by m(t) = Mb cos(2πfb + φ)
and the carrier signal can be represented by c(t) = Ac cos(2πfc + φ),
Now...
I have an image taken with a camera. I know the f/#, focal length, CCD characteristics, and an approximate distance to my scene. I computed the modulation transfer function but I am trying to map the pixel space to cy/m and having trouble. I essentially want to determine the cutoff spatial...
Q1. A device with input x(t) and output y(t) is characterized by y(t) = x(t). If a FM signal with frequency deviation 90 Khz and modulating frequency 5 Khz is applied to the input terminals of the device then what will be the bandwidth of the output signal received ?
What i did was...
Why isn't it possible to invent a custom digital modulation scheme that would use much less RF bandwidth than all the schemes available? What are the limiting factors that do not allow for high data rates to be coded so that the occupied bandwidth is much less than all the others like ASK, PSK...
I thought that the frequency was constant for AM modulation, and just the amplitude was modulated. So why are there a range of frequency's (side bands around the baseband) when the signal is plotted on a frequency domain graph?
Hey Everyone,
Can someone explain to me the natural of amplitude modulation in regards to sound. As in one modulator frequencies' amplitude modulating the amplitude of a carrier frequency. Because at low frequencies the modulator only affects the carrier in a way that makes its volume go up...
Hey everyone,
I am trying to understand the phenomena behind the technique of using amplitude modulation in sound synthesis. When you have two frequencies, for example, w1=200hz and w2=300hz, and you use the amplitude of one (w1) to modulate the amplitude of the other (w2), it creates 3...
Hi
I have read a paper, where they distinguish between wavelength and frequency modulation. More specifically:
"FMS (frequency modulation spectroscopy) can be broken down into two regimes: wavelength modulation (WM) and frequency modulation (FM). In the case of WM, the modulation depth is...
Hello, I have attached a diagram of QPSK modulation angles. I was wondering how would the red and yellow dots be interpreted.
Those dots are not exactly on either of the 4 different phase angles. But I understand QPSK has a discrimination of 90 degrees so would the red equate to 45 degrees and...
A signal,
x(t)=4sin(0.5\pi t),
is transmitted by a DSB modulator. What is the frequency range of the carrier wave corresponding to the given message (data) signal?
My basic misunderstanding here is if the given signal is the message signal that I should demodulate from a DSB modulated...
Hi
On page 11 of this book, http://books.google.dk/books?id=Wv2OIC_SaDUC&printsec=frontcover&hl=da#v=onepage&q&f=false, it is stated that:
"The phase modulation has an additional advantage: The first two sidebands at frequencies ω+Ω and ω-Ω have equal amplitudes, but opposite phases. A lock-in...
http://pokit.org/get/c2d0bb4355d353d0ff5bc47c7158ce45.jpg
Suppose we have an op-amp configured as a comparator.
At -ive lead, we are sending the carrier wave, specifically in my example, triangle wave.
At +ive lead, we are sending the input signal, the one that we want to modulate...
Hello, I am trying to understand how the most basic form of AM works.
Can someone please confirm if my brief description below is essentially correct ?
I know that upper and lower sidebands are created when a signal is modulated onto a carrier frequency. These sidebands result in a signal that...
ive been trying to proof the modulation index for Am transmission, it goes like this
Vmax = a(1+u)
Vmin = a(1-u)
it basicilly describes the amount of infromation in the total power transmitted and should allways be between 0 & 1
eventually the answer should come out to be
u =...
Homework Statement
Find the Fourier Transforms
f1(t) = \frac{2}{3-it}
f2(t) = \frac{2}{3-it}cos(t)
Homework Equations
F{H(t)et} = \frac{-1}{-1-it}
F{f(t)cos(\omegat)} = \frac{1}{2}[F(\omega+\omega0+F(\omega-\omega0)]
The Attempt at a Solution
For the first question, my...
Hi All,
I wonder if the modulation of RF waves (Amplitude Modulation, Frequency Modulation, and Phase Modulation) can be explained in terms of photons.
Thanks,
Srini
For Amplitude Modulation, it is understood that the bandwidth of a passband signal is always twice as much as that of a baseband signal, for example
if the bandwidth/max frequency of a message/baseband signal is 1 kHz and a carrier of 1 MHz is modulated with this baseband, then a "sum"...
Hi guys,
I need some help. I have the following modulation equations:
\Re:-\zeta a+\lambda a\cos 2\delta-\eta \cos (\delta+\phi)=0
and
\Im:\omega a+\lambda a\sin 2\delta-\eta \sin (\delta+\phi)=0
which, with proper manipulation (i.e. by squaring and adding and/or diving them with each...
Homework Statement
I'm going to do the experiment that generates a square wave using the 555 timer this weekend, but I'm wondering why sometimes we have to modulate the square waves to sin waves, and decode them in the terminal receiver?
Could square wave(or any other non-sin wave) itself...
Hi,
This is a general question rather than an explicit question, so apologies for not using the template.
I'm a bit confused by the relationship between frequency and data rate in a communications system and wondered if someone could help clarify please.
Say I want to achieve a data...
If I modulate a pulse X(t) with a.) a sine wave or b.) a cosine wave, I have the frequency spectrum expressions
a.) \frac{1}{2j}[X(f-f_0)-X(f+f_0)]
b.) \frac{1}{2}[X(f-f_0)+X(f+f_0)]
When I plot these for a pulse, I see a difference in the magnitude spectrum, but I should not expect...
In the context of electromagnetic wave propagation in ferromagnetic medium, what is meant by magnetostatic spin wave? This terminology one came across in the wave modulation in ferromagnetic medium.
Thanks in well advance..
Homework Statement
A carrier wave has an rms voltage of 10V. It is modulated by a signal having compenents of frequencies f1 and f2 and the rms voltage of the modulated carrier rises to 11.5V. If the modulation index due to one of the components is 60%, calculate the modulation index for...
I have a small electrode (5x5mm) connected to 200V via a 1Meg resistor.
A charged object is passed 1mm away from the electrode to produce a signal of 100mV.
The static capacitance changes from 25fF to 150fF.
How much of the 100nA drawn from the electric field is due to the change in...
Hi guys, my first post on these forums.
I am learning electronics and am still very new to this all.
My current tinker project is to learn how regular tv remote controls work.
So far I have understood that the remote sends blinking IR pulses through an 940 nm LED.
The remote uses...
Hi guys, I'm currently generating OFDM signal and send it to DAC and then upconvert them to 1 GHz carrier signal.
I want to multiplex several of them, like say I upconvert them to 1 GHz, 800 MHz, 1.2 GHz, which represents 3 different signals, then multiplex them together using FDM, is it...
While reading about frequency modulation, I found that it was clearly written that the amplitude of the carrier wave remains unchanged. However, i didn't find a statement stating that the frequency of the carrier wave remains unchanged for amplitude modulation. So, is the frequency of the...
Homework Statement
A binary signal is filtered with r = 1 and then modulated onto a carrier for transmission at
9600 bps.
a) What is the bandwidth requirements if the modulation is BFSK with f1 = 100kHz and f2 = 120kHz?
(Note: FSK bandwidth is B = 2fd + (1+r)R )
b) Using the same...
Hi everyone, plx help me on this!
I've worked out frequency modulation but can't understand amplitude modulation ...
A sinusoidal carrier wave has a frequency of 750kHz and an unmodulated amplitude of 4.0V. The carrier wave is to be amplitude-modulated by a sinusoidal signal of frequency...
fastest modulation: laser diode vs LED...
Hello Forum,
in the telecomm industry, the most common and economical form of modulation is direct modulation, acting on the current operating LEDs or diode lasers.
Using an external intensity modulator (OOK), like a super fast chopper, the...
Actually i m new to electrical sciences, can anyone please explain me the working principle of a PWM?? and its applications , please provide any relevant links concerning it. Thanks in advance
Hi there, I'm a bit beffudled by some of the workings of a MOSFET transistor.
First of all, in the saturation region of operation, I understand that the inversion channel is "pinched off" as it approaches the drain. In other words the inversion channel thickness tapers off as it approaches the...
We know to make antenna dimension reasonably small, we modulate baseband signal with a high frequency carrier. Antenna size as far as I know is in the order of one tenth of carrier signal wavelength. For example, for a 3 GHz carrier signal, receiver antanna size is 1 cm.
But, in frequency...
Hello,
So I was studying for my exam and came across this exercice we did in class and which I really don't know how we got the answer.
It says that if we have a FM with a carrier frequency of 4MHz, and the bandwidth is 400KHz, what is then the maximum deviation.. The answer is 200KHz...
We have recently developed a motion sensor that introduces charge into an electric field. From the 200V (containment field) we derive a modulation of 100mV. Although the sensor has passed pre-production tests we are struggling to come up with a simple formula to describe the operation. Can...
Hello everybody!
I have a question on amplitude modulation.
Homework Statement
I'm given an input signal m(t)=0.2sin(1000*Pi*t)+0.5cos(\sqrt{2}*1000*Pi*t)
and I'm asked to sketch the AM waveform and to find the modulation percentage.Homework Equations
The Attempt at a Solution
I'm asking for...