# 0.4 Analog (de)modulation  (Page 3/9)

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The output of this program is shown in [link] . The slowly increasing sinusoidal “message” $w\left(t\right)$ is modulated by the carrier $c\left(t\right)$ at ${f}_{c}=1000$ Hz. The heart of the modulation is the point-by-point multiplication of the message and the carrierin the fifth line. This product $v\left(t\right)$ is shown in [link] (c). The enveloping operation is accomplished byapplying a lowpass filter to the real part of $2v\left(t\right){e}^{j2\pi {f}_{c}t}$ . This recovers the original message signal, though it is offset by 1 and delayedby the linear filter.

Using AMlarge.m , plot the spectrum of the message $w\left(t\right)$ , the spectrum of the carrier $c\left(t\right)$ , and the spectrum of the received signal $v\left(t\right)$ . What is the spectrum of the envelope? How close are your results to the theoretical predictions in [link] ?

One of the advantages of transmissions using AM with large carrier is that there is no needto know the (exact) phase or frequency of the transmitted signal. Verify this using AMlarge.m .

1. Change the phase of the transmitted signal; for instance, let c=cos(2*pi* fc*t+phase) with phase=0.1, 0.5, pi/3, pi/2, pi , and verify that the recovered envelope remains unchanged.
2. Change the frequency of the transmitted signal; for instance, let c=cos(2* pi*(fc+g)*t) with g=10, -10, 100, -100 , and verify that the recovered envelope remains unchanged.Can g be too large? An undulation message (top) is modulated by a carrier (b). The composite signal is shown in (c), andthe output of an envelope detector is shown in (d).

Create your own message signal $w\left(t\right)$ , and rerun AMlarge.m . Repeat Exercise  [link] with this new message. What differences do you see?

In AMlarge.m , verify that the original message w and the recovered envelope envv are offset by 1, except at the end points where the filter does not have enough data.Hint: the delay induced by the linear filter is approximately fl /2.

The principal advantage of transmission systems that use AM with a large carrier is that exact synchronization is not needed;the phase and frequency of the transmitter need not be known at the receiver, as was demonstratedin Exercise  [link] . This means that the receiver can be simplerthan when synchronization circuitry is required. The main disadvantage is thatadding the carrier into the signal increases the power needed for transmission but does not increase the amount ofuseful information transmitted.Here is a clear engineering tradeoff; the value of the wasted signal strength must be balanced againstthe cost of the receiver.

## Amplitude modulation with suppressed carrier

It is also possible to use AM without adding the carrier.Consider the transmitted/modulated signal

$v\left(t\right)={A}_{c}w\left(t\right)\mathrm{cos}\left(2\pi {f}_{c}t\right)$

diagrammed in [link] (a), in which the message $w\left(t\right)$ is mixed with the cosine carrier. Direct application of the frequency shift property of Fouriertransforms [link] shows that the spectrum of the received signal is

$V\left(f\right)=\frac{1}{2}{A}_{c}W\left(f+{f}_{c}\right)+\frac{1}{2}{A}_{c}W\left(f-{f}_{c}\right).$

As with AM with large carrier, the upconverted signal $v\left(t\right)$ for AM with suppressed carrier has twice the bandwidth of the original message signal. If the original messageoccupies the frequencies between $±B$ Hz, then the modulated messagehas support between ${f}_{c}-B$ and ${f}_{c}+B$ , a bandwidth of $2B$ . See [link] .

what is variations in raman spectra for nanomaterials
I only see partial conversation and what's the question here!
what about nanotechnology for water purification
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
what is the stm
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
what is Nano technology ?
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
why we need to study biomolecules, molecular biology in nanotechnology?
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
why?
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
what does nano mean?
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
Daniel
how did you get the value of 2000N.What calculations are needed to arrive at it
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