# 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] .

#### Questions & Answers

anyone know any internet site where one can find nanotechnology papers?
research.net
kanaga
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 to know photocatalytic properties of tio2 nanoparticles...what to do now
it is a goid question and i want to know the answer as well
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
for screen printed electrodes ?
SUYASH
What is lattice structure?
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
what's the easiest and fastest way to the synthesize AgNP?
China
Cied
types of nano material
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
how did you get the value of 2000N.What calculations are needed to arrive at it
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