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Communication systems Laboratory Report 1

AM receiver

Aishwarya Rajendran 393334

Chee Hao Jun 41!"9

Aim:

Aishwarya Rajendran, Chee Hao Jun


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The aim of this lab work is to investigate some of the fundamental characteristics

parameters of an AM radio receiver, and to introduce swept-frequency measurement

techniques.

Theory:

The modulation is simply a method of combining two different signals and is used

in the transmitter section of a communication system. The two signals that are used

are the information signal and the carrier signal.

Amplitude Modulation is the simplest form of signal processing in which the carrier

amplitude is simply changed according to the amplitude of the information signal

hence the name Amplitude modulation.

Fig1.0.0 Modulation

When the information signals amplitude is increased the carrier signals amplitude is

increased and when the information signals amplitude is decreased the carrier

signals amplitude is decreased. The purpose of any detector or demodulator is to

recover the original modulating signal with the minimum of distortion and

interference. The simplest way of dealing with an AM signal is to use a simple half-

wave rectifier circuit. f the signal were simply passed through a diode to a resistive

load, the output would be a series of half-cycle pulses at carrier frequency. !o the

diode is followed by a filter, typically a capacitor and resistor in parallel. The

capacitor is charged by the diode almost to the peak value of the carrier cycles and

the output therefore follows the envelope of the amplitude modulation. "#$

Amplitude modulation applications [2]

Amplitude modulation is used in a variety of applications. %ven though it is not as

widely used as it was in previous years in its basic format it can nevertheless still be

found.



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Broadcast transmissions: AM is still widely used for broadcasting on the

long, medium and short wave bands. t is simple to demodulate and this

means that radio receivers capable of demodulating amplitude modulation are

cheap and simple to manufacture. &evertheless many people are moving to

high quality forms of transmission like frequency modulation, 'M or digitaltransmissions.

Air band radio: ()' transmissions for many airborne applications still use

AM. . t is used for ground to air radio communications as well as two way

radio links for ground staff as well.

Single sideband: Amplitude modulation in the form of single sideband is

still used for )' radio links. *sing a lower bandwidth and providing more

effective use of the transmitted power this form of modulation is still used formany point to point )' links.

Quadrature amplitude modulation: AM is widely used for the transmission

of data in everything from short range wireless links such as Wi-'i to cellular

telecommunications and much more. %ffectively it is formed by having two

carriers + out of phase.

These form some of the main uses of amplitude modulation. )owever in its basic

form, this form of modulation is being sued less as a result of its inefficient use of

both spectrum and power.

The Receiver ircuit



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Measurement !rocedure:

!art A

#. The AM signal is set up for ;)< AM with => depth of modulation and a

carrier frequency of about #M)< using !ignal 9enerators. The linearity of themodulator is checked using the 123 in #$% mode and the modulating and

modulated signals as inputs. A trape


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nitially, the !ignal 9enerator input on the receiver is used to set the 2' stage

8 to 63W. Then we tune the receiver for ma0imum audio ;)


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/. 'hat is the tuning range* As the tuning is adusted ho" "ell do the 3

)re4uency and the centre )re4uency o) the RF stage trac-*

Tuning rangeis the frequency range over which a receiver, transmitter

or other piece of equipment such as antennas/ can be adGusted by

means of a tuning control in consideration of required system

performance.

6imiting factors for the system performance within the tuning range

among others are

varying large signal behaviour of the receivers caused by thevariation of the receiver tuning components.

fast increase of oscillator phase noise and by e0tending the

tuning range, the impact on the overall system performance.

n !pectrum ranges with T( broadcast allocations, the tuning range of

some EM!% application relates to the bandwidth of one T( channel C

to @ M)


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Fig1.2 The 5,6 mode result.

Fig1.# 7"eep (and.



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Fig1.8 7ignal "ith least distortion.



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onclusion:

)ence from the e0periment conducted, the characteristics of the AM receiver have

been observed and recorded. t can be observed from the above that

#/ The modulator is linear.

:/ A91 improves quality of output signal, i.eH The signal is less distorted.

=/ The range can be adGusted according to design.



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Re)erences:

"#$ https744www.vidyarthiplus.com4vp4thread-:?#B.htmlI.(dM@D6Jqqkp

":$ http744www.radio-electronics.com4info4rf-technology-design4am-amplitude-

modulation4what-is-am-tutorial.php

"=$ http744www.radio-electronics.com4info4rf-technology-design4am-amplitude-

modulation4spectrum-bandwidth.php

3ther Re)erences :

";$ https744en.wikibooks.org4wiki41ommunicationK!ystems4AmplitudeKModulation

http://www.radio-electronics.com/info/rf-technology-design/am-amplitude-modulation/what-is-am-tutorial.phphttp://www.radio-electronics.com/info/rf-technology-design/am-amplitude-modulation/what-is-am-tutorial.phphttp://www.radio-electronics.com/info/rf-technology-design/am-amplitude-modulation/what-is-am-tutorial.phphttp://www.radio-electronics.com/info/rf-technology-design/am-amplitude-modulation/what-is-am-tutorial.php


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!art +

9ntroductory

Amplitude modulation AM/ is a modulationtechnique used in electronic communication, most

commonly for transmitting information via a radiocarrier wave.n amplitude modulation,

the amplitudesignal strength/ of the carrier wave is varied in proportion to the waveform being

transmitted. That waveform may, for instance, correspond to the sounds to be reproduced by

aloudspeaker, or the light intensity of television pi0els. This technique contrasts withfrequency

modulation, in which the frequencyof thecarrier signalis varied, andphase modulation, in which

itsphaseis varied.

Modulation is the addition of information to an electronic or optical carrier signal. A carrier signal

is one with a steady waveform -- constant height amplitude/ and frequency. nformation can be

added to the carrier by varying its amplitude, frequency, phase, polarim t ] . sin>c t;

y t; < A . sin >c t; = M?2 [ sin >c = >m; t ; = M?2 [ sin >c , >m; t;

The upper side(and is >c = >m and the lo"er side(and is >c @ >m

https://en.wikipedia.org/wiki/Modulationhttps://en.wikipedia.org/wiki/Radiohttps://en.wikipedia.org/wiki/Carrier_wavehttps://en.wikipedia.org/wiki/Carrier_wavehttps://en.wikipedia.org/wiki/Carrier_wavehttps://en.wikipedia.org/wiki/Amplitudehttps://en.wikipedia.org/wiki/Loudspeakerhttps://en.wikipedia.org/wiki/Loudspeakerhttps://en.wikipedia.org/wiki/Frequency_modulationhttps://en.wikipedia.org/wiki/Frequency_modulationhttps://en.wikipedia.org/wiki/Frequency_modulationhttps://en.wikipedia.org/wiki/Frequencyhttps://en.wikipedia.org/wiki/Carrier_signalhttps://en.wikipedia.org/wiki/Carrier_signalhttps://en.wikipedia.org/wiki/Phase_modulationhttps://en.wikipedia.org/wiki/Phase_(waves)https://en.wikipedia.org/wiki/Phase_(waves)https://en.wikipedia.org/wiki/Modulationhttps://en.wikipedia.org/wiki/Radiohttps://en.wikipedia.org/wiki/Carrier_wavehttps://en.wikipedia.org/wiki/Amplitudehttps://en.wikipedia.org/wiki/Loudspeakerhttps://en.wikipedia.org/wiki/Frequency_modulationhttps://en.wikipedia.org/wiki/Frequency_modulationhttps://en.wikipedia.org/wiki/Frequencyhttps://en.wikipedia.org/wiki/Carrier_signalhttps://en.wikipedia.org/wiki/Phase_modulationhttps://en.wikipedia.org/wiki/Phase_(waves)


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What is a sweep generatorL 5iagram # show the arrangement for a basic sweep generator.

Diagram 1

A basic system for the sweep generator is shown in figure #. A low-frequency sawtooth wave is

generated from some form of oscillator or waveform generator. The instantaneous voltage of the

sawtooth wave controls the frequency of an 2' oscillator with its centre frequency set at the

centre frequency of the device under test filter or ' channel etc/. 3ver a single sweep of

frequency, 2' output voltage from the device, as a function of time, is a plot of the filter response.Dy rectifying and 2' filtering in a simple AM detector, the output is converted to a 51 voltage

varying as a function of time and this voltage is applied to the vertical input of the 123. Dy

synchronising the sweep of the 123 with the sawtooth output, the device response is plotted on

the 123 screen.

This e0periment is to show how the modulation signal be generated and how can we mi0ed up the

carrier signal and the modulation signal. The charcteristics of an amplitude wave, determine the

gain, ' frequency and 63 frequency from part A. Eart D of the e0periment shows the the

modulated frequncy that been modulated where you can see the 5!D!1 modulation method,

which will show us the one carrier band suppressed by two sideband and moving from upper

sideband to loer sideband. We also can learn the mage reGection ratio and A91 operation throughpart D of the e0periment.

The AM receiver is tuned until it is synchroni


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= The function generator is set to produce a linear frequency sweep and is connected to the

12345!3 trough the e0ternal frequency. The modulated signal is shown in the 123 and

then it is switched to the MAT) M%&*. The output is shown at the picture below. The

double sideband and the carrier bandwidth sweep from upper frequency to lower

frequency back and forth.

The sweep rate of the modulated signal.



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The diagram above show the sweep rate in N format which is from center low frequency move

to high frequency then back to low, back and forth.



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; 2eceiver bandwidth from input to ' ouput F ?k) of the e0periment.


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