asst commsys
TRANSCRIPT
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Communication systems Laboratory Report 1
AM receiver
Aishwarya Rajendran 393334
Chee Hao Jun 41!"9
Aim:
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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
Aishwarya Rajendran, Chee Hao Jun
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
Aishwarya Rajendran, Chee Hao Jun
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.
Aishwarya Rajendran, Chee Hao Jun