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V.RAGHAVENDRA12881A04C9
vaguldasraghava@gmail.com
Department of Electronics and Communication Engineering
TECHNICAL SEINAR C!"!NENT#IRECEIVERS
VARDHAMAN CO!"! O# !N"$N!!R$N"$A%T!N!!%S&
S'ams'a(ad) H*dera(ad # +,--/
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RECEIVERS
R!C!$V!R%
2
Radio r&c&iv&r is a' &l&c(ro'ic&)ui*m&'( +hich *ic, u*s (h& d&sir&dsig'al- r&&c( (h& u'+a'(&d sig'al a'dd&modula(& (h& carri&r sig'al (o g&( /ac,
(h& origi'al modula(i'g sig'al.
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RECEIVERS
Function of Radio Receivers
Intercept the incoming modulated signal
Select desired signal and reject unwanted signals
Amplify selected R.F signal
Detect modulated signal to get back original modulating
signal
Amplify modulating frequency signal
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RECEIVERS
Design of Receiver
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he radio recei!er has to be cost effecti!eRequirements"#as to work according to application as for A$
or F$ signalsune to and amplify desired radio stationFilter out all other stationsDemodulator has to work with all radio stations
regardless of carrier frequency
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RECEIVERS
Classification of Radio Receivers
Depending upon application
A$ Recei!ers % recei!e broadcast of speech or music from A$
transmitters which operate on long wa!e& medium wa!e or short wa!e
bands.
F$ Recei!ers ' recei!e broadcast programs from F$ transmitters
which operate in (#F or )#F bands.
*ommunication Recei!ers % used for reception of telegraph and short
wa!e telephone signals.
ele!ision Recei!ers % used to recei!e tele!ision broadcast in (#F or)#F bands.
Radar Recei!ers ' used to recei!e radio detection and ranging signals.
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RECEIVERS
Depending upon fundamental aspects
uned Radio Frequency +RF,Recei!ers
Super%heterodyne Recei!ers
uned Radio Frequency +RF, Recei!er"
*omposed of RF amplifiers and detectors.
-o frequency con!ersion
It is not often used.
Difficult to design tunable RF stages.
Difficult to obtain high gain RF amplifiers
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RECEIVERS
3
Super%hetrodyne Recei!er
Downcon!ert RF signal to lower IF frequency
$ain amplification takes place at IF
*ommunication Recei!er
Downcon!ert RF signal to two IF frequency
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RECEIVERS
TRF (Tuned Radio frequency) RECEIVER
8
u'&d radio5r&)u&'c6am*li7&r
d&(&c(orA. #.
am*li7&r
Modula(i'g sig'al
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RECEIVERS
RF recei!er includes an
RF stage a detector stage
and an audio stage .
wo or three RF amplifiers are required to filterand amplify the recei!ed signal to a le!el sufficient
to dri!e the detector stage.
9
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RECEIVERS
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RECEIVERS
RF section +Recei!er front end,
used to detect the signal
bandlimit the recei!ed RF signal
and amplifying the recei!ed RF signal.A$ detector
Demodulates the A$ wa!e and con!erts it to the
original information signal.Audio section
)sed to amplify the reco!ered signal
11
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RECEIVERS
Advantages of TRF
RF recei!ers are simple to design and allow the
broadcast frequency /0/ 1#2 to 3456 1#2.
#igh sensti!ity.
Disadvantages of TRFAt the higher frequency& it produces difficulty in design.
It has poor audio quality.
Drawbacks
Instability
(ariation in 78
9oor Selecti!ity
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RECEIVERS
SUER !ETR"D#$E RECEIVER
h& shor(comi'gs o5 (h& R# r&c&iv&r ar&ov&rcom& /6 (h& su*&r h&(&rod6'&r&c&iv&r.
1
R# am*li7&r
ocaloscilla(or
mi&r$#
am*li7&rd&(&c(or
A#am*li7&r
Modula(i'g sig'al
"a'g&d(u'i'g
5s
5o
$#5o: 5s
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RECEIVERS
Heterodyne ' to mix two frequencies together in a nonlinear
device or to transmit one frequency to another using
nonlinear mixing.
Also known as frequency conversion & high frequency down
con!erted to low frequency.+IF,A super heterodyne recei!er con!erts all incoming radio
frequency +RF, signals to a lower frequency known as an
intermediate frequency +IF,.
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RECEIVERS
1
RF section
*onsists of a pre%selector and an amplifier
9re%selector is a broad%tuned bandpass filter
with an adjustable center frequency used to rejectunwanted radio frequency and to reduce the
noise bandwidth.
RF amplifier determines the sensiti!ity of the
recei!er and a predominant factor in determiningthe noise figure for the recei!er.
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RECEIVERS
%i&er'converter section
*onsists of a radio%frequency oscillator and a mier.
*hoice of oscillator depends on the stability and
accuracy desired.$ier is a nonlinear de!ice to con!ert radio
frequency to intermediate frequencies +i.e.
heterodyning process,.
he shape of the en!elope& the bandwidth and theoriginal information contained in the en!elope
remains unchanged although the carrier and sideband
frequencies are translated from RF to IF.1
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RECEIVERS
IF section
*onsists of a series of IF amplifiers and bandpass
filters to achie!e most of the recei!er gain and
selecti!ity.he IF is always lower than the RF because it is
easier and less epensi!e to construct high%gain&
stable amplifiers for low frequency signals.
IF amplifiers are also less likely to oscillate than
their RF counterparts.
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RECEIVERS
FR:;):-*< *=-(:RSI=- in the mier stage is
identical to the frequency con!ersion in the modulator
ecept that in the recei!er& the frequencies are down%
con!erted rather that up%con!erted.
In the mier& RF signals are combined with the local
oscillator frequency
he local oscillator is designed such that its frequency
of oscillation is always abo!e or below the desired RFcarrier by an amount equal to the IF center frequency.
herefore the difference of RF and oscillator frequency
is always equal to the IF frequency
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RECEIVERS
he adjustment for the center frequency of the pre%selector and the
local oscillator frequency are gang%tune +the two adjustments are tied
together so that single adjustment will change the center frequency of
the pre%selector and at the same time change the local oscillator,
when local oscillator frequency is tuned abo!e the RF ' high side
injection
when local oscillator frequency is tuned below the RF ' low side
injection
$athematically epressed "
#igh side injection
>ow side injection
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RECEIVERS
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RECEIVERS
COM;AR$%ON
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R# R&c&iv&r
No 5r&)u&'c6co'v&rsio'
No $# 5r&)u&'c6
$'s(a/ili(6 -varia(io' i' cul( (o d&sig'(u'a/l& R# s(ag&s.
Rar&l6 us&d
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RECEIVERS
COM;AR$%$ON
22
%u*&r h&(rod6'&R&c&iv&r#r&)u&'c6
co'v&rsio'
Do+'co'v&r( R#sig'al (o lo+&r $#5r&)u&'c6
No i's(a/ili(6- varia(io' i'
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RECEIVERS
C!ARACTERISTICS "F RADI"
RECEIVERS
2
Sensiti!ity
Selecti!ity
Fidelity
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RECEIVERS
Sensitivity
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Ability to amplify weak signals.$inimum RF signal le!el that can be detected at the input
to the recei!er and still produce a usable demodulatedinformation signal.
7roadcast recei!ers? radio recei!ers should ha!e reasonablyhigh sensiti!ity so that it may ha!e good response to thedesired signal
7ut should not ha!e ecessi!ely high sensiti!ity otherwiseit will pick up all undesired noise signals.
It is function of recei!er gain and measures in decibels.
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RECEIVERS
2
Sensiti!ity of a recei!er is epressed in micro!olts of therecei!ed signal.
ypical sensiti!ity for commercial broadcast%band A$
recei!er is /6 @(.
Sensiti!ity of the recei!er depends on "
3. -oise power present at the input to the recei!er
.Recei!er noise figure
0.7andwidth impro!ement factor of the recei!er
he best way to impro!e the sensiti!ity is to
reduce the noise le!el.
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RECEIVERS
2
Selecti!ity of radio recei!er is its ability to differentiatedesired signal from unwanted signals.
Selectivity
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RECEIVERS
0idelit*
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Fidelity is defined as ' a measure of the ability of acommunication system to produce an exact replica of the
original source information at the output of the receiver.
Any !ariations in the demodulated signal that are not in the
original information signal is considered as distortion.Radio recei!er should ha!e high fidelity or accuracy.
:ample% In an A.$. broadcast the maimum audio
frequency is / 1#2 hence recei!er with good fidelity must
produce entire frequency up to /1#2.
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RECEIVERS
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HAN? O
References1
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