This document discusses superheterodyne receivers and their operation. It describes how a superheterodyne receiver works by downconverting the received radio frequency signal to a lower intermediate frequency using frequency mixing in the receiver mixer with a local oscillator signal. The document outlines the key components of a superheterodyne receiver including the RF amplifier, mixer, local oscillator, intermediate frequency amplifier and detector. It also discusses issues like image frequencies and how they are dealt with in superheterodyne receiver design.

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Lecture 5
Superheterodyne Receivers.
Transmitters and Receivers
 Generalized Transmitters
 AM PM Generation
 Inphase and Quadrature Generation
 Superheterodyne Receiver
 Frequency Division Multiplexing

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Generalized Transmitters
   
     
     
     
   
Re cos
cos sin
Where
c
j t
c
c c
j t
v t g t e R t t t
v t x t t y t t
g t R t e x t jy t


 
 
  
 
 
 
  
Any type of modulated signal can be represented by
The complex envelope g(t) is a function of the modulating signal m(t)
Transmitter
Modulating
signal
Modulated
signal
Example:
( )
Type of Modulation g(m)
AM : [1 ( )]
PM : p
c
jD m t
c
A m t
A e


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Generalized Transmitters
R(t) and θ(t) are functions of the modulating signal m(t) as given in TABLE 4.1
Two canonical forms for the generalized transmitter:
     
cos c
v t R t t t
 
 
 
 
1. AM- PM Generation Technique: Envelope and phase functions are generated to modulate
the carrier as
Figure 4–27 Generalized transmitter using the AM–PM generation technique.

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Generalized Transmitters
x(t) and y(t) are functions of the modulating signal m(t) as given in TABLE 4.1
      t
t
y
t
t
x
t
v c
c 
 sin
cos 

2. Quadrature Generation Technique: Inphase and quadrature signals are generated to
modulate the carrier as
Fig. 4–28 Generalized transmitter using the quadrature generation technique.

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IQ (In-phase and Quadrature-phase) Detector

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Generalized Receivers
Receivers
Tuned Radio Frequency (TRF) Receiver:
Composed of RF amplifiers and detectors.
No frequency conversion
It is not often used.
Difficult to design tunable RF stages.
Difficult to obtain high gain RF amplifiers
Superheterodyne Receiver:
Downconvert RF signal to lower IF frequency
Main amplifixcation takes place at IF
 Two types of receivers:

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Tuned Radio Frequency (TRF) Receivers
Active
Tuning
Circuit
Detector
Circuit
Local
Oscillator
Bandpass
Filter
Baseband
Audio Amp
 Composed of RF amplifiers and detectors.
 No frequency conversion. It is not often used.
 Difficult to design tunable RF stages.
 Difficult to obtain high gain RF amplifiers

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Heterodyning
(Upconversion/
Downconversion)
Subsequent
Processing
(common)
All
Incoming
Frequencies
Fixed
Intermediate
Frequency
Heterodyning

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Superheterodyne Receivers
Superheterodyne Receiver Diagram

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Superheterodyne Receiver

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Superheterodyne Receivers
 The RF and IF frequency responses H1(f) and H2(f) are important in providing
the required reception characteristics.

12. The Mixer
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13. The Mixer
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14. The Mixer
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15. The Mixer: example
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Superheterodyne Receivers
fIF fIF
RF Response
IF Response

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Superheterodyne Receivers

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Superheterodyne Receiver Frequencies

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Superheterodyne Receiver Frequencies

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Frequency Conversion Process

23. Image frequency not a problem.
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Image Frequencies
Image frequency is also received

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Superheterodyne Receiver Typical Signal Levels