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RADIO PRINCIPLES
RADIO RECEIVERS
1.0. INTRODUCTION
In communications, a radio receiver is an electronic device that receives desired radio waves
and rejects the unwanted signals and converts the information carried by radio waves to a
usable or original form. Since modulation took place at the transmitter, the reverse process,
demodulation is performed in the receiver to recover the original modulated signal. It is used
with an antenna. The antenna intercepts radio waves (electromagnetic waves) and converts
them to tiny alternating currents which are applied to the receiver, and the receiver extracts the
desired information. The receiver uses electronic filters to separate the desired radio frequency
signal from all the other signals picked up by the antenna, an electronic amplifier to increase
the power of the signal for further processing, and finally recovers the desired information
through demodulation.
The information produced by the receiver may be in the form of sound (an audio signal),
images (a video signal) or data (a digital signal). A radio receiver may be a separate piece of
electronic equipment, or an electronic circuit within another device. Devices that contain radio
receivers include television sets, radar equipment, two-way radios, cell phones, wireless
computer networks, GPS navigation devices, satellite dishes, radio telescopes, bluetooth
enabled devices, garage door openers, baby monitors..etc
Function of Radio Receivers includes;
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
Some of the design requirements for a receiver include;
The radio receiver has to be cost effective
Has to work according to application as for AM or FM signals
Tune to and amplify desired radio station
Filter out all other stations
Demodulator has to work with all radio stations regardless of carrier frequency
2.0. CLASSIFICATION OF RADIO RECEIVERS
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Receivers can be classified depending on the type of modulation employed, be it AM, FM,
SSB, PM, e.t.c, the application, e.g. like communication receiver and by the type of a receiver.
There are two types of receivers;
a) Tuned Radio Frequency (TRF) Receiver
This type of receiver is a simple logical receiver. It is composed of RF amplifiers stage,
detectors stage and A.F amplifiers stage. In this type of receiver, there is no frequency
conversion. It is not often used because of it is difficult to design tunable RF stages
and also to obtain high gain RF amplifiers except as a fixed-frequency receiver in
special applications.
RF section (Receiver front end)
- Used to detect the signal and amplifying the received RF signal and is band
limited the received RF signal
- Two or three RF amplifiers are required to filter and amplify the received
signal to a level sufficient to drive the detector stage.
Detector
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- Demodulates the received signal and converts it to the original information
signal.
Audio section
- Used to amplify the recovered signal
Advantages of TRF
TRF receivers are simple to design and allow the broadcast frequency 535 KHz
to 1640 KHz.
High sensitivity.
Disadvantages of TRF
At the higher frequency, it produces difficulty in design.
It has poor audio quality.
Drawbacks/problems
- Instability
- Variation in BW
- Poor Selectivity/insufficient adjacent-frequency rejection
b) Superheterodyne Receiver
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Heterodyne means to mix two frequencies together in a nonlinear device (such as
transistor, diode mixer e.t.c.) or to transmit one frequency to another using nonlinear
mixing. Mixing two frequencies creates two new frequencies, one at the sum of the two
frequencies mixed and the other at their difference.
Heterodyne receiver is a telecommunication receiver which uses this effect to produce
frequency shifts. The receiver also known as frequency conversion, the high frequency
is down converted to low frequency (IF) and the main amplification takes place at IF
stage. A super heterodyne receiver converts all incoming radio frequency (RF) signals
to a lower frequency known as an intermediate frequency (IF). Super-heterodyne
receivers have superior characteristics to simpler receiver types in frequency stability
and selectivity. The shortcomings of the TRF receiver are overcome by the super
heterodyne receiver. These drawbacks overcomed are;
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RADIO PRINCIPLES
RADIO RECEIVERS
1.0. INTRODUCTION
In communications, a radio receiver is an electronic device that receives desired radio waves
and rejects the unwanted signals and converts the information carried by radio waves to a
usable or original form. Since modulation took place at the transmitter, the reverse process,
demodulation is performed in the receiver to recover the original modulated signal. It is used
with an antenna. The antenna intercepts radio waves (electromagnetic waves) and converts
them to tiny alternating currents which are applied to the receiver, and the receiver extracts the
desired information. The receiver uses electronic filters to separate the desired radio frequency
signal from all the other signals picked up by the antenna, an electronic amplifier to increase
the power of the signal for further processing, and finally recovers the desired information
through demodulation.
The information produced by the receiver may be in the form of sound (an audio signal),
images (a video signal) or data (a digital signal). A radio receiver may be a separate piece of
electronic equipment, or an electronic circuit within another device. Devices that contain radio
receivers include television sets, radar equipment, two-way radios, cell phones, wireless
computer networks, GPS navigation devices, satellite dishes, radio telescopes, bluetooth
enabled devices, garage door openers, baby monitors..etc
Function of Radio Receivers includes;
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
Some of the design requirements for a receiver include;
The radio receiver has to be cost effective
Has to work according to application as for AM or FM signals
Tune to and amplify desired radio station
Filter out all other stations
Demodulator has to work with all radio stations regardless of carrier frequency
2.0. CLASSIFICATION OF RADIO RECEIVERS
1
, RESTRICTED
Receivers can be classified depending on the type of modulation employed, be it AM, FM,
SSB, PM, e.t.c, the application, e.g. like communication receiver and by the type of a receiver.
There are two types of receivers;
a) Tuned Radio Frequency (TRF) Receiver
This type of receiver is a simple logical receiver. It is composed of RF amplifiers stage,
detectors stage and A.F amplifiers stage. In this type of receiver, there is no frequency
conversion. It is not often used because of it is difficult to design tunable RF stages
and also to obtain high gain RF amplifiers except as a fixed-frequency receiver in
special applications.
RF section (Receiver front end)
- Used to detect the signal and amplifying the received RF signal and is band
limited the received RF signal
- Two or three RF amplifiers are required to filter and amplify the received
signal to a level sufficient to drive the detector stage.
Detector
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- Demodulates the received signal and converts it to the original information
signal.
Audio section
- Used to amplify the recovered signal
Advantages of TRF
TRF receivers are simple to design and allow the broadcast frequency 535 KHz
to 1640 KHz.
High sensitivity.
Disadvantages of TRF
At the higher frequency, it produces difficulty in design.
It has poor audio quality.
Drawbacks/problems
- Instability
- Variation in BW
- Poor Selectivity/insufficient adjacent-frequency rejection
b) Superheterodyne Receiver
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Heterodyne means to mix two frequencies together in a nonlinear device (such as
transistor, diode mixer e.t.c.) or to transmit one frequency to another using nonlinear
mixing. Mixing two frequencies creates two new frequencies, one at the sum of the two
frequencies mixed and the other at their difference.
Heterodyne receiver is a telecommunication receiver which uses this effect to produce
frequency shifts. The receiver also known as frequency conversion, the high frequency
is down converted to low frequency (IF) and the main amplification takes place at IF
stage. A super heterodyne receiver converts all incoming radio frequency (RF) signals
to a lower frequency known as an intermediate frequency (IF). Super-heterodyne
receivers have superior characteristics to simpler receiver types in frequency stability
and selectivity. The shortcomings of the TRF receiver are overcome by the super
heterodyne receiver. These drawbacks overcomed are;
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