SlideShare a Scribd company logo
1 of 12
Download to read offline
Operational Diagrams
of
Radio Transmitters & Receivers

Professor Lance Breger and Professor Kenneth Markowitz
TABLE OF CONTENTS
Page

Preface . .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 4 - 5
Introduction. .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 6 - 7
Operation of Adder-Antenna Transmitter . .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 9
Operation of AM Transmitter in General. .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 10
Operation of AM Transmitter Showing AM Modulator in Detail. .  .  .  .  . 11
Operation of TRF AM Receiver. .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 12
Operation of Superheterodyne AM Receiver . .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 13
Operation of PM Transmitter. .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 14
Operation of FM Transmitter in General. .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 15
Operation of FM Transmitter with Indirect Modulation. .  .  .  .  .  .  .  .  .  .  .  . 16
Operation of FM Transmitter with Direct Modulation. .  .  .  .  .  .  .  .  .  .  .  .  . 17
Operation of FM Receiver. .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 18 - 19
Operation of PM Receiver. .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 20
Conclusion.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 21
 .
	

Copyright

2004 Lance Breger

3
PREFACE
	
The purpose of these diagrams is to graphically explain the overall operation of AM, PM, and
FM communications systems using very little mathematics. This explanation is accomplished by tracing a
simple sinusoidal signal through all stages of each system. Although students who are "mathematically
challenged" will find these diagrams very helpful, most students who are beginning the study of electrical
communications systems can benefit from these same diagrams. More advanced courses can also use
these diagrams as a basis on which to organize and present abstract mathematics.

●

S
 tudents: M. B. Suranga Perera, Nikolay Ostrovskiy and Johnny Lam. They produced the professional
graphics in these vector art diagrams and created the pages.

To pay these students, the following persons or organizations at NYCCT generously offered financial
advice or funds:

The unique features of these diagrams are the following:
presenting the signal in both the time domain and frequency domain together at each stage of the communication process
● using a color code to show the distribution of information in the signals in both the time domain and
frequency domain simultaneously.
●

Former Dean Phyllis Sperling of the School of Technology  Design

●

	

●

Former Dean Annette Schaefer of the School of Arts and Sciences

● Professor


Joseph Rosen, head of the Freshman Year Program at NYCCT and
current acting Dean of the School of Liberal Arts and Sciences

	
The history of preparing this booklet is a long one. Before beginning the arduous work of producing these diagrams, we inspected about 70 standard textbooks on electrical communications to determine
whether we could save ourselves a lot of effort by simply using their diagrams; but none of those books
contained the above simultaneous diagrams. Some of the basic ideas underlying these diagrams were presented by us in 2001 at a conference of FIE (Frontiers In Education) in Reno, Nevada. Completion of this
booklet took about three more years of devoted labor, research, and collaboration.

Ms. Jewel Escobar, Executive Director of NYCCT Foundation

●

	
These diagrams were produced by translating the statements and logic from the following two
textbooks into simple graphics:
Modern Electronic Communication, 6th edition,
by Gary M. Miller, Prentice Hall, Upper Saddle River, NJ, 1999.
Electronic Communication Techniques, 4th edition,
by Paul H. Young, Prentice Hall, Upper Saddle River, NJ, 1999.
Graphing calculators were used to plot equations, and some of the particularly difficult steps were
checked by simulation using Multisim or by TIMS (Telecommunications Instructional Modeling Systems)

●

F
 ederal Work Study Program administered by the Department of Financial Aid at NYCCT.

●

T
 he Department of Architectural Technology deserves thanks for allowing almost all of the computer
drawings to be done on their computers using Adobe Illustrator.

●

D
 ean Robin Bargar

●

P
 rofessor Joel Mason, Chair of the Department of Advertising Design and Graphic Arts (ADGA), for allowing the intermediate and final color prints to be produced on the ADGA Print Laboratory's DocuColor 2060
press under a grant by Xerox.	

	 our comments will be used to produce an improved second edition of this booklet. We, the authors, would
Y

greatly appreciate being informed of any mistakes or of other comments about this booklet by emailing me:
bookletauthor@hotmail.com

	
During the preparation of this booklet, many others at the New York City College of Technology
(NYCCT) aided us. Helpful technical suggestions were offered by several of our colleagues:
●
●

Professor John Fehling

●

Professor Misza Kalechman

●

Professor Mohammed Kouar

●

Professor Mohammad Razani.

●

4

Professor Aron Goykadosh

P
 rofessor Lloyd Carr, who initiated and directed the vector file production, page imposition for printed
versions and the final pdf files. Professor Carr also helped to edit the final text.

5
INTRODUCTION
	
To help the reader use this set of diagrams of AM, PM, and FM efficiently, two sets of comments
have been added to the diagrams to elucidate them. The first set of comments applies generally to all the
diagrams and is included in this introduction. The second set of comments applies specifically to individual
diagrams, and each of these comments is inserted in the main text adjacent to the diagram that it explains.
GENERAL COMMENTS
	
The main objective of these diagrams is to help students understand the operation of transmitters and
receivers of various types by showing how the signal changes as it propagates through each stage in a series
of cascaded stages, whose electrical operating characteristics are also usually shown in the diagrams. For
simplicity the information signal is assumed to be a sinusoid. The signal itself is shown in two adjacent forms:
• n time domain,
i
i.e., how the signal changes in time as it would be observed on an oscilloscope inserted at a particular
point in the system
• n frequency domain,
i
i.e., how the signal changes in sinusoidal composition as it would be observed on a spectrum analyzer
inserted into the system at the same point as the above oscilloscope. [The diagrams on the FM receiver
and the PM receiver violate this rule slightly by showing noise separately.]
Being able to relate these two views of the signal is a major lesson in communications, since beginners usually think only in the time domain; but experts in communications usually think in the more abstract frequency
domain. In addition, the mathematical equations for important signals in the time domain have also been
inserted to help the student correlate this information with the two graphic forms of the signal.
	
The general structure of each diagram is as follows. In the left-most column, the various cascaded
stages are arranged vertically from top to bottom. Arrows represent the signal flow between the stages. To
the right of each arrow and at the same level are the two graphic representations of the signal itself, i.e., first
in the time domain and then in the frequency domain. Thus, the three columns of the diagram are arranged
from left to right from most concrete to most abstract. In addition, the operating characteristics of some
devices, e.g., amplifiers and filters, are also shown. These characteristics are shown in the domain where
their operation is most easily represented. For example, the operation of filters is most easily described in
the frequency domain; while the operation of a limiter in an FM receiver is most easily described in the time
domain.
(continued on page 7)

6

	
A color code has been used to draw the various signals in these diagrams mainly to help students
trace the flow of information, which is vital to understanding the operation of a communications system. Of
course, the real signals or waves are invisible, i.e., colorless, to our eyes; but the colors arbitrarily assigned
to the signals in these diagrams show their content of information.
●

Blue signals in the time domain or in the frequency domain indicate the pure information signal.

●

Red signals indicate the pure carrier wave.

● Purple signals show that the information signal and the carrier wave have been mixed, just as blue and red

colors mix to form the color purple.
●

Green indicates the operating characteristic in graphs of various devices, like amplifiers and filters.

●

Black signals indicate noise.

A somewhat different color code has been used for the arrows showing signal propagation in the left-most
column. As above, red arrows mean the carrier wave; and blue arrows mean the information signal. However,
the mixed state of carrier plus information is indicated by the split arrow, half being red and half being blue.
In symbols and equations used these diagrams, the red carrier wave is symbolized by c; and the blue
information signal is symbolized by m (not i as is used by many texts) since m stands for the modulating
signal, i.e., the information.
	
The scale of the vertical voltage axis in the time domain differs from voltage scale in the frequency
domain because otherwise the size of the bars in the frequency domain would have been too small to have
been read easily. To remind the student that these scales are different, an arrow has been drawn and labeled
as amplitude in the earliest sinusoid in the time domain in each diagram. [Amplitude in all these drawings
means the amplitude of a sinusoid, not of any other function.] This arrow then reminds the reader of how big
the amplitude in the frequency domain really is in the time domain.
	
In general, the wave forms and operating characteristics shown in these diagrams are mere cartoons, or idealizations, of reality, not exact pictures. This approximation is appropriate because exact representations would be difficult to understand. For example, in the case of FM as seen in the frequency domain,
if the various sidebands were drawn to scale, the sidebands could not easily be distinguished from the carrier
in the size of diagrams drawn here.
	
Finally, the amount of detail shown varies from diagram to diagram.
For example, some diagrams show the operating characteristics of ideal amplifiers; others do not. In each
case, our aim was to show as much detail as possible without cluttering the diagram.

7
OPERATION OF ADDER-ANTENNA TRANSMITTER

This diagram shows a transmitter that does not work to emphasize the reason that real transmitters do work. That is, this transmitter leaves the information, which is shown in blue, at low frequencies so that it can not be radiated; the radiating antenna only
broadcasts high frequencies. This implies that only the high-frequency carrier wave is broadcast, which is useless. The aim of a
communications system is to broadcast information, not to broadcast the pure carrier wave!

fm

fc
Amplitude (Volts)
Voltage (Volts)

Em

Ec

fm

fc Frequency

Time
(Sec.)
Low Frequency
Information

High Frequency
Carrier

Voltage (Volts)

(Hz)

Amplitude (Volts)

Combined Signal

(fm  fc )

Ec

fm

Time
(Sec.)

Em

fc Frequency

(Hz)

Antenna Gain
1

Antenna removes low frequencies

0

Frequency
(Hz)
Amplitude (Volts)
Voltage (Volts)

Ec

Time
(Sec.)
High Frequency
Carrier

8

Copyright © 2004 Lance Breger

fm

fc Frequency

(Hz)

9
OPERATION OF AM TRANSMITTER IN GENERAL

This transmitter works, while the previous one fails, because the AM modulator raises the information, shown in blue, to high
frequencies so that it can be broadcast along with the carrier by the high-pass antenna. The AM modulator automatically raises
the frequency of the information when encoding information by changing the amplitude of the carrier sinusoid.

fm

fc

This diagram differs from the previous one only in that it shows the details of the AM modulator. The operation of the modulator consists of two stages. First, the information signal and carrier are passed through a nonlinear device, e.g., a transistor or
diode, to generate the required upper and lower sidebands along with unnecessary sinusoids of many other frequencies. [The
diagram mentions an ideal nonlinear device; ideal means that most of the unnecessary harmonics have been omitted for
clarity.] Second, a high-frequency bandpass filter removes the unnecessary sinusoids and passes only those in the required
AM-modulated carrier.

Amplitude (Volts)
Voltage (Volts)

Em

Ec

Time
(Sec.)

Amplitude

Low Frequency
Information

AM
MODULATOR

OPERATION OF AM TRANSMITTER SHOWING AM MODULATOR IN DETAIL

High Frequency
Carrier

fm

fc

fm

fc

Amplitude

Frequency
(Hz)
AM MODULATOR
IDEAL
NON-LINEAR
DEVICE

Amplitude (Volts)
Ec

Time
(Sec.)

Em/2

Voltage (Volts)

Em/2

AMPLIFIER

K1

Amplifier gain = constant K1.

Voltage (Volts)

fm

Combined Signal

ANTENNA

Antenna passes only high frequencies.

Voltage (Volts)

Combined Signal

Amplitude (Volts)

(Hz)

Antenna Gain

ANTENNA

Antenna passes only high frequencies.

Time
(Sec.)

10

(fc-fm) fc (fc+fm) Frequency

fm

Voltage (Volts)

Combined Signal

Frequency
(Hz)

Amplitude (Volts)

0

Frequency
(Hz)

K1

Time
(Sec.)

(Hz)

Antenna Gain

(Hz)

Amplifier Gain

Amplifier gain = constant K1.

(fc-fm) fc (fc+fm) Frequency

Em/2

(fc-fm) fc (fc+fm) Frequency

fm

Voltage (Volts)

Ec

Em/2

Combined Signal

AMPLIFIER

Frequency
(Hz)

Amplitude Input (Volts)

(fm  fc )

Time
(Sec.)

1

0

Time
(Sec.)

Frequency
(Hz)

Amplitude (Volts)

Voltage (Volts)

(Hz)

Gain of Filter

Filter selects carrier and sidebands.

Em/2

(fc-fm) fc (fc+fm) Frequency

dc fm

BAND-PASS
FILTER

Frequency
(Hz)

Ec
Em/2

Time
(Sec.)

(Hz)

Amplifier Gain

fc

Amplitude (Volts)

(fc-fm) fc (fc+fm) Frequency

fm

Ec

fm

High Frequency
Carrier (red)

Combined Signal

(fm  fc )

Em

Time
(Sec.)

Low Frequency
Information (blue)

Voltage (Volts)

Amplitude (Volts)

Voltage (Volts)

1

0

Amplitude (Volts)

Frequency
(Hz)

Time
(Sec.)

fm

Combined Signal

(fc-fm) fc (fc+fm) Frequency

(Hz)

Copyright © 2004 Lance Breger

fm

(fc-fm) fc (fc+fm) Frequency

(Hz)

Copyright © 2004 Lance Breger

Copyright © 2004 Lance Breger

11
OPERATION OF TRF AM RECEIVER

OPERATION OF SUPERHETERODYNE AM RECEIVER

The main point of interest here is the structure of the AM detector. The basic structure of the AM detector and of the AM modulator
are the same: a nonlinear device followed by a bandpass filter. In the detector, the nonlinear device reproduces the original signal
sinusoid from the AM-modulated carrier and also produces many unnecessary sinusoids of other frequencies; the filter removes
these unnecessary sinusoids and passes the original information signal. The main difference between the AM modulator and
the AM detector is the frequency band passed by the filter: the modulator passes a band at high radio frequencies; the detector
passes a band at low audio frequencies.

ANTENNA

The structure of this receiver and that of the TRF receiver are very similar. The main difference is the frequency range in which
most of the signal amplification is done. The TRF receiver amplifies the signal at the same high radio frequencies at which it is
received initially by the antenna. Unfortunately, amplification at these high frequencies is inefficient, i.e., the amplifier gains are
low. To correct this error, the superheterodyne receiver does most of its signal amplification at a lower intermediate frequency
band for greater efficiency. Since this intermediate frequency band is the fixed passband of the filter in the IF amplifier, each
incoming signal must be lowered to this fixed intermediate frequency band by using a frequency converter, which consists of
a mixer (which is a nonlinear device) connected to an oscillator of variable frequency. This is called the local oscillator. By
changing the oscillator frequency appropriately, any station's signal can be lowered to the given intermediate frequency range
for efficient amplification.

Amplitude (Volts)
Voltage (Volts)

ANTENNA

Time
(Sec.)

(fc-fm) fc (fc+fm)Frequency
(Hz)

(fc-fm) fc (fc+fm)Frequency

RF AMP. 
bandpass filter

(Hz)

Amplitude (Volts)

Voltage (Volts)

Amplitude (Volts)

Voltage (Volts)

Time
(Sec.)
RF AMP 
.
bandpass filter

fLO

Amplitude (Volts)

Voltage (Volts)
Time
(Sec.)

LO

(fc-fm) fc (fc+fm)Frequency

(Hz)

Time
(Sec.)

NON-LINEAR
DEVICE (mixer)

Amplitude (Volts)

Voltage (Volts)

(Hz)

IDEAL
NON-LINEAR
DEVICE

Amplitude (Volts)

Voltage (Volts)

(fi-fm) fi (fi+fm)

IF amplifier

FILTER

Gain

Filter selects band around fi
the intermediate frequency.

(fi-fm) fi (fi+fm)

dc fm

(fc-fm) fc (fc+fm) Frequency

(Hz)

Gain

IF AMPLIFIER
PER SE

0

Amplitude (Volts)

Frequency
(Hz)

(fi-fm) fi (fi+fm)

DETECTOR
IDEAL
NON-LINEAR
DEVICE

Time
(Sec.)

dc fm

fm

Frequency
(Hz)

BAND-PASS
FILTER

(fi-fm) fi (fi+fm)

Amplitude (Volts)

Amplitude

Amplitude (Volts)
Time
(Sec.)

fm

Copyright

Copyright © 2004 Lance Breger

Frequency
(Hz)

Time
(Sec.)
fm

Copyright © 2004 Lance Breger

Frequency
(Hz)

Amplitude (Volts)

Voltage (Volts)

Amplitude

Frequency
(Hz)
SPEAKER

12

0

AUDIO
AMPLIFIER

fm

Frequency
(Hz)

1

Filter selects information signal

Voltage (Volts)

Time
(Sec.)

SPEAKER

Frequency
(Hz)

Amplitude (Volts)

Voltage (Volts)

Gain

Voltage (Volts)

Frequency
(Hz)

Time
(Sec.)

Time
(Sec.)

AUDIO
AMPLIFIER

Frequency
(Hz)

Amplitude (Volts)

Voltage (Volts)

1

Filter selects information signal.

Amplitude

0

Time
(Sec.)

Time
(Sec.)

Voltage (Volts)

(fc-fm) fc (fc+fm)Frequency
(Hz)

1

Amplitude (Volts)

Voltage (Volts)

BAND-PASS
FILTER

fLO

Time
(Sec.)

(fc-fm) fc (fc+fm)Frequency

DETECTOR

(fm  fi  fc  fLO)

Frequency
(Hz)

2004 Lance Breger

Copyright © 2004 Lance Breger

13
OPERATION OF PM TRANSMITTER

Both the FM transmitter and PM transmitter have similar structures. The main difference between them is the kind of modulator
used. FM modulators encode information by changing the frequency of the carrier wave. PM modulators encode information by
changing the phase of the carrier wave.

fm

fc

Amplitude (Volts)
Voltage (Volts)
Amplitude

Low Frequency
Information

OPERATION OF FM TRANSMITTER IN GENERAL

FM transmitters differ from PM transmitters in yet another way: before the information signal is applied to the modulator, only
in the FM transmitter is the signal passed through a preemphasis stage. Preemphasis distorts the signal by amplifying high frequencies more than low frequencies, i.e., the high frequencies are emphasized before modulation. The purpose of this signal
distortion in the FM transmitter is to facilitate later on in the FM receiver the detection of these high frequencies of the signal in
the presence of much high-frequency noise generated in the FM demodulator in the receiver.

fm

Em

Amplitude

Time
(Sec.)
High Frequency
Carrier

Time
(Sec.)

Low Frequency
Information

fm

Frequency
(Hz)

Gain

fc

fm

Frequency
(Hz)

PREEMPHASIS

Preemphasis amplifies high frequencies
to overcome high-frequency noise
in FM receiver

PM
MODULATOR

1

Frequency
(Hz)

Amplitude (Volts)
Voltage (Volts)

Amplitude (Volts)

Voltage (Volts)
Time
(Sec.)
Combined Signal

EcJ2(m)

...

fc

EcJ1(m)
EcJ2(m)

fm

Frequency
(Hz)

Amplitude (Volts)

...

Voltage (Volts)

Em

Ec

fm

fc

Time
(Sec.)

(Hz)

Low Frequency
Information

Amplifier Gain

High Frequency
Carrier

Amplitude (Volts)

Amplitude (Volts)

Voltage (Volts)

Frequency
(Hz)

EcJ0(m)

Time
(Sec.)

EcJ1(m)

Combined Signal

Time
(Sec.)
Combined Signal

fm

fm

(fc-2fm) (fc-fm) fc (fc+fm) (fc+2fm) Frequency

(Hz)

(Hz)

Time
(Sec.)

Combined Signal

...

fm

0

...

(fc-2fm) (fc-fm) fc (fc+fm) (fc+2fm)Frequency

(Hz)

Antenna Gain

Amplitude (Volts)

Frequency
(Hz)

1

ANTENNA

Antenna passes only high frequencies.
0

Frequency
(Hz)

Voltage (Volts)

Time
(Sec.)

14

(fc-2fm) (fc-fm) fc (fc+fm) (fc+2fm) Frequency

Amplitude (Volts)

Antenna passes only high frequencies.

Combined Signal

...

EcJ2(m)

Voltage (Volts)

1

Voltage (Volts)

EcJ1(m)

AMPLIFIER

...

Antenna Gain

ANTENNA

Ec
...J2(m)

(fm  fc )

...

Frequency
(Hz)

FM
MODULATOR

K1

Voltage (Volts)

Low Frequency
Information

(fc-2fm) (fc-fm) fc (fc+fm) (fc+2fm) Frequency

Amplifier gain = constant K1.

Em
Time
(Sec.)

EcJ0(m)
EcJ1(m)

fm

(fm  fc )
AMPLIFIER

Amplitude (Volts)

Voltage (Volts)

Ec

...

fm

Amplitude (Volts)
Time
(Sec.)

...

(fc-2fm) (fc-fm) fc (fc+fm) (fc+2fm) Frequency

Combined Signal

fm

(Hz)

Copyright © 2004 Lance Breger

Copyright © 2004 Lance Breger

...

...

(fc-2fm) (fc-fm) fc (fc+fm) (fc+2fm)Frequency

(Hz)

15
OPERATION OF FM TRANSMITTER WITH INDIRECT MODULATION

There are two general types of FM modulators. In the first type, i.e., those with indirect modulation, the carrier wave is produced by a very stable oscillator located outside the modulator itself, as is also done in PM modulation. The indirect FM modulator is just a PM modulator preceded by a special stage that integrates the information signal; this integration is carried out by
passing the signal through an amplifier whose gain is inversely proportional to frequency.

OPERATION OF FM TRANSMITTER WITH DIRECT MODULATION

In the second type of FM modulation, i.e., direct modulation, the oscillator producing the carrier wave, is actually incorporated
into the FM modulator itself. Otherwise, FM transmitters with direct modulation and those with indirect modulation are essentially
the same.

fm

fm

Amplitude (Volts)
Voltage (Volts)
Amplitude

Time
(Sec.)

Amplitude

Low Frequency Information

PREEMPHASIS

fm

Preemphasis amplifies high frequencies
to overcome high-frequency noise
in FM receiver.

fm

Gain

Frequency
(Hz)

PREEMPHASIS

Preemphasis amplifies high frequencies
to overcome high-frequency noise
in FM receiver.
Voltage (Volts)

fm

Frequency
(Hz)

Gain

FM Modulator
Integrator multiplies amplitude by 1/f
and phase-shifts sinusoid by -900.

-90

0

High Frequency
Carrier

Low Frequency
Information

Em

fc

EcJ0(m)

Combined Signal

fm

(fm  fc )

...

AMPLIFIER

...

(Hz)

Amplitude (Volts)
Frequency
(Hz)

Time
(Sec.)

Time
(Sec.)
Combined Signal

Antenna Gain

...

(fc-2fm) (fc-fm) fc (fc+fm) (fc+2fm)Frequency
(Hz)

ANTENNA

(Hz)

0

Voltage (Volts)

Amplitude (Volts)

Frequency
(Hz)

Amplitude (Volts)

Frequency
(Hz)

Time
(Sec.)

Time
(Sec.)

16

...

(fc-2fm) (fc-fm) fc (fc+fm) (fc+2fm) Frequency

1

Antenna passes only high frequencies.

0

Combined Signal

...

Antenna Gain

1

Antenna passes only high frequencies.

Voltage (Volts)

fm

Combined Signal

fm

Frequency
(Hz)

Frequency
(Hz)

Voltage (Volts)

...

...

(fc-2fm) (fc-fm) fc (fc+fm) (fc+2fm)

(fc-2fm) (fc-fm) fc (fc+fm) (fc+2fm) Frequency

Amplitude (Volts)

EcJ1(m)
EcJ2(m)

K1

Amplifier gain = constant K1.

K1

Voltage (Volts)

...

Amplifier Gain

EcJ1(m)
EcJ2(m)

Amplifier Gain

Amplifier gain = constant K1.

EcJ1(m)
EcJ2(m)

fm

(fm  fc )

EcJ1(m)
EcJ2(m)

EcJ0(m)

Time
(Sec.)

Frequency
(Hz)

Amplitude (Volts)
Time
(Sec.)

ANTENNA

Amplitude (Volts)

Voltage (Volts)

Combined Signal

Voltage (Volts)

Frequency
(Hz)

FM
MODULATOR

PM
MODULATOR

AMPLIFIER

Em

fm

Ec

fm

Time
(Sec.)

Frequency
(Hz)

Amplitude (Volts)

Low Frequency
Information

Amplitude (Volts)

Voltage (Volts)

1

Time
(Sec.)

1
f

Frequency
(Hz)

fc

Frequency
(Hz)

Gain
1

Time
(Sec.)
Low Frequency Information

Time
(Sec.)

Low Frequency
Information

Frequency
(Hz)

Amplitude (Volts)

Voltage (Volts)

INTEGRATOR

Amplitude (Volts)

Voltage (Volts)

fm

...

...

Combined Signal

(fc-2fm) (fc-fm) fc (fc+fm) (fc+2fm)Frequency

(Hz)

Copyright © 2004 Lance Breger

Copyright © 2004 Lance Breger

fm

...

...

(fc-2fm) (fc-fm) fc (fc+fm) (fc+2fm) Frequency
(Hz)

17
OPERATION OF FM RECEIVER

ANTENNA

Voltage (Volts)

external noise

The FM receiver is very similar to the superheterodyne AM receiver. The main difference is that the FM
receiver uses an FM demodulator; while the superheterodyne AM receiver uses an AM demodulator.
	
In addition, the FM receiver has two stages for noise control that the AM receiver lacks. First, just
ahead of the demodulator, there is a limiter to clip off and thereby remove external noise. [This cannot be
done in AM because clipping the noise would also remove the information, that is encoded in the amplitude
of the carrier wave.] Second, after demodulation in the FM receiver, there is a deemphasis stage, that is
involved in combating internal noise. The deemphasis stage corrects the earlier distortion of the signal in
the preemphasis stage of the FM transmitter, where high-frequency sinusoids are amplified more than lowfrequency ones.
	
In the FM transmitter, the purpose of distorting the signal is to facilitate the FM receiver's detecting
the signal's high frequencies in the presence of high-frequency noise. This noise is generated inside the
FM demodulator in the receiver. Basically the deemphasis stage in the receiver is also a nonuniform amplifier which corrects the initial distortion in the transmitter by emphasizing the low frequencies over the high
frequencies (i.e., deemphasizes the high frequencies) which were preferentially amplified (i.e., emphasized)
by the preemphsis stage in the FM transmitter.
	
In contrast to the AM receivers, the diagram of the FM receiver also shows a noise signal although
noise is really present in both types of receivers. However, noise is only shown in the FM case because only
FM receivers have special stages to combat noise, i.e., the limiter for external noise and the deemphasis
stage for internal noise. AM receivers have no special stages to combat noise.

Amplitude (Volts)

Time
(Sec.)

	
Note that in contrast to all preceding diagrams, in the diagram of this FM receiver and of the following PM
receiver, the graphs of the time domain and of the frequency domain are not exactly the same as the output of an actual oscilloscope or of an actual system analyzer. This is because only in these diagrams noise is not combined with
the FM or PM signals to produce the total signal that the real instruments display in
different forms.

...

RF AMP 
.
bandpass filter

Voltage (Volts)

external noise

LO

external noise

...

...

Frequency
(Hz)

Amplitude (Volts)
fLO

Mixer and local oscillator copy
Fm signal and noise to lower
intermediate frequency range.

(fi-2fm) (fi-fm) fi (fi+fm) (fi+2fm)

Gain

IF amplifier

Filter selects band around f i
the intermediate frequency.
Voltage (Volts)

external noise

...

external noise

... external noise

...

Combined Signal

(fi-2fm) (fi-fm) fi (fi+fm) (fi+2fm)

450

Frequency
(Hz)

Amplitude (Volts)
external noise

...

Combined Signal

... external noise

(fi-2fm) (fi-fm) fi (fi+fm) (fi+2fm)

Demodulator noise power

FM demodulator introduces
increasing noise power
at higher frequencies.
Voltage (Volts)

Amplitude (Volts)
Time
(Sec.)

De-emphasis circuit attenuates
higher frequencies
to balance them
with lower frequencies.

Frequency
(Hz)

Frequency
(Hz)

Gain

Amplitude (Volts)

Voltage (Volts)

Frequency
(Hz)

demodulator noise

fm

Amplitude

Frequency
(Hz)

Limiter produces constant output voltage
for input voltage above a critical value.

Vin

Time
(Sec.)

Amplitude

... external noise

Amplitude (Volts)

Time
(Sec.)

Voltage (Volts)

Frequency
(Hz)

(fi-2fm) (fi-fm) fi (fi+fm) (fi+2fm)

IF AMPLIFIER
PER SE

Frequency
(Hz)

1

Amplitude (Volts)

Combined Signal

LIMITER

...

(fc-2fm) (fc-fm) fc (fc+fm) (fc+2fm)

0

Time
(Sec.)

Voltage (Volts)

external noise
...
...

...

(fm  fi  fc  fLO)

DE-EMPHASIS

Frequency
(Hz)
fLO

Time
(Sec.)

NON-LINEAR
DEVICE (mixer)

DEMODULATOR
(detector,
discriminator)

...

Amplitude (Volts)

Combined Signal

FILTER

...

fc

Vout

	
To simplify the description of the operation of the FM receiver in the presence of noise, we consider
that the external noise is white noise (i.e., noise consisting of sinusoids of all frequencies and all with the
same amplitude) generated by an impulse and that this noise can be treated separately from the modulated
FM signal. This latter simplification is justifiable when all of the modulated FM signal passes through a filter
but only the portion of the noise in the passband of the filter passes.

external noise

...

Time
(Sec.)

Frequency
(Hz)

demodulator noise

Frequency
(Hz)

fm

AUDIO
AMPLIFIER

Amplitude (Volts)

Voltage (Volts)
Time
(Sec.)

demodulator noise

fm

Frequency
(Hz)

SPEAKER

18

Copyright © 2004 Lance Breger

19
OPERATION OF PM RECEIVER

The PM receiver and the FM receiver are basically the same except that the PM receiver has no deemphasis stage, since there
is no need for one. This is because in the PM transmitter there is no preemphasis stage to initially distort the signal. Therefore,
there is no need in the PM receiver for a deemphasis stage to correct this non-existent distortion.

ANTENNA

Voltage (Volts)

external noise

external noise

...
RF AMP. 
bandpass filter

...

...

external noise

Amplitude (Volts)

Time
(Sec.)

LO

external noise

...

...

(fc-2fm) (fc-fm) fc (fc+fm) (fc+2fm)

NON-LINEAR
DEVICE (mixer)

Amplitude (Volts)

Voltage (Volts)

Gain

external noise

Amplitude (Volts)

...

... external noise

Frequency
(Hz)

	
Hence, these diagrams support and enhance the use of simulation by providing a more comprehensive view, operational characteristics of devices, and color coding to locate the information.

Amplitude (Volts)
external noise

Time
(Sec.)

... external noise

...

Combined Signal

(fi-2fm) (fi-fm) fi (fi+fm) (fi+2fm)

Vout

Voltage (Volts)

2)  perational characteristics:
o
The diagrams show the operational characteristic of the filters, amplifiers, and other parts of the circuit.
Simulation does not.
3)  istribution of information:
d
By using a color code, these diagrams show where in the signal the information lies; simulation does
not. Knowing the location of the information is critical to understanding the operation of the communication system

Frequency
(Hz)

1

(fi-2fm) (fi-fm) fi (fi+fm) (fi+2fm)

IF AMPLIFIER
PER SE

450

(fc-2fm) (fc-fm) fc (fc+fm) (fc+2fm)

0

Combined Signal

LIMITER

...

1)  lobal view:
g
The form of the signal can be seen simultaneously at all stages in the cascade instead of only at a few
stages at time as in the simulations. Thus, the overall operation of the system is much easier to grasp
in these diagrams than by simulation alone.

Frequency
(Hz)

(fi-2fm) (fi-fm) fi (fi+fm) (fi+2fm)

Time
(Sec.)

Voltage (Volts)

external noise
...
...

...

(fm  fi  fc  fLO)

Filter selects band around f i
the intermediate frequency.

Frequency
(Hz)
fLO

Mixer and local oscillator copy
Fm signal and noise to lower
intermediate frequency range.

IF amplifier

Frequency
(Hz)
fLO

Combined Signal

FILTER

...

(fc-2fm) (fc-fm) fc (fc+fm) (fc+2fm)

Voltage (Volts)

	
It is hopeful that the above comments will help the reader to better understand and use the associated diagrams. These relevant graphics can in a simple way give a student a global view of the complex
subject of radio transmitters and receivers.
	
The communications circuits that are diagrammed here can also be simulated on a computer, e.g.,
by using Multisim. However, our diagrams have the following advantages over simulation alone:

Amplitude (Volts)

Time
(Sec.)

CONCLUSION

Limiter produces constant output voltage
for input voltage above a critical value.

Vin

Frequency
(Hz)

Amplitude (Volts)
external noise

Time
(Sec.)

...

Combined Signal

... external noise

(fi-2fm) (fi-fm) fi (fi+fm) (fi+2fm)

DEMODULATOR
(detector,
discriminator)

Frequency
(Hz)

Amplitude (Volts)

Voltage (Volts)
Amplitude

Time
(Sec.)

demodulator noise

Frequency
(Hz)

fm

AUDIO
AMPLIFIER

Amplitude (Volts)

Voltage (Volts)
Time
(Sec.)

demodulator noise

fm

Frequency
(Hz)

SPEAKER

20

Copyright © 2004 Lance Breger

21
The purpose of these diagrams
is to graphically explain the overall operation of
AM, PM, and FM communications systems
using very little mathematics.

Copyright

2004 Lance Breger

More Related Content

Similar to Tele com breger

Fundamentals of dsp
Fundamentals of dspFundamentals of dsp
Fundamentals of dspismailkziadi
 
USRP Project Final Report
USRP Project Final ReportUSRP Project Final Report
USRP Project Final ReportArjan Gupta
 
[Signals and Communication Technology ] Joachim Speidel - Introduction to Dig...
[Signals and Communication Technology ] Joachim Speidel - Introduction to Dig...[Signals and Communication Technology ] Joachim Speidel - Introduction to Dig...
[Signals and Communication Technology ] Joachim Speidel - Introduction to Dig...George K. Karagiannidis
 
Modern Transformers And Electric Power Systems
Modern Transformers And Electric Power SystemsModern Transformers And Electric Power Systems
Modern Transformers And Electric Power SystemsLindsey Williams
 
The Rate A Drug Is Released In The Body
The Rate A Drug Is Released In The BodyThe Rate A Drug Is Released In The Body
The Rate A Drug Is Released In The BodyCatherine Bitker
 
Real-Time Vowel Synthesis - A Magnetic Resonator Piano Based Project_by_Vasil...
Real-Time Vowel Synthesis - A Magnetic Resonator Piano Based Project_by_Vasil...Real-Time Vowel Synthesis - A Magnetic Resonator Piano Based Project_by_Vasil...
Real-Time Vowel Synthesis - A Magnetic Resonator Piano Based Project_by_Vasil...Vassilis Valavanis
 
93755181 lte-hoping
93755181 lte-hoping93755181 lte-hoping
93755181 lte-hopingSadef Karish
 
Manuscrit de Doctorat_El Abdellaouy Hanane
Manuscrit de Doctorat_El Abdellaouy HananeManuscrit de Doctorat_El Abdellaouy Hanane
Manuscrit de Doctorat_El Abdellaouy HananeElabdellaouy Hanane
 
[PFE] Design and implementation of an AoA, AS and DS estimator on FPGA-based...
[PFE]  Design and implementation of an AoA, AS and DS estimator on FPGA-based...[PFE]  Design and implementation of an AoA, AS and DS estimator on FPGA-based...
[PFE] Design and implementation of an AoA, AS and DS estimator on FPGA-based...Yassine Selmi
 
Fm transmitter and future radio technology
Fm transmitter and future radio technologyFm transmitter and future radio technology
Fm transmitter and future radio technologyChima Chukwu
 
Principal Component Analysis Paper
Principal Component Analysis PaperPrincipal Component Analysis Paper
Principal Component Analysis PaperMelissa Dudas
 
Parallel Interference Cancellation in beyond 3G multi-user and multi-antenna ...
Parallel Interference Cancellation in beyond 3G multi-user and multi-antenna ...Parallel Interference Cancellation in beyond 3G multi-user and multi-antenna ...
Parallel Interference Cancellation in beyond 3G multi-user and multi-antenna ...David Sabater Dinter
 
Dissertation wonchae kim
Dissertation wonchae kimDissertation wonchae kim
Dissertation wonchae kimSudheer Babu
 
thesis2005
thesis2005thesis2005
thesis2005Jim Wu
 

Similar to Tele com breger (20)

RF_Path_eBook.pdf
RF_Path_eBook.pdfRF_Path_eBook.pdf
RF_Path_eBook.pdf
 
Fundamentals of dsp
Fundamentals of dspFundamentals of dsp
Fundamentals of dsp
 
repport christian el hajj
repport christian el hajjrepport christian el hajj
repport christian el hajj
 
USRP Project Final Report
USRP Project Final ReportUSRP Project Final Report
USRP Project Final Report
 
[Signals and Communication Technology ] Joachim Speidel - Introduction to Dig...
[Signals and Communication Technology ] Joachim Speidel - Introduction to Dig...[Signals and Communication Technology ] Joachim Speidel - Introduction to Dig...
[Signals and Communication Technology ] Joachim Speidel - Introduction to Dig...
 
Modern Transformers And Electric Power Systems
Modern Transformers And Electric Power SystemsModern Transformers And Electric Power Systems
Modern Transformers And Electric Power Systems
 
The Rate A Drug Is Released In The Body
The Rate A Drug Is Released In The BodyThe Rate A Drug Is Released In The Body
The Rate A Drug Is Released In The Body
 
Real-Time Vowel Synthesis - A Magnetic Resonator Piano Based Project_by_Vasil...
Real-Time Vowel Synthesis - A Magnetic Resonator Piano Based Project_by_Vasil...Real-Time Vowel Synthesis - A Magnetic Resonator Piano Based Project_by_Vasil...
Real-Time Vowel Synthesis - A Magnetic Resonator Piano Based Project_by_Vasil...
 
93755181 lte-hoping
93755181 lte-hoping93755181 lte-hoping
93755181 lte-hoping
 
Casa cookbook for KAT 7
Casa cookbook for KAT 7Casa cookbook for KAT 7
Casa cookbook for KAT 7
 
Manuscrit de Doctorat_El Abdellaouy Hanane
Manuscrit de Doctorat_El Abdellaouy HananeManuscrit de Doctorat_El Abdellaouy Hanane
Manuscrit de Doctorat_El Abdellaouy Hanane
 
[PFE] Design and implementation of an AoA, AS and DS estimator on FPGA-based...
[PFE]  Design and implementation of an AoA, AS and DS estimator on FPGA-based...[PFE]  Design and implementation of an AoA, AS and DS estimator on FPGA-based...
[PFE] Design and implementation of an AoA, AS and DS estimator on FPGA-based...
 
Fm transmitter and future radio technology
Fm transmitter and future radio technologyFm transmitter and future radio technology
Fm transmitter and future radio technology
 
Principal Component Analysis Paper
Principal Component Analysis PaperPrincipal Component Analysis Paper
Principal Component Analysis Paper
 
Parallel Interference Cancellation in beyond 3G multi-user and multi-antenna ...
Parallel Interference Cancellation in beyond 3G multi-user and multi-antenna ...Parallel Interference Cancellation in beyond 3G multi-user and multi-antenna ...
Parallel Interference Cancellation in beyond 3G multi-user and multi-antenna ...
 
Zhe huangm sc
Zhe huangm scZhe huangm sc
Zhe huangm sc
 
Ltu ex-05238-se
Ltu ex-05238-seLtu ex-05238-se
Ltu ex-05238-se
 
Dissertation wonchae kim
Dissertation wonchae kimDissertation wonchae kim
Dissertation wonchae kim
 
Basic
BasicBasic
Basic
 
thesis2005
thesis2005thesis2005
thesis2005
 

Recently uploaded

UWB Technology for Enhanced Indoor and Outdoor Positioning in Physiological M...
UWB Technology for Enhanced Indoor and Outdoor Positioning in Physiological M...UWB Technology for Enhanced Indoor and Outdoor Positioning in Physiological M...
UWB Technology for Enhanced Indoor and Outdoor Positioning in Physiological M...UbiTrack UK
 
Salesforce Miami User Group Event - 1st Quarter 2024
Salesforce Miami User Group Event - 1st Quarter 2024Salesforce Miami User Group Event - 1st Quarter 2024
Salesforce Miami User Group Event - 1st Quarter 2024SkyPlanner
 
Empowering Africa's Next Generation: The AI Leadership Blueprint
Empowering Africa's Next Generation: The AI Leadership BlueprintEmpowering Africa's Next Generation: The AI Leadership Blueprint
Empowering Africa's Next Generation: The AI Leadership BlueprintMahmoud Rabie
 
ADOPTING WEB 3 FOR YOUR BUSINESS: A STEP-BY-STEP GUIDE
ADOPTING WEB 3 FOR YOUR BUSINESS: A STEP-BY-STEP GUIDEADOPTING WEB 3 FOR YOUR BUSINESS: A STEP-BY-STEP GUIDE
ADOPTING WEB 3 FOR YOUR BUSINESS: A STEP-BY-STEP GUIDELiveplex
 
UiPath Community: AI for UiPath Automation Developers
UiPath Community: AI for UiPath Automation DevelopersUiPath Community: AI for UiPath Automation Developers
UiPath Community: AI for UiPath Automation DevelopersUiPathCommunity
 
activity_diagram_combine_v4_20190827.pdfactivity_diagram_combine_v4_20190827.pdf
activity_diagram_combine_v4_20190827.pdfactivity_diagram_combine_v4_20190827.pdfactivity_diagram_combine_v4_20190827.pdfactivity_diagram_combine_v4_20190827.pdf
activity_diagram_combine_v4_20190827.pdfactivity_diagram_combine_v4_20190827.pdfJamie (Taka) Wang
 
Basic Building Blocks of Internet of Things.
Basic Building Blocks of Internet of Things.Basic Building Blocks of Internet of Things.
Basic Building Blocks of Internet of Things.YounusS2
 
Computer 10: Lesson 10 - Online Crimes and Hazards
Computer 10: Lesson 10 - Online Crimes and HazardsComputer 10: Lesson 10 - Online Crimes and Hazards
Computer 10: Lesson 10 - Online Crimes and HazardsSeth Reyes
 
Meet the new FSP 3000 M-Flex800™
Meet the new FSP 3000 M-Flex800™Meet the new FSP 3000 M-Flex800™
Meet the new FSP 3000 M-Flex800™Adtran
 
Artificial Intelligence & SEO Trends for 2024
Artificial Intelligence & SEO Trends for 2024Artificial Intelligence & SEO Trends for 2024
Artificial Intelligence & SEO Trends for 2024D Cloud Solutions
 
Igniting Next Level Productivity with AI-Infused Data Integration Workflows
Igniting Next Level Productivity with AI-Infused Data Integration WorkflowsIgniting Next Level Productivity with AI-Infused Data Integration Workflows
Igniting Next Level Productivity with AI-Infused Data Integration WorkflowsSafe Software
 
AI You Can Trust - Ensuring Success with Data Integrity Webinar
AI You Can Trust - Ensuring Success with Data Integrity WebinarAI You Can Trust - Ensuring Success with Data Integrity Webinar
AI You Can Trust - Ensuring Success with Data Integrity WebinarPrecisely
 
AI Fame Rush Review – Virtual Influencer Creation In Just Minutes
AI Fame Rush Review – Virtual Influencer Creation In Just MinutesAI Fame Rush Review – Virtual Influencer Creation In Just Minutes
AI Fame Rush Review – Virtual Influencer Creation In Just MinutesMd Hossain Ali
 
Apres-Cyber - The Data Dilemma: Bridging Offensive Operations and Machine Lea...
Apres-Cyber - The Data Dilemma: Bridging Offensive Operations and Machine Lea...Apres-Cyber - The Data Dilemma: Bridging Offensive Operations and Machine Lea...
Apres-Cyber - The Data Dilemma: Bridging Offensive Operations and Machine Lea...Will Schroeder
 
Crea il tuo assistente AI con lo Stregatto (open source python framework)
Crea il tuo assistente AI con lo Stregatto (open source python framework)Crea il tuo assistente AI con lo Stregatto (open source python framework)
Crea il tuo assistente AI con lo Stregatto (open source python framework)Commit University
 
Videogame localization & technology_ how to enhance the power of translation.pdf
Videogame localization & technology_ how to enhance the power of translation.pdfVideogame localization & technology_ how to enhance the power of translation.pdf
Videogame localization & technology_ how to enhance the power of translation.pdfinfogdgmi
 
KubeConEU24-Monitoring Kubernetes and Cloud Spend with OpenCost
KubeConEU24-Monitoring Kubernetes and Cloud Spend with OpenCostKubeConEU24-Monitoring Kubernetes and Cloud Spend with OpenCost
KubeConEU24-Monitoring Kubernetes and Cloud Spend with OpenCostMatt Ray
 
IaC & GitOps in a Nutshell - a FridayInANuthshell Episode.pdf
IaC & GitOps in a Nutshell - a FridayInANuthshell Episode.pdfIaC & GitOps in a Nutshell - a FridayInANuthshell Episode.pdf
IaC & GitOps in a Nutshell - a FridayInANuthshell Episode.pdfDaniel Santiago Silva Capera
 
The Data Metaverse: Unpacking the Roles, Use Cases, and Tech Trends in Data a...
The Data Metaverse: Unpacking the Roles, Use Cases, and Tech Trends in Data a...The Data Metaverse: Unpacking the Roles, Use Cases, and Tech Trends in Data a...
The Data Metaverse: Unpacking the Roles, Use Cases, and Tech Trends in Data a...Aggregage
 

Recently uploaded (20)

UWB Technology for Enhanced Indoor and Outdoor Positioning in Physiological M...
UWB Technology for Enhanced Indoor and Outdoor Positioning in Physiological M...UWB Technology for Enhanced Indoor and Outdoor Positioning in Physiological M...
UWB Technology for Enhanced Indoor and Outdoor Positioning in Physiological M...
 
Salesforce Miami User Group Event - 1st Quarter 2024
Salesforce Miami User Group Event - 1st Quarter 2024Salesforce Miami User Group Event - 1st Quarter 2024
Salesforce Miami User Group Event - 1st Quarter 2024
 
Empowering Africa's Next Generation: The AI Leadership Blueprint
Empowering Africa's Next Generation: The AI Leadership BlueprintEmpowering Africa's Next Generation: The AI Leadership Blueprint
Empowering Africa's Next Generation: The AI Leadership Blueprint
 
ADOPTING WEB 3 FOR YOUR BUSINESS: A STEP-BY-STEP GUIDE
ADOPTING WEB 3 FOR YOUR BUSINESS: A STEP-BY-STEP GUIDEADOPTING WEB 3 FOR YOUR BUSINESS: A STEP-BY-STEP GUIDE
ADOPTING WEB 3 FOR YOUR BUSINESS: A STEP-BY-STEP GUIDE
 
UiPath Community: AI for UiPath Automation Developers
UiPath Community: AI for UiPath Automation DevelopersUiPath Community: AI for UiPath Automation Developers
UiPath Community: AI for UiPath Automation Developers
 
activity_diagram_combine_v4_20190827.pdfactivity_diagram_combine_v4_20190827.pdf
activity_diagram_combine_v4_20190827.pdfactivity_diagram_combine_v4_20190827.pdfactivity_diagram_combine_v4_20190827.pdfactivity_diagram_combine_v4_20190827.pdf
activity_diagram_combine_v4_20190827.pdfactivity_diagram_combine_v4_20190827.pdf
 
Basic Building Blocks of Internet of Things.
Basic Building Blocks of Internet of Things.Basic Building Blocks of Internet of Things.
Basic Building Blocks of Internet of Things.
 
Computer 10: Lesson 10 - Online Crimes and Hazards
Computer 10: Lesson 10 - Online Crimes and HazardsComputer 10: Lesson 10 - Online Crimes and Hazards
Computer 10: Lesson 10 - Online Crimes and Hazards
 
20150722 - AGV
20150722 - AGV20150722 - AGV
20150722 - AGV
 
Meet the new FSP 3000 M-Flex800™
Meet the new FSP 3000 M-Flex800™Meet the new FSP 3000 M-Flex800™
Meet the new FSP 3000 M-Flex800™
 
Artificial Intelligence & SEO Trends for 2024
Artificial Intelligence & SEO Trends for 2024Artificial Intelligence & SEO Trends for 2024
Artificial Intelligence & SEO Trends for 2024
 
Igniting Next Level Productivity with AI-Infused Data Integration Workflows
Igniting Next Level Productivity with AI-Infused Data Integration WorkflowsIgniting Next Level Productivity with AI-Infused Data Integration Workflows
Igniting Next Level Productivity with AI-Infused Data Integration Workflows
 
AI You Can Trust - Ensuring Success with Data Integrity Webinar
AI You Can Trust - Ensuring Success with Data Integrity WebinarAI You Can Trust - Ensuring Success with Data Integrity Webinar
AI You Can Trust - Ensuring Success with Data Integrity Webinar
 
AI Fame Rush Review – Virtual Influencer Creation In Just Minutes
AI Fame Rush Review – Virtual Influencer Creation In Just MinutesAI Fame Rush Review – Virtual Influencer Creation In Just Minutes
AI Fame Rush Review – Virtual Influencer Creation In Just Minutes
 
Apres-Cyber - The Data Dilemma: Bridging Offensive Operations and Machine Lea...
Apres-Cyber - The Data Dilemma: Bridging Offensive Operations and Machine Lea...Apres-Cyber - The Data Dilemma: Bridging Offensive Operations and Machine Lea...
Apres-Cyber - The Data Dilemma: Bridging Offensive Operations and Machine Lea...
 
Crea il tuo assistente AI con lo Stregatto (open source python framework)
Crea il tuo assistente AI con lo Stregatto (open source python framework)Crea il tuo assistente AI con lo Stregatto (open source python framework)
Crea il tuo assistente AI con lo Stregatto (open source python framework)
 
Videogame localization & technology_ how to enhance the power of translation.pdf
Videogame localization & technology_ how to enhance the power of translation.pdfVideogame localization & technology_ how to enhance the power of translation.pdf
Videogame localization & technology_ how to enhance the power of translation.pdf
 
KubeConEU24-Monitoring Kubernetes and Cloud Spend with OpenCost
KubeConEU24-Monitoring Kubernetes and Cloud Spend with OpenCostKubeConEU24-Monitoring Kubernetes and Cloud Spend with OpenCost
KubeConEU24-Monitoring Kubernetes and Cloud Spend with OpenCost
 
IaC & GitOps in a Nutshell - a FridayInANuthshell Episode.pdf
IaC & GitOps in a Nutshell - a FridayInANuthshell Episode.pdfIaC & GitOps in a Nutshell - a FridayInANuthshell Episode.pdf
IaC & GitOps in a Nutshell - a FridayInANuthshell Episode.pdf
 
The Data Metaverse: Unpacking the Roles, Use Cases, and Tech Trends in Data a...
The Data Metaverse: Unpacking the Roles, Use Cases, and Tech Trends in Data a...The Data Metaverse: Unpacking the Roles, Use Cases, and Tech Trends in Data a...
The Data Metaverse: Unpacking the Roles, Use Cases, and Tech Trends in Data a...
 

Tele com breger

  • 1. Operational Diagrams of Radio Transmitters & Receivers Professor Lance Breger and Professor Kenneth Markowitz
  • 2. TABLE OF CONTENTS Page Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 - 5 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 - 7 Operation of Adder-Antenna Transmitter . . . . . . . . . . . . . . . . . . . . . . . . 9 Operation of AM Transmitter in General. . . . . . . . . . . . . . . . . . . . . . . . 10 Operation of AM Transmitter Showing AM Modulator in Detail. . . . . . 11 Operation of TRF AM Receiver. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Operation of Superheterodyne AM Receiver . . . . . . . . . . . . . . . . . . . . 13 Operation of PM Transmitter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Operation of FM Transmitter in General. . . . . . . . . . . . . . . . . . . . . . . . 15 Operation of FM Transmitter with Indirect Modulation. . . . . . . . . . . . . 16 Operation of FM Transmitter with Direct Modulation. . . . . . . . . . . . . . 17 Operation of FM Receiver. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 - 19 Operation of PM Receiver. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Conclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 . Copyright 2004 Lance Breger 3
  • 3. PREFACE The purpose of these diagrams is to graphically explain the overall operation of AM, PM, and FM communications systems using very little mathematics. This explanation is accomplished by tracing a simple sinusoidal signal through all stages of each system. Although students who are "mathematically challenged" will find these diagrams very helpful, most students who are beginning the study of electrical communications systems can benefit from these same diagrams. More advanced courses can also use these diagrams as a basis on which to organize and present abstract mathematics. ● S tudents: M. B. Suranga Perera, Nikolay Ostrovskiy and Johnny Lam. They produced the professional graphics in these vector art diagrams and created the pages. To pay these students, the following persons or organizations at NYCCT generously offered financial advice or funds: The unique features of these diagrams are the following: presenting the signal in both the time domain and frequency domain together at each stage of the communication process ● using a color code to show the distribution of information in the signals in both the time domain and frequency domain simultaneously. ● Former Dean Phyllis Sperling of the School of Technology Design ● ● Former Dean Annette Schaefer of the School of Arts and Sciences ● Professor Joseph Rosen, head of the Freshman Year Program at NYCCT and current acting Dean of the School of Liberal Arts and Sciences The history of preparing this booklet is a long one. Before beginning the arduous work of producing these diagrams, we inspected about 70 standard textbooks on electrical communications to determine whether we could save ourselves a lot of effort by simply using their diagrams; but none of those books contained the above simultaneous diagrams. Some of the basic ideas underlying these diagrams were presented by us in 2001 at a conference of FIE (Frontiers In Education) in Reno, Nevada. Completion of this booklet took about three more years of devoted labor, research, and collaboration. Ms. Jewel Escobar, Executive Director of NYCCT Foundation ● These diagrams were produced by translating the statements and logic from the following two textbooks into simple graphics: Modern Electronic Communication, 6th edition, by Gary M. Miller, Prentice Hall, Upper Saddle River, NJ, 1999. Electronic Communication Techniques, 4th edition, by Paul H. Young, Prentice Hall, Upper Saddle River, NJ, 1999. Graphing calculators were used to plot equations, and some of the particularly difficult steps were checked by simulation using Multisim or by TIMS (Telecommunications Instructional Modeling Systems) ● F ederal Work Study Program administered by the Department of Financial Aid at NYCCT. ● T he Department of Architectural Technology deserves thanks for allowing almost all of the computer drawings to be done on their computers using Adobe Illustrator. ● D ean Robin Bargar ● P rofessor Joel Mason, Chair of the Department of Advertising Design and Graphic Arts (ADGA), for allowing the intermediate and final color prints to be produced on the ADGA Print Laboratory's DocuColor 2060 press under a grant by Xerox. our comments will be used to produce an improved second edition of this booklet. We, the authors, would Y greatly appreciate being informed of any mistakes or of other comments about this booklet by emailing me: bookletauthor@hotmail.com During the preparation of this booklet, many others at the New York City College of Technology (NYCCT) aided us. Helpful technical suggestions were offered by several of our colleagues: ● ● Professor John Fehling ● Professor Misza Kalechman ● Professor Mohammed Kouar ● Professor Mohammad Razani. ● 4 Professor Aron Goykadosh P rofessor Lloyd Carr, who initiated and directed the vector file production, page imposition for printed versions and the final pdf files. Professor Carr also helped to edit the final text. 5
  • 4. INTRODUCTION To help the reader use this set of diagrams of AM, PM, and FM efficiently, two sets of comments have been added to the diagrams to elucidate them. The first set of comments applies generally to all the diagrams and is included in this introduction. The second set of comments applies specifically to individual diagrams, and each of these comments is inserted in the main text adjacent to the diagram that it explains. GENERAL COMMENTS The main objective of these diagrams is to help students understand the operation of transmitters and receivers of various types by showing how the signal changes as it propagates through each stage in a series of cascaded stages, whose electrical operating characteristics are also usually shown in the diagrams. For simplicity the information signal is assumed to be a sinusoid. The signal itself is shown in two adjacent forms: • n time domain, i i.e., how the signal changes in time as it would be observed on an oscilloscope inserted at a particular point in the system • n frequency domain, i i.e., how the signal changes in sinusoidal composition as it would be observed on a spectrum analyzer inserted into the system at the same point as the above oscilloscope. [The diagrams on the FM receiver and the PM receiver violate this rule slightly by showing noise separately.] Being able to relate these two views of the signal is a major lesson in communications, since beginners usually think only in the time domain; but experts in communications usually think in the more abstract frequency domain. In addition, the mathematical equations for important signals in the time domain have also been inserted to help the student correlate this information with the two graphic forms of the signal. The general structure of each diagram is as follows. In the left-most column, the various cascaded stages are arranged vertically from top to bottom. Arrows represent the signal flow between the stages. To the right of each arrow and at the same level are the two graphic representations of the signal itself, i.e., first in the time domain and then in the frequency domain. Thus, the three columns of the diagram are arranged from left to right from most concrete to most abstract. In addition, the operating characteristics of some devices, e.g., amplifiers and filters, are also shown. These characteristics are shown in the domain where their operation is most easily represented. For example, the operation of filters is most easily described in the frequency domain; while the operation of a limiter in an FM receiver is most easily described in the time domain. (continued on page 7) 6 A color code has been used to draw the various signals in these diagrams mainly to help students trace the flow of information, which is vital to understanding the operation of a communications system. Of course, the real signals or waves are invisible, i.e., colorless, to our eyes; but the colors arbitrarily assigned to the signals in these diagrams show their content of information. ● Blue signals in the time domain or in the frequency domain indicate the pure information signal. ● Red signals indicate the pure carrier wave. ● Purple signals show that the information signal and the carrier wave have been mixed, just as blue and red colors mix to form the color purple. ● Green indicates the operating characteristic in graphs of various devices, like amplifiers and filters. ● Black signals indicate noise. A somewhat different color code has been used for the arrows showing signal propagation in the left-most column. As above, red arrows mean the carrier wave; and blue arrows mean the information signal. However, the mixed state of carrier plus information is indicated by the split arrow, half being red and half being blue. In symbols and equations used these diagrams, the red carrier wave is symbolized by c; and the blue information signal is symbolized by m (not i as is used by many texts) since m stands for the modulating signal, i.e., the information. The scale of the vertical voltage axis in the time domain differs from voltage scale in the frequency domain because otherwise the size of the bars in the frequency domain would have been too small to have been read easily. To remind the student that these scales are different, an arrow has been drawn and labeled as amplitude in the earliest sinusoid in the time domain in each diagram. [Amplitude in all these drawings means the amplitude of a sinusoid, not of any other function.] This arrow then reminds the reader of how big the amplitude in the frequency domain really is in the time domain. In general, the wave forms and operating characteristics shown in these diagrams are mere cartoons, or idealizations, of reality, not exact pictures. This approximation is appropriate because exact representations would be difficult to understand. For example, in the case of FM as seen in the frequency domain, if the various sidebands were drawn to scale, the sidebands could not easily be distinguished from the carrier in the size of diagrams drawn here. Finally, the amount of detail shown varies from diagram to diagram. For example, some diagrams show the operating characteristics of ideal amplifiers; others do not. In each case, our aim was to show as much detail as possible without cluttering the diagram. 7
  • 5. OPERATION OF ADDER-ANTENNA TRANSMITTER This diagram shows a transmitter that does not work to emphasize the reason that real transmitters do work. That is, this transmitter leaves the information, which is shown in blue, at low frequencies so that it can not be radiated; the radiating antenna only broadcasts high frequencies. This implies that only the high-frequency carrier wave is broadcast, which is useless. The aim of a communications system is to broadcast information, not to broadcast the pure carrier wave! fm fc Amplitude (Volts) Voltage (Volts) Em Ec fm fc Frequency Time (Sec.) Low Frequency Information High Frequency Carrier Voltage (Volts) (Hz) Amplitude (Volts) Combined Signal (fm fc ) Ec fm Time (Sec.) Em fc Frequency (Hz) Antenna Gain 1 Antenna removes low frequencies 0 Frequency (Hz) Amplitude (Volts) Voltage (Volts) Ec Time (Sec.) High Frequency Carrier 8 Copyright © 2004 Lance Breger fm fc Frequency (Hz) 9
  • 6. OPERATION OF AM TRANSMITTER IN GENERAL This transmitter works, while the previous one fails, because the AM modulator raises the information, shown in blue, to high frequencies so that it can be broadcast along with the carrier by the high-pass antenna. The AM modulator automatically raises the frequency of the information when encoding information by changing the amplitude of the carrier sinusoid. fm fc This diagram differs from the previous one only in that it shows the details of the AM modulator. The operation of the modulator consists of two stages. First, the information signal and carrier are passed through a nonlinear device, e.g., a transistor or diode, to generate the required upper and lower sidebands along with unnecessary sinusoids of many other frequencies. [The diagram mentions an ideal nonlinear device; ideal means that most of the unnecessary harmonics have been omitted for clarity.] Second, a high-frequency bandpass filter removes the unnecessary sinusoids and passes only those in the required AM-modulated carrier. Amplitude (Volts) Voltage (Volts) Em Ec Time (Sec.) Amplitude Low Frequency Information AM MODULATOR OPERATION OF AM TRANSMITTER SHOWING AM MODULATOR IN DETAIL High Frequency Carrier fm fc fm fc Amplitude Frequency (Hz) AM MODULATOR IDEAL NON-LINEAR DEVICE Amplitude (Volts) Ec Time (Sec.) Em/2 Voltage (Volts) Em/2 AMPLIFIER K1 Amplifier gain = constant K1. Voltage (Volts) fm Combined Signal ANTENNA Antenna passes only high frequencies. Voltage (Volts) Combined Signal Amplitude (Volts) (Hz) Antenna Gain ANTENNA Antenna passes only high frequencies. Time (Sec.) 10 (fc-fm) fc (fc+fm) Frequency fm Voltage (Volts) Combined Signal Frequency (Hz) Amplitude (Volts) 0 Frequency (Hz) K1 Time (Sec.) (Hz) Antenna Gain (Hz) Amplifier Gain Amplifier gain = constant K1. (fc-fm) fc (fc+fm) Frequency Em/2 (fc-fm) fc (fc+fm) Frequency fm Voltage (Volts) Ec Em/2 Combined Signal AMPLIFIER Frequency (Hz) Amplitude Input (Volts) (fm fc ) Time (Sec.) 1 0 Time (Sec.) Frequency (Hz) Amplitude (Volts) Voltage (Volts) (Hz) Gain of Filter Filter selects carrier and sidebands. Em/2 (fc-fm) fc (fc+fm) Frequency dc fm BAND-PASS FILTER Frequency (Hz) Ec Em/2 Time (Sec.) (Hz) Amplifier Gain fc Amplitude (Volts) (fc-fm) fc (fc+fm) Frequency fm Ec fm High Frequency Carrier (red) Combined Signal (fm fc ) Em Time (Sec.) Low Frequency Information (blue) Voltage (Volts) Amplitude (Volts) Voltage (Volts) 1 0 Amplitude (Volts) Frequency (Hz) Time (Sec.) fm Combined Signal (fc-fm) fc (fc+fm) Frequency (Hz) Copyright © 2004 Lance Breger fm (fc-fm) fc (fc+fm) Frequency (Hz) Copyright © 2004 Lance Breger Copyright © 2004 Lance Breger 11
  • 7. OPERATION OF TRF AM RECEIVER OPERATION OF SUPERHETERODYNE AM RECEIVER The main point of interest here is the structure of the AM detector. The basic structure of the AM detector and of the AM modulator are the same: a nonlinear device followed by a bandpass filter. In the detector, the nonlinear device reproduces the original signal sinusoid from the AM-modulated carrier and also produces many unnecessary sinusoids of other frequencies; the filter removes these unnecessary sinusoids and passes the original information signal. The main difference between the AM modulator and the AM detector is the frequency band passed by the filter: the modulator passes a band at high radio frequencies; the detector passes a band at low audio frequencies. ANTENNA The structure of this receiver and that of the TRF receiver are very similar. The main difference is the frequency range in which most of the signal amplification is done. The TRF receiver amplifies the signal at the same high radio frequencies at which it is received initially by the antenna. Unfortunately, amplification at these high frequencies is inefficient, i.e., the amplifier gains are low. To correct this error, the superheterodyne receiver does most of its signal amplification at a lower intermediate frequency band for greater efficiency. Since this intermediate frequency band is the fixed passband of the filter in the IF amplifier, each incoming signal must be lowered to this fixed intermediate frequency band by using a frequency converter, which consists of a mixer (which is a nonlinear device) connected to an oscillator of variable frequency. This is called the local oscillator. By changing the oscillator frequency appropriately, any station's signal can be lowered to the given intermediate frequency range for efficient amplification. Amplitude (Volts) Voltage (Volts) ANTENNA Time (Sec.) (fc-fm) fc (fc+fm)Frequency (Hz) (fc-fm) fc (fc+fm)Frequency RF AMP. bandpass filter (Hz) Amplitude (Volts) Voltage (Volts) Amplitude (Volts) Voltage (Volts) Time (Sec.) RF AMP . bandpass filter fLO Amplitude (Volts) Voltage (Volts) Time (Sec.) LO (fc-fm) fc (fc+fm)Frequency (Hz) Time (Sec.) NON-LINEAR DEVICE (mixer) Amplitude (Volts) Voltage (Volts) (Hz) IDEAL NON-LINEAR DEVICE Amplitude (Volts) Voltage (Volts) (fi-fm) fi (fi+fm) IF amplifier FILTER Gain Filter selects band around fi the intermediate frequency. (fi-fm) fi (fi+fm) dc fm (fc-fm) fc (fc+fm) Frequency (Hz) Gain IF AMPLIFIER PER SE 0 Amplitude (Volts) Frequency (Hz) (fi-fm) fi (fi+fm) DETECTOR IDEAL NON-LINEAR DEVICE Time (Sec.) dc fm fm Frequency (Hz) BAND-PASS FILTER (fi-fm) fi (fi+fm) Amplitude (Volts) Amplitude Amplitude (Volts) Time (Sec.) fm Copyright Copyright © 2004 Lance Breger Frequency (Hz) Time (Sec.) fm Copyright © 2004 Lance Breger Frequency (Hz) Amplitude (Volts) Voltage (Volts) Amplitude Frequency (Hz) SPEAKER 12 0 AUDIO AMPLIFIER fm Frequency (Hz) 1 Filter selects information signal Voltage (Volts) Time (Sec.) SPEAKER Frequency (Hz) Amplitude (Volts) Voltage (Volts) Gain Voltage (Volts) Frequency (Hz) Time (Sec.) Time (Sec.) AUDIO AMPLIFIER Frequency (Hz) Amplitude (Volts) Voltage (Volts) 1 Filter selects information signal. Amplitude 0 Time (Sec.) Time (Sec.) Voltage (Volts) (fc-fm) fc (fc+fm)Frequency (Hz) 1 Amplitude (Volts) Voltage (Volts) BAND-PASS FILTER fLO Time (Sec.) (fc-fm) fc (fc+fm)Frequency DETECTOR (fm fi fc fLO) Frequency (Hz) 2004 Lance Breger Copyright © 2004 Lance Breger 13
  • 8. OPERATION OF PM TRANSMITTER Both the FM transmitter and PM transmitter have similar structures. The main difference between them is the kind of modulator used. FM modulators encode information by changing the frequency of the carrier wave. PM modulators encode information by changing the phase of the carrier wave. fm fc Amplitude (Volts) Voltage (Volts) Amplitude Low Frequency Information OPERATION OF FM TRANSMITTER IN GENERAL FM transmitters differ from PM transmitters in yet another way: before the information signal is applied to the modulator, only in the FM transmitter is the signal passed through a preemphasis stage. Preemphasis distorts the signal by amplifying high frequencies more than low frequencies, i.e., the high frequencies are emphasized before modulation. The purpose of this signal distortion in the FM transmitter is to facilitate later on in the FM receiver the detection of these high frequencies of the signal in the presence of much high-frequency noise generated in the FM demodulator in the receiver. fm Em Amplitude Time (Sec.) High Frequency Carrier Time (Sec.) Low Frequency Information fm Frequency (Hz) Gain fc fm Frequency (Hz) PREEMPHASIS Preemphasis amplifies high frequencies to overcome high-frequency noise in FM receiver PM MODULATOR 1 Frequency (Hz) Amplitude (Volts) Voltage (Volts) Amplitude (Volts) Voltage (Volts) Time (Sec.) Combined Signal EcJ2(m) ... fc EcJ1(m) EcJ2(m) fm Frequency (Hz) Amplitude (Volts) ... Voltage (Volts) Em Ec fm fc Time (Sec.) (Hz) Low Frequency Information Amplifier Gain High Frequency Carrier Amplitude (Volts) Amplitude (Volts) Voltage (Volts) Frequency (Hz) EcJ0(m) Time (Sec.) EcJ1(m) Combined Signal Time (Sec.) Combined Signal fm fm (fc-2fm) (fc-fm) fc (fc+fm) (fc+2fm) Frequency (Hz) (Hz) Time (Sec.) Combined Signal ... fm 0 ... (fc-2fm) (fc-fm) fc (fc+fm) (fc+2fm)Frequency (Hz) Antenna Gain Amplitude (Volts) Frequency (Hz) 1 ANTENNA Antenna passes only high frequencies. 0 Frequency (Hz) Voltage (Volts) Time (Sec.) 14 (fc-2fm) (fc-fm) fc (fc+fm) (fc+2fm) Frequency Amplitude (Volts) Antenna passes only high frequencies. Combined Signal ... EcJ2(m) Voltage (Volts) 1 Voltage (Volts) EcJ1(m) AMPLIFIER ... Antenna Gain ANTENNA Ec ...J2(m) (fm fc ) ... Frequency (Hz) FM MODULATOR K1 Voltage (Volts) Low Frequency Information (fc-2fm) (fc-fm) fc (fc+fm) (fc+2fm) Frequency Amplifier gain = constant K1. Em Time (Sec.) EcJ0(m) EcJ1(m) fm (fm fc ) AMPLIFIER Amplitude (Volts) Voltage (Volts) Ec ... fm Amplitude (Volts) Time (Sec.) ... (fc-2fm) (fc-fm) fc (fc+fm) (fc+2fm) Frequency Combined Signal fm (Hz) Copyright © 2004 Lance Breger Copyright © 2004 Lance Breger ... ... (fc-2fm) (fc-fm) fc (fc+fm) (fc+2fm)Frequency (Hz) 15
  • 9. OPERATION OF FM TRANSMITTER WITH INDIRECT MODULATION There are two general types of FM modulators. In the first type, i.e., those with indirect modulation, the carrier wave is produced by a very stable oscillator located outside the modulator itself, as is also done in PM modulation. The indirect FM modulator is just a PM modulator preceded by a special stage that integrates the information signal; this integration is carried out by passing the signal through an amplifier whose gain is inversely proportional to frequency. OPERATION OF FM TRANSMITTER WITH DIRECT MODULATION In the second type of FM modulation, i.e., direct modulation, the oscillator producing the carrier wave, is actually incorporated into the FM modulator itself. Otherwise, FM transmitters with direct modulation and those with indirect modulation are essentially the same. fm fm Amplitude (Volts) Voltage (Volts) Amplitude Time (Sec.) Amplitude Low Frequency Information PREEMPHASIS fm Preemphasis amplifies high frequencies to overcome high-frequency noise in FM receiver. fm Gain Frequency (Hz) PREEMPHASIS Preemphasis amplifies high frequencies to overcome high-frequency noise in FM receiver. Voltage (Volts) fm Frequency (Hz) Gain FM Modulator Integrator multiplies amplitude by 1/f and phase-shifts sinusoid by -900. -90 0 High Frequency Carrier Low Frequency Information Em fc EcJ0(m) Combined Signal fm (fm fc ) ... AMPLIFIER ... (Hz) Amplitude (Volts) Frequency (Hz) Time (Sec.) Time (Sec.) Combined Signal Antenna Gain ... (fc-2fm) (fc-fm) fc (fc+fm) (fc+2fm)Frequency (Hz) ANTENNA (Hz) 0 Voltage (Volts) Amplitude (Volts) Frequency (Hz) Amplitude (Volts) Frequency (Hz) Time (Sec.) Time (Sec.) 16 ... (fc-2fm) (fc-fm) fc (fc+fm) (fc+2fm) Frequency 1 Antenna passes only high frequencies. 0 Combined Signal ... Antenna Gain 1 Antenna passes only high frequencies. Voltage (Volts) fm Combined Signal fm Frequency (Hz) Frequency (Hz) Voltage (Volts) ... ... (fc-2fm) (fc-fm) fc (fc+fm) (fc+2fm) (fc-2fm) (fc-fm) fc (fc+fm) (fc+2fm) Frequency Amplitude (Volts) EcJ1(m) EcJ2(m) K1 Amplifier gain = constant K1. K1 Voltage (Volts) ... Amplifier Gain EcJ1(m) EcJ2(m) Amplifier Gain Amplifier gain = constant K1. EcJ1(m) EcJ2(m) fm (fm fc ) EcJ1(m) EcJ2(m) EcJ0(m) Time (Sec.) Frequency (Hz) Amplitude (Volts) Time (Sec.) ANTENNA Amplitude (Volts) Voltage (Volts) Combined Signal Voltage (Volts) Frequency (Hz) FM MODULATOR PM MODULATOR AMPLIFIER Em fm Ec fm Time (Sec.) Frequency (Hz) Amplitude (Volts) Low Frequency Information Amplitude (Volts) Voltage (Volts) 1 Time (Sec.) 1 f Frequency (Hz) fc Frequency (Hz) Gain 1 Time (Sec.) Low Frequency Information Time (Sec.) Low Frequency Information Frequency (Hz) Amplitude (Volts) Voltage (Volts) INTEGRATOR Amplitude (Volts) Voltage (Volts) fm ... ... Combined Signal (fc-2fm) (fc-fm) fc (fc+fm) (fc+2fm)Frequency (Hz) Copyright © 2004 Lance Breger Copyright © 2004 Lance Breger fm ... ... (fc-2fm) (fc-fm) fc (fc+fm) (fc+2fm) Frequency (Hz) 17
  • 10. OPERATION OF FM RECEIVER ANTENNA Voltage (Volts) external noise The FM receiver is very similar to the superheterodyne AM receiver. The main difference is that the FM receiver uses an FM demodulator; while the superheterodyne AM receiver uses an AM demodulator. In addition, the FM receiver has two stages for noise control that the AM receiver lacks. First, just ahead of the demodulator, there is a limiter to clip off and thereby remove external noise. [This cannot be done in AM because clipping the noise would also remove the information, that is encoded in the amplitude of the carrier wave.] Second, after demodulation in the FM receiver, there is a deemphasis stage, that is involved in combating internal noise. The deemphasis stage corrects the earlier distortion of the signal in the preemphasis stage of the FM transmitter, where high-frequency sinusoids are amplified more than lowfrequency ones. In the FM transmitter, the purpose of distorting the signal is to facilitate the FM receiver's detecting the signal's high frequencies in the presence of high-frequency noise. This noise is generated inside the FM demodulator in the receiver. Basically the deemphasis stage in the receiver is also a nonuniform amplifier which corrects the initial distortion in the transmitter by emphasizing the low frequencies over the high frequencies (i.e., deemphasizes the high frequencies) which were preferentially amplified (i.e., emphasized) by the preemphsis stage in the FM transmitter. In contrast to the AM receivers, the diagram of the FM receiver also shows a noise signal although noise is really present in both types of receivers. However, noise is only shown in the FM case because only FM receivers have special stages to combat noise, i.e., the limiter for external noise and the deemphasis stage for internal noise. AM receivers have no special stages to combat noise. Amplitude (Volts) Time (Sec.) Note that in contrast to all preceding diagrams, in the diagram of this FM receiver and of the following PM receiver, the graphs of the time domain and of the frequency domain are not exactly the same as the output of an actual oscilloscope or of an actual system analyzer. This is because only in these diagrams noise is not combined with the FM or PM signals to produce the total signal that the real instruments display in different forms. ... RF AMP . bandpass filter Voltage (Volts) external noise LO external noise ... ... Frequency (Hz) Amplitude (Volts) fLO Mixer and local oscillator copy Fm signal and noise to lower intermediate frequency range. (fi-2fm) (fi-fm) fi (fi+fm) (fi+2fm) Gain IF amplifier Filter selects band around f i the intermediate frequency. Voltage (Volts) external noise ... external noise ... external noise ... Combined Signal (fi-2fm) (fi-fm) fi (fi+fm) (fi+2fm) 450 Frequency (Hz) Amplitude (Volts) external noise ... Combined Signal ... external noise (fi-2fm) (fi-fm) fi (fi+fm) (fi+2fm) Demodulator noise power FM demodulator introduces increasing noise power at higher frequencies. Voltage (Volts) Amplitude (Volts) Time (Sec.) De-emphasis circuit attenuates higher frequencies to balance them with lower frequencies. Frequency (Hz) Frequency (Hz) Gain Amplitude (Volts) Voltage (Volts) Frequency (Hz) demodulator noise fm Amplitude Frequency (Hz) Limiter produces constant output voltage for input voltage above a critical value. Vin Time (Sec.) Amplitude ... external noise Amplitude (Volts) Time (Sec.) Voltage (Volts) Frequency (Hz) (fi-2fm) (fi-fm) fi (fi+fm) (fi+2fm) IF AMPLIFIER PER SE Frequency (Hz) 1 Amplitude (Volts) Combined Signal LIMITER ... (fc-2fm) (fc-fm) fc (fc+fm) (fc+2fm) 0 Time (Sec.) Voltage (Volts) external noise ... ... ... (fm fi fc fLO) DE-EMPHASIS Frequency (Hz) fLO Time (Sec.) NON-LINEAR DEVICE (mixer) DEMODULATOR (detector, discriminator) ... Amplitude (Volts) Combined Signal FILTER ... fc Vout To simplify the description of the operation of the FM receiver in the presence of noise, we consider that the external noise is white noise (i.e., noise consisting of sinusoids of all frequencies and all with the same amplitude) generated by an impulse and that this noise can be treated separately from the modulated FM signal. This latter simplification is justifiable when all of the modulated FM signal passes through a filter but only the portion of the noise in the passband of the filter passes. external noise ... Time (Sec.) Frequency (Hz) demodulator noise Frequency (Hz) fm AUDIO AMPLIFIER Amplitude (Volts) Voltage (Volts) Time (Sec.) demodulator noise fm Frequency (Hz) SPEAKER 18 Copyright © 2004 Lance Breger 19
  • 11. OPERATION OF PM RECEIVER The PM receiver and the FM receiver are basically the same except that the PM receiver has no deemphasis stage, since there is no need for one. This is because in the PM transmitter there is no preemphasis stage to initially distort the signal. Therefore, there is no need in the PM receiver for a deemphasis stage to correct this non-existent distortion. ANTENNA Voltage (Volts) external noise external noise ... RF AMP. bandpass filter ... ... external noise Amplitude (Volts) Time (Sec.) LO external noise ... ... (fc-2fm) (fc-fm) fc (fc+fm) (fc+2fm) NON-LINEAR DEVICE (mixer) Amplitude (Volts) Voltage (Volts) Gain external noise Amplitude (Volts) ... ... external noise Frequency (Hz) Hence, these diagrams support and enhance the use of simulation by providing a more comprehensive view, operational characteristics of devices, and color coding to locate the information. Amplitude (Volts) external noise Time (Sec.) ... external noise ... Combined Signal (fi-2fm) (fi-fm) fi (fi+fm) (fi+2fm) Vout Voltage (Volts) 2) perational characteristics: o The diagrams show the operational characteristic of the filters, amplifiers, and other parts of the circuit. Simulation does not. 3) istribution of information: d By using a color code, these diagrams show where in the signal the information lies; simulation does not. Knowing the location of the information is critical to understanding the operation of the communication system Frequency (Hz) 1 (fi-2fm) (fi-fm) fi (fi+fm) (fi+2fm) IF AMPLIFIER PER SE 450 (fc-2fm) (fc-fm) fc (fc+fm) (fc+2fm) 0 Combined Signal LIMITER ... 1) lobal view: g The form of the signal can be seen simultaneously at all stages in the cascade instead of only at a few stages at time as in the simulations. Thus, the overall operation of the system is much easier to grasp in these diagrams than by simulation alone. Frequency (Hz) (fi-2fm) (fi-fm) fi (fi+fm) (fi+2fm) Time (Sec.) Voltage (Volts) external noise ... ... ... (fm fi fc fLO) Filter selects band around f i the intermediate frequency. Frequency (Hz) fLO Mixer and local oscillator copy Fm signal and noise to lower intermediate frequency range. IF amplifier Frequency (Hz) fLO Combined Signal FILTER ... (fc-2fm) (fc-fm) fc (fc+fm) (fc+2fm) Voltage (Volts) It is hopeful that the above comments will help the reader to better understand and use the associated diagrams. These relevant graphics can in a simple way give a student a global view of the complex subject of radio transmitters and receivers. The communications circuits that are diagrammed here can also be simulated on a computer, e.g., by using Multisim. However, our diagrams have the following advantages over simulation alone: Amplitude (Volts) Time (Sec.) CONCLUSION Limiter produces constant output voltage for input voltage above a critical value. Vin Frequency (Hz) Amplitude (Volts) external noise Time (Sec.) ... Combined Signal ... external noise (fi-2fm) (fi-fm) fi (fi+fm) (fi+2fm) DEMODULATOR (detector, discriminator) Frequency (Hz) Amplitude (Volts) Voltage (Volts) Amplitude Time (Sec.) demodulator noise Frequency (Hz) fm AUDIO AMPLIFIER Amplitude (Volts) Voltage (Volts) Time (Sec.) demodulator noise fm Frequency (Hz) SPEAKER 20 Copyright © 2004 Lance Breger 21
  • 12. The purpose of these diagrams is to graphically explain the overall operation of AM, PM, and FM communications systems using very little mathematics. Copyright 2004 Lance Breger