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Chapter 7: Angle Modulation Transmission – Review Notes

Chapter 7: Angle Modulation Transmission

This is the summary notes of the important terms and concepts in Chapter 7 of the book "Electronic Communications System" by Wayne Tomasi. The notes are properly synchronized and concise for much better understanding of the book. Make sure to familiarize this review notes to increase the chance of passing the ECE Board Exam.


CHAPTER 7

ANGLE MODULATION
TRANSMISSION


Items

Definitions

Terms

1

Two forms of angle modulation.

FM and PM

2

Angle modulation was first introduced in the year ________ as
an alternative to amplitude modulation.

1931

3

He developed the first successful FM radio system in 1936, and
in July 1939, the first regularly scheduled broad-casting of FM signals began
in Alphine, New Jersey. Also developed the superheterodyne receiver.

Major E. H. Armstrong

4

A modulation that results whenever the phase angle (θ) of
a sinusoidal wave is varied with respect to time.

Angle Modulation

5

Varying the frequency of a constant-amplitude carrier directly
proportional to the amplitude of the modulating signal at a rate equal to the
frequency of the modulating signal.

Direct Frequency Modulation ( FM )

6

Varying the phase of a constant-amplitude carrier directly
proportional to the amplitude of the modulating signal at a rate equal to the
frequency of the modulating signal.

Direct Phase Modulation ( PM )

7

The relative angular displacement (shift) of the carrier phase
in radians in respect to the reference phase.

Phase Deviation (Δθ )

8

The relative displacement of the carrier frequency in hertz in
respect to its unmodulated value.

Frequency Deviation (ΔF )

9

The original unmodulated carrier frequency in the resultant
angle-modulated waveform.

Carrier Rests Frequency

10

The instantaneous change in the phase of the carrier at a
given instant of time and indicates how much the phase of the carrier is
changing with respect to its reference phase.

Instantaneous Phase Deviation

11

The precise phase of the carrier at a given instant of time.

Instantaneous Phase

12

The instantaneous change in frequency of the carrier and is
defined as the first time derivative of the instantaneous phase deviation.

Instantaneous Frequency Deviation

13

The precise frequency of the carrier at a given instant of
time and is defined as the first time derivative of the instantaneous phase.

Instantaneous Frequency

14

Are the output–versus-input transfer functions for the
modulators, which give the relationship between what output parameter changes
in respect to specified changes in the input signal.

Deviation Sensitivities

15

Is called the modulation index or sometimes index of
modulation.

Peak Phase Modulation

16

The change in frequency that occurs in the carrier when it is
acted on by a modulating-signal frequency.

Frequency Deviation

17

The peak-to-peak frequency deviation (2Δf).

Carrier Swing

18

The ratio of the frequency deviation actually produced to the
maximum frequency deviation allowed by law stated in percent form.

Percent Modulation

19

A circuit in which the carrier is varied in such a way that
its instantaneous phase is proportional to the modulating signal.

Phase Modulator

20

A circuit which the carrier is varied in such a way that its
instantaneous phase is proportional to the integral of the modulating signal.

Frequency Modulator

21

________ of the first kind for several values of modulation
index provides the number of side frequency pairs and their corresponding
magnitude.

Bessel Function

22

A side frequency is not considered significant unless it has
amplitude equal to or greater than ____ of the unmodulated carrier amplitude.

1%

23

The modulation index is less than 1.

Low-index Case

24

The modulation index is greater than 10.

High-index Case

25

Modulation indices greater than 1 and less than 10.

Medium Index

26

Low-index FM systems are sometimes called?

Narrowband FM

27

A rule which is an approximation and gives transmission
bandwidths that are slightly narrower than the bandwidths. It defines a
bandwidth that includes approximately 98% of the total power in the modulated
wave.

Carson’s Rule

28

The worst-case modulation index and is equal to the maximum
peak frequency deviation divided by the maximum modulating-signal frequency.

Deviation Ratio ( DR )

29

The FCC has assigned the commercial FM broadcast service a
_______ band of frequencies that extends from 88 MHz to 108 MHZ.

20 MHz

30

The 20–MHz band is divided into 100, ________ wide channels
beginning at 88.1 MHz.

200 kHz

31

To provide high-quality, reliable music, the maximum frequency
deviation allowed is _______ with a maximum modulating-signal frequency of
_______.

75 kHz ; 15 kHz

32

The highest side frequencies from one channel are allowed to
spill over into adjacent channels, producing an interference known as
_______.

Adjacent Channel Interference

33

A _______ wide guard band is usually on either side of each
assigned channel.

200 kHz

34

The noise voltage at the output of an FM demodulator increases
linearly with frequency. This is called ______.

FM Noise Triangle

35

The high-frequency modulating signals are emphasized or
boosted in amplitude in the transmitter prior to performing modulation.

Pre-emphasis

36

The reciprocal of pre-emphasis that restores the original
amplitude-versus-frequency characteristics to the information signals.

De-emphasis

37

A circuit that provides a constant increase in the amplitude
of the modulating signal with an increase in frequency.

Pre-emphasis Network

38

When the frequency of the carrier is modulated by the information
signal, _______ results.

Direct FM ( Indirect PM )

39

When the phase of the carrier is modulated by the information
signal, _______ results.

Direct PM ( Indirect FM )

40

Angle modulation in which the frequency of the carrier is
varied directly by the modulating signal.

Direct FM

41

Three common methods for producing direct frequency
modulation.

Varactor Diode, FM Reactance, Linear IC
Modulations

42

Direct frequency modulator used for low-index Applications,
such as two-way mobile radio.

Varactor Diode Direct FM Modulator

43

A direct FM modulator using a JFET as the active device.

FM Reactance Modulator

44

A complete FM modulator on a single 8-pin DIP integrated
circuit chip.

MC1376

45

Can generate a direct FM output waveform that is relatively
stable, accurate, and directly proportional to the input modulating signal.

Linear IC VCO and Function Generators

46

Angle modulation in which the frequency of the carrier is
deviated indirectly by the modulating signal.

Direct PM

47

Two common methods for producing direct phase modulation.

Varactor Diode and Transistor Direct PM
Modulator

48

The process of up-converting the frequency of the modulated
carrier after modulation has been performed.

Frequency Up-Conversion

49

Two basic methods of performing frequency up-conversion.

Heterodyning and Frequency Multiplication

50

An up-conversion method where a low-frequency modulated
carrier can either be up- or down-converted to a different location in the
frequency spectrum without changing its modulation properties.

Heterodyne Method

51

An up-conversion method where the modulation properties of a
carrier can be increased at the same time that the carrier frequency is
up-converted.

Multiplication Method

52

Transmitters that produce an output waveform in which the
frequency deviation is directly proportional to the modulating signal.

Direct FM Transmitters

53

A circuit that compares the frequency of the non-crystal
carrier oscillator to a crystal reference oscillator and then produces a
correction voltage proportional to the difference between the frequencies.

Automatic Frequency
Control
( AFC )

54

A frequency-selective device whose output voltage is
proportional to the difference between the input frequency and its resonant
frequency.

Frequency Discriminator

55

A voltage added to the modulating signal to automatically
adjust the master oscillator’s center frequency to compensate for the
low-frequency drift.

dc Correction Voltage

56

A ________ preceded by a differentiator generates a PM
waveform.

FM Modulator

57

Transmitters that produce an output waveform in which phase
deviation is directly proportional to the modulating signal.

Indirect FM Transmitters

58

Probably the most significant advantage of angle modulation
transmission over amplitude modulation transmission.

Noise Immunity

59

Allows a receiver to differentiate between two signals
received with the same frequency.

Capture Effect

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