Chapter 5: Fundamentals of Frequency Modulation

Question 1

A ______________ carrier can be modified for the purpose of transmitting information from one place to another by varying its frequency. This is known as frequency modulation (FM).

Answer 1

Sine wave

Question 2

In _____, the carrier amplitude remains constant and the carrier frequency is changed by the modulating signal.

Answer 2

FM

Question 3

As the amplitude of the information signal varies, the carrier frequency shifts _____________________.

Answer 3

Proportionately

Question 4

As the modulating signal amplitude increases, the carrier frequency __________________.

Answer 4

Increases

Question 5

With no modulation the carrier is at its normal center or _____________.

Answer 5

Resting frequency

Question 6

___________________ is the amount of change in carrier frequency produced by the modulating signal.

Answer 6

Frequency deviation

Question 7

The _______________________ is how many times per second the carrier frequency deviates above or below its center frequency.

Answer 7

Frequency deviation rate

Question 8

The ________________of the modulating signal determines the frequency deviation rate.

Answer 8

Frequency

Question 9

A type of modulation called ____________________________ is used in transmission of binary data in digital cell phones and low-speed computer modems.

Answer 9

Frequency-shift keying (FSK)

Question 10

When the amount of phase shift of a constant- frequency carrier is varied in accordance with a modulating signal, the resulting output is a _________________________ signal.

Answer 10

Phase- modulation (PM)

Question 11

_____________________ produce a phase shift which is a time separation between two sine waves of the same frequency.

Answer 11

Phase modulators

Question 12

The greater the ___________________of the modulating signal, the greater the phase shift.

Answer 12

Amplitude

Question 13

The _________________________produced by a phase modulator occurs during the time that the modulating signal is changing at its most rapid rate.

Answer 13

Maximum frequency deviation

Question 14

In FM and in PM, the frequency deviation is _________________ to the amplitude of the modulating signal.

Answer 14

Directly proportional

Question 15

In _________, the maximum amount of leading or lagging phase shift occurs at the peak amplitudes of the modulating signal.

Answer 15

PM

Question 16

In PM the ______________ is proportional to both the modulating frequency and the amplitude.

Answer 16

Carrier deviation

Question 17

In order to make PM compatible with FM, the deviation produced by frequency variations in the modulating signal must be _________.

Answer 17

Compensated

Question 18

This compensation can be accomplished by ______the intelligence signal through a low-pass RC network.

Answer 18

Passing

Question 19

This RC low-pass filter is called a frequency- correcting network, predistorter, or 1/f filter and causes the higher modulating frequencies to be ___________.

Answer 19

Attenuated

Question 20

The FM produced by a phase modulator is called ____________.

Answer 20

Indirect FM

Question 21

The process of phase modulating a carrier with binary data is called _____________________ or ___________________________.

Answer 21

Phase-shift keying (PSK), Binary phase-shift keying (BPSK).

Question 22

The PSK signal has a ______________________, but the phase of the signal from some reference changes as the binary modulating signal occurs.

Answer 22

Constant frequency

Question 23

Any modulation process produces ____________. When a constant-frequency sine wave modulates a carrier, two side frequencies are produced.

Answer 23

Sidebands

Question 24

Side frequencies are the sum and difference of the carrier and ___________________.

Answer 24

Modulating frequency

Question 25

The bandwidth of an FM signal is usually much _______ than that of an AM signal with the same modulating signal.

Answer 25

Wider

Question 26

The ratio of the frequency deviation to the modulating frequency is known as the __________________.

Answer 26

Modulation index (m)

Question 27

In most communication systems using FM, maximum limits are put on both the _______________ and the __________.

Answer 27

Frequency deviation, modulating frequency.

Question 28

In standard FM broadcasting, the maximum permitted frequency deviation is ________ and the maximum permitted modulating frequency is 15 kHz.

Answer 28

75 kHz

Question 29

The modulation index for standard FM broadcasting is therefore __.

Answer 29

5

Question 30

The equation that expresses the phase angle in terms of the sine wave modulating signal is solved with a complex mathematical process known as _______________.

Answer 30

Bessel functions

Question 31

The higher the modulation index in FM, the ______ the number of significant sidebands and the wider the bandwidth of the signal.

Answer 31

Greater

Question 31

When ________ conservation is necessary, the bandwidth of an FM signal can be restricted by putting an upper limit on the modulation index.

Answer 31

Spectrum

Question 32

______ is interference generated by lightning, motors, automotive ignition systems, and power line switching that produces transient signals.

Answer 32

Noise

Question 33

Noise is typically narrow ______ of voltage with high frequencies.

Answer 33

spikes

Question 34

Noise (voltage spikes) add to a signal and ______ with it.

Answer 34

interfere

Question 35

Some noise completely _______________ signal information.

Answer 35

obliterates

Question 36

FM signals have a __________ modulated carrier amplitude.

Answer 36

constant

Question 37

FM receivers contain limiter circuits that deliberately restrict the ____________ of the received signal.

Answer 37

amplitude

Question 38

Any _______________ variations occurring on the FM signal are effectively clipped by limiter circuits.

Answer 38

amplitude

Question 39

This amplitude clipping does not affect the information content of the FM signal, since it is contained solely within the frequency variations of the _____________.

Answer 39

carrier

Question 40

Noise can interfere with an ___ signal and particularly with the high-frequency components of the modulating signal.

Answer 40

FM

Question 41

Noise is primarily sharp spikes of energy and contains a lot of _________ and other high-frequency components.

Answer 41

harmonics

Question 42

A simple high-pass filter can serve as a transmitter's ________________ circuit.

Answer 42

pre-emphasis

Question 43

To overcome high-frequency noise, a technique known as _____________ is used.

Answer 43

pre-emphasis

Question 44

Pre-emphasis provides more _____________ of only high- frequency components.

Answer 44

amplification

Question 45

A simple low-pass filter can operate as a __________________ circuit in a receiver.

Answer 45

deemphasis

Question 46

A de-emphasis circuit returns the frequency response to its normal ___________ level.

Answer 46

flat

Question 47

The combined effect of preemphasis and deemphasis is to increase the signal-to-noise ratio for the high- frequency components during transmission so that they will be _________________ and not masked by noise.

Answer 47

stronger

Question 48

FM has superior immunity to __________, made possible by clipper limiter circuits in the receiver.

Answer 48

noise

Question 49

In FM, interfering signals on the same frequency are rejected. This is known as the ______________.

Answer 49

capture effect

Question 50

FM signals have a constant amplitude and there is no need to use linear amplifiers to increase power levels. This increases ________________.

Answer 50

transmitter efficiency

Question 51

In the past, the circuits used for frequency modulation and demodulation involved were complex. With the __________________of ICs, complex circuitry used in FM has all but disappeared. ICs are inexpensive and easy to use. FM and PM have become the most widely used modulation method in electronic communication today.

Answer 51

proliferation

Question 52

FM uses considerably more frequency _______________ space.

Answer 52

spectrum

Question 53

FM has used more complex circuitry for ______________________ and _______________________.

Answer 53

modulation , demodulation