NAVEDTRA 14184A, NAVY ELECTRICTY AND ELECTRONICS TRAINING SERIES, MODULE 12-MODULATION

Question 1

Which year was the first practical telegraph established in London, England?

Answer 1

1838

Question 2

Which year did Marconi demonstrate the first practical wireless transmitter?

Answer 2

1897

Question 3

Which year was the first successful transatlantic transmissions achieved?

Answer 3

1902

Question 4

What is the ability to impress intelligence upon a transmission media?

Answer 4

Modulation

Question 5

What is the mixing two frequencies across a nonlinear impedance known as?

Answer 5

Heterodyning

Question 6

What is the basic alternating waveform for all complex waveforms?

Answer 6

Sine wave

Question 7

What is generated by rotating a coil in the magnetic field between two magnets?

Answer 7

Alternating current

Question 8

What indicates how much of a cycle has been completed at any given instant?

Answer 8

Phase angle

Question 9

Which cycle property is the elapsed time from the beginning of a cycle to its completion?

Answer 9

Period

Question 10

Which sine wave property is determined by its physical length?

Answer 10

Wavelength

Question 11

The frequencies involved in normal speech vary from a low of about 90 hertz for a deep bass to as high as what for a high soprano?

Answer 11

10 KHz

Question 12

What is the ability known as to faithfully reproduce the input in the output?

Answer 12

Fidelity

Question 13

What is the minimum frequency range that can be used for the transmission of speech?

Answer 13

500 to 2,000 hertz

Question 14

In the modulation process, waves from the information source are impressed onto a radio-frequency sine wave called a what?

Answer 14

Carrier

Question 15

What is an information wave normally referred to as?

Answer 15

Modulating wave

Question 16

Output rises and falls directly with the input in which type of devices?

Answer 16

Linear

Question 17

Which type of impedance is one in which the resulting current is not directionally proportional to the change in the applied voltage?

Answer 17

Nonlinear

Question 18

What is the sum of two individual sine waves?

Answer 18

Complex waveform

Question 19

What is the process of combining two or more frequencies in a nonlinear impedance which results in the production of new frequencies called?

Answer 19

Heterodyning

Question 20

How can the heterodyning process be analyzed?

Answer 20

Spectrum analysis

Question 21

What is the amound of the frequency spectrum that signals occupy known as?

Answer 21

Bandwidth

Question 22

How many conditions must be met in a circuit for heterodyning to occur?

Answer 22

Two

Question 23

What refers to any method of varying the amplitude of an electromagnetic carrier frequency in accordance with the intelligence to be transmitted by the carrier?

Answer 23

Amplitude modulation

Question 24

What is a radio-frequency wave suitable for modulation by the intelligence to be transmitted?

Answer 24

Carrier frequency

Question 25

What is on-off keying referred to as when applied to a continuously oscillating radio-frequency source?

Answer 25

CW signaling

Question 26

What was the first type of modulation used?

Answer 26

Continuous wave

Question 27

What is a system of on-off keying developed for telegraph that is capable of passing intelligence over wire at an acceptable rate?

Answer 27

Morse code

Question 28

What is one of the best methods for keying amplifier stages in transmitters?

Answer 28

Blocked-grid keying

Question 29

Which type of transmission has a high degree of clarity under severe noise conditions, long-range operation, and narrow bandwidth?

Answer 29

Continuous-wave

Question 30

What is required when keying takes place in an intermediate or final amplifier operating at comparatively high power?

Answer 30

Buffer

Question 31

Oscillators are too unstable for direct frequency control in what type of transmitters?

Answer 31

VHF and UHF

Question 32

In practice, the multiplication factor (number of times the input frequency is multiplied) is seldom larger than what in any one stage?

Answer 32

Five

Question 33

Who developed the principles on which modern communications are built?

Answer 33

Alexander Graham Bell

Question 34

What is an energy converter that changes sound energy into electrical energy?

Answer 34

Microphone

Question 35

What has the largest voltage output for a given mechanical stress and is the most commonly used crystal in microphones?

Answer 35

Rochelle salt

Question 36

Crystal microphones are delicate and must be handled with care. Exposure to temperatures above what may permanently damage the crystal unit?

Answer 36

125 degrees F

Question 37

The dynamic microphone has a uniform response over a frequency range that extends from 40 to what?

Answer 37

15,000 hertz

Question 38

An AM transmitter can be divided into what two major sections according to the frequencies at which they operate?

Answer 38

RF and AF

Question 39

What are all of the sum frequencies above the carrier spoken of collectively as?

Answer 39

Upper sideband

Question 40

What is the resultant wave called when the carrier and sidebands are combined in a single impedance and viewed simultaneously with an oscilloscope?

Answer 40

Modulation envelope

Question 41

Which agency assigns carrier frequencies for radio stations in the standard broadcast band?

Answer 41

Federal Communications Commission (FCC)

Question 42

The standard AM broadcast band starts at 535 kilohertz and ends at what?

Answer 42

1,605 kilohertz

Question 43

How many sidebands accompany a carrier wave which has been modulated by voice or music signals?

Answer 43

Two

Question 44

What generates unwanted (SPURIOUS) sideband frequencies

Answer 44

Overmodulation

Question 45

To measure degrees of modulation less than 100 percent, what can you use to indicate the relative magnitudes of the rf carrier and the audio-modulating signal?

Answer 45

Modulation factor

Question 46

Which two categories are modulator circuits usually placed into?

Answer 46

High or Low

Question 47

What does the FCC define in the Code of Federal Regulations as "modulation produced in the plate circuit of the last radio stage of the system"?

Answer 47

High-Level modulation

Question 48

What is the simplest modulator available which is also the easiest to adjust for proper operation?

Answer 48

Plate modulation

Question 49

Which action in the plate modulator effectively changes an audio frequency to a different part of the frequency spectrum?

Answer 49

Heterodyning

Question 50

What is widely used in portable and mobile equipment to reduce size and power requirements?

Answer 50

Control-grid modulator

Question 51

What is generally employed when audio power is limited and distortion of the grid-modulated circuit cannot be allowed?

Answer 51

Cathode modulator

Question 52

What is the process of re-creating original modulating frequencies (intelligence) from the RF carrier referred to as?

Answer 52

Demodulation

Question 53

Which type of modulation consists of on-off keying of a carrier wave?

Answer 53

Continuous-Wave (CW)

Question 54

Which reception method is highly selective and allows little interference from adjacent cw stations?

Answer 54

Heterodyne

Question 55

What is used to receive short-wave code signals because it is easy to adjust and has high sensitivity and good selectivity?

Answer 55

Regenerative detector

Question 56

What refers to any method of modulating an electromagnetic carrier frequency by varying its amplitude in accordance with the message intelligence that is to be transmitted?

Answer 56

Amplitude modulation

Question 57

What is normally used where large input signals are supplied and linear output is required?

Answer 57

Series-diode detector

Question 58

What is often used in receivers to supply an amplified detected output?

Answer 58

Common-Emitter Detector

Question 59

What is essentially a tank circuit which is turned into a frequency either slightly above or below the FM carrier frequency?

Answer 59

Slope detector

Question 60

What uses a double-tuned RF transformer to convert frequency variations in the received FM signal to amplitude variations?

Answer 60

Phase-shift discriminator

Question 61

The output of the Foster-Seeley discriminator is affected not only by the input frequency, but also to a certain extent by what?

Answer 61

Input amplitude

Question 62

What occurs when an input frequency higher than the center frequency is applied to the discriminator circuit and the current and voltage phase relationships change?

Answer 62

Phase shift

Question 63

What uses the amplitude of a pulse-amplitude modulated (PAM) signal or the duration of a pulse-duration modulated (pdm) signal to charge a holding capacitor and restore the original waveform?

Answer 63

Peak detection