NAVEDTRA 14184A, NAVY ELECTRICTY AND ELECTRONICS TRAINING SERIES, MODULE 12-MODULATION Flashcards
Which year was the first practical telegraph established in London, England?
1838
Which year did Marconi demonstrate the first practical wireless transmitter?
1897
Which year was the first successful transatlantic transmissions achieved?
1902
What is the ability to impress intelligence upon a transmission media?
Modulation
What is the mixing two frequencies across a nonlinear impedance known as?
Heterodyning
What is the basic alternating waveform for all complex waveforms?
Sine wave
What is generated by rotating a coil in the magnetic field between two magnets?
Alternating current
What indicates how much of a cycle has been completed at any given instant?
Phase angle
Which cycle property is the elapsed time from the beginning of a cycle to its completion?
Period
Which sine wave property is determined by its physical length?
Wavelength
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?
10 KHz
What is the ability known as to faithfully reproduce the input in the output?
Fidelity
What is the minimum frequency range that can be used for the transmission of speech?
500 to 2,000 hertz
In the modulation process, waves from the information source are impressed onto a radio-frequency sine wave called a what?
Carrier
What is an information wave normally referred to as?
Modulating wave
Output rises and falls directly with the input in which type of devices?
Linear
Which type of impedance is one in which the resulting current is not directionally proportional to the change in the applied voltage?
Nonlinear
What is the sum of two individual sine waves?
Complex waveform
What is the process of combining two or more frequencies in a nonlinear impedance which results in the production of new frequencies called?
Heterodyning
How can the heterodyning process be analyzed?
Spectrum analysis
What is the amound of the frequency spectrum that signals occupy known as?
Bandwidth
How many conditions must be met in a circuit for heterodyning to occur?
Two
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?
Amplitude modulation
What is a radio-frequency wave suitable for modulation by the intelligence to be transmitted?
Carrier frequency
What is on-off keying referred to as when applied to a continuously oscillating radio-frequency source?
CW signaling
What was the first type of modulation used?
Continuous wave
What is a system of on-off keying developed for telegraph that is capable of passing intelligence over wire at an acceptable rate?
Morse code
What is one of the best methods for keying amplifier stages in transmitters?
Blocked-grid keying
Which type of transmission has a high degree of clarity under severe noise conditions, long-range operation, and narrow bandwidth?
Continuous-wave
What is required when keying takes place in an intermediate or final amplifier operating at comparatively high power?
Buffer
Oscillators are too unstable for direct frequency control in what type of transmitters?
VHF and UHF
In practice, the multiplication factor (number of times the input frequency is multiplied) is seldom larger than what in any one stage?
Five
Who developed the principles on which modern communications are built?
Alexander Graham Bell
What is an energy converter that changes sound energy into electrical energy?
Microphone
What has the largest voltage output for a given mechanical stress and is the most commonly used crystal in microphones?
Rochelle salt
Crystal microphones are delicate and must be handled with care. Exposure to temperatures above what may permanently damage the crystal unit?
125 degrees F
The dynamic microphone has a uniform response over a frequency range that extends from 40 to what?
15,000 hertz
An AM transmitter can be divided into what two major sections according to the frequencies at which they operate?
RF and AF
What are all of the sum frequencies above the carrier spoken of collectively as?
Upper sideband
What is the resultant wave called when the carrier and sidebands are combined in a single impedance and viewed simultaneously with an oscilloscope?
Modulation envelope
Which agency assigns carrier frequencies for radio stations in the standard broadcast band?
Federal Communications Commission (FCC)
The standard AM broadcast band starts at 535 kilohertz and ends at what?
1,605 kilohertz
How many sidebands accompany a carrier wave which has been modulated by voice or music signals?
Two
What generates unwanted (SPURIOUS) sideband frequencies
Overmodulation
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?
Modulation factor
Which two categories are modulator circuits usually placed into?
High or Low
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”?
High-Level modulation
What is the simplest modulator available which is also the easiest to adjust for proper operation?
Plate modulation
Which action in the plate modulator effectively changes an audio frequency to a different part of the frequency spectrum?
Heterodyning
What is widely used in portable and mobile equipment to reduce size and power requirements?
Control-grid modulator
What is generally employed when audio power is limited and distortion of the grid-modulated circuit cannot be allowed?
Cathode modulator
What is the process of re-creating original modulating frequencies (intelligence) from the RF carrier referred to as?
Demodulation
Which type of modulation consists of on-off keying of a carrier wave?
Continuous-Wave (CW)
Which reception method is highly selective and allows little interference from adjacent cw stations?
Heterodyne
What is used to receive short-wave code signals because it is easy to adjust and has high sensitivity and good selectivity?
Regenerative detector
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?
Amplitude modulation
What is normally used where large input signals are supplied and linear output is required?
Series-diode detector
What is often used in receivers to supply an amplified detected output?
Common-Emitter Detector
What is essentially a tank circuit which is turned into a frequency either slightly above or below the FM carrier frequency?
Slope detector
What uses a double-tuned RF transformer to convert frequency variations in the received FM signal to amplitude variations?
Phase-shift discriminator
The output of the Foster-Seeley discriminator is affected not only by the input frequency, but also to a certain extent by what?
Input amplitude
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?
Phase shift
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?
Peak detection
