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MOD 5 > Unit 5 > Flashcards

Unit 5 Flashcards

1
Q

The process of superimposing an input signal, also called the intelligence signal onto a carrier wave is called___

A

Modulation

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2
Q

Time is not a form of modulation.
(T or F)

A

True

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3
Q

This type of modulation changes the voltage of the RF carrier for transmitting

A

Amplitude

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4
Q

What parts of the intelligence waveform affect the amplitude of the modulated waveform in amplitude modulation?

A

Amplitude

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5
Q

In amplitude modulation, what are the output signals of the modulator? (3)

A

Carrier, Upper Sideband, Lower Sideband

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6
Q

In amplitude modulation, the intelligence is carried in the (2)

A

Upper and Lower Sideband

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7
Q

What type of modulation inefficiently uses bandwidth and power during transmission?

A

Amplitude

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8
Q

What are 3 advantages of amplitude modulation?

A
  1. simple to implement
  2. can be demodulated using a single diode rectifier
  3. Cost
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9
Q

List 3 disadvantages of amplitude modulation

A
  1. prone to high noise levels
  2. inefficient use of power
  3. inefficient use of bandwidth
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10
Q

In amplitude modulation, how much power is found in the carrier?

A

50%

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11
Q

In Amplitude Modulation, how much power is found in the upper sideband?

A

25%

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12
Q

In amplitude modulation, how much power is found in the lower sideband?

A

25%

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13
Q

What are the variants of Single sideband?

A

LSB SSB
USB SSB
DSB
ISB
AME (amplitude modulated equivalent)

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14
Q

Single Sideband is widely used in the ___ portion of the frequency spectrum.

A

HF

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15
Q

3 advantages of single sideband

A

1.Reduction in transmitter power requirements
2.More effective solution for two way radio comm.
3.Reduced receiver bandwidth by half

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16
Q

Disadvantages of single sideband

A

1.More complex circuits
2.cost more than AM
3. Circuits require more maintenance

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17
Q

What modulation is resilient to noise and interference and used for high quality broadcast transmission?

A

Frequency

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17
Q

In FM, what parts of the intelligence waveform affect the frequency of the modulated waveform?

A

Frequency

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18
Q

In FM, the amount the signal deviates above and below the center frequency is known as___

A

deviation

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19
Q

2 methods to generate frequency modulated signals

A

Varactor Diode Oscillator
Phase Lock Loop

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20
Q

The FM demodulator may also be called

A

detector or discriminator

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21
Q

3 advantages of FM

A

1.Resilient to noise and interference
2.Easy to apply modulation at low power stage of the transmitter
3.Use of non-linear RF amplifiers are more efficient than the linear

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22
Q

3 disadvantages of FM

A

Poor spectrum efficiency
Complicated circuits
Some modes have higher spectrum requirements

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23
Q

Binary digit, logic 1 or 0

A

Bit

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24
Q

Composed of 8 bits

A

Byte

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25
Q

Bits that contain the user’s data to be transmitted

A

Information Bits

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26
Q

Bits inserted by communications devices that are NOT part of the user’s data.

A

Non-Information bits

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27
Q

First step in converting an analog signal to a digital signal.

A

Sampling

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28
Q

The process of combining the data of multiple users into a single output.

A

Multiplexing

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29
Q

A collection of data samples taken from the individual user channel during multiplexing.

A

Frame

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30
Q

Amount of time it takes for one frame to occur in between framing bits

A

Frame period

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31
Q

Amount of data transmitted across the network and expressed as bits per second.

A

Bandwidth

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32
Q

Dr. Harry Nyquist created what is known as the Nyquist Theorem which states that analog voice must be sampled __ the highest frequency.

A

Twice

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33
Q

____ Code Modulation converts analog voice to digital by sampling at ___ times per second.

A

Pulse, 8,000

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34
Q

Digitize is NOT a step of Pulse Code Modulation. True or False

A

True

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35
Q

What PCM step assigns a decimal value to sampled signal?

A

Quantize

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36
Q

What step step in PCM samples the analog input 8,000 times per second?

A

Sample

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37
Q

What PCM step converts decimal values to 8-bit binary words?

A

Encode

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38
Q

How many frequencies are used in FSK?

A

Two

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39
Q

What bits per symbol does FSK output?

A

1 or 0

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40
Q

How many voltages are used in ASK?

A

Two

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41
Q

What bits per symbol does ASK output?

A

1 or 0

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42
Q

ASK is susceptible to noise interference because it involves changing ___ levels between logic states.

A

Voltage

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43
Q

What type of shift keying creates a logic one for one voltage and a logic zero for another voltage?

A

ASK

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44
Q

What type of modulation modulates digital data by shifting the phase of an analog carrier in only 2 degrees: 0 and 180?

A

BPSK

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45
Q

How many bits per symbol does BPSK output?

A

1

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46
Q

What two different degrees does BPSK modulate digital date in? *

A

0 and 180

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47
Q

How many bits of data are transmitted per phase shift keying in QPSK? *

A

2

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48
Q

What type of phase shift keying transitions at 0, 90, 180, and 270 degrees with only two bits?

A

QPSK

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49
Q

What is the first modulation technique that transmits 3 bits of data per symbol?

A

QAM

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50
Q

What is widely used for transmitting higher data rates than ordinary amplitude modulated and phase modulated schemes?

A

QAM

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51
Q

In QAM, what does the third bit indicate?

A

Amplitude

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52
Q

Does coding for error correction for reception by adding error correcting bits to received data.

A

Channel Decoder

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53
Q

Takes a physical input and converts it to an electrical signal. Also consists of an analog to digital converter where a digital signal is needed for further processes.

A

Input transducer and A to D converter

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54
Q

Converts electrical signal into physical output.

A

Output Transducer and D to A converter

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55
Q

Digitized by sampling and quantizing. Recreates source output without loss of information *

A

Source Decoder

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56
Q

Compresses data into minimum number of bits to help in effective utilization of bandwidth. Removes the redundant bits and unnecessary excess bits such as zeroes. *

A

Source Encoder

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57
Q

Allows analog signal to transmit from the transmitter end to receiver end.

A

Channel

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58
Q

Signal is demodulated as well as converted again from analog to digital and reconstructed.

A

Digital demodulator and A to D converter

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59
Q

Does coding for error correction. Adds error correcting bits to transmitted data. *

A

Channel Encoder

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60
Q

Modulated by a carrier and converted to analog from the digital sequence.

A

Digital Modulator and D to A converter

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61
Q

What is the multiplexing technique that uses timeslots to divide the total bandwidth for all connected users?

A

Time Division Multiplexing

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62
Q

What is the multiplexing technique that divides total frequency bandwidth amongst its users?

A

Frequency Division Multiplexing

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63
Q

The synchronous mode of TDM uses ___ bits to establish synchronization between transmit and receive multiplexers.

A

Frame

64
Q

The asynchronous mode of TDM uses ___ bits to establish synchronization between transmit and receive multiplexers.

A

Start/Stop

65
Q

What mode of TDM is best used for voice and video apps where steady data stream is more important than accuracy?

A

Isochronous

66
Q

In the isochronous mode of TDM, ____ bits make an asynchronous transmission flow at a synchronous rate.

A

Pulse stuffing

67
Q

4 types of Return to Zero

A

RZ neutral
RZ Polar
RZ Bipolar
RZ Bipolar with zero suppression

68
Q

What is a signal format where logic ones are +5V and logic zero is 0V. They will not return to 0V halfway?

A

NRZ

69
Q

What is used to break up a long string of consecutive logic zeroes that could lead to synchronization loss?

A

BZS

70
Q

What uses phase transitions to represent logic 0s and 1s?

A

CDI

71
Q

Increases signal power to increase the transmit distance.

A

RF Amplifier

72
Q

An energy source. It provides power to the transmitter components and for broadcasting

A

Power Supply

73
Q

Takes the weak audio signal and amplifies it to be sent to the modulator

A

Audio Amplifier

74
Q

Generates a constant frequency; this frequency is called a carrier wave

A

Electronic Oscillator

75
Q

Enables an antenna to operate over different frequencies by matching the impedance of the transmitter and the antenna.

A

Antenna Tuner/Coupler

76
Q

Superimposes (overlay) the intelligence onto the carrier wave (VCO frequency)

A

Modulator/Mixer

77
Q

Creates electromagnetic (RF) wave that gets transmitted

A

Antenna

78
Q

Phase is NOT a characteristic of an antenna wave. T or F

A

True

79
Q

Antenna waves travel at the speed of light. T or F

A

T

80
Q

As frequency increases, the radio wavelength will___

A

decrease

81
Q

The distance between the crests of a RF wave is the ____

A

wavelength

82
Q

How radio signals radiate from the antenna is___

A

Outward

83
Q

2 types of propagation

A

Ground waves
Sky waves

84
Q

3 components of a ground wave

A

Direct wave
Ground Reflected Wave
Surface Wave

85
Q

Also known as a line-of-sight wave, this wave travels in a straight line and must be “seen” by both the transmitting and receiving antennas

A

Direct wave

86
Q

This wave is reflected from the surface of the earth between the transmitter and receiver.

A

Ground reflected wave

87
Q

This wave is electrically coupled to the surface of the earth.

A

Surface wave

88
Q

All ground waves arrive to their destination at the same time. T or F

A

False

89
Q

This wave is reflected/refracted off the ionosphere for beyond line-of-sight (BLOS)

A

Sky Wave

90
Q

When and what type of frequencies work better with sky waves?

A

Day and Higher

91
Q

300KHz-3MHz

A

Medium Frequency

92
Q

3MHz-30MHz

A

High Frequency

93
Q

30MHz-300MHz

A

Ultra High Frequency

94
Q

300MHz-3GHz

A

Very High Frequency

95
Q

3GHz-30GHz

A

Super High Frequency

96
Q

30GHz-300GHz

A

Extremely High Frequency

97
Q

The bending of a wave as it enters a medium of a different density

A

Refraction

98
Q

30-56 miles, it is the lowest and densest layer of the ionosphere. This density allows more molecules to collide, dissipating their energy. Dissipates at night

A

D Layer

99
Q

When a wave bounces off a surface or obstruction and the same angle as thr angle of incidence

A

Reflection

100
Q

The scientific process involving the bending of a wave as it encounters a constriction or edge.

A

Diffraction

101
Q

Theoretical space void of free electrons or ions

A

Free Space

102
Q

56-93 miles, it is not normally used for HF communications. Anomalies within the layer can cause unexpected behavior of the signal.

A

E layer

103
Q

A reduction in total power density of an electromagnetic wave as it propagates

A

Path Loss

104
Q

93-300 plus miles, divided into two sub-regions, F1 and F2. Increasing ionization during the day causes the layer to separate into these two regions and they recombine at night

A

F Layer

105
Q

The loss experienced by traveling through space

A

Free Space Loss

106
Q

The earths atmosphere is divided into distinct layers separated by____

A

Height

107
Q

The lowest layer where all the weather occurs is called the _____

A

Troposphere

108
Q

The troposphere extends to around ___ miles. (15km) high

A

11

109
Q

The layer important for radio communication after the troposphere is the ____.

A

Ionosphere

110
Q

____ is the bending of a wave as it enters a medium of different density.

A

Refraction

111
Q

The ionosphere is closer to the sun, causing particles to lose electrons & become ____.

A

Ionized

112
Q

Free electrons in the ionosphere form into electron clouds that vary in_____.

A

Thickness

113
Q

3 layers of Ionosphere

A

D, E, F

114
Q

F layer breaks into 2 layers, what are they?

A

F1 & F2

115
Q

The bending of a wave as it encounters a construction or edge is known as____.

A

Diffraction

116
Q

Signal absorption mainly of occurs in what layer of the ionosphere?

A

D layer

117
Q

The D layer is the lowest & densest layer, causing ____ of AM broadcast radio.

A

Absorption

118
Q

The E layer is known for _____ in the layer causing unexpected signal behavior.

A

Anomalies

119
Q

The F2 layer is most useful for long-range sky wave propagation due to its height. True or False

A

True

120
Q

The law of reflection states that the angle of incidence equals the______.

A

Angle of reflection

121
Q

Reflection of sky waves in the ionosphere involves a hybrid of ____ & reflection.

A

Refraction

122
Q

The critical angle determines whether a frequency will ____ off a layer or penetrate through.

A

Reflect

123
Q

Lower frequencies diffract more than higher frequencies due to their

A

Longer wavelengths

124
Q

____ is caused by temperate inversion, layers of warm air above layers of cooler air creating a duct.

A

Ducting

125
Q

A wave trapped in this wave continues to reflect between the two layers.

A

Ducting

126
Q

Caused by random pockets of air; humidity, temperature variations at different altitudes more severe at lower elevation angles, changes refractive index; rapid fluctuation of amplitude or phase of a wave.

A

Tropospheric Scintillation

127
Q

____ is development of multiple transmission paths; receiving signals arrive at different times.

A

Multipathing

128
Q

____ ____ is the weakening of signals in the atmosphere; amount fluctuates with frequency, geography, location etc.

A

Atmospheric Attenuation

129
Q

Loss incurred traveling in free space between transmitting and receiving antenna.

A

Free Space Loss

130
Q

Space between transmitting and receiving antenna.

A

Free Space

131
Q

Reduction in total power density of an electromagnetic wave as it propagates.

A

Path Loss

132
Q

Difference between power transmitted and power received.

A

Path Loss

133
Q

What are the 2 types of path loss?

A

Free Space Loss
Atmospheric Attenuation

134
Q

Define antenna efficiency

A

Compares power delivered to the antenna vs power radiated out the antenna

135
Q

Antenna losses are dissipated as what?

A

Heat

136
Q

The most common loss of radiated energy is due to….

A

Impedance matching

137
Q

What is an example of a low efficiency antenna?

A

Dummy Load

138
Q

What is VSWR?

A

Voltage Standing Wave Radio

139
Q

What frequency ranges are impedance mismatches more prevelant?

A

HF and lower frequency radios

140
Q

Antennas designed to work efficiently for a given frequency are _____ antennas

A

Resonant

141
Q

Antennas required to be tuned with an antenna tuner or coupler to allow maximum power transfer are ____ antennas.

A

non-resonant

142
Q

The difference in the length of a wave as its travels through a new medium as compared to free space is the ____ length.

A

Electrical

143
Q

Electrical length is measured in ____.

A

Wavelength

144
Q

The actual length of the conductor from end to end including the radio connected from the cable to the antenna is the _______.

A

Physical length

145
Q

Physical length is measured in _____.

A

Meters/Feet

146
Q

Receive and transmit properties of an antenna are identical is the law of ____.

A

Reciprocity

147
Q

Which field determines polarization of an antenna?

A

E

148
Q

Antennas with a 45 degree polarization mismatch will have a ___ power loss.

A

Half

149
Q

Linear polarization consist of what 2 types of polarization.

A

Vertical and Horizon

150
Q

It is possible to transmit in circular polarization and receive linear. T or F

A

True

151
Q

What radiation patters are plotted as a function of the square of the magnitude of electric and magnetic fields on a db scale?

A

Power

152
Q

What radiation patterns are plotted as a function of electric and magnetic fields on a logarithmic scale?

A

Field

153
Q

Directivity of an antenna. Ratio of power radiated in a particular direction vs radiated in all directions is known as….

A

Antenna gain

154
Q

A theoretical antenna that radiates well in all directions like a sphere is a what type of antenna?

A

Theoretical isotropic antenna

155
Q

The size of the antenna peak lobe where power decreases to 50% is beam ____.

A

width

156
Q

Another name for usable beam width is___ ___.

A

half power beam width

157
Q

Interference from 2 or more electrical systems affecting all systems equally is____

A

Mutual interference

MOD 5 (2 decks)

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