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FAA Radar Concepts > Module 4 > Flashcards

Module 4 Flashcards

1
Q

What is receiver sensitivity?

A

The minimum input RF signal a receiver needs to produce a specific intelligence signal at the output

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2
Q

What does the receiver do? (2 answers)

A

Detects and amplifies signals from an aircraft
Separates desired echoes from unwanted signals

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3
Q

What is noise

A

Undesired electrical signals

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4
Q

What are three types of external noise

A

Atmospheric
Human-made
Space

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5
Q

Interference is a type of external noise that is prevalent in ______ composed of undesired signals.

A

overcrowded airwaves

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6
Q

How can adjacent channel interference be eliminated

A

By allowing main equipment to produce triggers for all other systems

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7
Q

What does bandwidth do?

A

Helps determine receiver noise level and minimum sensitivity capability

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8
Q

A _______ IF results in higher noise from the mixer or LO, and a _______ IF results in higher noise from the IF amplifier.

A

lower, higher

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9
Q

The _______ the selected IF, the _______ the mixer or LO noise becomes

A

lower, higher

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10
Q

Bandwidth is a good approximation for a usable circuit because it tends to be _______ to account for instabilities in Doppler effects due to target velocity

A

higher in some systems

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11
Q

What causes adjacent system interference

A

Several stations operating in a frequency band

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12
Q

A lower noise factor indicates the receiver is introducing less noise which results in the ability to _________ the desired signal and noise.

A

differentiate between

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13
Q

The noise figure in a system can be determined by examining ___________.

A

known noise source

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14
Q

Transmitters have ________ power capabilities

A

limited

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15
Q

Radar performance is defined by the _____________ for a specified radar cross-section target.

A

maximum detection range

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16
Q

What is selectivity

A

The extent to which a receiver can differentiate between signals.

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17
Q

What is essential for maximum performance

A

Reducing front-end noise

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18
Q

What are some sources of an unwanted signal (3 answers)

A

Any object other than the desired target
Interference from other radars or communication systems
Signals coming from an aircraft

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19
Q

What are the major characteristics of a receiver? (2 answers)

A

sensitivity and selectivity

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20
Q

What are the types of internal noise (3 answers)

A

Shot
System
Thermal

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21
Q

The noise in a circuit is related to the input impedance’s temperature due to the relationship between ____________.
(3 answers)

A

bandwidth
Boltzmann’s constant
noise temperature

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22
Q

What are three sources of interference

A

Emissions from nearby radars
Intentionally generated signals in the radar’s frequency band
The radar’s other channel

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23
Q

What is Atmospheric noise

A

Caused by naturally occurring disturbances in the Earth’s atmosphere

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24
Q

What is Human-made noise

A

Generated by spark-producing mechanisms

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25
Q

What is SHOT noise

A

Introduced by carriers located in the pn-junctions of the semiconductors

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26
Q

What is Space noise

A

Composed of solar noise from the sun and cosmic noise from the stars

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27
Q

What is Thermal noise

A

Not limited to the receiver, generated within the receive path caused by thermal interaction between free electrons and vibrating ions within a conductor

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28
Q

What is Noise factor

A

Determines the amount of noise by relating the ratio of input signal power and input noise power to output signal power and output noise power

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29
Q

What is Noise figure

A

The increase in noise power of a network from input to output which is greater than signal gain

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30
Q

What is Probability of detection

A

The likelihood an input signal will be detected when deciding if a reading is the signal plus noise, or purely the signal

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31
Q

White noise

A

Frequency content is uniform across the spectrum

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32
Q

What is a large limiting factor to the minimum discernable signal that the radar can detect?

A

System noise

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33
Q

What is the correct order of Receiver components:
Attenuator
IF output
LNA
Mixer
Preselector
T/R limiter

A
  1. T/R limiter
  2. Attenuator
  3. LNA
  4. Preselector
  5. Mixer
  6. IF output
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34
Q

What component reduces the difference between the highest and lowest signals

A

STC (Sensitivity time control)

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35
Q

What component Prevents high-powered transmitter signals from entering the receiver and damaging front-end circuits

A

T/R Limiter

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36
Q

What component Measures the time needed for a receiver to recover to a given sensitivity

A

SRT

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37
Q

What component Improves signal-to-noise ratio of the receiver

A

LNA

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38
Q

What component Controls the attenuator and sends a signal telling it how much an incoming signal level should be reduced.

A

Gain Control Unit

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39
Q

What component Adds voltages together resulting in a voltage that changes at the rate of difference between two frequencies

A

Mixer

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40
Q

What component Determines the amount of signal phase shift

A

Hybrid coupler

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41
Q

What component Reduces the RF front-end’s bandwidth thereby reducing available noise power

A

Preselector

42
Q

What component Separates sidebands and converts each one to the IF frequency

A

Image rejection mixer

43
Q

What component Supplies most of the receiver’s gain and is a major determiner on receiver sensitivity and selectivity characteristics

A

IF amplifier

44
Q

The system’s minimum range capabilities depend on the _______.

A

T/R limiter

45
Q

What can produce strong returns that cause front-end amplifiers to go into saturation

A

Ground clutter

46
Q

The signal from the _________ is developed based on receiver gain settings and STC (Sensitivity time control) curves.

A

gain control circuit

47
Q

Receiver gain is essentially __________.

A

sensitivity

48
Q

Which component changes attenuation automatically as radar range increases

A

STC (Sensitivity time control)

49
Q

If the radar has two feedhorns, the ______ determines which beam to look at

A

attenuator

50
Q

An LNA is _____ at improving the noise figure when it is _____ the receiver signal source

A. equally effective, any distance from
B. less effective, closer to
C. more effective, closer to
D. more effective, further from

A

more effective, closer to

51
Q

What is normal video

A

The simplest type of radar video signal provided to an ATC display

52
Q

What does an MTI (Moving Target Indicator) do

A

Cancels stationary targets not canceled by normal video

53
Q

In legacy radar systems, one output from an IF amplifier supplies the ________. (3 answers)

A

amplifier
linear receiver
normal receiver

54
Q

How does normal video affect the controller’s ability to differentiate between aircraft targets and clutter

A

Normal video makes it more difficult for the controller to differentiate aircraft targets from clutter.

55
Q

What is a shortcoming of MTI

A

Valid aircraft targets can get lost in the cancellation process

56
Q

Normal receivers tend to ________ the accepted signal through a nonlinear device to display ________.

A. down convert, intelligence
B. up convert, intelligence
C. up convert, targets
D. Misconstrue, noise

A

down convert, intelligence

57
Q

What is one of the most effective nonlinear devices for detecting intelligence modulated in a high carrier frequency?

A

Diode detector

58
Q

Which problem with diode detectors made transistor detectors popular

A

The inability to amplify

59
Q

Which radar brought technological advances in radar signal processing that made using normal video obsolete in MTD systems?

A

ASR-9

60
Q

A logarithmic receiver/amplifier amplifies ________ level signals more than _______ level signals.

A. low, high
B. high, low
C. high, moderate
D. moderate, low

A

low, high

61
Q

What is a benefit of a wide dynamic range?

A

Limiting or overloading is not required.

62
Q

The logarithmic receiver/amplifier _______.
A. has an output proportional to the logarithm IF input.
B. has an output proportional to the logarithm RF input.
C. has the same output as the normal receiver/amplifier.
D. produces logarithmic video for the processor’s weather circuits.

A

has an output proportional to the logarithm RF input.
produces logarithmic video for the processor’s weather circuits.

63
Q

The logarithmic receiver’s effectiveness reaches the ______

A

maximum range

64
Q

A logarithmic function is achieved with _____________ and _________ the outputs detected with each amplification stage.

A. cascading stages of limiting IF amplifiers, subtracting
B. cascading stages of limiting IF amplifiers, summing
C. two limiting IF amplifiers, subtracting
D. two limiting IF amplifiers, summing

A

cascading stages of limiting IF amplifiers, summing

65
Q

The 3 dB bandwidth of a logarithmic receiver produces an output that is ________ by ________ times the transfer slope.
A. down converted, two
B. down converted, three
C. up converted, two
D. up converted, three

A

down converted, three

66
Q

The amplifier’s signal-to-noise ratio __________ its drive level.

A

changes with

67
Q

What is a logarithmic receiver used for?

A

Tracking aircraft through inclement weather

68
Q

In a phase detector receiver, down conversion transforms:

A

RF into IF

69
Q

WHat is a problem caused by sensitive phase detectors and radar systems transmitting as an antenna rotates seeing ground clutter differently each pulse

A

Antenna scanning

70
Q

What Determines the system’s ability to detect a target

A

S/N ratio

71
Q

what is it called when a moving target produces a phase shift between pulses such that the outputs from phase detectors have the same amplitude

A

Blind phase

72
Q

what Mitigates the likelihood of target loss and reduce the effects of the blind phase

A

I & Q phase detectors

73
Q

__________ will provide a reference phase for the phase detectors whose output is based on the difference between the reference phase and received echo IF.

A

COHO

74
Q

Which target parameters are not considered by an MTI circuit? ( 2 answers)

A

Range and Size

75
Q

In a phase detector receiver, modulated _______ is mixed with _________ for conversion to bipolar radar video intelligence.

A. IF, COHO
B. IF, STALO
C. RF, COHO
D. RF, STALO

A

IF, COHO

76
Q

Transmitter frequency is the sum of _____.

A

STALO and COHO

77
Q

The ____ is compared to the _______ to generate an IF.

A. COHO, receiver IF echo
B. COHO, receiver RF echo
C. STALO, receiver IF echo
D. STALO, receiver RF echo

A

STALO, receiver RF echo

78
Q

What are the types of phase detector characteristics? ( 3 answers)

A

Sinusoidal
Square
Triangular

79
Q

What does a phase detector’s output show? (2 answers)

A

Fixed and Moving targets

80
Q

What compares the received echo from a target’s amplitude with its received echo in the next transmitter interval?

A

Canceller

81
Q

A moving target’s ______ varies between transmitter intervals on a phase detector display.

A

amplitude

82
Q

Maximum outputs happen at ___ phase difference.

A

0° and 180°

83
Q

Normal and logarithmic video channels in a phase detector use a basic diode type detector circuit to remove the _____ frequency

A

IF

84
Q

What is the first step in detecting a moving target?

A

Determining its relative phase returns

85
Q

When do optimum phase conditions occur?

A

Maximum Positive and negative value

86
Q

What determines the minimum range of a radar system?

A

System recovery time

87
Q

Injecting a signal set below the limit into the waveguide and viewing the receiver output on an oscilloscope helps us determine __________.

A

System recovery time

88
Q

What is the MDS power level used to determine?

A

Receiver sensitivity

88
Q

For the _______ to be a valid input, the signal must represent the expected echo in terms of pulse width.

A

MDS

89
Q

What does using an input signal with a pulse width greater than the transmitted burst indicate?

A

A false increase in receiver sensitivity

90
Q

What is the time it takes a T/R limiter to come out of ionization and let received signals enter the receiver called?

A. Amplitude
B. Minimum range of a radar system
C. Pulse width
D. System recovery time

A

Minimum range of a radar system
System recovery time

91
Q

What is a limiting factor for the minimum range of a system?

A

T/R recovery

92
Q

What does an increase in SRT indicate?

A

Deterioration of a T/R device

93
Q

What is determined by looking at the magnitude of thermal noise, but not realized in practice due to additional receiver noise?

A

Maximum possible sensitivity

94
Q

A receiver’s __________ is measured by the weakest signal that produces a visible receiver output.

A

sensitivity

95
Q

What is the receiver’s ability to pick up weak signals called?

A

Receiver sensitivity

96
Q

What is a measurement of receiver sensitivity?

A

Minimum discernable signal

97
Q

Systems measure the detection percentage a known signal produces through ______.

A

calculated thresholds

98
Q

System noise displayed on an oscilloscope is referred to as ______.

A

the grass level

99
Q

The _______ delivered to the receiver is _______ proportional to pulse width.

A

FAA Radar Concepts (8 decks)

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