Module 4 Flashcards by Joseph Monast

What is receiver sensitivity?

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

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What does the receiver do? (2 answers)

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

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What is noise

Undesired electrical signals

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What are three types of external noise

Atmospheric
Human-made
Space

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

overcrowded airwaves

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How can adjacent channel interference be eliminated

By allowing main equipment to produce triggers for all other systems

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What does bandwidth do?

Helps determine receiver noise level and minimum sensitivity capability

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

lower, higher

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

lower, higher

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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

higher in some systems

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What causes adjacent system interference

Several stations operating in a frequency band

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

differentiate between

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

known noise source

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Transmitters have ________ power capabilities

limited

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

maximum detection range

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What is selectivity

The extent to which a receiver can differentiate between signals.

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What is essential for maximum performance

Reducing front-end noise

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

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

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

sensitivity and selectivity

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What are the types of internal noise (3 answers)

Shot
System
Thermal

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

bandwidth
Boltzmann’s constant
noise temperature

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What are three sources of interference

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

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What is Atmospheric noise

Caused by naturally occurring disturbances in the Earth’s atmosphere

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What is Human-made noise

Generated by spark-producing mechanisms

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What is SHOT noise

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

What is Space noise

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

What is Thermal noise

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

What is Noise factor

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

What is Noise figure

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

What is Probability of detection

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

White noise

Frequency content is uniform across the spectrum

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

System noise

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

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

What component reduces the difference between the highest and lowest signals

STC (Sensitivity time control)

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

T/R Limiter

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

SRT

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

LNA

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

Gain Control Unit

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

Mixer

What component Determines the amount of signal phase shift

Hybrid coupler

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

Preselector

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

Image rejection mixer

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

IF amplifier

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

T/R limiter

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

Ground clutter

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

gain control circuit

Receiver gain is essentially __________.

sensitivity

Which component changes attenuation automatically as radar range increases

STC (Sensitivity time control)

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

attenuator

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

more effective, closer to

What is normal video

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

What does an MTI (Moving Target Indicator) do

Cancels stationary targets not canceled by normal video

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

amplifier linear receiver normal receiver

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

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

What is a shortcoming of MTI

Valid aircraft targets can get lost in the cancellation process

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

down convert, intelligence

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

Diode detector

Which problem with diode detectors made transistor detectors popular

The inability to amplify

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

ASR-9

A logarithmic receiver/amplifier amplifies ________ level signals more than _______ level signals. A. low, high B. high, low C. high, moderate D. moderate, low

low, high

What is a benefit of a wide dynamic range?

Limiting or overloading is not required.

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.

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

The logarithmic receiver’s effectiveness reaches the ______

maximum range

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

cascading stages of limiting IF amplifiers, summing

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

down converted, three

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

changes with

What is a logarithmic receiver used for?

Tracking aircraft through inclement weather

In a phase detector receiver, down conversion transforms:

RF into IF

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

Antenna scanning

What Determines the system’s ability to detect a target

S/N ratio

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

Blind phase

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

I & Q phase detectors

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

COHO

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

Range and Size

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

IF, COHO

Transmitter frequency is the sum of _____.

STALO and COHO

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

STALO, receiver RF echo

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

Sinusoidal Square Triangular

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

Fixed and Moving targets

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

Canceller

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

amplitude

Maximum outputs happen at ___ phase difference.

0° and 180°

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

What is the first step in detecting a moving target?

Determining its relative phase returns

When do optimum phase conditions occur?

Maximum Positive and negative value

What determines the minimum range of a radar system?

System recovery time

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

System recovery time

What is the MDS power level used to determine?

Receiver sensitivity

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

MDS

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

A false increase in receiver sensitivity

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

Minimum range of a radar system System recovery time

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

T/R recovery

What does an increase in SRT indicate?

Deterioration of a T/R device

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

Maximum possible sensitivity

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

sensitivity

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

Receiver sensitivity

What is a measurement of receiver sensitivity?

Minimum discernable signal

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

calculated thresholds

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

the grass level

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

Module 4 Flashcards

(100 cards)