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128 Cards in this Set
- Front
- Back
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The term Radar is an acronym made up of the words
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radio detection and ranging
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term is used to refer to electronic equipment that detect the
presence, direction, height, and distance of objects by using reflected electromagnetic energy. |
Radar
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Radar sets use the echo to determine
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the direction and distance
of the reflecting object |
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Radar surface-angular measurements are referenced to true north and measured in what plane?
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HORIZONTAL PLANE.
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The distance from a radar set to a target measured along the line of sight is identified by what
term? |
RANGE.
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approximate time required for radar energy to travel one nautical mile
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6.18 micro seconds
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alternately switches
the antenna between the transmitter and receiver so that only one antenna need be used. |
DUPLEXER
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minimum range ability of the radar system is also affected by this timing. The two most important times in this action are
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PULSE WIDTH and RECOVERY TIME
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minimum range, in yards, at which a target can be detected is determined
using the following formula |
Min Range=
PW + Recovery time x 164 yds |
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maximum range of a pulse radar system depends upon
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CARRIER FREQUENCY
PEAK POWER PULSE-REPETITION FREQUENCY RECEIVER SENSITIVITY |
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The time between the beginning of one pulse and the start of the next pulse is called
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PULSEREPETITION TIME (prt)
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Returns that appear at these
incorrect ranges are referred to as |
AMBIGUOUS RETURNS or SECOND-SWEEP ECHOES
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What is the speed of electromagnetic energy traveling through air?
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Approximately the speed of light (162,000 nautical miles per second).
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How much time is required for electromagnetic energy to travel 1 nautical mile and return to the
source? |
12.36 microseconds
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In addition to recovery time, what determines the minimum range of a radar set?
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Pulse width.
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Formulas for Average power
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Peak Power X PW/PRT
or Peak power x PW x PRF or Peak power x duty cycle |
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is a ratio of the time on to the time off of the
transmitter |
duty cycle
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The formula for duty cycle is
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Duty Cycle= PW x PRF
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The formula for Peak power is
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Average power/duty cycle
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Radar Horizon formula
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Horizon distance= 1.25 x Antenna Height(Sq root)
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antenna-rotation rate also affects
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maximum detection range
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slower an antenna rotates, the
what the detection range of a radar system |
greater
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The number of strikes per antenna revolution is referred to as
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HITS PER SCAN
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Atmospheric interference with the travel of electromagnetic energy increases with what rf energy characteristic?
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Frequency.
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How is prt related to prf?
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inversely
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What type of radar transmitter power is measured over a period of time?
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Average power.
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What term is used to describe the product of pulse width and pulse-repetition frequency?
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Duty cycle.
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bearing angle to the radar target may also be measured in a clockwise direction from the centerline of your own ship or aircraft and is referred to as the
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RELATIVE BEARING
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designed to determine only the range and bearing of an object. Such radar systems are called
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TWO-DIMENSIONAL (2D) radars
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system that detects altitude as well as range and bearing is called a
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THREE-DIMENSIONAL (3D) radar
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Altitude- or height-finding search radars use a beam that is very narrow in the
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vertical plane
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that also determine bearing must have a beam that is very narrow in both the vertical and
horizontal planes. |
Height-finding radar systems
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What type of target bearing is referenced to your ship?
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Relative bearing.
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What characteristic(s) of radiated energy is (are) altered to achieve electronic scanning?
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Frequency or phase.
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of a radar is its ability to distinguish between targets that are very close together in either range or bearing
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TARGET RESOLUTION
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is the ability of a radar system to distinguish between two or more targets on the same bearing but at different ranges
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Range resolution
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Formula for Range Resolution
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PW x 164 yds
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is the ability of a radar system to separate objects at the same range but at different bearings
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Bearing, or azimuth resolution
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is a measure of the ability of a radar system to determine the correct range, bearing, and, in some cases, height of an object.
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Radar accuracy
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The ideal pulse shape is what having vertical leading and trailing edges.
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square wave
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is necessary for short ranges
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narrow pulse
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What term is used to describe a situation in which atmospheric temperature first increases with altitude and then begins to decrease
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Temperature inversion
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signals that time the transmitted pulses, the indicator, and other associated circuits
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SYNCHRONIZER
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generates electromagnetic energy in the form of short, powerful pulses
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TRANSMITTER
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allows the same antenna to be used for transmitting and receiving.
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DUPLEXER
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routes the electromagnetic energy from the transmitter, radiates it in a highly directional beam, receives any returning echoes, and routes those echoes to the receiver.
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ANTENNA SYSTEM
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amplifies the weak, electromagnetic pulses returned from the reflecting object and reproduces them as video pulses that are sent to the indicator.
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RECEIVER
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produces a visual indication of the echo pulses in a manner that, at a minimum,
furnishes range and bearing information. |
INDICATOR
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What is the simplest type of scanning?
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Single lobe.
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How does the operator of a single-lobe scanning system determine when the target moves off the lobe axis?
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The reflected signals decrease in strength.
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What are the two basic methods of scanning?
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Mechanical and electronic.
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Rotation of an rf-feed source to produce a conical scan pattern is identified by what term?
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Nutation.
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The Doppler effect causes a change in what aspect of rf energy that strikes a moving object?
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Frequency.
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The Doppler variation is directly proportional to what radar contact characteristic?
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Velocity.
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The Doppler method of object detection is best for what type objects
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Fast-moving targets.
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The beat frequency in a swept-frequency transmitter provides what contact information?
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Range
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What factor determines the difference between the transmitted frequency and the received frequency in an fm transmitter?
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Travel time.
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What type of objects are most easily detected by an fm system?
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Stationary.
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What transmission method does NOT depend on relative frequency or target motion?
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Pulse modulation.
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What transmission method uses a stable cw reference oscillator, which is locked in phase with the
transmitter frequency? |
Pulse-Doppler.
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What factor determines the difference between the transmitted frequency and the received frequency in an fm transmitter?
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Travel time.
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What type of objects are most easily detected by an fm system?
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Stationary.
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What transmission method does NOT depend on relative frequency or target motion?
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Pulse modulation
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What transmission method uses a stable cw reference oscillator, which is locked in phase with the
transmitter frequency? |
Pulse-Doppler.
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What type of radar provides continuous range, bearing, and elevation data on an object?
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Track radar.
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Radar altimeters use what type of transmission signal?
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Frequency modulated (fm).
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A surface-search radar normally scans how many degrees of azimuth?
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360 degrees.
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What limits the maximum range of a surface-search radar?
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Radar horizon.
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What is the shape of the beam of a surface-search radar?
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Wide vertically, narrow horizontally
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Air-search radar is divided into what two basic categories?
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2D and 3D.
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What position data are supplied by 2D search radar?
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Range and bearing
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Why do 2D air-search radars use relatively low carrier frequencies and low pulse-repetition
rates? |
Increased maximum range.
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Why is the range capability of 3D radar usually less than the range of 2D radar?
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Higher operating frequency
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Fire-control tracking radar most often radiates what type of beam?
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A narrow circular beam.
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Tracking radar searches a small volume of space during which phase of operation?
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Acquisition.
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What width is the pulse radiated by fire-control tracking radar
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Very narrow.
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Which beam of missile-guidance radar is very wide?
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Capture beam.
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What is the purpose of the synchronizer in a radar system?
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Controls system operation and timing
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What is the purpose of the majority of circuits in a radar system?
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Timing and control.
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A self-synchronized radar system obtains timing trigger pulses from what source?
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Transmitter.
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What type of multivibrator can be used as a radar master oscillator
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Free-running.
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In an externally synchronized radar, what determines the prr of the transmitter?
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The master oscillator
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what causes the initial and final pulses on the receiver output signal?
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Leakage from the duplexer.
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What basic circuits meet the requirements of an externally synchronized master oscillator?
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Sine-wave oscillator, single-swing blocking oscillator, and master-trigger (astable) multivibrator
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Name a disadvantage of sine-wave oscillator synchronizers
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It requires additional shaping circuits
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Which of the basic timing circuits produces sharp trigger pulses directly?
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Blocking oscillators.
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What are the two basic types of transmitters?
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Keyed oscillator and power-amplifier chain.
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What controls transmitter pulse width?
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The modulator
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In addition to a flat top, what characteristics must a modulator pulse have?
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Steep leading and trailing edges.
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What type of modulator is most commonly used in modern radar systems?
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Line-pulsed.
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What three types of storage elements most often are used in modulators?
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Capacitor, artificial transmission line, or pulse-forming network.
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What characteristic is determined by the time required for a voltage wave to travel from the input
end of an artificial transmission line to the output end and back again? |
Pulse width.
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What type of tube best meets the requirements of a modulator switching element?
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Thyratron.
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What modulator element controls the rate at which the storage element charges?
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The charging impedance
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What is the frequency range of magnetron oscillators?
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600-30,000 megahertz.
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What two forms of instability are common in magnetrons?
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Mode skipping and mode shifting
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What is the effect on magnetron operation if the magnetic field strength is too high?
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The magnetron will not oscillate.
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What is the typical frequency range about the center frequency of a tunable magnetron?
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±5 percent
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What is the primary advantage of power-amplifier transmitters over keyed-oscillator
transmitters? |
Frequency stability.
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In the power amplifier what two signals are mixed to produce the output
signal |
Local oscillator and coherent oscillator.
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What type of klystron is used as the final stage of a power-amplifier transmitter?
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Multicavity klystron.
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What transmitter component allows the radiation of a large number of discrete frequencies over
a wide band? |
Frequency synthesizer.
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What is the result of pulsing a pulsed rf amplifier when no rf is present?
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Oscillations at an undesired frequency.
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What type of switches are used as duplexers?
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Electronic.
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What tube in a duplexer has the primary function of disconnecting the receiver?
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Tr tube.
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How may the tr tube ionization speed be increased?
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Apply keep-alive voltage.
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The actions of the tr and atr circuits depend on the impedance characteristics of what length of
transmission line? |
Quarter-wavelength section.
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During which of the transmit or receive cycles are both the tr and atr tubes of a parallelconnected
duplexer ionized (arcing)? |
Transmit.
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In a series-connected duplexer, what tube (tr or atr), if any, fires during the receive cycle?
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Neither fires.
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To propagate energy down an arm of a hybrid ring duplexer, the two fields at the junction of the
arm and the ring must have what phase relationship? |
180 degrees out of phase.
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What is the greatest limiting factor in a receiver’s detectable range?
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Noise.
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What type of receiver is most often used in radar systems?
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Superheterodyne.
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What IF frequencies are normally used in radar receivers?
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Thirty or sixty megahertz
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Which component of the receiver produces the signal that is mixed with the received signal to
produce the IF signal? |
Local oscillator.
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What receiver circuit actually produces the IF frequency?
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Mixer.
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The IF amplifiers are connected in what amplifier configuration?
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Cascade.
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Which receiver component converts the IF pulses to video pulses?
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Detector.
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Which of the two types of automatic gain control, agc or iagc, is most effective in radar use for
the Navy? |
IAGC
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Immediately after the transmitter fires, stc reduces the receiver gain to what level?
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Zero.
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How does ftc affect receiver gain, if at all?
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FTC has no effect on receiver gain.
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What type of target has a fixed phase relationship from one receiving period to the next?
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Stationary.
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What signal is used to synchronize the coherent oscillator to a fixed phase relationship with the
transmitted pulse? |
Coho lock pulse
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What is the phase relationship between the delayed and undelayed video?
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Opposite
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When a large signal and a small signal are applied to a lin-log amplifier at the same time, what is the effect on the small signal?
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Amplification is reduced.
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What happens to the overall gain of a lin-log amplifier as each stage saturates?
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Decreases.
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A monopulse receiver has how many separate channels?
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Three.
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If a target is on the bearing axis of the radiated beam, what is the input to the bearing IF channel?
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Zero.
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What characteristic of the bearing and elevation output signals determines the direction of
antenna movement |
Phase.
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