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128 Cards in this Set

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