NAVEDTRA 14190A, NAVY ELECTRICITY AND ELECTRONICS TRAINING SERIES. MODULE 18-RADAR PRINCIPLES Flashcards
Which term is used to refer to electronic equipment that detect the presence, direction, height, and distance of objects by using reflected electromagnetic energy?
Radar
What is used by radar sets to determine the direction and distance of the reflecting object?
Echo
The surface of the earth is represented by an imaginary flat plane, tangent (or parallel) to the earth’s surface at that location. What is this plane referred to as?
Horizontal plane
What is the line from the radar set directly to the object referred to as?
Line of Sight (LoS)
What is the angle called between the horizontal plane and the los?
Elevation angle
Approximately how many statute miles per second does electromagnetic energy travel through the air?
186,000
Approximately how many nautical miles are equal to 186,000 statute miles?
162,000
Approximately how many feet are there per nautical mile?
6,080
What is radar timing usually expressed in?
Microseconds
Approximately how many feet per microsecond does radiated energy from a radar set travel at?
984
The range in nautical miles to an object can be found by measuring the elapsed time during a round trip of a radar pulse and dividing this quantity by what number?
12.36
Which pulse property determines the maximum range that the pulse can travel to a target and still return a usable echo?
Peak power
What is the smallest signal called that is detectable by a receiver system that can be processed and presented on an indicator?
Usable Echo
What is the frequency of the rf energy in the pulse radiated by a radar referred to as?
Carrier frequency
Radio frequency energy above what frequency is rapidly attenuated by the atmosphere?
3,000 megahertz
What is used to calculate both the peak power and average power of a radar system?
Duty cycle
Which radar target property is the angle between true north and a line pointed directly at the target?
True bearing
Which radar systems are designed to determine only the range and bearing of an object?
2D
Which type of search radar system detects altitude as well as range and bearing?
3D
Which radar property is defined as its ability to distinguish between targets that are very close together in either range or bearing?
Target resolution
Which two categories is resolution usually divided into?
Range and bearing
What is the ability referred to as of a radar system to distinguish between two or more targets on the same bearing but at different ranges?
Range resolution
What is the ability of a radar system to separate objects at the same range but at different bearings?
Azimuth resolution
What 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
What is the bending of electromagnetic waves caused by a change in the density of the medium through which the waves are passing?
Refraction
What ensures that all circuits connected with the radar system operate in a definite timed relationship?
Synchronizer
What is essentially an electronic switch that permits a radar system to use a single antenna to both transmit and receive?
Duplexer
What is the systematic movement of a radar beam in a definite pattern while searching for or tracking a target?
Scanning
Which type of scanning is unsuitable for use as a tracking radar?
Single-lobe
What are the two basic methods of beam scanning?
Mechanical and Electronic
Which type of scanning is used in fire-control tracking radars?
Monopulse
What can occur as the target maneuvers or moves and the radar pulses bounce off different areas of the target and causes random reflectivity and may lead to tracking errors?
Scintillation
When radio-frequency energy transmitted from a fixed point continuously strikes an object that is either moving toward or away from the source of the energy, the frequency of the reflected energy is changed. What is this shift in frequency known as?
Doppler effect
What is a requirement for any Doppler radar to function?
Coherence
What is the heart of a missile guidance system?
Radar system
Which type of radar is designed to continuously scan a volume of space to provide initial detection of all targets?
Search
Which type of radar provides continuous range, bearing, and elevation data on one or more targets?
Track
Which type of radar systems detect and process only moving targets?
Moving Target Indicators
What is the maximum range ability of surface-search radar primarily limited by radar horizon?
Radar horizon
Which type of radar is used to detect the presence of surface craft and low flying aircraft and to determine their presence?
Surface-search
The maximum range of air-search radar can exceed how many miles?
300
Which type of radar computes accurate ranges, bearings, and altitudes of aircraft targets detected by air search radars?
Height-finding
Which type of radar system provides the information used to guide a missile to a hostile target called?
Guidance
What is often referred to as the “heart” of the radar system because it controls and provides timing for the operation of the entire system?
Synchronizer
What is the function of the majority of circuits in radar?
Timing or control
Which types of waves will be generated by the multivibrator if it is symmetrical?
Square
What produces the short duration high-power rf pulses of energy that are radiated into space by the antenna?
Transmitter
What controls the radar pulse width by means of rectangular dc pulse of the required duration and amplitude?
Modulator
Magnetron oscillators are capable of generating rf pulses with very high peak power at frequencies ranging from 600 to how many megahertz?
30,000
Which type of modulator has lower efficiency, its circuits are more complex, a higher power supply voltage is required, and it is more sensitive to voltage changes?
Hard-tube
Pulse-forming networks are often insulated by immersing each circuit element in what?
Oil
Typical dc power supplies for radar modulators use a half-wave rectifier, a full-wave rectifier, or which other type of rectifier?
Bridge
What does the keyed-oscillator transmitter most often use as the power oscillator?
Magnetron
What are the two main types of magnetron mode instability?
Mode skipping and mode shifting
Which condition occurs when the magnetron fires randomly in an undesired, interfering mode during some pulse times, but not in others?
Mode skipping
Which condition occurs when the magnetron changes from one mode to another during pulse time?
Mode shifting
What are used in radar systems with a wide band of transmitted frequencies because they are stable over a wider frequency range?
Amplitrons
What allows the transmitter to radiate a large number of discrete frequencies over a relatively wide band?
Frequency synthesizer
Which term refers to the discharge of electricity through a gas-filled electron tube?
Glow discharge
Which type of duplexers are the most common in radar systems?
Waveguide and hybrid-ring
What is used as a duplexer in high-power radar systems?
Hybrid ring
Which term refers to a condition of the receiver in which the voltage pulse at the receiver input is too large?
Blocking
The superheterodyne receiver is almost always used in which type of radar systems?
Microwave
Most radar receivers use a 30 MHz or which intermediate frequency?
60 MHz
Which very stable microwave oscillator can be tuned by changing the repeller voltage?
Reflex klystron
Which circuit is used by most radar systems to control the output of the local oscillator?
Automatic Frequency Control (AFC)
Which part of a microwave receiver serves to convert the IF pulses into video pulses?
Detector
What is the simplest form of detector and the most commonly used in microwave receivers?
Diode detector
What is fundamentally an RC coupled amplifier that uses high-gain transistors or pentodes?
Video amplifier
What is not used as frequently as other types of gain control because of the widely varying amplitudes of radar return signals?
AGC
What is the appearance on a radar indicator of confusing, unwanted echos which interfere with the clear display of desired echos?
Clutter
Which type of non-saturating amplifier does not ordinarily use any special gain-control circuits?
Lin-log amplifier
Radar energy is distributed more or less symmetrically over a band of frequencies. What is this frequency distribution of energy known as?
Frequency spectrum
What presents a graphic display of energy versus frequency?
Spectrum analyzer
What does the distribution of power over the radar frequency spectrum depend on?
Modulation
The electronic frequency counter, wave meter, along with what else are the devices used to determine the basic carrier frequency of a radar transmitter?
Echo box?
What is defined as the weakest signal that produces a visable receiver output (on a scope?)
MDS
A typical receiver sensitivity reading on a modern radar should be in the vicinity of what?
-105 dBm
What is defined as the frequency spread between the half-power points on the receiver response curve?
Receiver bandwidth
In various radars, the recovery time may differ from less than 1 microsecond to about how many microseconds?
20
When present on transmission lines and waveguides what indicate an impedance mismatch between a transmitter or receiver and its antenna?
Standing waves
A high vswr (what or higher) indicates that the characteristic impedance of a transmission line differs greatly from the terminating impedance?
1.5 to 1
Most ac power distribution systems in naval vessels are how many-volt, 60-hertz, 3-phase, 3-wire, ungrounded systems?
440
Which type of equipment is used to provide power to vital loads?
Automatic Bus Transfer (ABT)
What do microwave components require, such as waveguides, cavities, and power amplifiers, to prevent arcing and internal corrosion?
Dry air
What is one of the best mediums for cooling high-power components, and, in many cases, the only medium that may be used?
Distilled water
Radar peak power may reach how many watts or more?
One million
Klystrons, magnetrons, rectifiers, or other tubes that employ an excitation of how many volts or more may emit X rays out to a few feet?
15,000
