1C853A V2 Flashcards
Radar stands for?
Radio Detection and Ranging
the _______ supplies the timing signals that time the transmitted pulses, the indicator, & other circuits
synchronizer
the ____________ generates electromagnetic energy in the form of short, powerful pulses
transmitter
the ______ allows the same antenna to be used for transmitting and receiving
duplexer
the _______ routes electromagnetic energy from the transmitter, radiates it, receives echoes, and routes the echoes to the receiver
antenna system
the ______ amplifies the weak, electromagnetic pulses returned & reproduces them as video pulses
receiver
the ______ produces a visual indication of the echo pulses furnishing range & azimuth info
indicator
______ purpose is to control friendly aircraft, detect hostile aircraft, and control interceptors
Air Control and Warning (AC&W) radar
______ assists a/c in making safe landings during poor wx conditions & is a key part of DATCALS
Precision Approach Radar (PAR)
What does the “T” in TPN-19 designate?
Ground/Transportable
What is used with proper receiving equipment to detect the presence of a distant object?
reflected energy
At what speed do radio waves travel?
speed of light
162k NM/s
How long does it take a radar pulse to travel one radar mile?
12.36 μs
The _______ supplies timing signals to coordinate the operation of the complete system
synchronizer
When a transmitter uses a high-power oscillator to produce the output pulse, what switches the oscillator on and off?
modulator high-voltage pulse
A ______ permits the use of a single antenna for both transmitting and receiving
duplexer
The two basic types of transmitters are _____ and _____
keyed-oscillator type; power-amplifier chain
In addition to a flat top, what characteristics must a modulator pulse have?
steep leading and trailing edges
The frequency range of magnetron oscillators of _________
600-30,000 MHz
The three types of storage elements are most often used in modulators are _______, ______, ________
capacitor, artificial transmission line, pulse formed network
What type of tube best meets the requirements of modulator switching element?
thyratron tube
The _________ controls the rate at which the storage element charges
charging impedance
The two forms of instability common in magnetrons are _______ and _________
mode skipping; mode shifting
What is the typical frequency range about the center frequency of a tunable magnetron?
+/- 5 percent
In the power amplifier, what two signals are mixed to produce the output?
local oscillator & coherent oscillator
A ________ klystron is used as the final stage of a power amplifier transmitter
multi-cavity
What is the result of pulsing a pulsed RF amplifier when no RF is present?
oscillations at an undesired frequency
The two general classes of antennas are _______ and ______
omnidirectional; directional
_________ determines the width of the antennas main lobe
The system’s purpose & degree of accuracy required
What is the directivity of a directional antenna?
the degree of sharpness of its beam
What are the two functions of a horn radiator?
impedance-matching & directional radiator
What are the functions of the antenna on transmit?
concentrate energy in predetermined beam shape, point in predetermined direction
What does it mean if an antenna is reciprocal?
transmit & receive patterns are identical
Why are reflector antennas extremely important and practical devices for use in radar systems?
economical method of distributing energy over large area, beams with high gain
Why is the paraboloid shape useful?
all rays leaving focal point & striking the reflector are reflected back along focal axis
What happens when you change the physical shape of the antenna?
gives fixed change to radiated beam pattern, but not continuous control or variation
How can you provide an amount of control over the received beam pattern?
two feedhorns, one active (low beam) & one passive (high beam)
What is the purpose of the passive feedhorn?
used only for receiving
What is an advantage of using MTI?
moving target indicator
can be used to reduce clutter
How is range gating adjusted in the 12-feedhorn system?
individually adjustable by 45 degrees in four azimuth quadrants, relative to north
Why is stacked-beam a good technique?
uses simultaneous pencil-beam radiation patterns to cover angles of interest
How many receivers are used for the pencil beam?
separate receiver for each pencil beam
How does the gain of the individual pencil beams compare to the fan-beam antenna?
provides a larger number of hits, higher data rate = higher gain
What phase-array ability is an important advantage if the required antenna is large?
steer a beam without needing to move a large mech structure
How does the two-dimensional planer array work in rectangular form; in circular aperture form?
rectangular; fan beams
circular; pencil beams
________ is the greatest limiting factor in a receiver’s detectable range
noise
What type of receiver is “almost, always” in radar systems?
superheterodyne
Which component of the receiver produces the signal that is mixed with the received signal to produce the IF signal?
local oscillator
What is the one major disadvantage of the unbalanced crystal mixer?
unable to cancel local oscillator noise
Which receiver component converts the IF pulses to video pulses?
the detector
Why is AGC (automatic gain control) not used as frequently as other types of gain control?
widely varying amplitudes of radar return signals
How does FTC affect receiver gain, if at all?
no effect, greatly reduces effect of jamming
What type of target has a fixed phase relationship from one receiving period to the next?
stationary objects
What signal is used to synchronize the coherent oscillator to a fixed phase relationship with the transmitted pulse?
COHO locked pulse
What is the phase relationship between the delayed and undelayed video?
pulses will arrive at exactly the same time; 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?
reduces amplification of small signal
The overall gain of a LIN-LOG amplifier _______ as each stage saturates
decreases
If a target is on the azimuth axis of the radiated beam, what is the input to the azimuth IF channel?
zero
What functions does the ASDP (advanced signal/data processor) provide for the radar?
S.REX.PC.T.WX
syncing, receiver/exciter (REX) control, pulse compression, target & wx processing
What does target processing in the ASDP consist of?
Doppler filtering, constant false alarm rate (CFAR) detection, sliding dwell binary integration, plot extraction, scan-to-scan
The _______ used to suppress large in-band interference returns produced by other radar sources
radar interference suppressor
What is the purpose of pulse compression in the ASDP?
recover radar range resolution w/ long pulse transmissions
What is the purpose of the CFAR function?
controls false alarms from fixed/moving clutter & system noise
When does the binary integrator output a detection?
2+ detections at same range in four processing intervals
What are permanent echoes used for?
monitoring primary surveillance radar performance
How does the weather processor remove second time around returns?
after 6 scans, maps are merged & data averaged
A___________ is used to coordinate timing events within the ASDP and REX
golf
field programmable gate array (FPGA)
What information does a plot consist of?
range & azimuth of target, quality measure
The ___________ collects the weather data for all 256 radials and assembles a weather map
plot processor
The primary radar can detect and process _______ aircraft in a single 360° scan
at least 700
4 reasons why it is important that minor lobes of radar antennas be small compared to the main lobe
High directivity
Reduce susceptibility to signal interference
Reduce detecting target in minor lobe
Reduce interference w/ other systems
How is the fictitious surface used?
aids in computing antenna performance; immediate front plane where radiation passes
How is the pattern of the antenna determined?
distribution of electromagnetic energy from antenna over aperture
3 primary performance parameters for an antenna?
gain
beamwidth
side-lobe level
Name two basic functions of the radar antenna.
launch & receive electromagnetic energy efficiently, direct the energy into appropriate beam shape
The ____________ determines the shape of the beam of radar energy and its antenna pattern
purpose of the radar
In the search radar, we need to measure _____ & ______, not ______.
range & azimuth; not height
A practical beamwidth is ______ degrees and vertical height is about ________ degrees
1 to 2; 30 to 35
A ___________ is used to shape the radar beam
parabolic reflector
The ___________ refers to the motion of the antenna axis (of the beam) as the radar looks for an aircraft
scanning method
When using a conical scan, what component of the return signal modulation is used by the radar system to maintain track in both azimuth and elevation?
the phase
_____________ is identified at the ECM receiver by its regular intervals between illuminations
circular
A scan in which a thin beam covers a rectangular area by sweeping it horizontally with the angle of elevation being incrementally stepped up or down with each horizontal sweep of the sector is a ____________
raster scan
The ___________ radar gets its name from the fact that each echo pulse from the aircraft being tracked yields a new azimuth and elevation correction signal
monopulse
A ______ scan is one in which the antenna rotates on an azimuth sweep, while the elevation angle rises slowly from 0° to 90°
helical
What happens to the speed of electromagnetic energy traveling through air as the altitude increases?
small, uniform increase
What effects can ducting have on radar coverage?
extend coverage or create holes
Name 4 types of propagation anomalies?
ducting
subrefraction
superrefraction
multipathing
__________ is the propagation of a wave from one point to another by more than one path
Multipathing
When multipath occurs in radar, of what does it consist?
a direct path & one or more indirect paths reflecting from earth surface or large man-made structures
When may a multipath also include more than one path through the ionosphere?
frequencies below 40MHz
What can near-simultaneous reception of “pulse-type” information cause?
delayed but separate pulses
When a low-altitude target is illuminated by a radar system, or for higher-angle situations involving appreciable antenna sidelobes, by what two paths can energy enter the tracking antenna?
direct path from target
indirect path from energy reflection of earth surface
What attempts are made to reduce multipath effects on radar tracking accuracy?
freq & polarization agility
high res antennas
clutter fences
angle-processing techniques
___________ provides critical information to provide ample time to prepare or evacuate in response to natural disturbances
Weather radar
The “P” in GPN–30 designates _______
Radar
It takes radio frequency (RF) _______ microseconds to travel one radar mile
12.36
The time from one pulse to the next that the radar sends out is called ______________
pulse recurrence time (PRT).
___________ amplifies the weak, electromagnetic (EM) pulses returned from the reflecting object and reproduces them as video pulses
Receiver
____________ controls the radar pulse width (PW) by means of a rectangular direct current (DC)
Modulator
In addition to a flat top, what characteristics must a modulator pulse have?
think mesa
Very steep leading edge and trailing edge
What type of modulator is most commonly used in modern radar systems?
Line-pulsed
What type of tube best meets the requirements of a modulator-switching element?
Thyratron
If the magnetic field strength is too high on the magnetron, the magnetron will
not oscillate
The power gain of an antenna is the ratio of its radiated power to
reference dipole
Which pattern is usually specified and measured for a reciprocal antenna?
Transmit
What is the most common reflector shape?
Paraboloid
What do you call the use of contiguous beams stacked in elevation?
Stacked beam radars
What is an advantage of the individual pencil beams when handling rain clutter or chaff?
Limits the volume of space observed
Which array is particularly useful in radar applications?
Two-dimensional planar
Which waveguide antenna is more suited for one-dimensional scanning than scanning in two coordinates?
Waveguide slot array
What intermediate frequencies are usually used in radar receivers?
30 MHz or 60 MHz
What receiver circuit/stage actually produces the intermediate frequency (IF)?
Mixer
Which stage of the intermediate frequency (IF) section is the most critical?
Input (1st stage)
Immediately after the transmitter fires, sensitivity time control (STC) reduces the receiver gain to what level?
Zero
What signal is used to synchronize the coherent oscillator (COHO) to a fixed phase relationship with the transmitted pulse?
Coherent oscillator lock pulse
What is the phase relationship between the delayed and non-delayed video?
Opposite polarity
What happens to the overall gain of a linear logarithmic (LIN-LOG) amplifier as each stage saturates?
Gain decreases
How many separate channels does a monopulse receiver have?
Three
What is used to interface target and weather channel signals to the signal processor?
Azimuth beam/sensitivity time control (STC) interface
What unit’s primary function is to accept the output of the receiver/exciter (REX), and decide, for every range and azimuth cell in the radar coverage area, whether a moving target is present or not?
Target processor
How many permanent echoes are permitted by the advanced signal data processor (ASDP)?
25
What processor function attempts to correlate plots to existing tracks?
Track processor
What type of reflector is used to shape the radar beam?
Parabolic
What refers to the orientation of the electromagnetic (EM) wave as it travels through space?
Polarization
What refers to the motion of the antenna axis (of the beam) as the radar looks for an aircraft?
Scanning method
What precision radar system uses continuous rotation of a pencil beam (narrow angle in both dimensions) around the aircraft and uses the phase of the return signal modulation to maintain track in both azimuth and elevation?
Conical scan
When using a conical scan, what component of the return signal modulation is used by the radar system to maintain track in both azimuth and elevation?
Phase
What scanning method is identified at the electronic countermeasure (ECM) receiver by its regular intervals between illuminations?
Circular
Which radar gets its name from the fact that each echo pulse from the aircraft being tracked yields a new azimuth and elevation correction angle?
Monopulse scan
What happens to the speed of electromagnetic (EM) energy traveling through air as the altitude increases?
Signal speed increases
The bending of electromagnetic (EM) waves caused by a change in the density of the medium through which the waves are passing is referred to as
refraction
What is it called when temperature first increases with height and then begins to decrease?
Temperature inversion
What do you call propagation of a wave from one point to another by more than one path?
Multipathing
When would you use an electrostatic instead of an electromagnetic CRT?..
requirements for lightweight, compact equipment
How is information presented on an A-scan indicator?
vertical deflection from horizontal baseline
How is time represented on an A-scan indicator?
horizontal distance between start trigger & input signal
How is the video presented on a B-scan indicator?
electron beam presents target as bright spot on the screen
What type of radar uses the B-scan indicator?
precision approach radar for azimuth & elevation
What target information does a PPI scan present?
range & azimuth in polar coordinates
What type of pattern does a Raster scan indicator use to scan the CRT?
electron beam scans CRT screen left to right and top to bottom
What components do all indicators have regardless of type?
Power supplies Data processing circuits Video circuits Deflection circuits CRT (cathode ray tube) Front panel controls
What furnishes the operating voltages for the CRT?
high voltage power supply
List the three functions performed by the data processing circuits.
control ops & data calcs
interface
data distribution
How do the video circuits protect the CRT during certain malfunctions?
disabling CRT high voltage power supply
How do the data processing circuits specify beam position?
using X & Y coordinates, with origin at center of CRT screen
List the two types of CRTs.
electrostatic, electromagnetic
What part of a CRT shields the electron beam from unwanted electric fields?
aquadag
What is the primary hazard involved with high-vacuum CRTs?
dangerous implosions
What do indicator front panel controls allow the operator to do?
select input signals/messages, enter op parameters, adjust indicator format
What are the SIF modes used to interrogate an aircraft?
Modes 1, 2, 3/A, C
What is the spacing between P1 and P3 pulses for the four SIF modes?
Mode 1 - 3 μs
Mode 2 - 5 μs
Mode 3 - 8 μs
Mode C - 21 μs
Explain the contents of the mode 4 preamble.
four pulses & a blank space
each pulse 0.5 μs wide, 2 μs apart
What is the transmitted frequency of interrogation pulses?
Interrogator to a/c - 1030 MHz
A/C to interrogator - 1090 MHz
What is the purpose of transmitting a P2 pulse?
To eliminate sidelobe reception
What is the limit of total possible codes in mode 1?
32
What is the largest single digit for any SIF modes 1, 2, and 3/A reply?
7
What type of code and what are the increments of the altitude information received in mode C?
Gray Code; 100’ altitude increments
What terms are used for the first and last pulse present in a SIF?
bracket/framing pulses
What is the bracket pulse spacing on a normal SIF code train?
20.3 μs apart, width of 0.45 μs
What signifies that the SIF reply has been transmitted by a missile or drone?
X pulse in reply code train
What is the purpose of a reply pulse that is 4.35 μs after the last bracket pulse of a SIF code train?
I/P (id position) response by a/c requested by operator
What is the only IFF/SIF mode that can decode civilian emergencies?
Mode 3/A
How is a communications failure emergency received by the ground station?
7600 emergency code
Which modes will decode military emergencies?
Any SIF mode (1,2,3,C)
What type of aircraft can present a single-arc IFF reply on the scope?
US military aircraft
What are the seven functions within the AN/UPM–155 test set?
CI.I.M.I.F.O.P
Control and interface IFF simulator measurement system interface front panel oscilloscope power distribution
AN/UPM–155: Used for automatic testing
Interface
AN/UPM–155: Used to view signals under test
Oscilloscope
AN/UPM–155: Provides overall control
Control and Interface
AN/UPM–155: Measure VSWR (Voltage Standing Wave Ratio)
Measurement
AN/UPM–155: Simulates interrogations
IFF Simulator
AN/UPM–155: Provides all required voltages
Power Distribution
AN/UPM–155: Contains keyboard and display
Front Panel
What is used to couple the components between waveguide sections to prevent RF leakage?
Waveguide choke joints
What process is used on waveguides to prevent arcing?
air compressors supply dry air to waveguide components to pressurize
How are waveguides pressurized in fixed environments?
with air or inert gases
Explain how a rotary joint works.
allows one waveguide section to remain stationary while other rotates, suppress unwanted RF signals
What component allows the waveguide system to be connected to both transmitter and receiver, while allowing them to share a common antenna?
duplexer
After the majority of the RF energy enters one port of a circulator, where will it exit?
next highest # port of circulator
What is the purpose of the TR (transmit-receive) tube?
closes RF system to receiver during transmission to protect the receiver from high-power transmitter pulses
When a radar set uses dual transmitting channels, what is needed to properly route the RF signals between the waveguide, antenna, and dummy load?
RF switch
Explain the differences between a low-power and high-power diplexer.
high-power – sulfur hexafluoride
low-power – no pressure windows/gas fittings/normal air
The RF filters will filter out all frequencies except what frequency?
the desired frequency of the circuit
State the purpose of the directional coupler.
enable mx to monitor signals, inject test signals into waveguide system
What important factor must you consider when making directional coupler measurements?
loss of signal strength when sampling/injecting, indicated on coupler
What component reduces precipitation and clutter to nearly zero?
polarizer
Explain the differences in radar returns from raindrops and aircraft.
Rain drops will return constant amplitude/same energy; a/c will show wide/irregular variations as polarization changes
Name the two most commonly used mediums to remote radar equipment.
cable/land lines & radio microwave links (RML)
What is the distance restriction when remoting radar systems with coaxial cable?
12,000’
What two things can assist a technician in determining the operational usability and troubleshooting of a radar system?
performance monitors or buit-in test equipment (BITE)
What radar unit displays corresponding radar information on a cathode ray tube (CRT)?
Indicator
What type of cathode ray tube (CRT) is mostly used in ground radar equipment?
Electromagnetic (EM)
The most basic type of scanning indicator is the
A-scan
The scanning indicator that plots target range and azimuth information in polar coordinates is the
plan-position indicator (PPI)
What type of scanning indicator do surveillance radars primarily use?
plan-position indicator (PPI)
What type of scanning indicator completes two vertical scan periods to produce one complete picture called a frame?
Raster
Which indicator power supply furnishes the cathode ray tube (CRT) operating voltages?
high voltage
Along with determining the overall operation of the indicator, the data processing circuits
provide data distribution and interface with the radar
What indicator circuit converts digital display data from the data processing circuits into analog drive signals?
Deflection
What part of the cathode ray tube (CRT) is tapered and lined with a conductive graphite coating?
Aquadag
The high vacuum and large surface area of the cathode ray tube (CRT) make it especially vulnerable to
implosions
Which is not an advantage of identification friend or foe/selective identification feature (IFF/SIF) equipment?
Only one mode is used for simplicity
An aircraft transponder answers an interrogation by transmitting a reply pulse train signal back to the ground station at a frequency of
1090 MHz
To eliminate interrogator side-lobe suppression (ISLS), the ground radar site transmits the P2 signal in what type of radiating pattern?
omnidirectional
What selective identification feature (SIF) mode has a limit of 32 codes?
Mode 1
What generates an identification of position (I/P) response?
aircraft pilot
A 7600 emergency reply signifies an aircraft
communications failure
What is the only type of aircraft that can present a single-arc identification friend or foe (IFF) reply on a scope?
Military
What function of the AN/UPM–155 test set provides overall control of the other functions?
Control and interface
What function of the AN/UPM–155 test set provides signal conditioning required for testing transponders and interrogators?
Interface
What are used to couple waveguide components and sections to prevent radio frequency (RF) leakage?
Choke joints
What do most radars use in their waveguide system to prevent arcing?
Air compressors
What waveguide compressor subsystem controls operation of airflow and indicates normal or malfunction conditions?
Electrical
What duplexer sub-component accepts radio frequency (RF) transmit power from the transmitter and directs it through the waveguide to the antenna assembly?
circulator
What waveguide component has a mechanical stop mounted on its base to limit movement to each extremity of travel?
Radio frequency (RF) switch
What antenna device reduces precipitation display to nearly zero on an indicator?
polarizer
The two most often used radar remoting configurations are
cable/land lines and radio microwave links
Due to high signal loss, about how many feet are coaxial cable remoting systems limited to?
12,000
