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108 Cards in this Set
- Front
- Back
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RADAR stands for |
Radio detection and ranging |
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What is the purpose of radar |
To determine the positions of ships, planes and land masses that are invisible to the naked eye due to distance, darkness or weather |
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Define Azimuth |
Direction to a detected object or target (Degrees)
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Define altitude |
Height of the detected object or target (ft) |
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Define Range |
Distance the detected object is from the antenna along the LOS (NM) |
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What are the four transmission methods |
Pulse modulation, frequency modulation, continuous wave, pulse doppler |
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What is the reference coordinate used to describe the surface of the earth, represented by an imaginary flat plane which is tangent or parallel to the earths surface at that location? |
Horizontal plane |
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What is the reference coordinate used to describe the angle between the horizontal plane and the LOS measured in the vertical plane? |
Elevation angle |
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What is true bearing? |
The angle between true north and the LOS, measured clockwise in the horizontal plane |
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What is relative bearing? |
The angle between the vertical plane, running down the center of the own ship and the LOS measured clockwise in the horizontal plane |
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T/F most radar systems use some variation of pulse doppler type transmission method? |
False: Pulse transmission |
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What are the six basic components that makeup a pulse radar system? |
Power supple, sychronizer/modulator, transmitter, antenna/duplexer, receiver, indicator |
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Why is the transmitter so dangerous? |
Produces very high voltages, current and microwave radiation levels. |
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What controls the radar pulse width by the use of a rectangular DC pulse of the required duration and amplitude? |
Modulator |
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T/F The duplexer defines beam shape |
False, duplexer is a switch |
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T/F The antenna system includes the antenna, transmission lines, the waveguide from the transmitter to the antenna and the transmission lines and waveguide from the antenna to the receiver |
TRUE |
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What is the duplexer and what is its purpose? |
Electronic switch that permits radar systems to use a single antenna to both transmit and receive |
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What provides the necessary voltages for the radar system? |
Power supply ass face |
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What is the primary operator interface for the radar system? |
The indicator |
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3D radars detect |
and determine ranges, bearing, height |
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2D radars detect |
and determine range and bearing |
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What types of radar are classified as 2D |
Search (air and surface), airborne, navigation |
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What types of radar are classified as 3D |
Fire-control, approach, height-finding and airborne |
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What type of radar has good range and bearing resolution and is normally short range surface search radar? |
Navigation |
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What are the 3 phases of fire-control radar? |
Designation (direct toward target), aquisition (locates target) and tracking (follows target) |
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What limits the range of surface search radars |
Radar horizon |
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What radar is used for initial detection of targets? |
Search radar |
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What are the characteristics of air search radars? |
High peak power, low pulse rep rate, wide pulse width |
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What is the difference between GCA and CCA radar |
one is ground one is carrier, carrier is more sophisticated due to movement of the ship and a more complicated landing environment |
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T/F Altitude or height-finding radars use a wide beam in the vertical plane? |
F narrow beam ya dummy |
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Another name for fire-control radar is.... |
Tracking radar |
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T/F The accuracy of fire-control radar is due to its very narrow, circular beam |
T |
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What are the characteristics of fire-control radar? |
High pulse rep rate, max definition of small targets, narrow pulse width, max range res, narrow beam width, max bearing res |
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What is the difference between a passive homing missile and active homing missile ? |
Passive-aircraft or ship illuminate target, causing the reflected energy that the missile homes in on, active contains a radar system on board that illuminates the target and missile guides in on reflected energy |
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What does the planned position indicator display? |
Bearing and range |
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How far does RF travel in one microsecond? |
328 yds |
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What is the formula for range? |
Range=elapsed time / 12.36 |
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How long does it take RF to travel one radar mile? |
12.36 microseconds |
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What is recovery time? |
Time required for the duplexer to complete the transition of switching from transmit to receive |
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What is MIN range |
range at which the radar is first able to detect objects |
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What is the formula for MIN range? |
(PW + RECOVERY TIME) X 164 YDS |
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What is pulse repetition frequency and how is it calculated? |
PRT=1/PRF |
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MAX range is determined by what four characteristics? |
Carrier freq, freq of the RF energy in the pulse, # of pulses per second, receiver sensitivity |
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What are ambiguous returns? |
Echoes returned at incorrect ranges |
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Formula for duty cycle |
PW X PRF OR PW / PRT |
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What is the formula for average power? |
Pavg=Ppk x PW X PRF |
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Does the temperature of the atmosphere increase or decrease uniformly as altitude increases? |
Decreases |
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What is temperature inversion? |
Temp increases with height and then begin to decrease? check this for correct definition |
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What is moisture lapse? |
Moisture content to decrease more rapidly at heights just above the sea |
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T/F Ducting causes the radar horizon to expand or contract depending on the direction the radar waves are bent? |
False will cause the radar horizon to be either increased or decreased depending on the direction the radar waves are bent |
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How will water or dust particle in the air affect MAX range? |
Can cause RF energy to be reflected, decrease the MAX range |
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What is the formula for radar horizon? |
square root of antenna height x 1.25 |
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Increasing the antenna height will have what affect on radar horizon? |
Increase radar horizon |
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What does the MDS test identify |
Weakest usable signal the receiver can detect |
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T/F Increasing radar sensitivity will have the same affect on range performance as increasing transmit power? |
True |
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What is range resolution? |
Radars ability to distinguish between closely grouped targets |
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What is the formula for range resolution? |
PW X 164 yds |
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How far apart must two targets be separated by in order to distinguish two closely-grouped objects range and bearing? |
Separated by at least one beam width (bearing) and 1/2 pulse width (range) |
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What is target resolution? |
Ability to distinguish between closely grouped targets |
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What is bearing resolution? |
Ability of a system to distinguish between targets at the same range but different bearings |
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What is the ideal pulse shape? |
Square wave, with sharp leading & trailing edges with a flat top |
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How does pulse width, PRF, MAX range, and range resolution correlate with one another? |
PW ^ RR V PRF V MR ^ |
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T/F radiation hazards exist in the vicinity of radar transmitting antennas this includes, not only in front of the antenna but the sides and rear as well |
True |
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What must you do prior to making any visual inspections of open waveguides, feed horns, or any other opening that emits RF radiation |
Tag that poop out properly |
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High power RF can cause.... |
Sparks or induce current in other electronic equips |
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What is the doppler effect? |
Change in freq of a wave (sound or electromagnetic) reflected from a moving object
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What happens to the frequency of a radiant energy reflected from a moving object as it moves closer to the observer ? |
Increases proportional to the rate at which the object approaches |
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What happens to the freq of radiant energy reflected from a moving object as it moves further away from the observer? |
Decreases |
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The amount of doppler effect is determined by ? |
The radial velocity of said object |
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What is radial velocity |
Speed that the object is moving toward or away from the radar |
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What is relative velocity |
Value proportional to magnitude of freq shift |
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T/F The doppler effect can be used to determine the velocity of stationary objects? |
false |
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T/F If a target were moving, but remained a set distance from an antenna, it would not produce a freq shift, because there would be no change in the distance between the target and the antenna therefore there would be no change in freq |
TRUE |
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The CW radar is commonly referred to as the? |
Doppler radar |
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What is the best means to detect moving objects if range resolution is not required? |
CW transmission |
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Pulse doppler is used in radar applications where __________________ is critical? |
range determination |
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In order for pulse doppler radar to use the doppler effect, the radar must be able to compare the echo signal with a reference signal that is_____________________. |
Coherent with the transmitted signal wtf disregard this |
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What are the three advantages of Pulse doppler over CW? |
Rejects stationary objects, easily detects moving targets, distinguishes between targets with the same radial velocity, but different angles |
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What are the four advantages of pulse doppler radar |
Blind target ranges, blind velocity, range and velocity ambiguity, range in max range capabilities |
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How do you calculate the distance to the radar horizon? |
1.25 x square root of height |
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A target may not be detected beyond the radars LOS. What is this called? |
Radar horizon |
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What does the minimum discernable signal test identify? |
Radar sensitivity or weakest usable signal |
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A radar should be able to distinguish targets separated by 1/2 the what? |
Pulse width |
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As the pulse width becomes narrower what happens to range resolution? |
Increases |
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What is the formula to determine range resolution? |
PW X 164 YDS |
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How much must two targets by separated by to be distinguished as two objects? |
1 beam width and 1/2 pulse width |
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What is the ideal pulse shape? |
Square wave, sharp leading and trailing edges and flat top |
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The PPI displays |
Range and bearing |
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What is the formula for range? |
Elapsed time/12.36 microseconds |
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How long does it take RF to travel one radar mile? |
12.36 microseconds |
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What are the two factors that determine MIN range? |
Recovery time and pulse width |
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What is the formula for MIN range? |
PW + RECOVERY TIME X 164 YDS |
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What four factors determine MAX range |
Carrier freq, peak power, PRF, receiver sensitivity |
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What are ambiguous returns? |
False returns |
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What is the formula for duty cycle? |
PW/PRT OR PW X PRF |
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What is the formula for peak power? |
Avg/DC |
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What is the formula for average power? |
pk pwr x DC |
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List 3 atmospheric conditions that can affect RF? |
Temp inversion, moisture lapse, induction |
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Which radars use a narrow vertical beam? |
Height finding |
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Can surface radar detect aircraft? |
Yes |
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What are two groups of radars? |
2D & 3D |
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T/F Airborne search radars output power match those of ship-board search radars? |
TRUE |
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What are the characteristics of air search radar? |
High pk power, wide pulse width, low PRF |
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What are four transmission methods of radar? |
CW, pulse doppler, pulse mod, freq mod |
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How is true bearing measured? |
True north to target |
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Elevation angle is between the horizontal plane and LOS |
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Distance is measured in |
NM |
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Reflected RF is also known as |
Echo |
