Radar
RADAR range is measured by the constant:
150 meters per microsecond
A radio wave will travel a distance of three nautical miles in
18.51 microseconds
What is the distance in nautical miles to a target if it takes 308.5 microseconds for the RADAR pulse to travel from the RADAR antenna to the target and back
25 nm
What are common wavelengths used in Merchant Marine shipboard radar?
3 and 10 cm
What would give the best radar echo?
600 foot freighter, beam on
With an antenna height of 52.5 ft and standard atmospheric conditions, what is the theoretical distance to the radar horizon?
8.84nm
X band radar operates in the ___________ band?
9.3 to 9.5 GHz and 9300 to 9500 MHz are correct
Good bearing resolution largely depends upon:
A narrow antenna beam in the horizontal place
What device located between the magnetron and the mixer and prevents received signals from entering the magnetron?
ATR
The purpose of the modulator
Adjust the pulse repetition rate
The closest point of approach (CPA) of a contact on a relative motion radar may be determined ____.
After the contact has been marked at least twice
Energy can best be described by a pulses:
Amplitude
What is the purpose of function of the RADAR duplexer/ circulator?
An electronic switch that allows the use of one antenna for both transmission and reception
How is variable range marker accuracy determined?
By comparing it to the fixed range rings on minimum and maximum
The true course of a vessel represented by a pip moving toward the center of the radar scope:
Cannot be determined by scope inspection alone
The purpose of a modulator in the transmitter section of a RADAR is to
Control magnetron power output
An RF mixer has what purpose in a RADAR system?
Converts a low-level signal to a different frequency.
You are underway at 10 knots. At 1800 you note a radar contact dead ahead at a range of 10 miles. At 1812 the contact is dead ahead at a range of 8 miles. The estimated speed of the contact is _______.
DIW
The STC circuit is used to
Decrease sea return on a RADAR receiver
The 3 cm radar as compared to a 10 cm radar with similar specifications will ____________.
Display a more maplike presentation for inshore navigation
Which of the following will NOT be found in the receiver section of the radar?
Duplexor
The primary cause of noise in a RADAR receiver can be attributed to
Electrical causes
Rain rate - rain clutter - differentiator all refer to what front panel control ?
FTC
Energy coming out of the radar antenna is best described as ionizing radiation. (T/F)
False
Pulse width and pulse length mean the same. (T or F)
False
The ability of radar to detect objects is unaffected by weather conditions (t/f)
False
The panel control that can be used to improve bearing resolution:
Gain
To build up a pip that is intermittent or barely visible, the operator should adjust the
Gain
What function is not affected by the timing circuit?
Gain
The magnetron is used to
Generate the output signal at the proper operating frequency
The major advantage of s-band over x-band radar is
Greater range
Which of the following inputs is required to indicate azimuth?
Gyro signals
Marine radar makes use of ___________ polarization for the transmitted radio frequency.
Horizontal
Sea stabilized display requires:
Input from the ship's gyro and speed log
On a range scale of 24 nm a small island .30 nm offshore merges with the coast:
Is an example of range resolution
When an operator uses the radar's tune control?
It changes the local oscillator frequency so that when it is mixed with the return signal a constant IF is maintained
What does a SART signal sound or look like?
It will appear on a radar unit's PPI as a line of dots radiating outward with the outermost dot indicating the SART's position
In RADAR unit, the local oscillator is a
Klystron
A small contact many miles away will be best detected by:
Lower PRR with longer pulse width
Coastal features that appear as conspicuous on a navigational chart:
May be unrecognizable on the radar display due to range resolution and bearing resolution
Which of the following is not part of the transmitting system?
Modulator
A radar contact will remain stationary on a relative motion radar display only when it is -
On the same course and speed as your vessel
What statement best describes the term sweep?
One antenna rotation
Your radar is set on a true motion display. Which of the following will appear to move across the PPI scope?
Own ship's marker
What is the contact shape that returns the best echoes?
Perpendicular flat surface
The center of the transmitted lobe from a slotted waveguide array is:
Perpendicular to the antenna
Purpose of Pulse forming Network is to
Produce a pulse of the correct width
The 10 cm radar as compared to a 3 cm radar of similar specifications will
Provide better range performance on low lying targets during good weather and calm seas
What statement is most correct when considering the relationship between pulse amplitude and pulse length?
Pulse amplitude is fixed in marine radars so power is determined by pulse length
A shipboard RADAR uses a PFN driving a magnetron cathode through a step-up transformer. This results in which type of modulation?
Pulse modulation
Which of the following best describes how marine radar modulates the RF energy in order to determine range?
Pulse modulation
You are using a radar in which your own ship is shown at the center, and the heading flash always points to 000'. If bearings are measured in relation to the flash, what type of bearings are produced?
Relative
The characteristic of the magnetron output pulse that relates to accurate range measurement is its:
Rise time
Frequencies used for marine radar are in the _________ spectrum.
SHF
One control that may minimize the effects of side lobe echoes and ringing is
STC
Sea clutter on the RADAR scope cannot be effectively reduced using front panel controls. What circuit would you suspect is faulty?
STC
The radar control used to reduce sea return at close ranges is the
Sensitivity time control
A point of land lies between your ship and a small sailboat. The sailboat may not be seen on the radar because of what condition?
Shadow effect
Which statement concerning the operating of radar in fog in TRUE?
Small wooden boats may not show up on radar
A radar display in which North is always at the top of the screen is a
Stabilized display
Many ships have blind spots. What should you do to help eliminate the effects of a blind spot?
Swing off course frequently depending on your speed
The triggering section is also known as
Synchronizer
What RADAR component controls timing throughout the system?
Synchronizer
The echo box is used for
Testing and tuning of the RADAR unit by providing artificial targets
Bearing resolution is
The ability to distinguish two adjacent targets of equal distance
You have been observing your radar screen and notice that a contact on the display has remained in the same position, relative to you, for several minutes. Your vessel is making 10 knots through the water. Which statement is TRUE?
The contact is on the same course and speed as your vessel.
How does antenna length affect the horizontal beamwidth of the transmitted signal?
The longer the antenna the narrower the horizontal beamwidth
How is the variable range marker usually adjusted for accuracy?
The minimum and maximum ranges are aligned with the matching fixed range ring
PRR refers to
The pulse rate of the magnetron
What is the relationship between pulse repetition rate and pulse width?
The pulse repetition rate does not change with pulse width
The minimum range of a RADAR is determined by
The transmitted pulse length
At microwave frequencies, waveguides are used instead of conventional coaxial transmission lines because
They have considerably less loss
A radar sweep refers to
Time required for the pulse to travel out and back for a given range scale and can be seen as a trace on the display
Operation of any RADAR system begins in the
Triggering section
150 meters is the roundtrip distance a pulse travels in 1 usec (75 m out 75m back) (T/F)
True
An echo box is used to determine performance of the radar (T/F)
True
Every deck officer on vessels of 300 gross tons and above, and on uninspected towing vessels over 26 feet, must be a qualified radar observer (T or F)
True
FTC can be used to provide better range resolution and definition. (T/F)
True
Loss of signal strength with range is known as attenuation. Radar Theory Q 5. (T or F)
True
PPS , PRR, PRF all mean the same (T or F)
True
Radar aids to navigation make us of vertically polarized EM waves (T/F)
True
The FTC only detects the portion of the pulse where signal strength is increasing (leading edge) and not the whole pulse. (T or F)
True
The normal range of pulse repetition rates on most marine radar is between 500 and 2000 pulses per second. (T or F)
True
The presence of sea clutter is a positive indication that your radar is operating properly (T or F)
True
The purpose of a local oscillator in the receive portion of a marine radar is so that the received signal can mixed with locally produced frequency to produce an intermediate operating frequency for processing. (T or F)
True
The need to use this front panel control would indicate a radar performance issue:
Tune
In a EM wave the electric field is in vertical plane, this would be interpreted as
a vertically polarized wave
Increasing the height of your antenna may increase detection ranges and eliminate the effects of blind sectors, however, distances over 21 m from the transceiver to the scanner will tend to reduce the signal quality due to:
attenuation of the signal
If the STC gain is poorly adjusted:
close in contacts may be lost
The automatic frequency control (AFC) system is used to :
control the frequency of the klystron or local oscillator
Echo referencing refers to
course up stabilized display
Radar makes the most accurate determination of the ____________
distance of a target
The accuracy of the variable range marker is checked against the
fixed range rings
What must be used in concert with STC
gain
What is the result of a slow rise time from a magnetron?
poor range detection
On long range scales the transmitter sends out a long pulse with low PRR, The purpose of this is to
put out more energy
The radar control that reduces weak echoes out to a limited distance from the ship is the
sensitivity time control (sea clutter control)
A wide horizontal beam width makes a contact appear
wider in azimuth
