what is the meaning of radarr

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    1. What is the meaning of radar?

    The word radar is derived from Radio Detecting and Ranging. Radarsystems operate on an echo principle: high-energy radio waves in pulseform are directed in a beam toward a reflecting target. When a pulse of

    energy strikes a target, which may be a mountain, rain clouds, it reflectsback and a portion of the pulse is may reach the originating antenna usedto receive the reflected energy back to the radar system.

    2. What is the difference between primary radar and secondary radar ?

    Primary radar Secondary radar Cant used on longer range

    because the measure timedepend on the range.

    Can used over longer rangefor ATC transponder andDME system.

    Relies on reflected signals(echos) from target

    Echos are not considered

    The time is the range. The direction of the targetis the bearing and the timeis the range

    Depend on pulses. Depend on continouoswave pulses.

    3.If the distance of an object is 123.6 nautical miles, what is the timerequired for the signal of the weather radar to hit the target andreturn?

    Distance X 1 radar mile = Time

    Distance = 123.6 nm

    Time required = x

    1 radar mile = 12.36s

    123.6 nm 12.36 s

    = 1527.70 s.

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    4. If the time taken for a signal to hit a target and return in 1545microseconds, what is the distance of the target?

    Distance X 1 radar mile = Time

    Distance = Time

    1 radar mile

    = 1545 s

    12.36 s

    = 125 nm

    5. What is the maximum distance A scan display indicates?

    In early types of radar systems, the display on the CRT was a horizontalscale and was called an A scan. The time between the transmitted pulseand the received pulse indicated the distance of the target from thetransmitter. With this type of scan, the direction of the target could not bedetermined except by changing the direction in which the antenna waspointed.

    6. What type of radar is the :

    (a) wheather radar - primary radar

    (b) radar altimeter - primary radar

    (c) radio altimeter - primary radar

    (d) ATC transponder - secondary radar

    (e) DME system - secondary radar

    7. Draw a complete pulse to indicate :

    Peak power

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    Pulse width

    Pulse interval

    Rest time

    Average power

    Fall time

    Rise time

    8. Whats the pulse repetition frequency, if the width is 4 microsecondand rest time is 16 microsecond?

    PRF = 1 / pulse width + rest time

    Pulse width = 4 s

    Rest time = 16 s

    PRF = 1 / 4 s + 16 s

    = 0.05 s

    9. What is duty cycle?

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    It is the fraction of time that a system is in an active state.Duty cycle isthe proportion of time during which a component, device , or system isoperted. It usually measured as a percentage.

    10. What advantage of pulse system compare to carrier wave (CW)

    in term of transmission power?

    The advantage of pulse radar compared to the carrier wave are :

    A) Rapid triggering

    B) Fast cooling

    C) Quick rise time compared to sine wave (CW)

    11. Why wave guide are used for wheather radar system and nottwin feeder or coaxial cable?

    Waveguide is used to connect an antenna to an r-t unit since the radarfrequency is too high to be transmitted through conventional wiring.Waveguide is precision tube of a size critical to the operating frequencywithin which it is possible to propagate RF at GHz levels. To improveefficiencies in the system, a waveguide should be as short as possible. Onsome systems the r-t unit is mounted directly to the base of the antenna.

    This eliminates the need for any waveguide outside of the antenna or r-tunit.

    12. What type of transmission in radar propagation?

    It uses a quater wavelength antennas , formed into a solid tube, whichat 12.5 GHz (X-Band) will only be 9.375 mm long.

    13. The wheather radar transceiver divided into 3 section, name andexplain the purpose?

    Transmitter

    The transmitter section is designed to produce pulses at C- or X-bandfrequencies, at sufficient power to illuminate target at range up to 300 nmand transmit that energy to the antenna section at the correct time. Mostmodern radars use a completely solid state digital interface forcommunication between the various sections of the radar system. Thetransmitter generates a stable Intermediate Frequency (IF) using a

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    crystal-controlled oscillator. The IF is translated up to the X- or C-bandthrough a varactor multiplexer.

    Receiver :

    The receiver section contains the signal detection and amplificationcircuits. It will receives the reflected radar signal through the antenna andduplexer. This signal is received only during the listening time, whichoccurs between bursts of transmitted energy. The first step is to amplifythe received signal to eliminate the loss of any resolution. The amplifiedsignal is sent to the mixer, which produces a lower-frequency IF. Using alower-frequency IF allows for less complicated circuitry than if the radarfrequency was used.The IF is then amplified, decoded, and filtered by thedata processor section of the r-t unit.

    Data processing : The data processing circuits use the received Rf return signal to produce adata signal encoding the range , bearing and target information fordisplay on the system indicator. These circuit decode the analogue Rf return signal, example reflected from a target and then digitally encodethe information into a format, usually video that decoded by the indicator.

    14. What colour used for wheather radar mode and map mode?

    Radar mode :

    Black : no detectable weather. (0mm ~ below)

    Green : moderate level of moisture, light level of turbulence.(0mm ~ 4mm)

    Yellow : medium level of moisture, light-moderate level of turbulence, possiblity of lightening. (4mm ~ 8mm)

    Red : high moisture level ,severe level of turbulence, possiblelightening. (8mm ~ 12mm)

    Magenta : highest moisture level , severe level of turbulence withlightening and high gusting wind speed with hail. (12mm ~above)

    Map modes:

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    Cyan : minimum detectable ground return.

    Yellow : medium ground return.

    Magenta : high level of ground return.

    15. What the purpose of the following buttons on the wheatherradar?

    STBY: When the button is push the system is energized to warm up themagnetron and other circuits but there is no transmitter output.

    CYC: When the button is push, the radar function as a normal weatheroperation but with a flashing contour function. Example, it flash

    on and off for the highest return.MAP: When the button is push, the system operates in ground mapping

    mode but usually only on the 10 NM and 25 NM ranges.

    Range Control: The range switch selects the maximum selectable range of the weather radar displays and has full scale selection of 10 ,25 , 50 , 100 , 200 and 300 NM. There is a final TEST position,which when selected produces a test patterns on the display.With the majority of weather radar systems, when they are putinto their system test, they do not provide transmitted output butscanner moves.

    STAB Control: This switches the antenna stabilization in the pitch and rollaxis on and off.

    TILT Control: This rotary knob controls the tilt angles of the scannerbetween +- 15 degree.

    FREEZE Control: When pressed the weather display is frozen and a flashingHOLD annunciation alternates with the weather radar mode

    indications. The first button press enables the function and thesecond press disables it. The weather radar systems continues toupdated when this function is in operation so that the latestinformation is available when it is deselected.

    SEC Control: When selected this reduces the scan width by 50%,typically from 120 degree to 60 degree doubling the normal scan

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    rate. This function is useful on short ranges when the weatherpicture is changing quickly. The first button press enables thefunction and the second press disables it.

    16. What advantage of flat plate antenna compare to parabolicantenna?

    Flat-plate antennas have approximately twice the efficiency of conventional parabolic antennas.

    With the flat-plate antenna, there is less signal loss to the sides of theantenna.

    This more efficient antenna extends the range and resolution of any given radar transmitter.

    Less powerful transmitter can be used to achieve a radar systemwith comparable range and resolution.

    Radar system performance is also improved when a larger antenna(narrow beam-width) is used.

    A narrower beam-width improves the ability of the radar system todetect targets at longer ranges, minimizes beam-width distortion, andimproves display resolution.

    17. Where does the transceiver receive the pitch and roll information?

    It received the information from weather radar system, stabilizer controlswitches the antenna stabilization in the pitch and roll axis on and off.

    18. What happen when a self test is initiated?

    When the self test switch is initiated, it will produce a test pattern on thedisplay. All system have a self test feature which is usually initiated by aswitch on the indicator or a specific test switch on a convenientinstrument panel. Most system provide a 50 ft presentation whenactivated, and if the DH value is set above 50ft, it will also test the DHfunction. The indication that will normally show when testing radioaltimeter indicator using 7 segment digital display are : decision height ,

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    test altitude and 8888 (all the eights to ensure illumination of everysegment). The test altitude displayed will vary with the manufacturer.Example, COLLIN ALL101 test altitude is 40 feet, the BENDEX 250 feetand the TRT is 100 feet).

    19. A cloud is painted on the PPI in red, green, and yellow.what doesthese colour represent?

    Red cloud- represents high moisture level at 8mm ~ 12mm, severe levelsof turbulence possible with lightening.

    Green cloud- represents a moderate level of moisture at 0mm ~ 4mm,light levels of turbulence possible.

    Yellow cloud- represent medium level of moisture at 4mm ~ 8mm , light-moderate levels of turbulence are possible with the possibility of lightening.

    20. What advantage of SCR compare to magnetron?

    The Silicon Controlled Rectifier (SCR) produced less electrical noisecompared to magnetron because it conducts current in one direction only.

    21 Explain on range resolution and azimuth resolution?

    Range resolution - ability to separate individual target like storm cells withrespect to range. If the range resolution incorrect, the target will mergetherefore pulse width will be altered (narrower). The pulse widthmeasured in microseconds divided by the velocity of light.

    Azimuth resolution - ability to separate adjacent targets at the samerange but a few degree apart. Its function of the transmitted beam width,which spreads from the aircraft as range increases. Storm cells thatseparated by a distance less than the width of the beam at a given rangewill appear as a one target on the indicator.

    22. What maximum range of radar altimeter and its purpose of thissystem?

    The purpose of the Radar Altimeter System is:

    a. To measure the vertical distance from the aircraft to the ground

    b. To provide the pilot with an indication of the absolute altitudeabove the terrain

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    Maximum range for radar altimeter is normally up to 5000ft but can goas high as 30000ft.

    23. The output of the radio altimeter is fed to what system?

    Radio altimeter is fed to :Autopilot and flight director system.

    Ground Proximity Warning System (GPWS).

    Cabin indication.

    24. If the DH is set to 200 feet and self test is activated. Explain thedisplay?

    The displays will show decision height, test altitude, and the 8888 (alleight to ensure illumination of every segment).

    25. What typical frequency range of radio altimeter?

    The typical frequency range for radio altimeter is at 4.35 GHz to 4.25 GHz

    and operates with a carrier wave (CW).

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