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Pulse Class > Weather Radar > Flashcards

Weather Radar Flashcards

1
Q

What are the 5 colours on a weather radar display and what does each mean?

A
  • Black (less than 0.4inch of rain)
  • Green (.04-.17inch of rain, weak, light to moderate turbulence)
  • Yellow (.17-.5inch of rain, moderate, possible lightning)
  • Red (.5-2inch of rain, strong, severe turbulence)
  • Magenta (<2inch of rain, intense, severe turbulence, lightning, hail, extensive wind)
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2
Q

Where is the storm most turbulent?

A

Where the colours are changing rapidly

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3
Q

What is RADAR an acronym of?

A

Radio Detecting and Ranging

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4
Q

What is the principle of RADAR?

A

Emits a high frequency RF pulse and listens for its return

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5
Q

What is the PRF of radar?

A

100pp/s

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6
Q

At what frequency does radar operate at?

A

9375MHz (9.375GHz)

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7
Q

How long does it take for the RF pulse to travel one nautical mile out and back?

A

12.36uS

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8
Q

What is RADAR STC, what is its purpose and how does it work?

A
  • STC stands for Sensitivity Time Control (sweep gain)
  • To make sure rainfall returns, near and far are displayed roughly the same (not exaggerated)
  • It works by making sure the initial transmission has a reduced gain then is increased over time
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9
Q

What does the STC control?

A

The STC controls the IF gain within the radio

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10
Q

In radar, what is sensitivity referred to and what is the typical sensitivity?

A

Minimum Discernible Signal (MDS)

-110dbm

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11
Q

Would we prefer narrow or larger beam widths? How is it achieved?

A
  • Narrow beam widths are preferred

- Achieved by getting a larger array

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12
Q

A big beam width gives the user what type of issues?

A

Bearing resolution issues

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13
Q

Gain is _______ to beam width

A

inverse

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14
Q

What are the 2 type of radar antennas?

A

Reflectors and Flat Plates

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15
Q

Frequency is fixed by the choice of the what?

A

Magnetron

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16
Q

A typical weather cell is how many miles in diameter?

A

3 miles

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17
Q

What is a secondary function of the weather radar?

A

Ground mapping

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18
Q

The gain characteristics of STC follow what type of shape when plotted against time (range)?

A

Square Law Shape

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19
Q

The higher the frequency, the ______ the echo power from water droplets

A

greater and narrower beam

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20
Q

What is the result of lower frequency on radar?

A

Less atmospheric attenuation

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21
Q

What is the preferred band of all manufacturers?

A

X band

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22
Q

What is the pulse width of a weather radar?

A

3.75uS (1/3mile)

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23
Q

What type of issues can pulse width give us?

A

Range issues

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24
Q

What is a pro and con of higher PRF with weather radar?

A

Pro: You strike more moisture at each sweep
Con: Second trace echoes

25
Q

What is the power output for a weather radar?

A

10kW

26
Q

Can the pilot adjust the gain?

A

The pilot can only reduce gain to declutter the screen

27
Q

What is the detent position?

A

Also known as the calibrated position, it sets the gain correctly (max gain)

28
Q

The weather is plotted on what?

A

Time and direction

29
Q

What is contour mode?

A

No longer used, but created a black hole on the display where the storm is strongest

30
Q

The STC works within how many miles?

A

45NM

31
Q

What does the Vertical gyro give us?

A

Pitch and Roll

32
Q

What is the MODULATOR/POWER SUPPLY triggered by?

A

The trigger pulse

33
Q

Why does the MODULATOR/PSU produce such extremely high voltage(5-10kV) and where does it go?

A

To produce the amount of current needed to go into the PFN

34
Q

What is the PFN and what does it do?

A
  • Pulse Forming Network

- changes the current/voltage into a trapezoidal pulse to fire through the MAGNETRON

35
Q

This component has a magnet and is a special vacuum and is made up of multiple tuned circular circuits

A

MAGNETRON

36
Q

What does the Magnetron put out?

A

Power and Frequency

37
Q

What does the magnetron do?

A

Takes the pulse and high voltage from the PFN and turns it into a high powered output

38
Q

How do we get oscillations at 9375MHz

A

The magnetron resonant cavities

39
Q

How much power does the magnetron produce?

A

10-50kW

40
Q

What varies the output frequency of the MAGNETRON?

A
  • Inconsistent Voltage

- Heat

41
Q

What type of energy does the magnetron need?

A

Electromagnetic energy

42
Q

What is the circulator and what is its purpose?

A
  • A piece of waveguide
  • To make sure the magnetron energy goes out the antenna
  • Forces Rx signal to TR LIMITER
43
Q

How does the circulator work?

A

Has ferrite beads that are positioned in a way to divert the RF energy

44
Q

The CIRCULATOR is similar to what?

A

A duplexer

45
Q

This component has a glass filling on both ends containing gas, what is it?

A

TR LIMITER

46
Q

How does the TR Limiter work?

A

During Tx, a 1kV is sent to the TR Limiter to ionize the gas and therefore increases its resistance to prevent the RF from going through

47
Q

How do we sample the Tx frequency?

A

Using a waveguide with a sample probe, it goes through attenuation, through a diode detector then into the AFC (frequency might be 4-5Mhz)

48
Q

What is the AFC and what is its purpose?

A
  • Automatic Frequency Control
  • To compare the LOscillator and Tx signal and make the IF is correct, if not it will adjust accordingly
  • Sends a tuning voltage to LO/Mixer
49
Q

What is the correct IF?

A

30MHz

50
Q

How often does the AFC monitor the IF difference?

A

Every transmission

51
Q

This component uses 2 diodes that are balanced and has an output of 30Mhz

A

Mixer

52
Q

What is the purpose of the IF AMP?

A

Amplifies the 30MHz, detects then digitize into 2 bit code

53
Q

How long till the STC fully regains its gain?

A

450uS

54
Q

What are the 2 types of vacuum tubes that the Local Oscillator use?

A 
Kleistron (old) 
Magic T (new)
55
Q

How do you tune the Kleistron?

A

A tuning voltage from the AFC

56
Q

What are the 2 diodes contained in a Magic T and which is the tuning diode and which is the oscillating diode?

A

Varactor(tuning) and Gunn(oscillating)

57
Q

How do you tune the Varactor diode?

A

Tuning V from AFC (capacitance change=resonant frequency change)

58
Q

When you want to test the radar, what should you do?

A

Pull the disable switch which disables the Modulator

59
Q

What format do we use?

A

XY format

Pulse Class (6 decks)

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