Weather Radar

Question 1

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

Answer 1

• 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)

Question 2

Where is the storm most turbulent?

Answer 2

Where the colours are changing rapidly

Question 3

What is RADAR an acronym of?

Answer 3

Radio Detecting and Ranging

Question 4

What is the principle of RADAR?

Answer 4

Emits a high frequency RF pulse and listens for its return

Question 5

What is the PRF of radar?

Answer 5

100pp/s

Question 6

At what frequency does radar operate at?

Answer 6

9375MHz (9.375GHz)

Question 7

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

Answer 7

12.36uS

Question 8

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

Answer 8

• 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

Question 9

What does the STC control?

Answer 9

The STC controls the IF gain within the radio

Question 10

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

Answer 10

Minimum Discernible Signal (MDS)

-110dbm

Question 11

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

Answer 11

• Narrow beam widths are preferred

- Achieved by getting a larger array

Question 12

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

Answer 12

Bearing resolution issues

Question 13

Gain is _______ to beam width

Answer 13

inverse

Question 14

What are the 2 type of radar antennas?

Answer 14

Reflectors and Flat Plates

Question 15

Frequency is fixed by the choice of the what?

Answer 15

Magnetron

Question 16

A typical weather cell is how many miles in diameter?

Answer 16

3 miles

Question 17

What is a secondary function of the weather radar?

Answer 17

Ground mapping

Question 18

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

Answer 18

Square Law Shape

Question 19

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

Answer 19

greater and narrower beam

Question 20

What is the result of lower frequency on radar?

Answer 20

Less atmospheric attenuation

Question 21

What is the preferred band of all manufacturers?

Answer 21

X band

Question 22

What is the pulse width of a weather radar?

Answer 22

3.75uS (1/3mile)

Question 23

What type of issues can pulse width give us?

Answer 23

Range issues

Question 24

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

Answer 24

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

Question 25

What is the power output for a weather radar?

Answer 25

10kW

Question 26

Can the pilot adjust the gain?

Answer 26

The pilot can only reduce gain to declutter the screen

Question 27

What is the detent position?

Answer 27

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

Question 28

The weather is plotted on what?

Answer 28

Time and direction

Question 29

What is contour mode?

Answer 29

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

Question 30

The STC works within how many miles?

Answer 30

45NM

Question 31

What does the Vertical gyro give us?

Answer 31

Pitch and Roll

Question 32

What is the MODULATOR/POWER SUPPLY triggered by?

Answer 32

The trigger pulse

Question 33

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

Answer 33

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

Question 34

What is the PFN and what does it do?

Answer 34

- Pulse Forming Network | - changes the current/voltage into a trapezoidal pulse to fire through the MAGNETRON

Question 35

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

Answer 35

MAGNETRON

Question 36

What does the Magnetron put out?

Answer 36

Power and Frequency

Question 37

What does the magnetron do?

Answer 37

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

Question 38

How do we get oscillations at 9375MHz

Answer 38

The magnetron resonant cavities

Question 39

How much power does the magnetron produce?

Answer 39

10-50kW

Question 40

What varies the output frequency of the MAGNETRON?

Answer 40

- Inconsistent Voltage | - Heat

Question 41

What type of energy does the magnetron need?

Answer 41

Electromagnetic energy

Question 42

What is the circulator and what is its purpose?

Answer 42

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

Question 43

How does the circulator work?

Answer 43

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

Question 44

The CIRCULATOR is similar to what?

Answer 44

A duplexer

Question 45

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

Answer 45

TR LIMITER

Question 46

How does the TR Limiter work?

Answer 46

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

Question 47

How do we sample the Tx frequency?

Answer 47

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

Question 48

What is the AFC and what is its purpose?

Answer 48

- 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

Question 49

What is the correct IF?

Answer 49

30MHz

Question 50

How often does the AFC monitor the IF difference?

Answer 50

Every transmission

Question 51

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

Answer 51

Mixer

Question 52

What is the purpose of the IF AMP?

Answer 52

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

Question 53

How long till the STC fully regains its gain?

Answer 53

450uS

Question 54

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

Answer 54

``` Kleistron (old) Magic T (new) ```

Question 55

How do you tune the Kleistron?

Answer 55

A tuning voltage from the AFC

Question 56

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

Answer 56

Varactor(tuning) and Gunn(oscillating)

Question 57

How do you tune the Varactor diode?

Answer 57

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

Question 58

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

Answer 58

Pull the disable switch which disables the Modulator

Question 59

What format do we use?

Answer 59

XY format