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Radar Theory > Radar Theory > Flashcards

Radar Theory Flashcards

1
Q

What is the Doppler Shift?

A
  • The actual frequency shift that takes place as a result of movement between the Target & Antenna.
  • The difference between transmitted & received frequency.
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2
Q

What is the Doppler Tone?

A

The Doppler shift frequency divided down for listening comfort.

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3
Q

Why is reflection important for the operation of the radar?

A

Radar relies upon energy reflected from the target to function.

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4
Q

When should testing be completed on the silver eagle II & who performs the test?

A
  • At the commencement of speed enforcement - the operator
  • At hourly intervals - the operator
  • At the conclusion of speed enforcement - the operator
  • Every 12 months - REU
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5
Q

What are the fundamental categories for interference?

A
  • Man made

* Natural

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6
Q

What range of speeds does the Silver Eagle II measure?

A

Target - Typically 16kph - 320kph

Patrol - Typically 16kph - 239kph

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7
Q

List the rules regarding placement of the antenna?

A
  • Mounted externally
  • Between 1m & 2m above the ground
  • Must be parallel to the ground
  • Facing directly forward in moving mode
  • Facing to the front or rear in stationary mode
  • Electronically isolated
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8
Q

Set out, in order, the functions of the radar in moving mode?

A
  • Determine and display Patrol Speed
  • Determine closing rate speed
  • Determine and display target speed
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9
Q

Why is correlation of patrol speed and the check speedometer important for a valid speed check?

A

To negate the possibility of

  • an effect; or
  • any interference
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10
Q

Why is a clear tone necessary for a valid speed check?

A

Indicates that the radar is;

  • monitoring only one target
  • not subject to interfence
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11
Q

How does interference commonly affect the radar?

A
  • Display of a target speed in the absence of a target

* No display when there is a target

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12
Q

List the statutory defence to speed measuring evasion article?

A
  • Device was not designed as a speed measuring evasion article
  • On a journey to surrender the device
  • vehicle is subject to a notice and the notice has not expired
  • The defendant did not know & could not reasonably have known the article was there
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13
Q

In moving mode, what must the operator do to negate the possibility of gross error?

A

Correlation between the patrol speed and the checked speedometer.

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14
Q

What is the name of the test performed by the operator at hourly intervals?

A

Internal calibration test or manual test.

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15
Q

In stationary mode, why is cosine ALWAYS in favour of the target?

A

Because;

  • the radar only measures the component of the target speed which is directly toward it (relative velocity)
  • as the target approaches or recedes at an angle,
  • The relative velocity to the radar is slower than the actual speed of the target.
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16
Q

Under what circumstances is the radar likely to encounter add-on speed?

A
  • When the police vehicle is travelling below the threshold speed of the radar.
  • when any oncoming car is within 50m of the police vehicle.
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17
Q

Explain what happens when the radar encounters differential effect?

A
  • Vehicle in front is treated as a stationary object.
  • A stronger reflection will be obtained from the vehicle
  • Displayed patrol speed is the difference between the speed of the vehicles
  • Closing rate speed will be the true speed plus target speed, and
  • Target speed displayed is the speed of the target plus the difference between the two patrol speeds.
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18
Q

What should an operator do to keep the cosine angle within acceptable limits?

A

Apply the 7:1 Ratio

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19
Q

In moving mode, how does the radar calculate target speed?

A

Combined (CRS) minus patrol speed.

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20
Q

Explain multipath interference?

A
  • Likely to occur on long straight roads with Armco railings
  • it is the arrival of two energies
  • at different intervals
  • On arrival, energies will appose each other,often resulting in the cancellation of both
  • Short blips will be heard in the audible tone
  • Only occurs for short periods
  • Does not affect the accuracy of any speed reading.
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21
Q

Set out VERBATIM the requirements of a valid speed check?

A
  1. Visual observation and estimation of the targets speed
  2. Observe the numerals displayed in the patrol and target displays
  3. Clear and continuous tone (pitch may vary)
  4. Correlation between patrol speed and checked speedometer.
  5. Duration of check (steps 2,3,4) must not be less than 3 seconds
  6. Minimum of 200m between targets of similar size.
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22
Q

Why is cosine the most common situation you will encounter as a radar operator?

A
  • Ideally a target should travel directly toward the radar, and in the centre of the effective beam
  • This creates a dangerous situation for the operator, therefore
  • to overcome this danger the radar is operated offset to the target, thus creating an angle.
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23
Q

As an operator, why must you keep a reasonably constant patrol speed?

A
  • to allow easier acquisition of a patrol speed, allowing

* more time being devoted to the calculation of the closing rate speed

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24
Q

Why does the size of a target affect the range of a radar?

A

Because radar obeys inverse square law;

  • the amount of energy returned to the antenna from the target depends on;
  • the reflective area of the target; and
  • the distance between the antenna and the target.
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25
Q

As an operator what guildeline should you apply to avoid double bounce?

A

Keep the radar in hold until a target is visually a observed.

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26
Q

For Doppler shift to occur what must exist between the radar & target?

A

Relative velocity (movement)

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27
Q

Whilst checking the radar you notice that the tamperproof seal has been violated, what must you do?

A
  • cease all speed enforcement.

* contact and return to REU

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28
Q

What must a vehicle be equipped with before being used for speed enforcement with a radar?

A
  • A shielded cable

* a check speedometer

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29
Q

How is patrol speed obtained by the radar?

A

Energy being reflected off

  • the roadway
  • surrounding stationary objects
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30
Q

In moving mode, why must a radar only be used in areas where traffic is sparse?

A

To ensure ease of target identification .

31
Q

Set out, in order, the functions of the radar in moving mode?

A
  • Determine and display patrol speed
  • Determine CRS
  • Determine and display target speed.
32
Q

Explain what occurs when the radar is subjected to double bounce?

A
  • Radar obtains patrol speed from the roadway
  • the energy continues to travel forward and collides with a bridge or other stationary object but is not further compressed
  • energy is reflected back and collides with the police vehicle where it is further compressed by the speed of the police vehicle
  • Reflected back to stationary object but not further compressed
  • Beam is reflected back to antenna
  • Amount of energy returned to the radar is extremely small therefore cannot interfere with any signal arriving from a legitimate target.
33
Q

What do you establish from performing the tuning fork test?

A
  • that the transmitter / receiver is functioning; and

* the accuracy of the logic control unit

34
Q

For a section 137 certificate to be tendered as prima facie evidence, it must be issued within what time period?

A

Within 12 months preceding the offence

35
Q

As an operator how would you know that multi path interference has occurred?

A

Short audible blips will be heard

36
Q

What is the purpose of correlating the patrol display with the checked speedometer during set up procedure?

A

To ensure correct antenna alignment.

37
Q

In moving mode, when carrying out the tuning fork test what do the following numbers represent & where are they displayed?

80
45
35

A

80 - represents CRS - not displayed.
45 - represents patrol speed - displayed in patrol window
35 - represent target speed - displayed in target window

38
Q

What evidence must you give if there is a change in pitch?

A

Evidence of a altering speed.

39
Q

As the operator, what are you determining by applying the 7:1 ratio?

A

The range at which the speed check is to conclude or commence.

40
Q

How would the operator a know that the Silver Eagle II is being subjected to Radio Frequency interference?

A

RFI will appear in the target window.

41
Q

You are operating the radar in moving mode behind another vehicle, what would the vehicle in front of you have to do to cause a reading on the radar?

A
  • travel at twice the speed of the police vehicle, plus

* the threshold speed of the radar.

42
Q

Is the Silver Eagle II radar capable of registering the speed of a motor cycle when a truck is in sight?

A

It is possible, however the radar obeys inverse square law, therefore

  • the truck having the greater reflective surface than a motor cycle would reflect more energy at a greater distance
  • the motor cycle would have to be much closer than the truck tot the radar to register the speed of the motor cycle.
43
Q

You are operating the radar when a differential effect occurs, explain how the radar obtains patrol speed as a result of this effect?

A
  • Due to the vehicle in front being treated as a stationary object
  • a stronger reflection will be obtained from a vehicle in front, resulting in
  • the difference in speed of the two vehicles being displayed as patrol speed.
44
Q

Explain add on speed?

A
  • usually occurs when the PV is travelling at a speed below the threshold of the radar
  • instrument tries to establish patrol speed
  • any oncoming vehicle within 50m will return a better signal than the roadway
  • so the radar treats it as a stationary object
  • closing rate speed between the PV and oncoming vehicle is displayed as patrol speed.
45
Q

Ideally, where should the SEII radar obtain patrol speed?

A

From energy reflected from the roadway at a minimum distance of 7m to the front of the vehicle.

46
Q

In moving mode, what must an operator do to negate the possibility of a ‘Gross Error’?

A

Correlation between the patrol speed and the checked speedometer.

47
Q

Will a radar display a speed as a result of random movement? Why?

A

No, radar requires a continuous movement toward or away from the source to compress or expand the wavefronts.

48
Q

As the operator, when are you require to conduct the internal calibration test of the radar?

A

At the commencement of speed enforcement
At hourly intervals
At the conclusion of speed enforcement

49
Q

You are operating a radar when a split speed occurs, explain what happens to the radar as a result of this effect?

A

Occurs when PV is travelling in excess of 120kph
Radar is unable to obtain P/S from the roadway in front
Obtains a PS from stationary objects to the side.
Radar then obtains true ground speed and treats it as CRS
The difference between the two is displayed as target speed

50
Q

What is the effective beam range of the SEII?

A

600m

51
Q

What is the operating voltage of the SEII?

A

10.8 to 16.5 volts

52
Q

What is the 3dB beam width of the SEII?

A

12 degrees (+/- 1 degree)

53
Q

What is the operating frequency of the SEII?

A

34.9GHz

54
Q

How do you perform a manual test on the SEII radar?

A

Press the test button & observe all the segments illuminate.

55
Q

What energy type does the SEII use?

A

Electromagnetic energy

56
Q

What speed does the electromagnetic energy of the SEII travel at?

A

300 million metres per second - the speed of light.

57
Q

What does radar stand for?

A

Radio detection & ranging.

58
Q

With some exceptions EM energy behaves in much the same way as?

A

Visible light

59
Q

Electromagnetic energy obeys what law?

A

Inverse square law

60
Q

Can interference effect the accuracy of speed readings?

A

No

61
Q

Prior to performing any speed enforcement using a check speedometer what checks must an operator complete?

A
  1. Visual check of the speedometer and wiring for damage
  2. Ensure that the tamperproof seals are intact
  3. Turn on digital speedometer and observe all segments illuminated
  4. At them commencement of shift correction of digital speedometer and radar patrol speed
  5. If there is a difference greater than +/- 2 cease all speed enforcement & bring to the attention of your supervisor
62
Q

What is the manufacturers speed accuracy tolerance of the SEII radar?

A

Stationary mode: +/- 2kph

Moving mode: +2kph or -3kph

63
Q

What is the accuracy tolerance of a tuning fork test?

A

+/- 1kph

64
Q

What are the requirements relating to care of tuning forks?

A

1: must never be struck against a surface harder then the fork.
2: When not in use the forks should be carried in the police vehicle.
3: When the radar is sent to REU for service the allocated tuning forks must accompany the radar.

65
Q

What would be displayed on the radar if harmonic detection occurs?

A
    • in the target window.
66
Q

When would harmonic detection be achieved?

A
  1. When the police vehicle and the target are travelling at the same speed.
  2. When double bounce is effecting the radar.
67
Q

What are the requirements to be met when conducting speed enforcement duties?

A

They are not to be used;
1. Within 50m of a change of speed zone unless;
* speed is excessive ( in excess of 20kph over speed limit)
* subject of a complaint
* there is a high accident history
(Does not apply to school zones)

  1. At a location which would engender legitimate critics (or give rise tot the complaint of revenue raising)
68
Q

Who is responsible for notifying REU when a radar expert is required at court?

A

The operator at the time of the offence.

69
Q

When does the SEII perform an automatic self test?

A
  1. When the mode of operation is changed

2. Upon lapse of a maximum time period of 5 minutes, whilst it is powered up

70
Q

If during a automatic self test, the radar detects an error, what will be displayed on the logic control, & where is it displayed?

A

Target display will indicate ‘ErX’ and further speed endings will be inhibited.

71
Q

If the radar detects an error, can it continue to complete speed readings?

A

No

72
Q

When you lock a target speed, where is it displayed?

A

Lock/et window

73
Q

When a speed is locked can the radar continue to complete speed readings?

A

Yes.

74
Q

What is the speed tolerance of the check speedometer?

A

+/-2

Radar Theory (2 decks)

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