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Radar Theory > Radar Theory - Learners Pack > Flashcards

Radar Theory - Learners Pack Flashcards

1
Q

What is the Doppler shift?

A

The actual frequency that takes place as a result of a movement a between the target and the radar antenna.

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2
Q

What is the Doppler tone?

A

The Doppler shift frequency divided down for listening comfort.

Stationary mode divided down by 6
Moving mode divided down by 12

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3
Q

Why is reflection important for the effective operation of the radar?

A

Radar relies upon energy reflected from the target to function & calculate a speed reading.

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4
Q

When should the operator complete testing on the SEII radar?

A
  1. Beginning of speed enforcement
  2. At hourly intervals whilst performing speed enforcement
  3. Conclusions of speed enforcement
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5
Q

What are the fundamental categories of interference that may affect the radar?

A
  1. Natural interference

2. Man made interference

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6
Q

What is the range of speed the SEII measure when reading a target?

A

Typically 16-320kph

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7
Q

What is the range of patrol speed that can be measured any the SEII?

A

Patrol - typically 16kph - 239kph

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8
Q

What rules must be followed regarding the placement oaf the SEII radar antenna?

A
  1. Is to be mounted externally
  2. Between 1m & 2m above the ground
  3. Must be parallel to the ground
  4. Facing directly forward in moving mode
  5. Facing to the rear or the front in stationary mode
  6. Electronically isolated
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9
Q

Set out in chronological order, the functions that are performed by the radar in moving mode?

A
  1. Determine & display patrol speed.
  2. Determine closing rate speed.
  3. Determine and display target speed.
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10
Q

Explain Double Bounce?

A
  • Radar obtains patrol speed from the roadway
  • The energy continues to travel forward & collides with a large stationary object, but is not further compressed
  • Energy is reflected back and collides with the the police veh where it is further compressed by the speed of the police vehicle.
  • Energy is reflected back to the large stationary object, but not further compressed.
  • Beam is reflected back to antenna
  • Amount of energy returned to the radar is extremely small and cannot interfere with any signal arriving from a legitimate target
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11
Q

If cosine is a factor in a radar reading, who is the reading in favour of?

A

Always in favour of the target.

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12
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 recedes or approaches at an angle’ the relative velocity to the radar is slower than the actual speed of the target.

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13
Q

Why is the correlation of speed readings important?

A

To negate the possibility of:
An effect; or
An interference.

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14
Q

Is correlation between the radar & the check speedometer essential to obtain a valid speed check? Why?

A

Yes.

It negates the possibility of the radar reading being subjected to an effect or interference

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15
Q

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

A

Yes.
It indicates that the radar is
* Only monitoring only one target &
* Not subject to interference

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16
Q

If the radar was to encounter interference, what would commonly occur?

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

* No display when there is a target.

17
Q

What are the defences to possession of a speed measuring device?

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 yet expired
  • The defendant did not know & could not have reasonably known the article was there.
18
Q

When using a radar in moving mode, what must the operator do to stop a gross error from occurring?

A

Ensure correlation between the radar & the check speedometer.

19
Q

What test is to be performed by the operator at hourly intervals?

A

An internal calibration test or manual test

20
Q

When would a radar likely to encounter an add-on speed?

A
  • When the police vehicle is travelling below the threshold of the radar
  • When an oncoming vehicle is within 50m of the radar.
21
Q

Explain differential effect.

A
  • Vehicle in front is treated as a stationary object
  • A stronger reflection will be obtained from the vehicle in front
  • Displayed patrols speed is the difference between the speed of the two vehicles
  • Closing rate speed will be the true speed plus the target speed
  • Target speed will be displayed as the speed of the target pls a the difference between the two patrol speeds
22
Q

What should an operator alway keeps to, to ensure cosine is within acceptable limits?

A

7:1 ratio

23
Q

When moving, how does the radar calculate the target speed?

A

Combined speed (CRS) - patrol speed

24
Q

Which is obtained first?

a) closing rate speed
b) patrol speed
c) target speed

A

Patrol speed

25
Q

Explain multi path interference?

A

It is likely to occur on long straight roads with Armco railing.
It is the arrival of two energies, at different intervals.
On arrival, the energies will oppose each other, often resulting in the cancellation of both.
Short blips will be heard
Only occurs for short periods
Does not affect the accuracy of any speed readings

26
Q

What is the purpose of keeping a reasonably constant patrol speed?

A

It allows easier acquisition of a patrol a speed which allows more time for the radar to devote to the calculation of CRS

27
Q

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

A

Because the radar obeys inverse square law.
The amount of energy that is returned to the radar from the target depends on two things.
* The reflective area of the target
* the distance between the antenna & the target

28
Q

What is the operating frequency of the SEII

A

34.9GHz

29
Q

What is the 3dB beam width of the SEII?

A

12 degrees (+/- 1 degree)

30
Q

What is the operating voltage of the SEII?

A

10.8 to 16.5 volts

31
Q

What is the effective beam range of the SEII?

A

600m

32
Q

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

A

Press the test button and observe all the segments illuminate.

33
Q

What energy type does the SEII use?

A

Electromagnetic energy.

34
Q

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

A

300 million metres per second - the speed of light.

35
Q

What does radar stand for?

A

RAdio Detection And Ranging

36
Q

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

A

Visible light.

37
Q

Electromagnetic energy obeys which law?

A

Inverse square law.

38
Q

Can interference affect the accuracy of speed readings?

A

No

Radar Theory (2 decks)

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