# FCC Element 8-radar Endorsement

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FCC Commercial Element 8 Question Pool (approved 25 June 2009)Subelement A – RADAR Principles – 10 Key Topics – 10 Exam Questions – 8 Drawings

Questions and Answers
• 1.

### 8-6A4 If the RADAR unit has a pulse repetition frequency (PRF) of 2000 Hz and a pulse width of 0.05 microseconds, what is the duty cycle?

• A.

0.0001

• B.

0.0005

• C.

0.05

• D.

0.001

Correct Answer
A. 0.0001
Explanation
The duty cycle of a radar unit is the ratio of the pulse width to the pulse repetition period. In this case, the pulse repetition period can be calculated by taking the reciprocal of the pulse repetition frequency (PRF), which is 1/2000 Hz. The pulse width is given as 0.05 microseconds. Dividing the pulse width by the pulse repetition period, we get 0.05 microseconds / (1/2000 Hz) = 0.05 microseconds * 2000 Hz = 100. Therefore, the duty cycle is 0.0001.

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• 2.

### 8-5A1 For a range of 5 nautical miles, the RADAR pulse repetition frequency should be:

• A.

16.2 Hz or more.

• B.

16.2 MHz or less.

• C.

1.62 kHz or more.

• D.

16.2 kHz or less.

Correct Answer
D. 16.2 kHz or less.
Explanation
The correct answer is 16.2 kHz or less because the pulse repetition frequency (PRF) of a RADAR system determines the maximum range it can detect. A higher PRF allows for shorter range detection, while a lower PRF allows for longer range detection. In this case, the question states that the range is 5 nautical miles, which is relatively short. Therefore, the PRF should be 16.2 kHz or less to ensure that the RADAR system can accurately detect targets within this range.

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• 3.

### 8-39E5 How does antenna length affect the horizontal beamwidth of the transmitted signal?

• A.

The longer the antenna the wider the horizontal beamwidth

• B.

The longer the antenna the narrower the horizontal beamwidth.

• C.

The horizontal beamwidth is not affected by the antenna length.

• D.

None of the above.

Correct Answer
B. The longer the antenna the narrower the horizontal beamwidth.
Explanation
The horizontal beamwidth of a transmitted signal refers to the width of the signal's coverage in the horizontal direction. A narrower beamwidth means that the signal is more focused and concentrated in a specific direction, while a wider beamwidth means that the signal is spread out over a larger area. When the antenna length is longer, it allows for more precise control and directionality of the signal, resulting in a narrower horizontal beamwidth. Therefore, the correct answer is "The longer the antenna the narrower the horizontal beamwidth."

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• 4.

### 8-4A1 A pulse RADAR has a pulse repetition frequency (PRF) of 400 Hz, a pulse width of 1 microsecond, and a peak power of 100 kilowatts. The average power of the RADAR transmitter is:

• A.

25 watts.

• B.

40 watts.

• C.

250 watts

• D.

400 watts.

Correct Answer
B. 40 watts.
Explanation
The average power of a RADAR transmitter can be calculated using the formula: Average Power = Peak Power * Duty Cycle. The duty cycle is the ratio of pulse width to pulse repetition period. In this case, the pulse repetition period can be calculated as 1/PRF, which is 1/400 Hz = 0.0025 seconds. The duty cycle is then 1 microsecond / 0.0025 seconds = 0.4. Therefore, the average power is 100 kilowatts * 0.4 = 40 watts.

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• 5.

### 8-47F3 Loss of distant targets during and immediately after wet weather indicates:

• A.

A leak in waveguide or rotary joint.

• B.

High atmospheric absorption.

• C.

Dirt or soot on the rotary joint.

• D.

High humidity in the transmitter causing power supply loading.

Correct Answer
A. A leak in waveguide or rotary joint.
Explanation
Loss of distant targets during and immediately after wet weather indicates a possible leak in the waveguide or rotary joint. This is because wet weather can cause moisture to enter the system, leading to a loss of signal. A leak in the waveguide or rotary joint would allow water to enter and disrupt the transmission, resulting in the loss of distant targets.

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• 6.

### 8-1A4 What RADAR component controls timing throughout the system?

• A.

Power supply.

• B.

Indicator.

• C.

Synchronizer.

• D.

Receiver.

Correct Answer
C. Synchronizer.
Explanation
The correct answer is Synchronizer. In a RADAR system, the synchronizer component is responsible for controlling the timing throughout the system. It ensures that all the different components of the RADAR system are synchronized and operate in harmony. Without proper synchronization, the RADAR system may not function accurately and efficiently. The power supply provides electrical power to the system, the indicator displays the radar information, and the receiver receives and processes the radar signals, but none of these components specifically control the timing throughout the system like the synchronizer does.

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• May 14, 2024
Quiz Edited by
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• Feb 12, 2010
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