This set of Radar Multiple Choice Questions & Answers (MCQs) focuses on “Pulse Repetition Frequency”.

1. By which of the following technique, pulse repetition frequency can be determined?
a) Doppler frequency shift
b) Probability function
c) Maximum unambiguous range
d) Predetection integration

Explanation: The pulse repetition frequency can be determined by the maximum unambiguous range beyond which targets are not expected. In simple words, it is the longest distance where consecutive transmitted pulses can travel out to and come back again.

2. In multiple time around echoes, the clutter echoes from range greater than Run can mask unambiguous target echoes at the shorter ranges.
a) True
b) False

Explanation: It’s true that one of the problems with multiple time around echoes is that clutter echoes from range greater than Run can mask unambiguous target echoes at the shorter ranges due to which even though the signal is said to hit the target the first time, is masked by the second time or multiple time around echo.

3. Why are pulse Doppler radars operated with a pulse repetition frequency (PRF)?
a) To generate false alarm
b) To obtain range ambiguities
c) To generate high duty cycle
d) To reduce the existence of probability distribution function

Explanation: Pulse Doppler radar are operated with a pulse repetition frequency since due to that range ambiguities can be generated in order to know if the transmitted pulses have exceeded the distance. Doppler radar makes use of range ambiguities in order to detect targets even in the presence of clutter.

4. Which problem is generated when the pulse repetition frequency or sweep are superimposed on an A scope radar display for ambiguous and unambiguous echoes?
a) Ambiguous echo appears more vivid compared to unambiguous echo
b) Both of them look the same
c) Unambiguous echo appears more vivid compared to ambiguous echo
d) Both of them disappears

Explanation: When the pulse repetition frequency or sweep are superimposed on an A scope radar display for ambiguous and unambiguous echoes, the ambiguous echoes look no different from the unambiguous range echo. The unambiguous echo cannot be determined from the display that the others are not at their apparent range.

5. What can be recognized by changing the pulse repetition frequency of the radar?
a) Ambiguous range echoes
b) Pulse width
c) Unambiguous range echoes
d) Multiple time around echoes

Explanation: Ambiguous range echo can be recognized by changing the pulse repetition frequency of the radar. When the PRF is changed, the unambiguous echo remains at its true range. But ambiguous echo appears at the different apparent range for each PRF.

6. How is the pulse repetition frequency changed in order to distinguish between ambiguous and unambiguous range echoes?
a) Multiple pulses at a time
b) Depending upon the range
c) Pulse to pulse
d) Depending upon the target

Explanation: The pulse repetition frequency can be changed pulse to pulse, every half beam width (with a scanning antenna), or on every rotation of the antenna. Both of these methods can be used since they both have their own benefits as well as limitations.

7. What is the benefit of high pulse repetition frequency?
a) Make distinguishing easier between echoes and noise
b) Make detection of signal easier
c) To increase the maximum range
d) To make the resolution more better

Explanation: By using high pulse repetition frequency, it is possible to increase the maximum range. In normal conditions the target can be detected only in the unambiguous range and the rest comes under ambiguous range, but if there is a change in PRF, the range for the unambiguous region also increases.

8. The distance beyond which target appears as a second time around or multiple time around echo signal is called maximum ambiguous range.
a) True
b) False

Explanation: Targets appearing as a second time around or multiple time around after a fixed distance is called as maximum unambiguous range. Whenever the first pulse is sent to detect the target, but when its echo signal returns after the generation of second pulse is how the second time around echo signal works.

9. How is pulse repetition time related to pulse repetition frequency?
a) PRT = PRF
b) PRT = 1/PRF
c) PRT = 1/2PRF
d) PRT = 2PRF

Explanation: Pulse repetition time is the overall time in between the beginning of the first pulse and the start of the next pulse or in simple words, it’s the time a pulse takes to recourse. It is inversely proportional to pulse repetition frequency so we can write it as PRT = 1/PRF.

10. Which out of the following systems do not use pulse repetition frequency?
a) Sphygmomanometer
b) Sonar
d) Laser range finder

Explanation: Pulse repetition frequency is an important part for devices that measure distance. It is true that based on the value of PRF we can perform different functions on different applications. Therefore, the sphygmomanometer does not use pulse repetition frequency since it does not measure distance but blood pressure.

Sanfoundry Global Education & Learning Series – Radar.

To practice all areas of Radar, here is complete set of Multiple Choice Questions and Answers.

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