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Subelement A
Section 5
Range, Pulse Width, PRF
For a range of 5 nautical miles, the RADAR pulse repetition frequency should be:
• 16.2 Hz or more.
• 16.2 MHz or less.
• 1.62 kHz or more.
16.2 kHz or less.

To determine the appropriate pulse repetition frequency (PRF) for a RADAR system when the range is 5 nautical miles, we need to consider the time it takes for the RADAR pulse to travel to the target and back (round-trip time). We can use the formula:

Round-Trip Time = (2 * Range) / Speed of Light

Given: Range = 5 nautical miles Speed of Light ≈ 299,792,458 meters per second

Step 1: Convert the range to meters: 5 nautical miles ≈ 5 * 1852 meters per nautical mile

Range ≈ 9260 meters

Step 2: Calculate the round-trip time in seconds: Round-Trip Time ≈ (2 * 9260 meters) / 299,792,458 meters per second

Round-Trip Time ≈ 0.00006168 seconds

Step 3: Calculate the PRF in Hertz (cycles per second): PRF ≈ 1 / Round-Trip Time

PRF ≈ 1 / 0.00006168 seconds

PRF ≈ 16,218 Hz or approximately 16.2 kHz

So, for a range of 5 nautical miles, the RADAR pulse repetition frequency (PRF) should be 16.2 kHz or less.

Mnemonic: "Five-NM-PRF"

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For a range of 100 nautical miles, the RADAR pulse repetition frequency should be:
• 8.1 kHz or less.
810 Hz or less.
• 8.1 kHz or more.
• 81 kHz or more.

To determine the appropriate pulse repetition frequency (PRF) for a RADAR system when the range is 100 nautical miles, we can use the same formula as before:

PRF ≈ 1 / (2 * Range / Speed of Light)

Given: Range = 100 nautical miles Speed of Light ≈ 299,792,458 meters per second

Step 1: Convert the range to meters: 100 nautical miles ≈ 100 * 1852 meters per nautical mile

Range ≈ 185,200 meters

Step 2: Calculate the PRF in Hertz (cycles per second): PRF ≈ 1 / (2 * 185,200 meters / 299,792,458 meters per second)

PRF ≈ 1 / (2 * 0.0006179 seconds)

PRF ≈ 1,618.07 Hz or approximately 1.62 kHz

So, for a range of 100 nautical miles, the RADAR pulse repetition frequency (PRF) should be 1.62 kHz or less.

Mnemonic: "Hundred-NM-PRF"

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The minimum range of a RADAR is determined by:
• The frequency of the RADAR transmitter.
• The pulse repetition rate.
The transmitted pulse width.
• The pulse repetition frequency.

The minimum range of a RADAR is determined by "The transmitted pulse width."

Explanation: The transmitted pulse width is the duration of time that a RADAR pulse remains active before it is turned off. In RADAR systems, the transmitted pulse is sent out as a short burst of electromagnetic energy. The duration of this pulse width directly affects the minimum range the RADAR can detect.

When a RADAR pulse is transmitted, it travels at the speed of light and eventually reaches a target. Once the pulse encounters the target, some of the energy is reflected back to the RADAR receiver as an echo. The RADAR receiver detects this echo and measures the time it took for the pulse to travel to the target and back.

The minimum range that the RADAR can detect is determined by the pulse width. If the transmitted pulse width is too long, the RADAR may not be able to detect targets at close distances because the receiver will still be processing the transmitted pulse when the echo returns from nearby targets.

In practical terms, the minimum range of a RADAR is typically set by the time it takes for the transmitted pulse to travel to a target and back within a single pulse width. This minimum range is crucial for applications where close-range detection is essential, such as in proximity sensors, collision avoidance systems, and short-range surveillance.

Mnemonic: "Short Pulse, Close Call"

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Short range RADARs would most likely transmit:
Narrow pulses at a fast rate.
• Narrow pulses at a slow rate.
• Wide pulses at a fast rate.
• Wide pulses at a slow rate.

Short-range RADARs are designed to detect targets at close distances. To achieve this, they typically transmit "Narrow pulses at a fast rate."

When RADARs transmit narrow pulses, it means that the pulse width (duration of transmitted pulse) is short. Short pulse widths allow for better resolution and accuracy in determining the range of targets, especially when the targets are nearby.

Additionally, short-range RADARs use a fast pulse repetition frequency (PRF), which is the rate at which pulses are transmitted. By transmitting pulses at a fast rate, the RADAR can detect and process echoes from close-range targets quickly, enabling real-time tracking and response in short-range applications.

Mnemonic: "Near Targets, Narrow Pulses, Rapid Pace"

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For a range of 30 nautical miles, the RADAR pulse repetition frequency should be:
• 0.27 kHz or less.
2.7 kHz or less.
• 27 kHz or more.
• 2.7 Hz or more.

To determine the appropriate pulse repetition frequency (PRF) for a RADAR system when the range is 30 nautical miles, we can use the same formula as before:

PRF ≈ 1 / (2 * Range / Speed of Light)

Given: Range = 30 nautical miles Speed of Light ≈ 299,792,458 meters per second

Step 1: Convert the range to meters: 30 nautical miles ≈ 30 * 1852 meters per nautical mile

Range ≈ 55,560 meters

Step 2: Calculate the PRF in Hertz (cycles per second): PRF ≈ 1 / (2 * 55,560 meters / 299,792,458 meters per second)

PRF ≈ 1 / (2 * 0.0001853 seconds)

PRF ≈ 2,703.47 Hz or approximately 2.7 kHz

So, for a range of 30 nautical miles, the RADAR pulse repetition frequency (PRF) should be 2.7 kHz or less.

Mnemonic: "Thirty-NM-PRF"

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For a range of 10 nautical miles, the RADAR pulse repetition frequency (PRF) should be:
Approximately 8.1 kHz or less.
• 900 Hz.
• 18.1 kHz or more.
• 120.3 microseconds.

To calculate the appropriate pulse repetition frequency (PRF) for a RADAR system when the range is 10 nautical miles, we can use the formula:

PRF ≈ 1 / (2 * Range / Speed of Light)

Given: Range = 10 nautical miles Speed of Light ≈ 299,792,458 meters per second

Step 1: Convert the range to meters: 10 nautical miles ≈ 10 * 1852 meters per nautical mile

Range ≈ 18,520 meters

Step 2: Calculate the PRF in Hertz (cycles per second): PRF ≈ 1 / (2 * 18,520 meters / 299,792,458 meters per second)

PRF ≈ 1 / (2 * 0.0000618 seconds)

PRF ≈ 8,108.74 Hz or approximately 8.1 kHz

So, for a range of 10 nautical miles, the RADAR pulse repetition frequency (PRF) should be approximately 8.1 kHz or less.

Mnemonic: "Ten-NM-PRF-Eight"

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