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Subelement A
RADAR Principles
Section 1
Marine RADAR Systems
Choose the most correct statement containing the parameters which control the size of the target echo.
  • Correct Answer
    Transmitted power, antenna effective area, transmit and receive losses, RADAR cross section of the target, range to target.
  • Height of antenna, power radiated, size of target, receiver gain, pulse width.
  • Power radiated, antenna gain, size of target, shape of target, pulse width, receiver gain.
  • Magnetron gain, antenna gain, size of target, range to target, wave-guide loss.

This statement includes the key parameters that influence the size of the target echo in radar systems. Let's break down each parameter:

  1. Transmitted power: The power of the radar signal transmitted towards the target affects the strength of the returned echo.

  2. Antenna effective area: The effective area of the radar antenna determines the amount of power captured from the returning echo. A larger effective area allows for better reception of the signal.

  3. Transmit and receive losses: These losses account for any reduction in power during the transmission and reception processes. The losses affect the overall signal strength and, consequently, the size of the target echo.

  4. RADAR cross section of the target: The RADAR cross section (RCS) is a measure of how effectively the target reflects the radar signal. A larger RCS indicates a stronger echo return.

  5. Range to target: The distance between the radar system and the target affects the received power of the echo. The size of the target echo is influenced by the signal's propagation loss over the given range.

Mnemonic: "Power, Area, Losses, RCS, Range"

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Which of the following has NO effect on the maximum range capability?
  • Carrier frequency.
  • Correct Answer
    Recovery time.
  • Pulse repetition frequency.
  • Receiver sensitivity.

The recovery time refers to the time it takes for a system or component to return to its normal state after being subjected to a disturbance or disruption. In the context of maximum range capability, recovery time does not directly impact the ability of a system to detect targets at longer distances.

The maximum range capability of a system, such as a radar system, is primarily determined by factors such as the transmitted power, antenna characteristics, receiver sensitivity, and signal-to-noise ratio. These factors affect the system's ability to detect and process weak signals reflected from targets at long distances.

Recovery time, on the other hand, relates to the system's internal response and its ability to recover from a disturbance. While recovery time can be important for system stability and performance in certain applications, it does not directly influence the maximum range capability of the system.

Mnemonic: "Range Unaffected by Recovery"

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What type of transmitter power is measured over a period of time?
  • Correct Answer
    Average.
  • Peak.
  • Reciprocal.
  • Return.

From KD9TIP:

Measured over a period of time is the Average.


When we refer to the average power of a transmitter, we are interested in determining the average amount of power delivered by the transmitter over a specific duration. This measurement takes into account variations in power that may occur during that time interval.

To calculate the average power, we consider the instantaneous power values at different points in time and then average them out. This provides a more comprehensive and representative measurement of the power output of the transmitter over a given period.

Mnemonic: "Power Over Time"

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What RADAR component controls timing throughout the system?
  • Power supply.
  • Indicator.
  • Correct Answer
    Synchronizer.
  • Receiver.

In a RADAR system, timing is crucial for coordinating various operations and ensuring proper functioning of the system. The synchronizer plays a vital role in controlling and maintaining precise timing synchronization among different components.

The synchronizer is responsible for generating and distributing timing signals to various parts of the RADAR system, including the transmitter, receiver, signal processing modules, and other related components. It ensures that all these elements operate in sync and at the correct time intervals.

By maintaining accurate timing throughout the system, the synchronizer enables proper coordination of the transmitted pulses, reception of the echoes, and synchronization of the signal processing operations. It helps achieve accurate range measurements, target tracking, and overall system performance.

Mnemonic: "Timing Master"

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Which of the following components allows the use of a single antenna for both transmitting and receiving?
  • Mixer.
  • Correct Answer
    Duplexer.
  • Synchronizer.
  • Modulator.

Which of the following components allows the use of a single antenna for both transmitting and receiving?

(B). Duplexer.

Duplexer let send/receive happen at the same time, so you don't have to wait until someone says "Over." To do this, they used different but closely related frequencies.

For more info, please see Wikipedia's article on Duplexer

A solid Duplexer info is on Repeater Builder site, article Duplexers


YouTube: A complete video well explains the topic from TRX Lab channel, #141 Basics of Duplexers for radio repeaters; function, alignments and tests

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The sweep frequency of a RADAR indicator is determined by what parameter?
  • Carrier frequency.
  • Pulse width.
  • Duty cycle.
  • Correct Answer
    Pulse repetition frequency.

The sweep frequency of a RADAR indicator is determined by the pulse repetition frequency (PRF).

The PRF refers to the number of pulses transmitted by the RADAR system per unit of time. It controls the rate at which pulses are emitted and plays a crucial role in determining the sweep frequency of the RADAR indicator.

When the RADAR indicator displays the received signals, it typically represents them as blips or targets on a screen. The sweep frequency determines how quickly these blips move across the screen, creating the perception of motion.

The relationship between the PRF and the sweep frequency can be understood as follows: If the PRF is high, meaning a large number of pulses are transmitted per unit of time, the sweep frequency will be faster. As a result, the blips on the RADAR indicator will move rapidly across the screen, giving the appearance of high-speed motion.

Conversely, if the PRF is low, meaning fewer pulses are transmitted per unit of time, the sweep frequency will be slower. In this case, the blips on the RADAR indicator will move at a slower pace, simulating slower motion.

Mnemonic: "Pulses Determine Sweep"

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