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Subel. D
6 questions
Subelement D

Display & Control Systems

Section 35

Memory Systems

In a digitized RADAR, the 360 degree sweep is divided into how many digitized segments?

  • 16
  • 64
  • 255
  • Correct Answer
    4,096

If the 360 degree sweep were divided into only 255 digitized segments then the minimum resolution would be just over 1.4 degrees per segment:

360 / 255 = 1.4

This resolution must be better than one degree per segment, so Answer D. with 4,096 segments (and a resolution of 5.5 minutes per segment) is the right answer.

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While troubleshooting a memory problem in a raster scan RADAR, you discover that the "REFRESH" cycle is not operating correctly. What type of memory circuit are you working on?

  • SRAM
  • Correct Answer
    DRAM
  • ROM
  • PROM

The term "Raster Scan" indicates the memory problem lies with the RADAR's video diplay.

DRAM - Dynamic Random Access Memory is the working memory used by video cards to store the image that is being displayed on-screen, so Answer B. is the right one.

SRAM - Static Random Access Memory is a much faster, more expensive and more power-hungry memory that is used by microprocessor chips for high-speed low latency cache memory access, thus Answer A. is incorrect.

ROM - Read-Only Memory is only suitable for storing unmodifiable data or software (e.g. firmware), thus Answer C. is incorrect.

PROM - Programmable Read-Only Memory is re-writable ROM (e.g. suitable for updatable firmware,) thus Answer D. is incorrect.

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The term DRAM stands for:

  • Digital refresh access memory.
  • Digital recording access memory.
  • Correct Answer
    Dynamic random access memory.
  • Digital response area motion.
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How does the dual memory function reduce sea clutter?

  • Correct Answer
    Successive sweeps are digitized and compared. Only signals appearing in both sweeps are displayed.
  • The dual memory system makes the desired targets larger.
  • It reduces receiver gain for closer signals.
  • It increases receiver gain for real targets.

Sea clutter is due to the RADAR picking-up returns from nearby waves. Since waves usually move relative to the ship they will never be in the same position from one RADAR sweep to the next and can therefore be easily identified as such and not be rendered on-screen, thus Answer A. is the right answer.

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How many sequential memory cells with target returns are required to display the target?

  • 1
  • Correct Answer
    2
  • 4
  • 8
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What is the primary purpose of display system memory?

  • Correct Answer
    Eliminate fluctuating targets such as sea return.
  • Display stationary targets.
  • Display the last available targets prior to a power dropout.
  • Store target bearings.

For this exam "the primary purpose of display system memory" is used to store the last two RADAR sweeps so as to detect and eliminate fluctuating targets, so Answer A. is the correct answer.

Outside the scope of this exam, "the primary purpose of display system memory" is to be able to display an image on a computer display.

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