MMC Upgrade Radar Practice Questions

Sample questions — Radar

Drawn from the same bank used on USCG licensing exams. Correct answers and explanations are shown — read every explanation, even for questions you get right.

1. 1. Marine radar systems most commonly operate in which two frequency bands?

   • A.X-band (9 GHz) and S-band (3 GHz)✓
   • B.L-band (1 GHz) and C-band (5 GHz)
   • C.Ka-band (35 GHz) and Ku-band (15 GHz)
   • D.UHF (300 MHz) and VHF (150 MHz)

   Why: Marine radars operate primarily in X-band (approximately 9 GHz, 3 cm wavelength) for high resolution, and S-band (approximately 3 GHz, 10 cm wavelength) for better performance in precipitation and sea clutter. These two bands are designated by the ITU for maritime use.

2. 2. A radar with a horizontal beam width of 1.8° will have a bearing accuracy of approximately:

   • A.±0.1°
   • B.±0.9° (half the beam width)✓
   • C.±1.8°
   • D.±3.6° (twice the beam width)

   Why: Bearing accuracy is generally considered to be approximately ±½ the horizontal beam width, because a target will paint on the display from when the leading edge of the beam strikes it to when the trailing edge passes. A 1.8° beam therefore gives approximately ±0.9° bearing accuracy.

3. 3. What is the MOST accurate method for measuring the range to a radar target?

   • A.Visually comparing the target's position between fixed range rings
   • B.Using the Variable Range Marker (VRM) and adjusting it to exactly bisect the target echo✓
   • C.Counting the number of range rings between own ship and the target
   • D.Using the Electronic Bearing Line (EBL) set to the target's bearing

   Why: The Variable Range Marker (VRM) provides the most accurate range measurement. The operator expands or contracts the VRM circle until it exactly bisects the nearest edge of the target echo, and reads the precise range from the digital display. This is far more accurate than visually estimating between fixed rings.

4. 4. Which of the following would cause the greatest error in radar bearing measurements?

   • A.Using a short pulse length setting
   • B.A misalignment between the radar antenna heading marker and the ship's lubber's line (heading error)✓
   • C.Selecting a range scale that is too large for the target's distance
   • D.Excessive receiver gain causing target blooming

   Why: Bearing accuracy depends critically on proper alignment of the radar antenna's heading marker with the vessel's fore-and-aft line (lubber's line). Any misalignment directly introduces a systematic error into all bearing measurements. This is one of the most important calibration checks for a marine radar installation.

5. 5. When plotting relative motion on a maneuvering board, the Relative Motion Line (RML) represents:

   • A.The path of the target as seen from own ship✓
   • B.The true course of the target over the ground
   • C.The course own ship must steer to avoid collision
   • D.The bearing line from own ship to the target

   Why: The Relative Motion Line is constructed by connecting successive plotted positions of the target on the maneuvering board, showing how the target appears to move relative to own ship's position.

6. 6. Two vessels are on reciprocal courses (head-on) each making 12 knots. The rate of closure between them is approximately:

   • A.24 knots✓
   • B.12 knots
   • C.0 knots — they maintain constant range
   • D.6 knots

   Why: When two vessels are on reciprocal (directly opposing) courses, their closing speeds add together. With each vessel making 12 knots, the combined rate of closure is 12 + 12 = 24 knots.

7. 7. A vessel is observed on radar in relative motion mode. Its radar trail shows the target moving directly toward the center of the screen with no change in bearing. What action is required?

   • A.Take early and substantial action to avoid collision as required by COLREGS✓
   • B.Sound one prolonged blast and maintain course and speed
   • C.Increase speed to pass ahead of the oncoming vessel
   • D.Switch to true motion mode for a better assessment before maneuvering

   Why: A target moving directly toward the center of the screen in relative motion mode is on a collision course (CPA = 0). COLREGS Rules 8 and 16 require the give-way vessel to take early, substantial, and seamanlike action to avoid collision.

8. 8. When a target is acquired manually on an ARPA, what action does the operator take?

   • A.Place the acquisition cursor over the target echo and activate the acquire function✓
   • B.Enter the target's estimated speed and course into the ARPA keyboard
   • C.Set the acquisition zone boundary to encompass the target
   • D.Switch the ARPA to manual tracking mode before the target enters radar range

   Why: Manual acquisition requires the operator to place the cursor over the desired target echo and initiate acquisition, after which the ARPA begins tracking that specific target. This is distinguished from automatic acquisition, which triggers when a target enters a pre-set guard zone.

9. 9. What is the primary purpose of an ARPA guard zone (acquisition zone)?

   • A.To automatically acquire targets that enter the zone and alert the watchkeeper✓
   • B.To inhibit display clutter in a specified area around own ship
   • C.To mark areas of known navigational hazards on the display
   • D.To define the area within which the ARPA computes CPA/TCPA

   Why: The guard zone serves as an automatic acquisition and alarm boundary; when a new radar echo penetrates the zone, the ARPA acquires it as a tracked target and triggers an audible/visual alarm to alert the watchkeeper of the intruder.

10. 10. A target undergoing a rapid course change may cause the ARPA to display erroneous vector information for a short period. This phenomenon is known as:

    • A.Tracking lag or vector smearing due to the ARPA's averaging algorithm✓
    • B.Target swap between two closely spaced echoes
    • C.Acquisition zone false alarm
    • D.Ground discrimination error

    Why: ARPA tracking algorithms smooth positional data over multiple scans to reduce noise; when a target maneuvers rapidly, the smoothed solution lags behind the actual movement, producing an erroneous vector until the algorithm converges on the new course and speed.

11. 11. An ARPA is sea-stabilized (log input). A target shows a true vector of 000° at 10 knots. Own ship is making 10 knots through the water on course 090°. What can the navigator infer about the target?

    • A.The target is heading north at 10 knots through the water✓
    • B.The target is stationary relative to the sea surface
    • C.The target is on a collision course with own ship
    • D.The target is making 10 knots over the ground toward own ship

    Why: In sea-stabilized mode, true vectors represent courses and speeds through the water. A vector of 000° at 10 knots means the target vessel is steering north at 10 knots through the water; the navigator would need ground stabilization (GPS) to determine ground track.

12. 12. A vessel observes a curved arc of echoes appearing symmetrically on both sides of a large nearby target at the same range. This is most likely caused by:

    • A.Rain clutter from a nearby squall
    • B.Multiple echoes between the vessel and the target
    • C.Side lobe radiation from the antenna✓
    • D.An indirect (reflected) echo off a superstructure

    Why: Side lobes produce arcs of false echoes symmetrically distributed about the main lobe bearing at the same range as the true target, forming a characteristic curved pattern around strong nearby returns.

13. 13. Which of the following situations is most likely to create a radar shadow zone for a vessel approaching a harbor?

    • A.A heavy rain squall directly ahead
    • B.A high headland or breakwater between the vessel and the harbor entrance✓
    • C.Atmospheric ducting from a thermal inversion
    • D.Operating on a short pulse length in calm conditions

    Why: A high headland or breakwater physically blocks the radar beam, creating a shadow zone behind it where vessels, buoys, or other hazards cannot be detected, a critical consideration when navigating in confined coastal waters.

14. 14. The FTC (Fast Time Constant) or rain clutter control reduces precipitation clutter by:

    • A.Decreasing the pulse length to avoid overlapping returns from raindrops
    • B.Differentiating the received signal so only the leading edge of extended returns is displayed, breaking up diffuse clutter✓
    • C.Increasing the scan rate so raindrops are averaged out over successive sweeps
    • D.Reducing transmission power to prevent strong returns from heavy rain

    Why: The FTC circuit differentiates (takes the time derivative of) the received video signal, emphasizing rapid signal changes (discrete target edges) while suppressing the slowly varying extended returns characteristic of rain clutter.

15. 15. A navigator using radar to monitor vessel traffic in a busy port notices that no targets appear from a particular direction despite AIS showing vessels in that sector. After ruling out AIS errors, the navigator should FIRST consider:

    • A.Increasing the gain control to detect vessels in that direction
    • B.The possibility that a radar shadow zone exists due to a structure, pier, or landmass blocking the beam✓
    • C.Reducing the range scale to improve target resolution in that sector
    • D.Activating the rain clutter control to clear the sector

    Why: When AIS indicates traffic that radar fails to show, a shadow zone caused by a physical obstruction is the primary radar-related explanation; the navigator should identify the blocking structure and use alternative means (VHF, AIS, lookout) to monitor that sector.

16. 16. On an ARPA, a true vector displayed on a target shows the target's:

    • A.Motion relative to own ship
    • B.Actual course and speed over the ground/water✓
    • C.Range only
    • D.Bearing only

    Why: True vectors show each target's real course and speed (and own ship's), useful for identifying a target's aspect and intentions. Relative vectors instead show motion relative to own ship and point toward the CPA situation.

17. 17. A racon is a radar beacon that, when triggered by a vessel's radar, produces:

    • A.A loud audible signal
    • B.A coded response (often a Morse character) on the radar display at the racon's position✓
    • C.A change in the vessel's heading
    • D.A GPS position fix

    Why: A racon responds to incoming radar pulses by transmitting a coded signal that appears as a distinctive mark (frequently a Morse letter) radiating outward from the beacon's location on the PPI, aiding identification of an aid or landfall.

18. 18. Sensitivity Time Control (STC), also called the sea-clutter or anti-clutter sea control, reduces:

    • A.Returns from rain at long range
    • B.Strong close-in returns from waves near own ship✓
    • C.The transmitter power
    • D.Interference from other radars

    Why: STC progressively reduces receiver gain for close-range echoes, suppressing the bright sea clutter near own ship. Overuse can erase small close targets, so it must be applied only as much as needed.

19. 19. Super-refraction (ducting) of the radar beam tends to:

    • A.Reduce detection range below normal
    • B.Bend the beam downward and increase detection range beyond the horizon✓
    • C.Have no effect on range
    • D.Eliminate sea clutter

    Why: Super-refraction occurs when temperature/humidity gradients bend the beam more sharply toward the surface, extending detection range. Sub-refraction does the opposite, bending the beam up and shortening range.

20. 20. ARPA 'target swap' is an error in which:

    • A.The radar loses all targets
    • B.The tracker transfers its track from one target to another that passes close to it✓
    • C.The display freezes
    • D.The range scale changes by itself

    Why: When two tracked echoes pass close together, the ARPA may swap or merge the tracks, producing a sudden false course/speed for one target. The operator must watch closely during close encounters and not trust the vectors blindly.

Frequently asked questions

Is Radar on the MMC Upgrade exam?

Yes — Radar is one of the tested modules on the MMC Upgrade licensing exam. Candidates must score 70% on each module to pass.

How many Radar questions are on the MMC Upgrade exam?

The USCG draws from a bank of 167 Radar questions across all exams. The exact number on any single sitting varies, but Rules of the Road is typically the largest module and has the highest passing threshold (90%).

What is the best way to study Radar for the MMC Upgrade exam?

Work through the practice questions in this bank until you can answer them consistently above the passing threshold. Review every explanation — understanding why the wrong answers are wrong matters more than memorizing facts.