FCC Ship Radar Endorsement flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Radar range equation (time)

Range equals the speed of light times round-trip time divided by two. One microsecond of round-trip delay corresponds to about 150 meters, or roughly 0.081 nautical mile.

Maximum unambiguous range

Rmax equals c divided by twice the pulse repetition frequency. A 1,000 Hz PRF yields about 150 kilometers, or 81 nautical miles, before second-trace echoes appear.

Range resolution formula

Range resolution equals c times pulse length divided by two. A 0.1 microsecond pulse resolves about 15 meters, while a 1 microsecond pulse resolves about 150 meters.

Beamwidth formula

Horizontal beamwidth in degrees approximately equals 70 times wavelength divided by antenna aperture. A longer antenna at X band narrows the beam and improves bearing accuracy.

X band versus S band

X band near 9,410 MHz gives fine resolution from a small antenna but suffers rain attenuation. S band near 3,050 MHz penetrates precipitation better and is preferred in heavy rain.

Radar horizon approximation

Detection range in nautical miles is roughly 1.23 times the square root of antenna height in feet plus 1.23 times the square root of target height in feet, allowing for atmospheric refraction.

Magnetron principle

A crossed-field oscillator in which electrons move radially in an electric field and axially in a magnetic field. Resonant cavities set the output frequency, which is fixed at manufacture.

Duplexer function

The TR cell or circulator routes transmitter pulses to the antenna while blocking them from the receiver, then passes weak echoes to the receiver. Failure can damage the receiver.

Average power calculation

Average power equals peak power times duty cycle, where duty cycle equals pulse length times PRF. A 10 kW peak, 0.1 microsecond, 1,000 Hz radar averages 1 watt.

STC control

Sensitivity time control reduces receiver gain at short ranges to suppress sea clutter, then restores gain with increasing range so distant targets remain visible.

FTC control

Fast time constant differentiates the video signal to suppress long-duration returns such as rain clutter, at the cost of reducing the visible size of real targets.

Fixed-tune devices

Components set to a single frequency at installation, including the magnetron, local oscillator, and preselector filters. The tuning meter confirms the receiver matches the magnetron.

Weak magnetron symptoms

Aging magnetrons show reduced output power, poor short-range detection, unstable tuning indication, and a dim performance monitor echo. Replacement restores transmitter output.

Slotted waveguide antenna

A resonant array of slots cut in rectangular waveguide that radiates a narrow horizontal beam. Aperture length sets beamwidth; the guide must stay dry and undamaged.

Waveguide moisture effects

Water inside the guide raises VSWR, reduces radiated power, and can damage the magnetron through reflected energy. Seals and pressurization prevent ingress.

Heading marker alignment

The heading flash must coincide with the vessel's bow. Misalignment offsets all relative bearings and must be corrected before using the display for navigation.

EBL and VRM

The electronic bearing line and variable range marker measure target bearing and range. They are read against the selected relative or true bearing reference.

Head-up display mode

The display is unstabilized, with the vessel's heading always at the top. Targets smear in turns and bearings change with yaw, so it is unsuitable for accurate plotting.

NMEA heading input

The gyrocompass supplies heading to the radar using sentences such as HDT or HDG. Loss of this input drops stabilization and degrades bearing accuracy.

Radar radiation hazard

The rotating antenna's main beam can be hazardous at close range. Personnel must stay outside the manufacturer's safe distance before the transmitter is energized.

Performance monitor use

The built-in monitor or a known fixed target confirms transmitter output and receiver sensitivity. Readings are logged and compared with the baseline to detect degradation.

Radar-to-radar interference

Other radars appear as spiral or dotted patterns. Reduce gain, engage FTC, or change PRF where permitted; never transmit outside the authorized frequency band.

High voltage safety

The transmitter and magnetron circuits carry lethal voltages. Discharge capacitors and remove power before service, and never look into an open waveguide.

No picture troubleshooting

Check power, display unit, and magnetron heater. If the display is alive but no echoes appear, suspect the transmitter, duplexer, or receiver chain.

Part 13 radar endorsement

A restricted permit element added to a commercial operator license that authorizes operation and adjustment of ship radar. It is not a stand-alone license class.

Marine radar frequencies

Civil marine radar uses 9,300 to 9,500 MHz at X band and 2,900 to 3,100 MHz at S band. Operation outside these bands is not authorized.

Station versus operator license

The ship station license is issued to the vessel owner, while the operator endorsement is personal to the holder. Both must be valid when the station operates.

FCC ULS and FRN

Applications, renewals, and address changes are filed in the FCC Universal Licensing System. The FRN identifies the licensee and the call sign identifies the station.

Repair authorization limits

Routine operational adjustments may be made by the endorsed operator. Internal repair and magnetron replacement require qualified personnel holding the appropriate commercial operator license.

Second-trace echoes

Echoes from a previous pulse arriving after the next pulse is transmitted appear at a false short range. Lowering PRF extends unambiguous range and removes them.

Ducting and anomalous propagation

Temperature inversions bend the radar beam beyond the normal horizon, producing extended detection and false echoes. Sub-refraction shortens range and creates blind zones.

ARPA versus basic radar

ARPA acquires and tracks targets, computing CPA and TCPA with alarms. Basic radar controls such as gain, STC, and FTC remain separate operational adjustments.