Your examiner asks: "What is Pulse Repetition Frequency, and how does it limit the maximum range at which a radar can display a target without ambiguity?"

A. Pulse Repetition Frequency (PRF) is the number of pulses transmitted per second. Between transmitting one pulse and the next, the set must wait long enough for the echo from the most distant target of interest to return before it can safely transmit again — if a second pulse is sent before the first echo returns, an echo received after the second pulse may be misinterpreted as belonging to the second pulse, producing a false, short-range echo (this is the mechanism behind second-trace echoes). Because of this, longer maximum range scales require a LOWER PRF (longer time between pulses), while shorter range scales can use a HIGHER PRF, which improves picture refresh rate and target discrimination at short range.

B. PRF has no effect on range — it only controls the radar's bearing accuracy. Range is set purely by the transmitter power output.

C. A higher PRF always gives a longer maximum range with no drawback, which is why radars use the highest possible PRF on every range scale.

D. PRF determines only the colour or brightness of the target return on the display and has no relationship to timing or range measurement at all.

A. Nothing — a test lift can proceed immediately after repairs

B. Testing should wait until cargo operations begin

C. The area within the grab's swing radius should be cleared of personnel before the lift

D. Only the crane operator needs to be aware the lift is happening

A. Who must remain clear of the exclusion zone while the lift takes place

B. The lunch schedule for the deck team

C. Only the weather forecast for the next watch

D. The cargo manifest for the next port