What is the difference between simplex and duplex VHF channels and when does it matter to a leisure sailor?

A. Duplex channels are always louder — use them for long-distance calls

B. Simplex: transmit and receive on the same frequency — you can't talk and listen simultaneously (press-to-talk). Duplex: separate transmit and receive frequencies — allows two-way simultaneous conversation like a telephone. Most ship-to-ship channels are simplex; duplex is used for some port operations and satellite link calls

C. Duplex channels require a separate radio transmitter and are not fitted on leisure craft

D. All channels above Ch 60 are duplex; all below are simplex

A. To send a digitally coded distress alert containing the vessel's MMSI and position automatically to all DSC-equipped stations and the Coastguard

B. To broadcast weather forecasts to other vessels

C. To make telephone calls from the vessel to shore

D. To operate the radar system remotely

A. A GPS waypoint identifier used in coastal navigation

B. Maritime Mobile Service Identity — a unique 9-digit number identifying the vessel; without it a DSC distress alert cannot identify the vessel to rescuers

C. A VHF channel number allocated by Ofcom for distress use only

D. A vessel survey certificate number required by the MCA