🔍 Key Concepts

• Difference between simplex and duplex operation in maritime radio communications • How ship–ship versus ship–shore communications typically use VHF channels • ITU definition of a simplex channel in contrast to paired transmit/receive frequencies

💭 Think About

• Ask yourself: In simplex operation, do both stations use the same frequency in turn, or separate frequencies at the same time? • Consider how you normally talk on a handheld VHF: when you press the PTT button, are you listening and transmitting on the same or different frequency? • Which options actually describe duplex (paired) operation rather than simplex operation?

✅ Before You Answer

• Be clear on the definition of simplex (one frequency, alternating transmit/receive) vs duplex (two different frequencies, simultaneous transmit/receive). • Check which choices describe a single frequency used by both stations rather than a frequency pair. • Verify that you are thinking of standard VHF marine channels used between ships, not special coast station repeated channels.