🔍 Key Concepts

• Difference between INT (International) and US (USA) channel sets on a VHF radio • How alpha channels work (simplex vs. duplex, ship vs. coast frequencies) • Which side (ship or coast station) changes frequency when switching between INT and US modes

💭 Think About

• Think about whether your transmit frequency changes when you switch the radio from INT to US, or only the channel label on the display. • Ask yourself: on an alpha channel, are the ship and coast station using the same frequency or different ones? How does that interact with INT vs US mode? • Consider in which situation one party could transmit and the other could not hear—who is actually off‑frequency in this scenario?

✅ Before You Answer

• Verify which channels become 'alpha' channels only in the US set (e.g. 13/67 vs 13A/67A) and what that means for the ship frequency. • Check whether in INT mode, your radio is transmitting on the same ship frequency that the VTS expects on an alpha channel. • Confirm which side of the link (your ship or the VTS) would end up transmitting on a different frequency if your set is on INT instead of US.