🔍 Key Concepts

• Higher vs. lower radio frequencies and how they travel different distances over the sea • Effect of day vs. night on ionospheric (sky wave) propagation for MF/HF bands • Difference between ground wave (shorter range) and sky wave (longer range) propagation

💭 Think About

• Think about which frequencies tend to bend off the ionosphere and travel long distances, and which tend to go more in straight lines and are used for local/line-of-sight work • Consider how the ionosphere changes in the daytime: does it support higher or lower frequencies better during the day? • Ask yourself: for a nearby vessel or coast station, would you typically choose a higher or lower frequency than for long‑range ocean communications?

✅ Before You Answer

• Be clear on whether higher frequency signals usually travel farther or shorter distances for typical marine communications bands • Recall that in daytime, the ionosphere absorbs some frequencies more than others – which ones are favored for reliable long‑range comms? • Double‑check that your choice is consistent for both distance and time‑of‑day in the same option (no internal contradictions).