🔍 Key Concepts

• VHF-FM range limitations and typical line-of-sight distances • How MF (Medium Frequency) and HF (High Frequency) signals propagate, especially over water during daytime • The effect of time of day (mid-day vs night) on radio wave propagation and skip distance

💭 Think About

• Which of these frequency bands is normally limited to line-of-sight, and is 75 miles usually beyond that range for a ship-to-shore path? • During mid-day, which bands are more effective for reliable ground-wave or sky-wave communication over medium distances like 75 miles? • How does the ionosphere affect higher HF bands around 16–22 MHz at mid-day compared with lower-frequency MF?

✅ Before You Answer

• Confirm the typical service range for marine VHF-FM under standard conditions (ship to shore, no unusual antenna height). • Check which band(s) are commonly used for medium-range (50–150 NM) ship–shore communications, especially on commercial ships. • Consider how daytime ionospheric absorption impacts MF vs higher HF bands like 16 MHz and 22 MHz.