Module 2 - VHF Radio Basics
Antenna and Range
What you will learn
Explain why VHF coverage is mainly line of sight and judge antenna height, condition and surroundings before treating transmit power as the solution.
Marine VHF coverage depends heavily on the radio horizon between both antennas. A sound masthead installation normally reaches farther than a low handheld, but no fixed mileage is guaranteed.
VHF signals travel mainly by line of sight. Raising either antenna usually extends the radio horizon, so a masthead antenna on a yacht often gives better coverage than a handheld at cockpit or sea level. The height of the receiving coast or ship station matters too.
Cliffs, harbour walls, buildings, vessel structure and terrain can screen a signal. Coaxial cable loss, corrosion, loose connectors, water ingress or a damaged antenna can also weaken the path. A high-power set connected to a poor antenna system may perform worse than expected.
Published sea-area coverage is not a personal range guarantee. The MCA notes that a vessel with an antenna below four metres or a portable set may have a smaller coverage area. Treat a handheld as valuable backup with lower antenna height, limited battery endurance and device-specific waterproofing—not as an automatic substitute for a sound fixed installation.
Interpret a failed call behind a headland
A yacht can hear a coast station outside the harbour but loses contact after moving behind a high breakwater.
1. Consider geometry
Ask whether terrain or structure now blocks the line between the two antennas.
2. Inspect the installation
Check the selected antenna, visible cable run, connectors and signs of damage before assuming the radio itself has failed.
3. Choose a safe response
If the call is routine, reposition or use the appropriate procedure; if safety is affected, escalate according to the real priority and available equipment.
Sense check: A strong transmission heard in open water and lost behind solid terrain points to propagation or screening, not necessarily the volume setting.
Common mistake or limitation
- Memorising one maximum VHF range without considering the height and condition of both antenna systems.
- Assuming increased transmitter power can bend a signal around every obstruction.
- Testing a transmitter into a disconnected or known-damaged antenna system.
Recap
- Marine VHF range is mainly line of sight.
- Both antenna heights and the path between them affect coverage.
- Installation condition and obstructions matter as well as transmit power.
- A handheld is useful backup but normally has range and battery limits.
Optional quick check
Section 3 of 9
Why will a sound masthead antenna usually outperform the same type of radio used with a cockpit-height handheld antenna?
Sources and factual review
Reviewed 20 August 2026 - Compass Revision editorial review.
Continue studying VHF Radio Basics
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