VHF Equipment, Channels, Frequencies and Limitations
What this domain tests
This domain tests practical equipment knowledge - which channel does what, how much power to use, and why VHF stops working when the antenna is low or a headland is in the way.
The channel plan
- The marine VHF band sits around 156–163 MHz, planned under the ITU Appendix 18 channel scheme.
- Ch 6 156.300 MHz - inter-ship.
- Ch 13 156.650 MHz - bridge-to-bridge navigation safety.
- Ch 16 156.800 MHz - distress, safety and calling.
- Ch 67 156.375 MHz - small craft safety and working channel.
- Ch 70 156.525 MHz - DSC only. Never voice.
- Ch 75 and 76 are restricted channels used at minimum power because they sit next to Ch 16 and Ch 70.
- Duplex channels (for example the 60-series) need a coast station; two ships cannot talk to each other on them.
Power, range and hardware
- Fixed sets transmit up to 25 W; handhelds typically 1–5 W. Use the lowest power that works.
- VHF is line-of-sight. A usable estimate of range in nautical miles is about 1.23 × (√h₁ + √h₂), with antenna heights in feet.
- Antenna height beats transmitter power. Keep the antenna vertical, clear of metal and bodies, and never key the set with the antenna disconnected.
Worked example
A 16 ft antenna on your mast and a coast station antenna 400 ft high. Reasoning: √16 = 4, √400 = 20, so range ≈ 1.23 × 24 ≈ 30 nautical miles in open water. Shorten the mast and the range drops sharply; that is why a handheld on deck reaches a fraction of this.
Traps that cost marks
- Voice calls on Ch 70, which jams DSC.
- Running 25 W on Ch 16 or in harbour.
- Expecting VHF beyond the horizon, or relying on it instead of an EPIRB offshore.