Entry & progression
Syllabus area: VHF radio operation (RYA/MCA SRC). Governing: MGN 324 (M+F) Amendment 2; ITU Radio Regulations.
How VHF behaves
Marine VHF sits between about 156 and 162 MHz. At these frequencies radio travels in nearly straight lines, so range depends on how high the aerials are, not on how loud you shout. A fixed set with its aerial at the masthead of a 50 m yacht talks much further than a handheld in a tender at water level. HM Coastguard's remote aerials give VHF coverage out to about 30 miles around the UK coast (MSI leaflet).
Sets have a high and low power switch (commonly 25 W and 1 W). Use low power for short-range work in harbour; it keeps channels clear for others and saves handheld batteries.
Channels that matter
| Channel | Frequency | Use |
|---|---|---|
| 16 | 156.8 MHz | Distress, urgency, very brief safety, and calling only |
| 70 | 156.525 MHz | DSC only, no voice |
| 13 | Bridge-to-bridge navigation safety, worldwide | |
| 6 | 156.3 MHz | Ship-to-aircraft SAR on scene; also ship-to-ship |
| 6, 8, 72, 77 | UK routine ship-to-ship (MGN 324 A2) | |
| 62, 63, 64 | HM Coastguard MSI broadcasts and link calls | |
| 10 | HMCG MSI back-up and pollution control | |
| AIS 1 / AIS 2 | 161.975 / 162.025 MHz | AIS data, not voice |
MGN 324 A2 is blunt: Channel 16 may only be used for distress, urgency, very brief safety communications and calling to establish other communications, which then move to a working channel. Channel 70 carries DSC and nothing else. Port and VTS channels carry only messages about the movement and safety of ships and persons.
Simplex and duplex
Most ship-to-ship channels are simplex: one frequency, one person talks at a time, press to talk and release to listen. Coast station channels such as 62 to 64 are duplex, using two frequencies so both parties can talk as on a telephone, which is why HM Coastguard uses them for medical link calls.
The controls
| Control | Purpose |
|---|---|
| Channel selector and 16/9 key | Quick return to 16 |
| Squelch | Cuts background hiss; set just past the point where noise stops |
| Volume | Loud enough to hear on deck |
| Power (H/L) | 25 W / 1 W typical |
| Dual watch / triple watch | Scans 16 and one or two working channels; you may miss part of a call |
| PTT (press-to-talk) | On the handset; release to listen |
| DSC keys and distress button | See the next lesson |
Aerials, cables and the handheld
A fixed set is only as good as its aerial and cable. Salt in the connector, a crushed coax run or an aerial knocked by a crane can cut range to a fraction without any fault showing on the set. Handhelds are low-power, short-range and dependent on their battery; on yachts they are used for deck operations, tender work and the GMDSS two-way radios in the survival craft.
CAUTION — Channel discipline on yachts Deck teams talk constantly on handhelds during mooring and tender work. Use a working channel your yacht has agreed, never 16, and remember that the yacht next door may be on the same one.
TIP — Before a trip Check the fixed set with a radio check to a coast station or the harbour on a working channel, not on 16. A DSC test call to a coast station, where offered, checks the DSC side too.
Why VHF is not a collision avoidance tool
MGN 324 A2 describes collisions where ships agreed manoeuvres by VHF, misidentified each other or misunderstood, and turned into each other. VHF can support the COLREGs; it cannot replace them.