The UK government, for instance, allocates the name “00” to 156.000MHz, and allows it to be used only by the Coastguard and recognized search and rescue organisations such as the RNLI.
Similarly, in the UK, 157.850MHz is known as Channel M and 161.425 is known as M2: they are “private” channels that have been allocated by the UK government specifically for use by marinas, yacht clubs, and pleasure craft.
Channel M and M2 should only be used in UK waters: other countries have allocated those frequencies for different purposes.
Private channels do not necessarily require an operator’s certificate. In the UK, channels M and M2 can be used by unqualified operators, without supervision.
Some radios cannot display the letter M. In such cases, Channel M is often called “37” or “P1”. Channel M2 is often called “P1” or “P4”.
American channels
A few countries, most conspicuously the USA, do not conform to the international channel designation and usage. Whilst there are similarities between international and US channel designations, there are also significant differences: in particular, many channels which are duplex in the international scheme are simplex in the US version. Most modern radios can be converted from one system to another by flicking a switch or by going through a set-up menu. Make sure you aren’t using the wrong system by mistake.
If you call a UK marina using the US channel 80, the marina will hear you, but you won’t hear their reply. Channel 80 is a duplex channel under the international system, but a simplex channel in the USA.
Channel 16 and guard band
Some channels are of particular significance.
Channel 16 is the outstanding example, because it is designated as the Distress, Safety, and Calling channel.
It is so important that Channel 16 should not suffer any interference that the two channels closest to it in the international frequency table — channels 75 and 76 — are regarded as a guard band. At one time, transmissions in the guard band were illegal, and any radio which allowed transmissions on those frequencies would fail its type-approval trials. The rules have now been relaxed very slightly, and these two channels are available for port operations use, but with the maximum power limited to 1 watt.
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