When you use a marine VHF, the first thing you need to do is to tune in to the channel that you want to use. This is just like tuning your FM radio to the correct station. 

The main difference is that marine VHF channels are numbered, so you do not need to remember the frequency of every channel. All frequencies are pre-programmed into a marine VHF radio already.

The main VHF channels and frequencies to be aware of are:

ChannelFrequencyUse
Ch13156.650 MHzBridge-to-bridge
Ch 15156.750 MHzLow power only
Ch 16156.800 MHzDistress / Safety / Calling
Ch 17156.850 MHzLow power only
Ch 70156.525 MHzDSC
Ch 87B161.975 MHzAIS 1
Ch 88B162.025 MHzAIS 2

With VHF channels and frequencies, different countries have different rules about what each channel is used for.

The channels in the table above are the main channels that have almost uniform usage worldwide. This means that these channels are used for the same thing, no matter where you are in the world.

The most important VHF channel is 16. Ch16 is used internationally for distress, safety and calling. It is illegal to use this channel for any other purposes.

Either side of ch 16, you find 15 & 17. The specific use of each of these does change from country to country, but I have included them because they share one specific characteristic. They can only be used on low power (1W).

This is because they are the closest channels to ch 16, and we do not want the use of either of them to interfere with a potential mayday situation.

As they are low power, they are typically used for communication within a vessel, or across a short distance.

Ch 70 is used for Digital Selective Calling (DSC). It is not a voice communication channel.

When you make a DSC call, your radio will use ch 70 to send the alert to the MMSI number that you input.

Finally, CH 87B & 88B are both used for AIS. AIS uses your VHF antenna to automatically transmit your vessel’s information. Both of these channels cannot be used for voice communication.

For more detail about how AIS works, you can read this article: How Does AIS Work?

Aside from these “universal” channels, we have around 60 other VHF channels whose specific usage varies from country to country. In the rest of this article, we will break it down further so that you have a full understanding of the range of VHF channels and frequencies available.

Where are marine VHF frequencies in the radio spectrum?

Marine VHF runs on frequencies between 156 MHz and 161 MHz.

The radio spectrum describes different frequencies and wavelengths of electromagnetic waves.

When it comes to radio communication, we use electromagnetic radiation with relatively low energy, and a long wavelength. Communication frequencies range from 3 kHz to 300 GHz, with wavelengths from 100km to 1mm.

VHF is just one small part of the spectrum that is used for communications.

Illustration of where VHF fits within the radio spectrum
VHF is in the 30-300 MHz band within the radio spectrum.

As you can see from the diagram above, VHF frequencies range from 30 MHz to 300 MHz. Similarly, wavelengths can be anywhere between 10m and 1m.

Pro Tip: Antenna length is directly proportional to wavelength. HF antennas are longer than VHF antennas which are longer than UHF antennas.

Within the entire VHF spectrum, only a small portion is reserved for use in marine VHF specifically. The rest is used for things like aviation, television, radio, DAB etc.

The small part assigned to marine VHF is 156 MHz – 161 MHz.

Breaking down the marine VHF frequencies even further, you get into specific channels.

For example, 156.750 MHz MHz is one channel. 156.800 MHz is another channel.

We label them with channel numbers instead of writing out the frequency every time. 

156.750 MHz is channel 15, and 156.800 MHz 16.

The channel numbers are just a consistent way of labelling marine VHF frequencies, standardised across radio manufacturers.

It means navigators only need to remember channel numbers rather than individual frequencies.

Types of VHF channel

We have seen that VHF channels are just labels for specific frequencies within the marine VHF radio spectrum.

The other concept to understand with marine VHF is that you can find two different types of channel.

  • Simplex channels
  • Duplex channels

Simplex VHF channels

A simplex marine VHF channel is a radio channel where you transmit and receive on the same frequency.

Although we call it “simplex”, it is actually a “half-duplex” channel. A true simplex channel is one where information only flows in one direction.

For example, a true simplex channel would be something like a TV channel. The TV antenna can only transmit, and the aerial on your roof can only receive.

In marine VHF usage, however, we mean that the channel can only carry a single transmission at any one time.

Either the ship station can transmit, or the shore station can transmit. Both cannot transmit at the same time.

These channels are the traditional ones where you make your broadcast, then end it with the word “over” to let the recipient know you are finished.

While the transmission is taking place, it is acting as a simplex channel. One person is transmitting, and the other person is receiving.

Marine VHF equipment contains both a transmitter and a receiver, which is why it is technically a “half-duplex” channel instead. You can immediately switch between transmission mode and reception mode.

Duplex VHF channels

A duplex marine VHF channel is a radio channel where you can transmit and receive at the same time. With a duplex channel, you can have a conversation with another party, potentially both speaking at the same time, just like you can on a telephone.

As radio frequencies can only carry a single message at once, a duplex channel actually consists of two different frequencies. Each station transmits on one frequency and receives on the other.

StationTransmission FrequencyReception Frequency
ShipFrequency AFrequency B
ShoreFrequency BFrequency A

As they are working on different frequencies, both can transmit at the same time while simultaneously listening to the broadcast from the other station.

A duplex channel just tells your radio to tune in to the different frequencies for transmission and reception.

For example, VHF 84 is a duplex channel where a ship station transmits on 157.225 MHz, and the shore station transmits on 161.825 MHz.

A ship’s VHF would tune its transmitter into 157.225 MHz and its receiver to 161.825 MHz.

How are VHF channels numbered?

VHF channels are labelled with channel numbers. Broadly speaking, they are numbered from 1-28 and 60-88.

The International Telecommunication Union (ITU) assigns a channel number to each frequency for simplex channels, or pair of frequencies in the case of duplex channels.

This standardised set of frequencies and channel numbers is used by marine VHF manufacturers to program their VHFs.

Some countries, like the USA, produce their own standards instead. We’ll cover that in more detail below, but for now it is important to understand that they still use the same general system of numbering channels.

Original VHF channels

Original VHF channels were numbered from 1 to 28.

The idea was that they were spaced at 0.05 MHz intervals across the part of the electromagnetic spectrum reserved for marine VHF use.

For example, VHF Ch 9 and VHF Ch 10 are at 156.450 MHz and 156.500 MHz respectively.

The interval was chosen because that was the limit of what could be reliably used on the available technology at the time.

When frequencies are too close together, radio equipment cannot easily differentiate between the signals, resulting in interference.

You need the interval between channels to be large enough to minimise interference, yet small enough so that you can get sufficient channels within the available space.

As technology improves, however, it becomes possible to tune in to more precise frequencies.

Newer VHF channels

Newer VHF channels are those numbered between 60 to 88.

With newer radio technology, it became possible to assign more channels within the same band of frequencies by reducing the interval between them.

Originally the interval was 0.05 MHz, but the newer technology could half that to 0.025MHz intervals instead.

The result was that you could squeeze newer channels between original ones.

ChannelFrequency
Ch 9 (old)156.450 MHz
Ch 69 (new)156.475 MHz
Ch 10 (old)156.500 MHz

Rather than re-name all the original channels, the new ones were given channel numbers between 60 and 88 instead.

As the channel numbers are just labels for frequencies that are programmed into VHF units, it doesn’t matter that they don’t run sequentially. Users only use the labels, they don’t need to remember each of the frequencies.

Pro Tip: Check old vs new channels if you have interference. For example, on Ch 9 it is more likely interference is coming from Ch 69 rather than from Ch 10.

What does “A” or “B” mean in a VHF channel?

VHF channels are labelled with an “A” or “B” when they are a new simplex channel that has been derived from an original duplex channel.

For example, when AIS was developed there was not sufficient space within the VHF spectrum to assign it a new frequency. The only option was to repurpose another channel that was already in use.

You can repurpose a duplex channel and create two simplex channels instead.

In the case of AIS, they started with the two duplex channels, 87 and 88.

ChannelTypeShip Frequency (A)Shore Frequency (B)
87Duplex157.375 MHz161.975 MHz
88Duplex157.425 MHz162.025 MHz

If you re-designate them as simplex channels, you free up the shore frequencies that are no longer needed. The result is four new channels.

ChannelTypeFrequency
87ASimplex157.375 MHz
88ASimplex157.425 MHz
87BSimplex161.975 MHz
88BSimplex162.025 MHz

87B and 88B were given to AIS and renamed as AIS1 and AIS2. 

The simplex ship frequencies were retained for voice communication and the “A” suffix was dropped to make it simpler for numbering on a VHF set. 

It was only possible to drop the suffix because it no longer acts as a duplex channel anywhere in the world. If it was still used as a duplex channel somewhere, the suffix would need to remain to differentiate between the two.

When you see an “A” or “B” on a VHF channel number, it just means that it was originally one half of a duplex channel.

What is the difference between USA and International VHF channels and frequencies?

VHF radios in the US use different channels to the rest of the world.

The reason for this is that some parts of the radio spectrum that are used for maritime communication internationally have been auctioned off in the USA for use in other industries, like the railways. 

This means that if you make a broadcast on some international VHF frequencies within the US, you might be illegally transmitting on an unauthorised channel.

To get around this, most VHF radios give you the option of switching between “USA” or “Int”.

“Int” or “International” gives you access to all the frequencies that are used throughout most of the world.

“USA” gives you access to frequencies that are used specifically in the USA, while also removing access to channels that cannot be used for maritime transmissions in the USA.

A lot of channels are common between both the “USA” and “Int” versions, but the potential for incorrect use of the others means it is essential to make sure your VHF is set on the correct setting.

Lots of USA channels have the “A” suffix

You’ll notice that many channels used in the US are labelled with the letter “A”.

For example, in the US Ch 1A is a simplex channel operating on 156.050 MHz. Internationally, Ch 1 is a duplex channel operating across frequencies 156.050 MHz and 160.050 MHz.

In the US, the second part of the duplex channel, the 160.050 MHz frequency, is used by railways instead.

As a result, only the “A” part of the duplex channel is available for maritime communication. US radios, therefore, give you Ch 1A to use as a simplex channel.

The same principle applies with other international duplex channels that have been repurposed in the USA after part of the spectrum was sold off.

You will also see these channels labelled with a “10” prefix, rather than an “A” suffix. Going forward, it will become more common to have a “10” prefix instead.

For example, the US channel 1A is also known as channel 1001. 

Why are channels 75 and 76 missing?

Channels 75 and 76 are both not available to use because they are “guarding” channel 16.

When the lower increments were introduced in between original VHF channels it increased the chance of interference on channels that are close together.

Given its importance, channel 16 was given special protection from interference by removing the new channels that were introduced on either side of it.

Channel 75 is 0.025 MHz below the channel 16 frequency, and channel 76 is 0.025 MHz above it.

List of VHF frequencies in the USA

A complete list of channels and frequencies and their use is available from the USCG: US VHF Channel Information.

ChannelTypeFrequencyNotes
1ASimplex156.050 MHz
5ASimplex156.250 MHz
6Simplex156.300 MHz
7ASimplex156.350 MHz
8Simplex156.400 MHz
9Simplex156.450 MHz
10Simplex156.500 MHz
11Simplex156.550 MHz
12Simplex156.600 MHz
13Simplex156.650 MHzBridge-to-bridge
14Simplex156.700 MHz
15Simplex156.750 MHzLow power
16Simplex156.800 MHzDistress / Safety / Calling
17Simplex156.850 MHzLow power
18ASimplex156.900 MHz
19ASimplex156.950 MHz
20Duplex157.000 MHz
161.600 MHz
20ASimplex157.000 MHz
21ASimplex157.050 MHz
22ASimplex157.100 MHz
23ASimplex157.150 MHz
24Duplex157.200 MHz
161.800 MHz
25Duplex157.250 MHz
161.850 MHz
26Duplex157.300 MHz
161.900 MHz
27Duplex157.350 MHz
161.950 MHz
28Duplex157.400 MHz
161.000 MHz
63ASimplex156.175 MHz
65ASimplex156.275 MHz
66ASimplex156.325 MHz
67Simplex156.375 MHz
68Simplex156.425 MHz
69Simplex156.475 MHz
70Simplex156.525 MHzDSC
71Simplex156.575 MHz
72Simplex156.625 MHz
73Simplex156.675 MHz
74Simplex156.725 MHz
77Simplex156.875 MHz
78ASimplex156.925 MHz
79ASimplex156.975 MHz
80ASimplex157.025 MHz
81ASimplex157.075 MHz
82ASimplex157.125 MHz
83ASimplex157.175 MHz
84Duplex157.225 MHz
161.825 MHz
85Duplex157.275 MHz
161.875 MHz
86Duplex157.325 MHz
161.925 MHz
87Simplex157.375 MHz
88Simplex157.425 MHz
87BSimplex161.975 MHzAIS 1
88BSimplex162.025 MHzAIS 2

List of international VHF channels and frequencies

ChannelTypeFrequencyNotes
0Duplex156.000 MHz
160.600 MHz
Private Channel
1Duplex156.050 MHz
160.650 MHz
2Duplex156.100 MHz
160.700 MHz
3Duplex156.150 MHz
160.750 MHz
4Duplex156.200 MHz
160.800 MHz
5Duplex156.250 MHz
160.850 MHz
6Simplex156.300 MHz
7Duplex156.350 MHz
160.950 MHz
8Simplex156.400 MHz
9Simplex156.450 MHz
10Simplex156.500 MHz
11Simplex156.550 MHz
12Simplex156.600 MHz
13Simplex156.650 MHzBridge-to-bridge
14Simplex156.700 MHz
15Simplex156.750 MHzLow power
16Simplex156.800 MHzDistress / Safety / Calling
17Simplex156.850 MHzLow power
18Duplex156.900 MHz
161.500 MHz
19Duplex156.950 MHz
161.550 MHz
20Duplex157.000 MHz
161.600 MHz
21Duplex157.050 MHz
161.650 MHz
22Duplex157.100 MHz
161.700 MHz
23Duplex157.150 MHz
161.750 MHz
24Duplex157.200 MHz
161.800 MHz
25Duplex157.250 MHz
161.850 MHz
26Duplex157.300 MHz
161.900 MHz
27Duplex157.350 MHz
161.950 MHz
28Duplex157.400 MHz
161.000 MHz
31Duplex157.550 MHz
162.150 MHz
M1Simplex157.850 MHz
60Duplex156.025 MHz
160.625 MHz
61Duplex156.075 MHz
160.675 MHz
62Duplex156.125 MHz
160.725 MHz
63Duplex156.175 MHz
160.775 MHz
64Duplex156.225 MHz
160.825 MHz
65Duplex156.275 MHz
160.875 MHz
66Duplex156.325 MHz
160.925 MHz
67Simplex156.375 MHz
68Simplex156.425 MHz
69Simplex156.475 MHz
70Simplex156.525 MHzDSC
71Simplex156.575 MHz
72Simplex156.625 MHz
73Simplex156.675 MHz
74Simplex156.725 MHz
75Simplex156.775 MHzRestricted (Ch 16 guard)
76Simplex156.825 MHzRestricted (Ch 16 guard)
77Simplex156.875 MHz
78Duplex156.925 MHz
161.525 MHz
79Duplex156.975 MHz
161.575 MHz
80Duplex157.025 MHz
161.625 MHz
81Duplex157.075 MHz
161.675 MHz
82Duplex157.125 MHz
161.725 MHz
83Duplex157.175 MHz
161.775 MHz
84Duplex157.225 MHz
161.825 MHz
85Duplex157.275 MHz
161.875 MHz
86Duplex157.325 MHz
161.925 MHz
87Simplex157.375 MHz
88Simplex157.425 MHz
M2Simplex161.425 MHz
87BSimplex161.975 MHzAIS 1
88BSimplex162.025 MHzAIS 2
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