Weekly quiz: Marine VHF duplex and simplex channels
VHF(Very High Frequency) Radio wave frequency band, between 30 and 300 MHz. By extension, the most widespread marine radio sets, operating on a series of predetermined channels between 156 and 174 MHz, with a range of a few miles to a few dozens of miles. More is the marine communication means of choice.
Rather than bother with frequencies, its numbered channels was a great idea. It made radio simple to understand and use for boaters.
That is, until different needs led different countries to use it in different ways…
Question of the day
🔹 How are duplex and simplex VHF(Very High Frequency) Radio wave frequency band, between 30 and 300 MHz. By extension, the most widespread marine radio sets, operating on a series of predetermined channels between 156 and 174 MHz, with a range of a few miles to a few dozens of miles. More channels different?
And bonus question
🔹 How is this relevant especially when switching from North American to international waters or vice-versa?
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Answer
Thanks to all who have taken part in this quiz.
Many of you correctly pointed out that simplex channels only allow one-way communication at a time because they operate on a single frequency in both directions. On the other hand, duplex channels allow simultaneous two-way communication because they use two different frequencies. This last part is the crucial point here. Many users remember that both a coastal station and a ship can transmit at the same time on a duplex channel and that is true. In practice, understanding one another while talking simultaneously is rarely a thing, though. And most recreational equipment does not even have duplex audio anyways, hence the need to press on a “push-to-talk” button (PTT).
However, the fact that two frequencies are used in duplex channels does have other important implications. These frequencies are generally denominated A and B, A being the one where the ship transmits (TX) and the shore station receives, and B the frequency emitted by the shore station transmitter. Thus, a common marine VHF(Very High Frequency) Radio wave frequency band, between 30 and 300 MHz. By extension, the most widespread marine radio sets, operating on a series of predetermined channels between 156 and 174 MHz, with a range of a few miles to a few dozens of miles. More transceiver for recreational boats will have the settings set up accordingly.
Let’s take up the example of channel 80. It is made up of two frequencies (A: 157.025 MHz and B: 161.625 MHz). When tuned in to channel 80, the boat marine VHF(Very High Frequency) Radio wave frequency band, between 30 and 300 MHz. By extension, the most widespread marine radio sets, operating on a series of predetermined channels between 156 and 174 MHz, with a range of a few miles to a few dozens of miles. More radio will be configured so as to transmit on 157.025 MHz (A) and listen on 161.625 MHz (B). On the contrary, the shore station’s transceiver will listen on 157.025 MHz (A) and send on 161.625 MHz (B). Let’s now imagine that a ship to shore communication on channel 80 is overheard by another ship. Because that second vessel is only listening to B, it will only receive the transmissions sent by the coastal station, but not those transmissions made by the ship, who is talking on frequency A.
Understanding this difference is crucial for effective communication, especially in busy maritime environments, such as commercial harbors, where duplex channels ensure that traffic control’s transmissions are not polluted by any mariner’s signal and that ships only receive communications from harbor authorities.
Having a list of VHF channels at hand can be of help in remembering which channels are simplex and which are duplex. To assist in determining which is which, most VHF(Very High Frequency) Radio wave frequency band, between 30 and 300 MHz. By extension, the most widespread marine radio sets, operating on a series of predetermined channels between 156 and 174 MHz, with a range of a few miles to a few dozens of miles. More radios display some kind of message on their screen, such as DUP, to identify duplex channels.
Why this is relevant when switching from US to international waters
Each frequency in the VHF(Very High Frequency) Radio wave frequency band, between 30 and 300 MHz. By extension, the most widespread marine radio sets, operating on a series of predetermined channels between 156 and 174 MHz, with a range of a few miles to a few dozens of miles. More channel scheme originally took up a width of 50 kHz, thus leading to 28 frequencies taking up the space between 156.000 MHz and 162.000 MHz (channels 1 to 28), the second frequency (B) for duplex channels being 4.6 MHz higher than the first one (A). Improvements in technology later allowed the channel bandwidth to be reduced to 25 kHz each, and to introduce 28 more frequencies interspersed in between the existing ones (channels 60 to 88). The enormous increase in maritime traffic, however, soon put that enlarged scheme under strain.
Some countries started to “split” duplex VHF(Very High Frequency) Radio wave frequency band, between 30 and 300 MHz. By extension, the most widespread marine radio sets, operating on a series of predetermined channels between 156 and 174 MHz, with a range of a few miles to a few dozens of miles. More channels in order to make them into two simplex channels. For example, duplex channel 23 using frequencies 157.150 MHz (A) and 161.750 MHz (B) has been split in two and the A frequency is now used as simplex channel 23A in the US (the new name now being 1023).
Unfortunately, this splitting has been done somewhat piecemeal, each jurisdiction coming up with various schemes in order to optimize the VHF(Very High Frequency) Radio wave frequency band, between 30 and 300 MHz. By extension, the most widespread marine radio sets, operating on a series of predetermined channels between 156 and 174 MHz, with a range of a few miles to a few dozens of miles. More radio band for its own use and under its own constraints. The resulting situation for mariners today is that correct use of the marine VHF(Very High Frequency) Radio wave frequency band, between 30 and 300 MHz. By extension, the most widespread marine radio sets, operating on a series of predetermined channels between 156 and 174 MHz, with a range of a few miles to a few dozens of miles. More radio is often misunderstood.
Two main schemes are generally available on marine VHF(Very High Frequency) Radio wave frequency band, between 30 and 300 MHz. By extension, the most widespread marine radio sets, operating on a series of predetermined channels between 156 and 174 MHz, with a range of a few miles to a few dozens of miles. More transceivers destined to recreational boats, however. This helps keep manufacturing costs reasonable. These are often designated “International” (or INT or the marine VHF’s screen) and US or USA for use in the United States and more generally in North America. The latter includes several half-duplex channels which are set up for simplex operation such as 21A, 22A, 23A, etc. The US Coast Guard maintains a list of both schemes here:
If a boat’s VHF(Very High Frequency) Radio wave frequency band, between 30 and 300 MHz. By extension, the most widespread marine radio sets, operating on a series of predetermined channels between 156 and 174 MHz, with a range of a few miles to a few dozens of miles. More radio is set to INT and it attempts to communicate in US waters on half-duplex channels, communication problems will most likely happen, with each party either not receiving the other, or only one of them hearing but not the other. For this reason, when switching area, it is important not only to understand what the differences between simplex and duplex channels are, but most importantly and practically to know how to change the VHF(Very High Frequency) Radio wave frequency band, between 30 and 300 MHz. By extension, the most widespread marine radio sets, operating on a series of predetermined channels between 156 and 174 MHz, with a range of a few miles to a few dozens of miles. More channel scheme set on the transceiver. This is generally explained in the marine VHF(Very High Frequency) Radio wave frequency band, between 30 and 300 MHz. By extension, the most widespread marine radio sets, operating on a series of predetermined channels between 156 and 174 MHz, with a range of a few miles to a few dozens of miles. More radio’s instruction manual and may involve pressing several keys simultaneously or restarting the radio.
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