Three Hand-Held VHF's None Work in Duplex?

[prof_mariner]

I had a new-ish West Marine VHF-85 handheld radio that I hardly used. I decided to give it a test the other day using the automated system on channel 27 and it didn't work. So tried it with my built in VHF and verified it wasn't transmitting on 27. But I tried channels 9, 12, 16 and 68 (simplex channels) and it worked fine. But on all the duplex channels I tried it didn't work.

So I returned it to West Marine and got a replacement VHF 85, got it back to the boat and gave it a test. Same issue. So I took it back to West Marine and returned it for a different model, the VHF 75. Gave that a test and still didn't work on the duplex channels.

Before I go back to West Marine a third time to get yet another hand held VHF, is there something I'm missing? All three radios are suffering the exact same issue. I checked the UIC and tested them in US, Canadian, and International, so it's not that. Any other ideas? I'm about to give up on West Marine electronics entirely and get a real name brand.

[Jim Cate]

So, how are you testing them? I don't know what your "automated" system on 27 is, but you can't just call another ship based VHF on a duplex channel and expect to hear it. In duplex mode, the ship calls on one frequency and the shore station listens on that frequency, but transmits on a different one... the one that the ship VHF is listening on. That's the whole point of duplex mode!

I think your radios are likely just fine... it is the operator that needs replacement!

Jim

[StuM]

Duplex explained simply:

VHF radio, simplex and duplex explained

[prof_mariner]

The automated radio check system is operated by the local towing company on channel 27. I hadn't thought about it, but you're right. Testing duplex with two ocean based radios won't work. I suspected I was forgetting something. Funny how the electronics expert at West Marine didn't think of it either. So the automated system is probably down. Thanks, mystery solved.

[MarkJ]

I guess you are talking about an autimated radio checking facility?
It might not be down at all.... Just out of range for a handheld.

Duplex isnt used much world wide. It would be great to reduce the number of duplex frequencies and open up more working channels.

I know the USA uses more and needs more, but the international bands certainly don't.


Mark

[StuM]

Originally Posted by MarkJ

I guess you are talking about an autimated radio checking facility?
It might not be down at all.... Just out of range for a handheld.

Duplex isnt used much world wide. It would be great to reduce the number of duplex frequencies and open up more working channels.

I know the USA uses more and needs more, but the international bands certainly don't.


Mark

They are a number of changes coming:
New VHF channels

"
Given the growth in shipping traffic, there is an increasing need for more simplex VHF channels for Vessel Traffic Management Systems, port operations, small vessel operations, etc.
The recent ITU World Radio Conference has developed a new channel plan for the VHF marine radio band.
The changes are summarised below.
1. From January 1 2017 in Regions 1 and 3 (basically, everywhere apart from the Americas), channels 78, 19, 79 and 20 will be split into single frequency channels, as follows:
Using 78 as an example - it has 2 frequencies: 156.925 MHz (ship transmit) and 161.525 MHz (Coast Station transmit). The ship transmit frequency becomes new channel 1078 (156.925 MHz), and the Coast transmit frequency (161.525 MHz) becomes new channel 2078.
So, the new channels will be numbered:
1078 2078 1019 2019 1079 2079 1020 2020
In Region 2 (The Americas), channels 78, 19, 79 and 20 are simplex channels now, using the ship transmit frequencies.
2. From January 1, 2017, channels 80, 21, 81, 22, 82, 23, 83, 24, 84, 25, 85, 26 and 86 will be available for digital modes.
3. Channels 27, 87, 28 and 88 may be used for testing of new AIS applications.
4. The frequency 160.9 MHz (a spare Coast Station transmit frequency between channels 65 and 66) may be used for testing of new applications. This will be known as channel 2006."

[clownfishsydney]

Unless you are within transmitting and receiving distance of the duplex repeater, it will not work. Therefore, as others have pointed out, it is unlikely you have a faulty radio.

[colemj]

Originally Posted by MarkJ

I know the USA uses more and needs more, but the international bands certainly don't.

The US bands have much fewer duplex channels than the international bands.

Mark

[skipmac]

Originally Posted by StuM

Duplex explained simply:

VHF radio, simplex and duplex explained

Thanks Stu. I knew duplex meant different transmit and receive frequencies but did not know that on marine VHF that meant going through a repeater.

Happen to know why it's done this way? I can't think of any reason why the radio couldn't implement duplex internally other than higher cost and complexity.

[transmitterdan]

Originally Posted by skipmac

Thanks Stu. I knew duplex meant different transmit and receive frequencies but did not know that on marine VHF that meant going through a repeater.

Happen to know why it's done this way? I can't think of any reason why the radio couldn't implement duplex internally other than higher cost and complexity.

The radio does implement duplex. But a handheld would have to be programmed to act as a shore station to communicate. No handheld that I know has the ability to become a shore station for duplex purposes.

I think Stu meant "shore station" rather than "repeater". The Sea Tow operators have programmed their shore station radios to record incoming calls on 24,26,27, or 28. It depends on where you are as to which channel is available. After the caller stops talking then the radio automatically replays the recording on the duplex transmit channel. In areas where there are lots of boaters this was implemented to reduce the number of silly "radio check please" calls on channel 16. You can read about it on their web site:

https://www.seatow.com/tools-and-edu...ed-radio-check

[StuM]

> I think Stu meant "shore station" rather than "repeater"

I didn't actually mention "repeater". That was in the linked article.

But duplexing can be performed either at a shore station or a repeater. As an example, the RPYC operates a shore station on Channel 84 via a repeater on a nearby hilltop. The duplexing is done on the hilltop repeater, not at the RPYC radio installation.

That means that vessels can operate ship to ship on Channel 84 as well as communicating with the RPYC. (although it is not strictly legal to do so - Channel 84 is designated as a Ship To Shore channel in the Spectrum Regs.)

[prof_mariner]

I guess you are talking about an autimated radio checking facility?
It might not be down at all.... Just out of range for a handheld.

I'm rewiring my mast so don't have a mast head antenna for my boat's main VHF radio at the moment. So I wanted to test my hand held so I at least had one vhf on board while I moved the boat from the marina to the boat yard. That's why I gave the hand held a test, which led to the series of events indicated in my first post.

The automated radio check repeater is located in the next marina, maybe 1/4 mile away. I can't confirm that the repeater is working because I can't use my main VHF, but I was pretty sure the hand held would reach at least 1/4 mile.

I feel like an idiot now having replaced a perfectly functioning radio, not once, but twice! LOL

[skipmac]

Originally Posted by transmitterdan

The radio does implement duplex. But a handheld would have to be programmed to act as a shore station to communicate.

Guess I'm confused. My question is why does the marine VHF system implement duplex by using a shore station? Why not use radios that that are internally duplex and can communicate directly on duplex channels?

I do believe that there are radios (perhaps HAM or marine SSB?) that implement duplex in the radio IE transmit on one freq and receive on another without requiring any outside shore stations or repeaters. I cannot think of any technical reason why a hand held radio cannot be made and programmed to transit and receive on different freqs other than to comply with regulations pertaining to a certain band.

[Auspicious]

Originally Posted by skipmac

Happen to know why it's done this way? I can't think of any reason why the radio couldn't implement duplex internally other than higher cost and complexity.

The duplex channels were intended for communication with shore stations. The high-end shore stations including those used for ship-to-shore telephone and many official functions had some pretty spiffy filtering, separate receivers and transmitters, and often multiple antenna locations. That meant that the shore station could hear the ship station even while they (the shore station) was transmitting.

The rise of cell phones pretty much killed the demand for short-range ship-to-shore.

[skipmac]

Maybe ignore my last post. I started thinking about it and decided I don't understand duplex radio at all.

If you are on a channel that is duplex how can you transmit on one frequency and then other stations on the same channel receive that transmission on a different frequency, unless the transmitted signal goes to a shore station to be retransmitted on the receive frequency.

But I thought there were HF bands on HAM or SSB that used duplex channels. How does that work or am I mistaken?