VHF: Simplex to Duplex comms.

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electrosys

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I've been offered a vintage handheld VHF (simplex only), the manual of which says it 'covers' all marine channels. Hmmm ...

I know that shore-based stations can handle either Simplex or Duplex VHF traffic, but what would happen at sea between a couple of handheld radios: one duplex, the other being such a legacy unit, with simplex only. After moving away from 16, to a duplex channel - say 18 - would they still be able to communicate with each other ?

Any radio experts out there ?
 
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I believe that the simplex radio will only be able to communicate using the press to send button and will receive nothing while this is being done, the duplex will have to revert to this system also can't talk and listen at the same time as normal.
 
Identical radios can't communicate with each other on a duplex channel.

On those ships and talk to shore, and shore to ship, but not ship to ship or shore to shore.
 
As said two ships radios ( at least of the type we have), be they fixed or H/H cannot communicate with each other on a dual frequency (duplex) channel such as CH 18 which is not an intership channel anyway

The Channels allocated to intership working are all single frequency channels.

Splitting hairs a bit but, duplex and simplex really refer to whether or not both parties can talk simultaneously as you do with a telephone.

Duplex operation (telephone like) requires two frequencies.
With a single frequency only simplex operation is possible.

With the radios in our yachts we are in fact limited to simplex operation , ie taking it in turn to talk, even when using the dual frequency channels.
It used to be referred to as "semi-duplex" but I have not seen the term used recently.
 
Ok - thanks for the info thus far - appreciated.

Staying with Ch 18 for the moment, I can now see that:
Code: 
	Tx	Rx
18   156.900  161.500  (Duplex)
18A  156.900  156.900  (Simplex)

So - yes - I can see that 18 couldn't be used with 2 indentical radios, whereas 18A could. Which raises two further questions ...

1) Ok - so it may look impressive in the manual, but what's the point in a handheld VHF having access to so many duplex channels, if most of them can't be used ?

2) And - when moving away from 16, without the benefit of a look-up table handy, how do you know which of the channels is suitable for ship-to-ship comms, or is this down to user familiarity ?

(You can see who's new to this radio marlarky ... )
 
Staying with Ch 18 for the moment, I can now see that:
Code:
Tx Rx
18 156.900 161.500 (Duplex)
18A 156.900 156.900 (Simplex)

So - yes - I can see that 18 couldn't be used with 2 indentical radios, whereas 18A could.
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The single frequency 18A channel is an American channel. There are a number of channels which are similarly single frequency in America

Its common for modern radios to be switchable between the American channels and the International channels.

1) Ok - so it may look impressive in the manual, but what's the point in a handheld VHF having access to so many duplex channels, if most of them can't be used ?
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One model of radio then covers all uses. From amateur intership use to use as the ship station for professional port
operations and other ship to shore use.

2) And - when moving away from 16, without the benefit of a look-up table handy, how do you know which of the channels is suitable for ship-to-ship comms, or is this down to user familiarity ?
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You learn all this stuff for your Short Range Operators Certificate ... something you clearly have yet to obtain. :(
 
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electrosys said:
Thanks Vic - you're a mine of info. Not a lot of point getting a cert until I've got a radio - and one which works. Man's gotta get his priorities in order ...
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I got my certificate, or at least passed the test, before I got the radio ...... by about 1/2 hour IIRC

Don't forget the Ship's Radio licence That's free if you do it on line.

Even if you are only getting a H/H its probably worth going for a full Ship's Radio licence as that will give you a call sign for the boat and you will be able to add the radar, the epirbs the radar target enhancer fixed radio, etc etc as you acquire them

If there is any likelihood that you will want to use your hand held radio on an unlicensed boat you can also get a Ship Portable Radio licence ( costs nothing) then you can do so legally.
I have both licences.
 
Duplex radio

Around here duplex is used for repeater VHF stations up and down the coast. Being fairly sparsely populated the repeater will pick up your call and retransmit it to the big smoke. It receives a reply from big smoke and retransmits to you. It is therefor necessary to use a duplex channel where receive and transmit are some distance apart in frequency. (big smoke is Ocker for a place where people live (city)).
You need to determine if duplex repeaters are used or planned any place you might be going to sail. good luck olewill
 
elton said:
Do the course then you'll know which radio is better for you and your boat.
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I don't need a course for that - the only radio I would ever consider having is one I could repair myself. Hence radio first, course second.

It's hardly a major issue in my life - after all, I've sailed for a fair few years without one - all that's changed is that I now take a fishing boat out during the winter months, and it can get a bit rough at times in, what is after all, essentially an open boat - so I thought a radio would be good insurance to take along.
I already have a Seavoice 550 fixed set (works fine into a dummy load, but I've never actually installed it), but what I really want is an older ICOM handheld as, a) they're repairable, and b) a handheld is self-contained power-wise.

But this 'what channel to use ?' stuff has really opened-up a can of worms, for allocation appears to be in something of a mess. Channels that OfCom specify for S&R for example, are used in The Solent for Water Taxis !

But anyway, what I've already learned this evening, thanks to you guys, is not to discount a vintage handheld because it only handles simplex comms, or because it only has a reduced number of available channels. And that's worth knowing.
 
But this 'what channel to use ?' stuff has really opened-up a can of worms, for allocation appears to be in something of a mess. Channels that OfCom specify for S&R for example, are used in The Solent for Water Taxis !

But anyway, what I've already learned this evening, thanks to you guys, is not to discount a vintage handheld because it only handles simplex comms, or because it only has a reduced number of available channels. And that's worth knowing.
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The channels Ofcom specify for S&R are used for water taxis? You got me confused now. Which are they ? The GMDSS/DSC system and Channel 16 are all you need to worry about as far as S&R is concerned. Water taxis use the intership channels as far as I know but may require the initial call on ch 16.

I think you are getting confused about the simplex and duplex issue.
The so called simplex channels transmit and recieve on the same frequency. One set can therefore talk to another.

With the so called duplex channels the ship station transmits and the shore station recieves on one frequency, the ship recieves and the shore transmits on the other frequency. Two ship radios cannot therefore talk to each other.
It all happens without your knowledge, you wont notice any difference in practice between using the duplex channels and the simplex channels.
Your Seavoice does the same!

You might find this webpage of interest

Do the course, at least do the studying for it. You will know the answers to all of this then.

Two inexpensive RYA booklets cover it G22 and G26 for the exam sylabus.

Not available when I did my test but I'd also suggest the RYA VHF Handbook G31 Written by some stroppy bu$$er called Tim Bartlett who posts here from time to time.
 
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William_H said:
Around here duplex is used for repeater VHF stations up and down the coast. Being fairly sparsely populated the repeater will pick up your call and retransmit it to the big smoke. It receives a reply from big smoke and retransmits to you. It is therefor necessary to use a duplex channel where receive and transmit are some distance apart in frequency. (big smoke is Ocker for a place where people live (city)).
You need to determine if duplex repeaters are used or planned any place you might be going to sail. good luck olewill
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No repeater stations that I am aware of in the UK.
 
If Electrosys did the course then all his questions would probably be answered!

As long as your radio is set to the correct area (Europe) then you don't worry about simplex/duplex: just use the radio. You radio will have all the channels you are allowed to use but will appear to have some missing ones. These are designated as private channels. I have a private channel set on my h/h, one of my club's licensed channels.

The h/h that you acquired is probably more than suitable but, as has been said, you need the licence to operate it (as well as the fixed set you have).

Take the course and find out what it is all about and operate legally.
 
electrosys said:
But anyway, what I've already learned this evening, thanks to you guys, is not to discount a vintage handheld because it only handles simplex comms, or because it only has a reduced number of available channels. And that's worth knowing.
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Note that the Simplex duplex is not an issue either. MArine hand helds and leisure type fixed radios do not have the duplex facility ie twin channel operation simultaneously. However they all have what is referred to as semi duplex which means they will communicate on a duplex frequency but will swing between two different frequencies depending whether transmitting or receiving.

The old shore station frequencies were duplex such as 24 26 28 etc and these radios coped well using semi duplex.

The older radios which just had a small choice of frequencies could be reset to allocate different frequencies to the channel switch. In the very old this is done by switching crystals.Very fiddly. Later radios had a system of setting frequencies using a matrix board and switching connections. Icam have some friendly engineers who are usually helpful:)
 
electrosys said:
Thanks Vic - you're a mine of info. Not a lot of point getting a cert until I've got a radio - and one which works. Man's gotta get his priorities in order ...
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When you have your radio, to use legally except for emercency calling only, you need an Operator's License for you and you need a Ship's Radio License for the set if fixed or Transportable Radio License if handheld, unless you add H/H to fixed set license. SRL or TRL will give you a call sign.
 
VicS said:
The channels Ofcom specify for S&R are used for water taxis? You got me confused now. Which are they ?
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Ch 6 - used by Sally water taxi Cowes
http://www.ship-tracking.co.uk/Document Chest/AIS/Marine Channels.pdf


Channel 6 - Under GMDSS this channel is used for communications between ships and aircraft for co-ordinating search and rescue operations.
http://www.ofcom.org.uk/static/archive/ra/publication/ra_info/ra264/ra264.htm

I think you are getting confused about the simplex and duplex issue.
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And not just me:
"The end of ship to shore link calls has left many duplex channels. These are often now used as simplex channels (A frequency) and weather broadcasts, AIS etc. (B frequency). Some of the B frequencies are now used by non marine services. This has left the original maritime in the UK band plan in a bit of a mess. Some vessels visiting the area can be heard using various A channels as ship to ship simplex."
Yeah - and they've been on 'the course' and have got the certificate ...

Do the course, at least do the studying for it. You will know the answers to all of this then.
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And there's me thinking that this forum was for asking questions ...

... silly me.
 
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Look at the various dates mentioned in the OFCOM article, I think you will find that is very much out of date, and countries vary the useage. France quite often uses 16 for ship to ship, which really messes things up in the Solent. Things change. Just because 6 is designated a S&R channel it doesn't preclude its use for other purposes, hence this is the channel that the water taxi listens on to avoid congestion on 16. I think you will find that a lot of S&R working is on channel 0.

The other list is Solent area usage hence the appearance of Solent area unique services.

The service may appear to be in a muddle but it works. What is Duplex service in the UK is often a Simplex service in the USA (look at the frequencies!).

Your questions have been answered on the forum. Going on the course would fill in a more detail and, perhaps, understanding.
 
Ch 6 - used by Sally water taxi Cowes

Channel 6 - Under GMDSS this channel is used for communications between ships and aircraft for co-ordinating search and rescue operations.
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Channel 6 is the primary intership channel therefore not un-reasoanable that Sally water taxis use it.
ITYWF The harbour launch and the other ferries on the Medina use other intership cahnnels

The footnote says Ch 6 may also be used for coordinating S&R.

"The end of ship to shore link calls has left many duplex channels. These are often now used as simplex channels (A frequency) and weather broadcasts, AIS etc. (B frequency). Some of the B frequencies are now used by non marine services. This has left the original maritime in the UK band plan in a bit of a mess. Some vessels visiting the area can be heard using various A channels as ship to ship simplex."
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I am a not sure to what extent the old public correspondence channels are used. I believe the coastguard now use some of the old shore station frequencies for broadcasting safety and weather bulletins. If so it is just one way. You cannot speak to them.

And there's me thinking that this forum was for asking questions ...
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It is and for giving answers. In this case one of the answers is "read the books and do the course... then you will learn the answers to your questions". We always are willing to help with any outstanding problems but the forums are not a substitute for the normal tuition and learning processes. We know the answers and are able to help because we have taken the trouble to do the course
 
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