Simplex vs Duplex

[Solitaire]

Hi - anyone got a very simple definition of simplex vs duplex? A good web site would also be useful! Many thanks in advance.

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[Stemar]

As I understand it (with no pretentions to expertise)

Simplex uses one frequency, so you can't receive and transmit at the same time, but anyone listening in can hear both sides of the conversation.

Duplex uses two frequencies, one, for example, ship to shore, the other shore to ship, so traffic in both directions can happen at once. If you're a ship, you can hear what the shore station is saying, but you can't hear other ships.

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[stephenmartin]

Simplex transmission is when you talk and listen on the same frequency but you can only do one or the other at the same time...

Duplex transmission is when you talk and listen on different frequencies....similar to a telephone conversation....you can talk and listen at the same time...

Hope this helps...

Steve

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[bigmart]

Assuming you are talking about VHF Radio Channels.

A Simplex Channel is one where the transmission & recieve frequency is the same.

A Duplex Channel is one where the transmission is on a different frequency to the recieve frequency.

For the leisure boater there it really has no meaning. I believe that certain profesional boaters may have a reason to need the Duplex channels.

I don't know of any websites to explain.

Martin

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[starboard]

Originally for use by coast radio stations i.e Niton, Portishead, Portpatrick etc.in the days you had to place a link call through them to connect to the BT telephone network. The use of duplex channelsi.e. 26 27 etc would enable you to talk whilst the person recieving could talk back at the same time as you do over the telephone
now. I think you will find one of the marina channels is also duplex either 37 or 80 cant remember which.

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[tome]

In terms of radio comms, there are 3 possibilities:

Simplex, where a single frequency is shared

Half-duplex where seperate frequencies are used for send and receive but only 1 can be used at one time. This was used in link calls and meant that listeners could only hear the shore side of the conversation.

Full-duplex where two frequencies are used simultaneously enabling normal conversations to take place without all that over stuff. Only practical on larger ships as you need good antenna separation.

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[chriscallender]

Pretty much it. As others have said, duplex uses two frequencies - one for ship to shore and another for shore to ship. That means that if you did have a radio set that could transmit and receive at the same time you could have a two way conversation like you do on the phone. However, all of the small VHF radios we have on boats have a push to talk buttion and you are either listening or talking - they don't allow a 2 way conversation even on duplex channels.

In the olden days duplex channels were often patched through to the telephone network to allow people on ships to call a landline and allowed both parties to talk/interrupt the other to have a natural conversation. Obviously the need for this service is gone with the advent of mobile phones.

Nowadays the only real relevance is that you can only talk to another ship on a simplex channel - since otherwise both parties would be transmitting on the ship to shore frequency and receiving on the shore to ship frequency, and therefore wouldn't hear each other

Something you will hear from time to time is two boats making contact on channel 16, going to a working channel which is duplex and then coming back on 16, trying another duplex channel and so on! This is all covered on the VHF licence course so if you hear it happen it suggests that neither party has a VHF operators licence - shock, horror! - or else they just forgot the list of which channels are ship-ship.

Chris

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[Heckler]

sorry to nitpick old boy, everything correct except about antenna separation. duplex uses the same antenna to transmit and recieve. i set up a motorola installation in my last posting in africa and we only ever used i antenna on the masts
stu

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[MainlySteam]

I will nit pick a little more, but agree with you sonsy_lass as long as you put "can use" in front of "the same antenna to transmit and recieve". Duplex operation can use two antennas and does where it is more convenient/easier than isolating the receiver and transmitter from each other by duplexors, etc if one antenna was to be used.

The obvious single antenna duplex radios we all use are cellphones and cordless phones.

John

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[Heckler]

accepted, was going to be a smarty pants and say we use some duplex channels on our vhfs but cant remember which channels they were
stu

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[Heckler]

portishead radio, portishead radio this is texas 2 calling portishead radio.
texas 2 stand by, you are turn number 2,

10 mins go by as a matelot on one of her majesties finests talks to his popsie

texas 2 this is portishead radio what is your position?
portishead radio this is texas2 we are at the mouth of the river congo, position etc etc.
texas 2 this is portishead radio what can we do for you this evening?
portishead radio this is texas 2, could you place a reverse charge call to my wife on number so and so

and so it went on, ahh memories, SSB, over and her indoors forgetting.

now what have we got, portishead shut, things move on
stu

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[starboard]

Still few channels in duplex. here on the Clyde Clyde coastguard use ch86 as working channel..if you try to listen in to conversation you will only her CG and not the other station replying, unlike ch67 which is simplex and you can listen to both sides of the conversation!!!!

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[Solitaire]

Thanks everybody - I knew how it worked in principal but was just looking for some better ways of describing it - very helpful indeed!

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[catmandoo]

Generally simplex is what it means - simple form ie in terms of hardware its simplest form ie one . Duplex means two fold ie in terms of fluid filters we can get duplex ie two filters in parallel one standby and one working whereas the simplex is only one .
The next stage is triplex applied to glass ie three layers and then quadruplex which one might apply to a horse and so on .

Applying this logic then a ketch might be described as duplex and a sloop as simplex . A monohull as simplex and a catamaran as duplex etc etc



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[MainlySteam]

Thanks for the comment Starboard.

The "duplex" (actually semi duplex) VHF channels are very widely used here for the many private repeators around the coast run by societies on behalf of small commercial vessels (fishermen, passenger, charter yachts, etc), pleasure boats and resorts. They maintain a manned listening watch on their repeator(s) (normally not for 24 hrs though and is by very competent volunteers usually, and often women) and provide an excellent service also providing a safety watch if asked, routine and on request weather forecasts, and general help. I can think of around 6 or so just in an around 60 or so mile radius of Wellington. While access is not restricted, you are supposed to be a member of the society in order to use them (except in an emergency, of course).

Regards

John

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[wakeup]

I was taught to remember it this way when learning to fly...

Simplex = One man talking to another, one listens while patiently the other talks and then allows the other man to talk. All on the same wavelenght.

Half Duplex= One man talking to a woman, same as above but both on different wavelength.

Full Duplex = Two woman talking to each other simmultaneously , neither listening and both on totally different wavelenghts.

I am now going to duck...

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