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post #1 of 10 Old 02-03-2008 Thread Starter
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VHF duplex channels

I'm new to the VHF marine radio and was wondering if someone could give me reference for the use. I've noted the duplex channels won't work on the handhelds, so need to clarify how to operate the radio.
Thanks

Alecs123
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post #2 of 10 Old 02-03-2008
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Originally Posted by alecs123 View Post
I'm new to the VHF marine radio and was wondering if someone could give me reference for the use. I've noted the duplex channels won't work on the handhelds, so need to clarify how to operate the radio.
Thanks
What kind of radio do you have?

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post #3 of 10 Old 02-03-2008
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Here are the U.S. VHF channels and a short explanation of their use:
http://www.navcen.uscg.gov/marcomms/vhf.htm

In general, duplex VHF channels are for ship-to-shore radiotelephone use, e.g., to make a telephone call through a shore-based marine operator. There are not many of those left so, mostly, the duplex channels don't get used.

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I found a really good online video tutorial on the Boat US Foundation Website. I don't think I can post links yet, but try googling "boat us vhf" and you can find it. It's a sales pitch for the newer Digital Selective Calling radios too, but it covered VHF basics really well too. I sorta encoded the URL below, if you can figure that out.

www dot boatus dot com slash foundation slash dsc slash player.html

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The link maybe is: http://www.boatus.com/boattech/vhf.htm

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Last edited by artbyjody; 02-03-2008 at 04:40 PM.
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post #7 of 10 Old 02-03-2008
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if the radio is intended for service in the country (i.e. for that band plan) it should be able to automatically switch between the two channels for TX/RX. If it can't do that--perhaps it simply is too old or cheap to have automatic switching in it. I'd suggest contacting the maker to find out what it can do, and perhaps if it simply indicates your TX channel--but automatically is RXing on the RX match for it, with just a little "duplex" icon somewhere to let you know about it.

I have no idea what that might look like--when i went to school, no one spoke Iconese.
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post #8 of 10 Old 02-03-2008
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Most radios are capable of being switched from American to International channel setup. The American channels, IIRC, are usually indicated with by ##a as the channel label.

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post #9 of 10 Old 02-04-2008 Thread Starter
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Thanks for the replies.... I have a Uniden VHF marine radio don't recall right now the model but was purchased last week, so I think is not too old.
I have been researching the internet, basically I understand that duplex channels need a "repeater" in order to be able to contact another radio.
The initial test I made was at home with 2 VHF radios on the international setup.
Didn't work on duplex becuase no repeater was in range, but when switched to simplex, communication was successful.
I have a table of frecuencies for each channel (came with the radio) in either US, Can or Int, there are far more simplex channels in the US than Can or Int.
Thanks a lot

Alecs123
Alejandro Viveros
Valle de Bravo, Mexico
Merit 25, #302. 1982
Flying Tern 14', 1968


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Alejandro, "duplex" refers to a simulatneous two-way conversation, such as the one you have with a good telephone call. Both parties can talk at the same time, and both parties can listen at the same time, because each party has one "channel" open to the other party.

Most radio is "simplex", meaning, when one party talks, the other one cannot be heard. You need to let go of the microphone button and switch back to listening, and take turns with each other.

What you heard about repeaters is probably a misunderstanding. Repeaters normally USE duplex, with incoming calls to the repeater on one frequency, and outbound transmissions on another. But, people who are using the repeater normally are switched (automatically, by their own radios) to talk on the inbound frequency and listen on the outbound. From your point of view, the repeater is going to appear to be using simplex--not duplex--unless there is special provision made for it.
I don't know about Mexico but this would be unheard of for a marine VHF in the US.

I would suggest you contact your autorities down there to find out what modes are normal--and legal--for marine VHF, and then find out what your Uniden supports.

True duplex operation on a single transceiver is not possible, unless the radio has at least the ability to receive on one channel while simultaneously transmitting on a second, which means extra electronics, and extra cost. And at least in the US, I don't think there is any market to support that expense, since we switch from transmit to receive mode instead. (Whether the radio switches channels as it does that, doesn't matter. It is still SIMPLEX as far as the user is concerned. Looks, acts, functions, as simplex.)
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