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Old 08-09-2019, 06:03 PM   #1
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do vhf duplex channels actually go to ground station and get retransmitted

https://www.thecoastalpassage.com/vhf.html

If you talk on 24 and another radio is on 24 on your boat, you can not hear it??
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Old 08-09-2019, 07:52 PM   #2
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I havent looked at the channel list, but duplex channels are intended for ship to shore and shore to ship, but not ship to ship.

One half is ship to shore, the other shore to ship. This means that transmiting doesn't block receiving, and vice versa, allowing for a more telephone like conversation if there isnt conflicting traffic.
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Old 08-09-2019, 08:01 PM   #3
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No, marine VHF isn't on a repeater. Duplex simply means that TX & RX are on different frequencies. They're still radio to radio. The guy at the link doesn't have it right. But, then it IS on the internet so it HAS to be true...???


Pre-cell phone days we used radios in the trucks to keep in touch. They were repeater systems. Transmit on one frequency, the repeater received it and simultaneously transmitted it on a different frequency. Significantly extended range, provided you had line of sight to the repeater tower. Later, digital radios could be programmed for a multitude of frequencies, so there was a "talkaround" channel that bypassed the repeater and worked truck to truck. Handy to reduce traffic on the repeater that was shared with multiple users or for field work where we were out of tower reach. Each radio transmitted a tone that was unique to the separate businesses using the repeater. It would open the squelch on the radios sharing the tone. Hanging the mic would close the tone squelch so you wouldn't hear the other operations. Party line...
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Old 08-09-2019, 08:31 PM   #4
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This FCC list of channel uses might be of interest to those in the US:

- https://wireless.fcc.gov/marine/vhfchanl.pdf
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Old 08-09-2019, 10:39 PM   #5
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I have tested this with 2 radios on the boat, and so far for all duplex channels, neither radio hears the other. For all simplex radios, both radios talk to each other, meaning I talk on one, the other radio plays my voice. It actually makes sense as the frequencies for tx and recieve are different. AFAIK.
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Old 08-09-2019, 10:41 PM   #6
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Originally Posted by gkesden View Post
I havent looked at the channel list, but duplex channels are intended for ship to shore and shore to ship, but not ship to ship.

One half is ship to shore, the other shore to ship. This means that transmiting doesn't block receiving, and vice versa, allowing for a more telephone like conversation if there isnt conflicting traffic.
Yes, so the shore radio for marine duplex must be different than a ship radio for marine duplex to allow that to work. In past years, sometimes I would hear only one side of a conversation, which must mean all I could hear was the shore station, not the boat talking and they must have been using a duplex channel.
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Old 08-09-2019, 10:44 PM   #7
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sdowney,

That is as it should be, because your radios are only the ship half of the ship-shore pair. They send on one of the channel's frequencies and receive on another -- but the opposite pairing as a shore station.
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Old 08-09-2019, 10:46 PM   #8
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sdowney,

Bingo!

(Although, this sometimes happens on simplex channels because shore may be more powerful or higher up, etc)
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Old 08-11-2019, 06:05 AM   #9
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Quote:
Originally Posted by Maerin View Post
No, marine VHF isn't on a repeater. Duplex simply means that TX & RX are on different frequencies. They're still radio to radio. The guy at the link doesn't have it right. But, then it IS on the internet so it HAS to be true...???



Actually he may have it right, It would appear that the article maybe correct, it looks like it was written by an Australian, and in Australia we do have VHF marine repeaters, I think he was trying to highlight that in Australia we use the International setting on the radio, which has different offsets in the DUPLEX channel allocation to the USA settings, I have lost count of how many people I have helped change their radio to "international" settings to be able to access the VHF marine repeaters here in Australia. Interestingly the last 4 VHF marine radios I purchased brand new here in Oz where all set to USA channels. And the repeaters here are mostly used as SHIP to SHIP (via a land based repeater, ship-shore-ship)
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Old 08-11-2019, 08:57 AM   #10
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Actually he may have it right, It would appear that the article maybe correct, it looks like it was written by an Australian, and in Australia we do have VHF marine repeaters, I think he was trying to highlight that in Australia we use the International setting on the radio, which has different offsets in the DUPLEX channel allocation to the USA settings, I have lost count of how many people I have helped change their radio to "international" settings to be able to access the VHF marine repeaters here in Australia. Interestingly the last 4 VHF marine radios I purchased brand new here in Oz where all set to USA channels. And the repeaters here are mostly used as SHIP to SHIP (via a land based repeater, ship-shore-ship)
Seems he also mention 80 mile range though, that cant be right. I thought 20 miles was about it. Just how many repeaters get involved?

Maybe if more watts wre used.

Quote:
Your personal conversation has travelled up to 80 miles back and forth, a
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Old 08-12-2019, 12:23 PM   #11
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Seems he also mention 80 mile range though, that cant be right. I thought 20 miles was about it. Just how many repeaters get involved?

Maybe if more watts wre used.
80 miles is possible for a VHF repeater that is sat on top of a mountain near the sea. As long as anyone that wants to send or receive on the repeater is line of sight with the top of the mountain it works fine and the horizon line of sight is extended with heights.

More watts won't help.

I've communicated with VHF frequencies at 30 miles direct with only 15 watts. With my station at the top of a mountain and the other station at sea level with direct line of sight between the two.
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