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Old 13 April 2012, 18:42   #41
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Only the colours /colors, the shapes are the same...

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D@mn! You cunningly neutralised/neutralized my intended riposte regarding spelling
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Old 14 April 2012, 01:28   #42
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it all makes sense now
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Old 14 April 2012, 03:53   #43
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It has a guideline range of 1 mile per watt, depending on how high the antenna is, so I could reasonably expect a range of 25 miles with my setup.
I'd be suspect of your expectations. Unless you're on a ship, or some other vessel that puts the antenna way, way above the waterline, you're probably looking at something more like 7 to 10 miles max on a good day, when communicating with another small craft.

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Old 14 April 2012, 04:52   #44
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with an antenna on the top of a 30ft mast surley 25 miles should be achievable
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Old 14 April 2012, 05:54   #45
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Range in nautical miles equals 1.4 times root of the height of the transmitting antenna plus the root of the height of the receiving antenna. Heights in feet.
If your antenna is at 30' and the other boat has an antenna at 6' the range is just over 11 miles.
If the other boat has an antenna also at 30', the range is just over 15 miles.

You need at least one of the antennas to be really high to get 25 miles, fortunately Coast Guard stations are located very high above sea level.
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Old 14 April 2012, 06:10   #46
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so does that equation apply to the way dsc works too?
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Old 14 April 2012, 06:11   #47
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I have had clear comms with Solent coastguard from Grandcamp-Maisy in France, about 90nm. Probably due to the quality & height of the coastguards kit than ours.
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Old 14 April 2012, 06:13   #48
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so does that equation apply to the way dsc works too?
Yup! dsc uses the VHF band, iirc channel 70, but it only transmits at 2w, not the 25w of full power vhf, so that's also a consideration.
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Old 14 April 2012, 06:21   #49
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so as previously discussed if you have a series of boats using dsc over a 30mile distance,say 10 boats 3 miles apart will that not get 30mile using the others as a repeater
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Old 14 April 2012, 06:24   #50
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I have had clear comms with Solent coastguard from Grandcamp-Maisy in France, about 90nm. Probably due to the quality & height of the coastguards kit than ours.
There's a phenomenon known as tropospheric ducting that allows huge distances, but you can't rely on it. I think the record is about 600 miles!
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