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Old 09-01-2013, 01:06   #16
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Re: 100 mile AIS range?

Originally Posted by rabbi View Post
We always received the spanish CG station located in the mediterranean while being moored in the Canary Islands, somtimes almost 1000nm away. Reliably, but only the CG stations. So there must be some kind of repeater mechanism in place for these signals.
Oops I forgot... CANARY ISLANDS. That is Spanish. You are probably getting these signals from a local transmitter in the Canaries.

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Old 09-01-2013, 02:42   #17
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I have regularly had the VHF come alive with all the idiot radio chatter from SoCal when hundreds of miles down the Baja. Must be a local ducting phenom. Repeaters? Not likely.

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Old 09-01-2013, 08:53   #18
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Re: 100 mile AIS range?

USCG, on the west coast, positions antennas on the highest peaks along the coast. From you can see that an antenna at 5000 ft talking to a ship with antenna at 40 ft could easily achieve a 100-150 mile range. I was recently delivering my boat from Hawaii to SF. At 300 miles from the coast I called the USCG and was shocked to get a response from Humboldt Bay as they were a bit to the North. I could hear SF and LA at least sporadically. This was likely a case of ducting but their antenna is up pretty high. On AIS range, I live at 1500 feet, 40 mi south of SF, with a clear view of the bay. I have a homemade AIS set up with a vertical antenna. I can often read signals offshore up to 100 miles to the north where there are gaps in the coastal range, and of course can read all the ships on the bay. On days when there is a temperature inversion nearly all the bay reports disappear. This is due to the inverted temp layer reflecting the low angle VHF signals down. At the same time I can easily hear signals that emanate above the inversion layer from peaks up to 200 miles distant (line of sight propagation).

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