AIS Reception

[alan]

Just a bit of info for those into AIS and reception statistics:
Must have had a good day today!! .................... Was trying my AIS for the first time outside of the marina and was getting a lot of shipping in the middle of the "channel" between mainland Italy and Sardinia; also got a ship in Sardinia at 140 miles away!!!!!

This is with Easy AIS, Raymarine C70 and VHF antenna on the pushpit; am very happy with performance and was amazed how many ships there were going north/south which were from Nettuno (obviously) for me not visible.

Alan.

 

[lenseman]

It is a very impressive /forums/images/graemlins/cool.gif

I was introduced for the first time to a working AIS system on a recent yacht delivery (May 2008) from Cobb's Quay Poole down to Gibraltar. The laptop was the display and all I can say it is a very good "Poor Man's Radar" coupled to the fact that it would not draw anywhere near the current from the batteries as a conventional radar.

Ships more than 8-10 miles away cannot really be seen under clear conditions at sea level (4'-6'asl) but still very useful to know of their course and speed.

The fact that you could receive the AIS from a ship 140miles away was caused by enhanced RF ducting and can be regularly expected in the Med during the summer months and also small periods in the winter.

An interesting thing to note regarding enhanced RF ducting is the fact that it will not usually occur 'across' a weather front and will always exist 'along' a weather front. so this might assist you with passage planning or gleaning a useful snippet of info about the weather which is hidden from mere mortals. The same goes for Sporadic-'e'. This is always along and not across a weather front.

 

[Ballistix]

I've got the 250 transponder on my little boat, and it's great to see all these big boats, also can see which way they are heading and speed and so, radar can't tell you that can it?

T

 

[Piers]

Yes it can, but you need to plot for a few mins first, or have a really good MARPA (underline really good).

 

[alan]

Thanks for that info Lenseman; I didn't know about the ducting happening only along a weather front. I have seen ducting at UHF used to advantage to create radio links between small Pacific islands, but was unaware of the connection with weather fronts. Thanks.

Alan.

 

[lenseman]

No problems, the Royal Surrey Gas Board (RSGB) did some research in the early 1980's where they asked every radio amateur in the World to look at any enhanced conditions and to send in the reports.

It was only when they started to notice that all the Sporadic-e ducts were happening in a certain directions , whether you were living in Japan, the Mediterranean or the USA.

When it was all collated, specific directions were noted and someone then put two and two together and noticed that on any particular day, at no time did a Sporadic-e duct 'cross' a weather front but ALWAYS travelled 'along and 'in front' of the front.

Once the weather front crosses your location, the duct will collapse, again useful secondary, hidden from the masses, information.

So armed with this information, if you ever hear an AIS signal from a ship proceeding up the Red Sea about 200 miles away whilst you are in the Med, then you can be sure that the weather front is left or right of a line laying in the general direction of the Med to the Red Sea and not at 90° to that direction.

Hope this helps?

 

[alan]

Thanks for the explanation David. It could be useful to try and predict fronts moving in from the western med. I'll try and give some time to checking this out when I see a weather front rolling in!!

Alan.

 

[lenseman]

It doesn't work on every weather front, so don't expect to get enhanced conditions whenever a weather front closes in but if you get enhanced conditions, they will be along the front. /forums/images/graemlins/smile.gif