AIS oddity

[Bilgediver]

Tropospheric ducting.
Tropospheric propagation - Wikipedia

In my days as a radio ham, it's what we lived for.

Had signals in the past from Germany into the middle of the uk

I had 5 APRS stations appear on the screen recently from the Stavanger area. I suspect some bright spark put a wide 1-2 digi on the Rogoland mast and it found Aberdeen

 

[bikedaft]

In an apartment at Fort Picklecombe last week, facing S, on S side Mt Edgecombe (Plymouth), 2 of the 5 phones in our flat automatically changed time to French time. As did one of the neighbour's phones. 100nm from French coast... High pressure. Did not think mobile phone reception/data could go that far, but 3 phones did. Our two didn't roam however. Dunno about the neighbour. Interesting thread, thanks.

 

[KeelsonGraham]

Used to get the same result in the old AM CB radios when a high was around. It was called 'skip' back then.

Ink

Skip is an HF phenomenon. So, for VHF AIS this must have been ducting.

 

[david_bagshaw]

While testing my new Emtrack AIS transponder, @PaulRainbow and I noticed one return coming from 83 km away. Neither of us could understand it! AIS is VHF wavelengths, so it should be line of sight or not very much more. There wasn't any identifying data on the return, but it was in a plausible location on the Belgian/Dutch coast.. My antenna is at the top of the mast, so maybe 12 m ASL, and we were in Shotley, so a few metres above chart datum - perhaps the antenna was about 15 m above datum, so the distance to the horizon from my mast is about 14 km. Estimating wildly, a ship's monkey island is maybe 30m ASL, giving a distance to the horizon of about 20km, which makes sense as other than this outlier, the most distant returns were from around 35 km away (i.e. 14+20, ish!)

Any suggestions as to why we got one rogue response?

I see ships over 200 miles away, but only when the baro is very high, was off cork and looking at shipping in the dover straight! digitial yacht ait 2000 with Ariel at 10m

 

[Habebty]

Can often hear Ostende Port Radio in Harwich Harbour on a nice day.