AIS propgation

[Skylark]

..................you could check on Marine Traffic to see if there are any signals either at sea or in the anchorage that you should be picking up.

Richard

I was going to post pretty much the same comment. If GHA has any doubts as to his local AIS radio reception it's always worth a quick check on Marine Traffic website. The site is also useful for checking aged tracks.

This was my track last Thursday.

 

[GHA]

Are you trolling or something as this is getting silly?

You know perfectly well that I wouldn't be picking up AIS signals from ships 500 miles away unless it was due to atmospheric effects.

And if you know that these anchored boats are within sight and have their AIS on permanently but you are not seeing them on your system then you clearly have a technical fault or an operator error.

I suggest that you start this thread again once your head has cleared from last night's excess.

Richard

Not trolling at all, you said AIS gets better at night - I suspect that's rubbish. Lower frequencies can get much better at night when the ionisation changes once the suns ultraviolet rays aren't around any more, but not up at 160Mhz. Ionispheric reflection generally stops at 30Mhz so long distance AIS propagation will be troposhpheric, are you saying this changes at night?

So why does 160Mhz propagation get better at night as you say, or are you mistaken?
(your chance to back out gracefully )

Technical fault is possible but very unlikely to slowly appear after sunset as the data shows, a few more days recorded data will show if it's a one off or happens every night.

 

[GHA]

I was going to post pretty much the same comment. If GHA has any doubts as to his local AIS radio reception it's always worth a quick check on Marine Traffic website.

On marine traffic most days seeing if any of the gang have actually moved

I know some of the boats transmitting near here, they leave it on all the time. Though even at just 5 miles away it's not fantastic reception. This boat is on the hard, antenna prob about 10m above water line. Might connect up the masthead metz antenna and see what comes out of that later. All the AIS is being recorded to a txt file if anyone is actually interested and wants a play.


Edit. SH gx2100 now receiving from masthead metz instead of the nasa ais engine so will be interesting to see tonight what happens. Picking up from 90 miles.
Long distance fading could well be explained but troposhperic changes when the sun goes but line of sight?

Ahh, when's low tide????.... 8.30 last night, could well be! Nothing coming in yet from the anchorage but a few between here and the lagoon entrance.

 

[lw395]

Not trolling at all, you said AIS gets better at night - I suspect that's rubbish. Lower frequencies can get much better at night when the ionisation changes once the suns ultraviolet rays aren't around any more, but not up at 160Mhz. Ionispheric reflection generally stops at 30Mhz so long distance AIS propagation will be troposhpheric, are you saying this changes at night?

So why does 160Mhz propagation get better at night as you say, or are you mistaken?
(your chance to back out gracefully )

Technical fault is possible but very unlikely to slowly appear after sunset as the data shows, a few more days recorded data will show if it's a one off or happens every night.

Sometimes anomolous reception is a problem not a bonus.
If atmospheric effects allow interfering signals to block the weak ones you want, system performance will be worse.
It sounds like you have a fault.

 

[GHA]

Sometimes anomolous reception is a problem not a bonus.
If atmospheric effects allow interfering signals to block the weak ones you want, system performance will be worse.
It sounds like you have a fault.

The real world when sailing is absolutely fine, this is just interesting.

Low tide is top of the list IMHO for the anchorage boats disappearing, they only just get received at the best of times.

An intermittent fault on 2 completely different systems is very unlikely.

 

[RichardS]

Not trolling at all, you said AIS gets better at night - I suspect that's rubbish.

What has happened to your thinking processes? I always had you down as one of the brighter sparks on here.

We've had so many threads on here about how we can pick up targets at 300, 400, 500 miles away across open sea at night but I've never heard from anyone who can do that during the day. I certainly can't. Do you really believe that these extreme range targets are nothing to do with nightfall? :ambivalence:

Richard

 

[GHA]

What has happened to your thinking processes? I always had you down as one of the brighter sparks on here.

We've had so many threads on here about how we can pick up targets at 300, 400, 500 miles away across open sea at night but I've never heard from anyone who can do that during the day. I certainly can't. Do you really believe that these extreme range targets are nothing to do with nightfall? :ambivalence:

Richard

What so many threads about better reception at night and not during the day? Don't remember all those - Links?

Right now I'm getting over 100Nm, up to 400 yesterday during the day then tailed right off over night.


This is the local marinetraffic station show area of reception, how come it was huge during the day then dropped right off in the evening? What I was seeing as well. Yesterday daytime looks like it was quite a big tropo event.
https://www.marinetraffic.com/en/ais/details/stations/2324/_:d01f236864faae9bb42ba76e529a1ec4

For everyone else, anyone noticed AIS reception going long distance at night but only getting short distance during the day?

And what unspecified "atmospheric effects" are you talking about? That was the main thing - what are you talking about??

A few boats showing up now in the anchorage, just might be the tide after all.

5Mb of ais messages here if anyone is remotely interested, not sure how to plot time against distance using lat & long though - any hints?

https://www.dropbox.com/s/6s305ddiiot8w6u/AIS_Decoded_output2.csv?dl=0

 

[RIBW]

C'mon (again), please!
Dear All,
If you want a PBO discussion of AIS, this is the place. (I am with MoodySabre #6 on this).

If there is to be a discussion of VHF propagation then take it to a ham website. (I think they operate nearby at 144MHz).

On very rare occasions the Barfleur Light (near Cherbourg) can be seen in Ventnor on the Isle of Wight. Interesting but it has no Practical Boat Owning relevance unless you think it may be a buoy that is not on your chart!

PBO response: If there are no AIS signals at night, start isolating/diagnosing the possible causes: Step 1 - put the simplist of antennas (known in professional radio circles as 'wet string') onto the receiver directly. Are there local AIS incoming signals? I use a tiny telescopic antenna on a stand alone NASA 'radar' in the cockpit - more than adequate for crossing the Channel.

Cheers
Bob

 

[RichardS]

C'mon (again), please!
Dear All,
If you want a PBO discussion of AIS, this is the place. (I am with MoodySabre #6 on this).

If there is to be a discussion of VHF propagation then take it to a ham website. (I think they operate nearby at 144MHz).

On very rare occasions the Barfleur Light (near Cherbourg) can be seen in Ventnor on the Isle of Wight. Interesting but it has no Practical Boat Owning relevance unless you think it may be a buoy that is not on your chart!

PBO response: If there are no AIS signals at night, start isolating/diagnosing the possible causes: Step 1 - put the simplist of antennas (known in professional radio circles as 'wet string') onto the receiver directly. Are there local AIS incoming signals? I use a tiny telescopic antenna on a stand alone NASA 'radar' in the cockpit - more than adequate for crossing the Channel.

Cheers
Bob

Errrrrrr .... as the title of the thread is "AIS Propagation", I guess that's what we should be discussing.

Richard

 

[lw395]

...

For everyone else, anyone noticed AIS reception going long distance at night but only getting short distance during the day?

And what unspecified "atmospheric effects" are you talking about? That was the main thing - what are you talking about??

A few boats showing up now in the anchorage, just might be the tide after all.

5Mb of ais messages here if anyone is remotely interested, not sure how to plot time against distance using lat & long though - any hints?

https://www.dropbox.com/s/6s305ddiiot8w6u/AIS_Decoded_output2.csv?dl=0

Mostly I've used AIS receivers and transceivers which discard contacts out of the max radius.
So many people could be familiar with AIS which is self-limiting in terms of range.
I've experienced quite long range voice VHF reception in day time. Never identified anything weirdly long range at night, but you never know where wittering french trawlers are coming from.
I'd be concerned about not receiving from nearby. That is a real problem, while freak distant reception is only of academic interest.

Although I've worked a lot in radio, propagation is not my 'thing'. I think a little knowledge is dangerous in this area, if I need to know I defer to a man with a relevant PhD.

 

[mattonthesea]

Quite busy out there
Rings are 100Nm.
There were 2 not under command earlier..

Whatever is causing the propagation seems pretty stable, so far today anyway.

In 2010 in the Azores one of my neighbouring boats was summoned by a VHF call to the 'yacht nearby'. He replied to this large vessel and asked where he was as he couldn't see a large vessel. "Off Gibraltar" was the reply!

So,GHA, why aren't you picking the AIS up from there? :highly_amused:

 

[GHA]

In 2010 in the Azores one of my neighbouring boats was summoned by a VHF call to the 'yacht nearby'. He replied to this large vessel and asked where he was as he couldn't see a large vessel. "Off Gibraltar" was the reply!

So,GHA, why aren't you picking the AIS up from there? :highly_amused:

Picking up virtual ATN's from Cueta couple days ago so I was getting AIS from Gib .

Hardly anything today, what has been interesting though is a little test just done.

20 minutes logged messages from the Metz masthead - about 200 messages, mostly base station & repeated Sagres TSS virtual ATN's.

Straight afterwards 20 minutes logged from the Ham dual band antenna on the radar arch - about 300 messages.

So does that mean the lower antenna is actually better? Bit hard to tell from just that & no idea how else you would test but interesting anyway.