GPS "hole" where??

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Seagreen

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GPS \"hole\" where??

Just read the spring 09 RYA Magazine, and was totally confused by the end of the first paragraph describing a hole in GPS coverage at "the north-west entrance to the Menai Straits".

Where? I know that there's a north-east and a south-west end, or possibly just an east or west end to the straits. But a 'north-west' entrance? Would that be near Puffin Bar or Caenarvon Island?

Can anyone clarify this, please?


/forums/images/graemlins/wink.gif
 
Re: GPS \"hole\" where??

I've not read the article but I'm confused as to how there can be a "hole" in GPS coverage. As I understand it there's a few dozen satellites zooming around in various orbits and you get a pretty much random selection of these anywhere at any time. Does the article explain how/why this "hole" occurs in one place?
 
Re: GPS \"hole\" where??

I understand there are occasional experiments with jamming GPS signals that can affect this area. They are published in Notices to Mariners and NOTAMS.

There is no permanent "Hole" in GPS coverage anywhere.
 
Re: GPS \"hole\" where??

I think it might mean which side of Puffin Island you pass. The more popular route is by the lighthouse but at high water you can come around the Island from the Great Orm side, there is (used) to be a buoyed channel.

I am sure a menai skipper will be along shorty to correct my assumption. It is many years since I have been past Puffin and have forgotten the names of the places and passages.

puffin-island.jpg
 
Re: GPS \"hole\" where??

The 'Puffin' entrance to the Straits is at the 'Nothern' end.
The Straits kinda run North South.
If you look at an 'Ordenance' map or a chart you can see that Puffin as at the 'East' side of the Island.
So some peeps call it the north west entrance!! Wrong tiss the North east if anything.
The lateral bouys take you through 'Puffin sound' leaving the lighthouse indicated on Doggies map on your starboard side and a port hand lateral can to port obviously.
The item indicated as 'perch rock' is a bit confusing as it looks conical.
Anyway that is by the by as Doggies map is just to indicate the area.

Passage is possible at LAT 'underneath' the Island of Puffin, where the map says 'Monastic settlement' but the gap over the reef which extends south needs to be pinpointed accurately.

The comment in the RYA publication does not relate to which side of Puffin one enters the Straits.
Tiss a generalisation referring to this area Mr canine watcher!!!

AntarticPilot says there are no permanent 'Holes' in GPS coverage.
Cannot argue with that statement factually.

Passing through the area stated fairly regularly I can confirm that GPS signal sometimes vanishes briefly.

I don't have cutting edge leccies on me boat.
Or even my previous one.
The 'Gadgett' I have now is a Geonav 6 plus.
Bought secondhand from a previous poster on this thread !! ?
The 'Gadgett' has gone wonkey on Me about this spot from time to time.
On numerous occasions I have cursed said poster!

Tiss wierd that this subject has popped up.
Yesterday I was discussing the reception of 'dongle' lap top connection in Caernarfon with another Forumite.
The subject drifted, as it does on here.
I mentioned that from time to time I lose GPS signal at the North East side of Anglesey off Amlwch where the Wylfa power station is located.

Tother Forumite (who has done lots of sea miles all over the UK) mentioned that the only time He has ever lost a GPS signal was somewhere in the Straits.
He couldn't remember where exactly.
Now I am a self confessed numpty with putes and leccie navigation kit and don't know answers to this phenonemon but I think land based stuff seems to have an effect.
It does seem however that there are 'Bermuda Triangles' about Anglesey.
Oo Err /forums/images/graemlins/smirk.gif
 
Re: GPS \"hole\" where??

I've sailed extensively with and without GPS all round these parts and I've never noticed any failure of GPS coverage.
It's possible(?) that some transmissions might interfere with some GPS receivers. There is a number of major masts and transmitter aerials around there. Notably Point Lynas and on the hill two or three miles miles down the straits. There is a powerful radar at Lynas too.

General notes on Navigation. "The North West entrance" probably means the normal North West Entrance to the North East entrance of the strait between Penmon and Puffin Island marked by Penmon Lighthouse and the Perch. It's also possible to find deep water on the other side of Puffin Island but there is a bank extending Eastward from the Southern tip of the island . There is a swatchway, which dries almost directly from Conway to the aforesaid transmitter aerials.
With regard to the Penmon Lighthouse, I don't know if it's possible to navigate inshore of it myself but I do know a yacht hit rocks trying to do it. It does display the hint "No Landward Passage" written clearly on it but yes, it might be possible.I know that during the 2008 round Anglesey race a yacht hit an outlier rock on the seaward side of Penmon lighthouse and was badly damaged,
 
Re: GPS \"hole\" where??

Don't know about the places mentioned in the RYA mag article, but I know of one area quite near Hong Kong, where for several miles no GPS will work. Been through there several times, and on each occasion all three GPSs (different makes, wired and portable) just stop working. Probably deliberate jamming by Chinese military.
 
Re: GPS \"hole\" where??

Way I read it Danny, there arent any holes - thats just non technical journo stuff. All the article seemed to say was that GPS was subject to electronic interference if there was a nearby emitter of noise on a similar frequency. Like SWMBO's vacuum cleaner interefering with the TV.

So really it was someone "bigging it up" to tell you what you already know anyway, and pointing out that in some specific locations there was a transmitter having this effect.
 
Re: GPS \"hole\" where??

[ QUOTE ]
So really it was someone "bigging it up" to tell you what you already know anyway, and pointing out that in some specific locations there was a transmitter having this effect.

[/ QUOTE ]

I thought a very useful article - of course I knew about GPS Holes / Interference........as had it off the east coast of Jersey enroute to France on the odd occassion. But wasn't aware (hadn't noticed?!) the same problem near St Malo. I blame the French /forums/images/graemlins/grin.gif

But not everyone is aware that GPS <u>can</u> be less than 100% perfect. even if 99.99% so......indeed especially with a coloured pictured attached I suspect that some folk treat the GPS signal as if it came direct from God /forums/images/graemlins/tongue.gif Therefore IMO useful to add a note of caution.
 
Re: GPS \"hole\" where??

Not only GPS .... run a boat up east coast past Great Yarmouth with a radar set and wait for the spiking on the screen. Girt big defence radars covering N.Sea and N.Europe do wonders for the shipping radars ! When I was woking seismic from GY - we had it near continuous for large area as we were heading out to shoot area.
 
Re: GPS \"hole\" where??

[ QUOTE ]
Where? I know that there's a north-east and a south-west end, or possibly just an east or west end to the straits. But a 'north-west' entrance? Would that be near Puffin Bar or Caenarvon Island?

Can anyone clarify this, please?

[/ QUOTE ]

'Tis marked on the chart:

puffinis.gif


I haven't got the actual chart to hand, but I'm pretty sure that this area relies on soundings made about 150 years ago. A few men in a wooden sailing boat with a sextant and a lead-line hold up remarkably well against dozens of nuclear powered satellites and microelectronics, don't you think? /forums/images/graemlins/wink.gif

And just 'cos someone above mentioned it, the route through to Conwy is Penmaen Swatch towards the bottom of the picture.


Andy
 
Re: GPS \"hole\" where??

[ QUOTE ]
I don't have cutting edge leccies on me boat.
Or even my previous one.
The 'Gadgett' I have now is a Geonav 6 plus.
Bought secondhand from a previous poster on this thread !! ?
The 'Gadgett' has gone wonkey on Me about this spot from time to time.
On numerous occasions I have cursed said poster!

[/ QUOTE ] Yes, it took me ages to reprogram it to do that.
 
Re: GPS \"hole\" where??

[ QUOTE ]
I understand there are occasional experiments with jamming GPS signals that can affect this area. They are published in Notices to Mariners and NOTAMS.

There is no permanent "Hole" in GPS coverage anywhere.

[/ QUOTE ]

I'm pretty sure this is true - there are areas of poor reception (between skyscrapers) and there are areas where jamming may occur. There are no permanent "holes" and it isn't possible for the operators to degrade the signal locally in any meaningful way.

GPS is equally accurate at the poles as it is at the tropics or the equator (WAAS excepted).
 
Re: GPS \"hole\" where??

However, GPS jamming is possible. At a Trinity House visit recently we were given a presentation on the subject and shown the results of their experiments off Scarborough I think. The jamming transmitter was only a few watts ( I don't remember exactly but it was pretty small) and caused GPS obliteration over quite a large area, but more importantly, a zone of confusion at the edges. They are seriously looking at e Loran as a backup.
 
Re: GPS \"hole\" where??

[ QUOTE ]
[ QUOTE ]


[/ QUOTE ] Yes, it took me ages to reprogram it to do that.

[/ QUOTE ]

I thought so!

As an Arab 'friend' once said to Me when I upset Him
'May the fleas of a thousand Camels lie in Your Mother's bed'!
/forums/images/graemlins/grin.gif
 
Re: GPS \"hole\" where??

A useful article by the RYA. The statement "SA [Selective Availability] is still a system capability of GPS and the random errors could, in theory, be reintroduced at any time" is factually correct for the time being. However the Block III satellites, due for launching from about 2013, will not have an SA capability. The Galileo club might wish to note http://www.insidegnss.com/node/200 before using SA as a lever to extract even more funding from the EU agriculture budget.
 
Re: GPS \"hole\" where??

There is an article on the Trinity House GPS Jamming trials off Flamborough Head that you refer to at http://www.insidegnss.com/auto/janfeb-gnss-solutions.pdf
An interesting point is that as well as reporting of incorrect positions, tracks and speeds, the jamming disrupted aids to navigation such as dGPS corrections, AIS and synchronized lights. Presumably the latter rely on GPS timing.
 
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