GPS Signals Poole Bay/Radar Jamming

[Robin]

Over the weekend and last weekend our Raytheon 114 dGPS has lost it's signal several times. It finds itself again within a minute or so but is off just long enough to make the electronic plotter go on strike and switch off the 'route' loaded, irritating because re-loading the route starts it back at WP1 and you have to keep pressing 'next leg' to get back to where you are along the way, plus the 'off track' now starts again, previous data now gone. We have a 2nd fixed GPS that went off at the same time as the other one time but not the others, though if the position is lost only momentarily I doubt I would notice on this set.

I had assumed a fault in the GPS, but then I listened to the Nav warnings on VHF and there is one for a 'RADAR JAMMING EXCERSIZE' in Poole Bay, daily 0900 to 1700 in 15 minute chunks 16th -27th June and the Lat/Longs given correspond to where I have had a problem.

Has anyone else had this? I need to be sure before I start the long long process of un-wiring the Raystar to send it back!

What is a radar jamming excersize anyway and who is doing it from where? Nobody asked me if I minded!

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[blackbeard]

Can't help with this query, but I've had a GPS problem recently ... it seems to not want to work near Newtown or Lymington. Fine everywhere else (including Poole). Has anyone else experienced this? is there a logical explanation?

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[Robin]

Poole Bay was the locality given in the WZ nav message, the Lat/Longs given gave a line running from (memory, left figs on boat) SE from Bournemouth to SW of Needles. It does not specify what the width of the jamming beam is. Certainly my first problem was on the line or very close, subsequent ones have been wide of that line.

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[nicho]

Last Tuesday I got a "position fix lost" warning twice, once in the Hamble, and again in Southampton Water - having switched the unit off and on again, I immediately got the signal back. I wordered if there is some kind of jamming going on with the Hythe and Marchwood military bases. Left it on all day on Wednesday (in Hythe Marina) and it was OK. I must admit I presumed it was a GPS receiver problem (Raymarine), as my original one failed totally on it's first day and had to be replaced, but now I'm not so sure.

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[Twister_Ken]

WD40

Few people except my mum can claim to be as non-technical as me, but surely radar (and thus radar jamming) and GPS work on different freqs. otherwise there would be no end of hullabaloo, crashes, etc.

More likely to be a dodgy set. Give it a squirt of WD40 - that seems to fix most things.



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[tcm]

Re: un-jamming the radar

Putting wd40 on would definitely stop the the radar from jamming, same as door hinges.

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[Robin]

Mine is also Raymarine and also was replaced after total failure early on. Like you it seems to run all day OK if left running in our berth. When it loses a fix (3 times in 3hrs) it will find it again very quickly, but not quickly enough to stop the plotter (also Raytheon) from switching off the set route and sounding the warning alarm. Our second GPS seems to keep going OK but then is not connected to the plotter and may tolerate a loss of position for a longer period before setting off it's alarm. On one occasion however BOTH sets lost position simultaneously.

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[Robin]

Re: WD40

Yes, totally different frequencies. However 'stray' interference from VHF sets is known to upset GPS signals if the GPS aerial is too close (NASA DSC set in wheelhouse, GPS aerial on top of wheelhouse on a friends boat), the signal strength dropped dramatically when the VHF was receiving as well as transmitting. The WZ warning said it could interfere with radars in the area and the installion instructions for the GPS aerial says do not mount it in the path of radar transmissions from on board radar. Also this is a short period loss, a few minutes at most and usually less but long enough for the plotter to consider that it should turn off the follow route and require you to replan it, losing any accumalated data such as cross track so far in the process.



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[Robin]

Re: PS

Spoke to specialist dealer who said microwaves have been known to affect GPS, microwave signal links in this case and the North Sea oil rig areas apparently were problem spots. Shipmate GPS aerials were apparently designed to combat this effect and this is our no 2 set, affected one time but mostly OK otherwise.



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[petery]

The Governement always tell the truth...

I suppose the Government would tell us if they were testing GPS jamming as well as radar jamming... they would - wouldn't they? Perhaps they re-commissioned the Russian units they found in Iraq!!

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