I just wondered how good satellite reception is on a Tom Tom or similar sat nav, in fog?
I have an old school Garmin Etrex Vista GPS which I've had for years; from experience I know it doesn't find and lock onto satellites as well as a Tom Tom, but usually still works adequately in bad weather. But on Tuesday I was driving in thick fog, on Wednesday in less-thick fog, trying to find addresses in unfamiliar areas, and could get no satellite reception whatsoever. I managed without the GPS, but it would have been handy and made me wonder "is everyones Sat Nav bad in fog or is it just mine". Yesterday in clear weather it worked fine so there is no fault with the GPS.
From my point of view there are not enough foggy days per year for it to be a problem, I'm just curious...
Cheers,
Rich.
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Any sat nav should work perfectly well in fog. GPS, after all, is used as an aid to navigation and shipping the world over relies on it in poor weather.
The reception problem you describe is more likely to be caused by the Garmin unit having a lower power receiver that is unable to lock on satellites when the ariel is close to the ground and obscured by buildings, whereas the Tom Tom will have been designed with this in mind.
My Garmin 760C isn't able to lock onto satellites when indoors at ground level, but works fine on the first floor, or outside, for the same reason. But it was bought for use in the cockpit of a boat, so I'm not complaining!
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I have a Garmin Streepilot III and reception is affected by fog. As you say thick fog is a rarity, but on one journey it consistently gave our position away from the roads we were on.
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I have a couple of sat-nav units and reception is slightly affected by poor weather - in heavy fog, rain or snow I usually get fewer satellites. I guess the signal is being absorbed by the water vapour. One receiver is a SIRFII chipset and the other a new SIRFIII unit - both are affected to some extent. Best reception is with a cloudless sky. I always have enough sats to navigate though...
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With the correct antenna they nearly all work correctly,ships navigate in thick fog and planes land in fog using gps if you had a good roof mounted antenna it would solve your problem.
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i dont need to repeat my non interest in sat nav systems, but if reception is poor when you need it most????????
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i dont need to repeat my non interest in sat nav systems, but if reception is poor when you need it most????????
Well, navigation still works fine, but the signal is just a little weaker so less satellites showing. Its not really a problem, just an observation.
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if you had a good roof mounted antenna it would solve your problem.
True, but its not really a problem since I always get a minimum 3 sats. There is more of a problem when driving under tree foliage.....
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if you had a good roof mounted antenna it would solve your problem.
I know that is a problem with mine, it has a compact internal antenna and no provision for connecting an external antenna, its renowned for not getting as good a satellite signal as other makes get. When I bought it I wanted a lightweight handy one with walking/ hiking use in mind; in hindsight I should have gone for better reception, bigger screen, etc. Just wondered how other makes/ models compared with my Etrex.
Also I think my car (Saab 9-3) has a metallised windscreen, which is a known problem for satellite reception, but mine usually works okay in most weathers.
I'll have to treat myself to a new one!
;o)
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I see that Makro are now selling the full Tom Tom range.
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Often the GPS is mounted in an unswept area of the windscreen and the water droplets forming on the glass can attenuate the signal. This shows up on mine as perfectly all right on the move, i'e' water running off, but stop and the satellites slowly drop off. You are talking very very small signal strengths here. Not tried mine in the snow yet. Navman 570 with Smartmap V5
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With the correct antenna they nearly all work correctly,ships navigate in thick fog and planes land in fog using gps if you had a good roof mounted antenna it would solve your problem.
I agree about the ships, but have to correct you on the planes, the approach control and blind landing is all radar controlled and GPS has nowt to do with it.
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LeighB
Correct for now - but read this:
www.gpsworld.com/gpsworld/article/articleDetail.js...5
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Thanks for the link, very interesting and seems to be the way to go.
I guess that would be the end to "selective availability"?
The US military would just have to accept that all the world is depending on accurate GPS data that cannot be downgraded on a whim.
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I agree about the ships, but have to correct you on the planes, the approach control and blind landing is all radar controlled and GPS has nowt to do with it.
Precision approach radar is no longer available at most civilian airports. Blind landing is carried out using the aircraft's Instrument landing System (ILS) which locks on to radio beams for runway line up and glideslope broadcast from the ground. Controllers direct the aircraft to intercept the ILS beams using radar.
The planes are quite capable of self positioning to the ILS using GPS or other systems but radar allows tighter separation to optimise the traffic flow.
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Fog 'shouldn't have a massive effect on the GPS downlink, however heavy rain definately would. Speaking as having had 14 years experience in radar and x-band satellite comms.
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