Re: GPS underwater
From: Peter (prathman_at_comcast.net)
Date: 01/23/05
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Date: Sun, 23 Jan 2005 07:24:31 -0800
Jack Erbes wrote:
> Stan Gosnell wrote:
>
>> Even the water in your hand will block GPS signals. Putting your hand
>> over a GPS antenna completely stops it from receiving anything.
>> Actually, even a rather thin film will do it, such as the rain on your
>> car windshield.
>
>
> You've not done any research on this have you? Immersion under water
> will severely limit signal reception but I think you're overstating the
> effect for other situations.
My GPS receivers also have no problem getting signals inside my house
or in most heavily wooded areas, but I agree with Stan that just
wrapping my hand around the antennas will effectively block the
signals due to the water content.
>
> Receiver sensitivity will vary from one model to another and the antenna
> type is a key factor in performance. Here is a good discussion of the
> effect of different antenna types:
> http://www.gpsinformation.org/joe/gpsantennaspecs.htm
>
> My Magellan 330M will acquire 3 to 5 satellites and a 3D fix (in 3
> minutes or less) in the basement of my single story home (wood frame,
> composition shingle roof).
>
> In my living room, not near a window or with any line of sight to a sky
> view, it will get a 3D fix much more quickly with 6 to 10 satellites
> visible.
>
> It works well almost anywhere in a fibreglas boat.
>
> It will maintain a fix laying on the transmission console, the
> dashboard, back seat, or rear cargo area in my car (a Dodge Durango).
> The fix may drop to 2D or be lost in an area with tall buildings, in
> tunnels, or on the lower level of multi-level freeways.
>
> It maintains a 3D fix, with an occasional lapse to 2D, strapped to the
> cargo rack on my ATV in heavy woods around my home. If I stop for a
> minute or so in a heavily wooded area with no sky view, it may drop to
> 2D and once or twice Ozi-CE (I am normally using the 330M as a NMEA
> input for Ozi-CE on a iPAQ 3630) has reported no fix for a short period
> of time.
>
> The optimal receiving position for the 330M is when it is held vertical
> or near vertical (the typical position as you hold it and look at it). I
> seldom use mine in that position, and the results above in mobile use
> are with it laying more or less horizontally either face up or down.
>
> Jack
>
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