DPRG mailing list archives: [DPRG] Further Quandries on GPS...

Wed Jan 2 07:55:11 CST 2008

The first thing I would try is a bigger ground plane under the patch
antenna. You should have a minimum of 40mm x 40mm, but anything bigger
is better and it needs to be grounded to vehicle ground. Bigger should
help reduce ground reflections.

Kip

On Tue, 2008-01-01 at 21:18 -0600, Kenneth Maxon wrote:
>  
> Hello DPRG...
>  
> Here is one for further conversation in the "Hmmm...?" realm...
>  
> It was up to a fair 8-deg today and although there is a significant
> snow pack on the ground the sun was bright and the sky was clear for a
> few hours so ProtoBot ventured back out into the back yard for more
> GPS expiremental data gathering.
>  
> This time I made sure that ProtoBot was a full 12 ft away from the
> house and this time, the house does not have a 1/2"~3/4" glaze of ice
> hanging on it.   There is however a 3/4" layer of solid ice under the
> snow back that ProtoBot is sitting on.   I pulled a bonehead move and
> forgot to take my hand held Garmin + adapter & extension cord out to
> verify the readings, however, surprisingly ProtoBot still recorded
> erronous readings, like it was doing inside and in the previous
> outdoor trial up along side the house.
>  
> I have taken time to swap out the GPS module / antenna combination on
> ProtoBot with the spare unit that I'll be using on an upcoming
> project.  And given that ProtoBot's last round of testing performed in
> a similar (although less drastic from an error standpoint) manner than
> did the comercial Garmin unit, I still have a quandry here.   Yes, I
> am still wondering *IF* this could be coming from multipath off of the
> ice layer.  I theroise that it is not as the 10" of snow pack sitting
> on top of the ice should be enough to completely disburse the energy,
> and all of the sattelites reported by the module as being used in the
> actual position calculation had a good signal strength reading.
>  
> I don't know that anyone on this list will have input, however it is
> an interesting quandry that I am working through and I thought it
> might be of interest to the group, as there are others in this group
> that activly use GPS on their robots.
>  
> Of course I'll post futher when I get to the bottom of the issue...
> -Kenneth
>  
> BTW, Ron, the package arrived, thank you.  You didn't have to return
> it but since you did I'll put it to good use in the next project.
> (IE, you've saved me from some eBay surfing).  -Thanks...
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-- 
Kipton Moravec KE5NGX
"Always do right; this will gratify some people and astonish the rest."
--Mark Twain