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[aprssig] Re GPS off track

Amir Findling K9CHP sarlabs at twcny.rr.com
Wed Apr 2 20:54:13 UTC 2008


Having looked briefly at the websites you mentioned, the Fortuna uses a 
SirfStar IILP chip and the Globalsat uses a SirfStar III chip. Now if 
you look at the specs The Globalstar with WAAS activate is accurate to 4 
meters vs 10 for the Forutna. The Globalsat is also a 20 channel GPS vs. 
12 for the Fortuna. Finally the Globalsat mentions being EGNOS ready and 
the Fortuna only mentions WAAS.

To me it all indicated the Globalsat is a more accurate unit. Now the 
Fortuna has features the Globalsat does not have.


I once compared a Garmin 60CS (non Sirfstar)  a Garmin 60CSx (Sirfstar 
III) and the difference in locations, holding each unit in one hand was 
in the last digits of the UTM reading, meaning a difference in single 
meters.



    * 73 de K9CHP Amir Findling, Member ARRL, WAC
    * www.K9CHP.net <http://www.k9chp.net>
    * Senior K9 Handler, Cayuga County Highland SAR
    * K9 Certification Tester, NYS Federation of SAR Teams
    * 1st Special Response Group (1SRG)



Phillip wrote:
> Hi Stephen,
>                         The GPSmart is manually set to WGS84 and the 
> Globalsat is default WGS84
> Both are SIRF powered both give the same amount of error I am 
> wondering if there is an error in the chipset .
>  
> http://www.fortuna.com.tw/gpsmart.htm                 GPSmart
>  
> http://www.globalsat.com.tw/eng/product_detail_00000044.htm              
> Globalsat BU-353
>  
> 73 Phillip
> ZL2TZE
>  
> ----------------------------------------------------------------------------------------------------
>  
> Message: 14
> Date: Wed, 02 Apr 2008 02:05:47 -0700
> From: "Stephen H. Smith" <wa8lmf2 at aol.com <mailto:wa8lmf2 at aol.com>>
> Subject: Re: [aprssig] GPS off track
> To: TAPR APRS Mailing List <aprssig at lists.tapr.org 
> <mailto:aprssig at lists.tapr.org>>
> Message-ID: <47F34C6B.9060206 at aol.com <mailto:47F34C6B.9060206 at aol.com>>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>  
> Phillip wrote:
> > Hi,
> >      Have am using a Toshiba Laptop Satellite 2140CDS, AGW engine,,
> > UI-View
> > 32, and a DRSI TNC2 as my mobile tracker
> >
> > I have 2 New GPS units a GPSmart 12 channel  and new today a Globalsat
> > BU-353 SIRF powerd both of them
> >
> > Both these GPs give me an error of 55 mtrs East and 30 North in
> > Google  when
> > checking with www.aprs.if <http://www.aprs.if>   and www.findu.com 
> <http://www.findu.com>
> >
> > I did a track tonight   (02/04/08 NZT)   zl2tze-15 with the new 
> BU-353 it
> > has me not packed at my correct address.
> >
> > On Saturday  ( 29/03/08)  I travelled to Nelson using the GPSmart GPS
> > this
> > also has the same error.
> >
> > Is this a GPS , UI-View , an error in the Google maps  or is it that
> > these
> > cheaper GPS units are not the great ???
> >
> > My correct address is zl2tze-4 on the Maps Google
> > Any help on this will be appreciated
> > 73 Phillip
> > ZL2TZE
> >
> >
> >
>  
> What datum are the GPS units set for?   If they are not set to WGS84
> (WORLD Geodetic System 1984) mode, you will see hundreds of feet error.
>  
> This is a constant issue in the U.K. where many paper and electronic
> maps use the British Ordinance Survey datum rather than the WGS84 datum
> that is native and default on most GPS devices.    Google Maps (used by
> both findu and aprs.fi) are aligned with the world-wide GPS-inspired
> WGS84 datum.    Many British APRS users set their GPS units to use the
> UK ordinance datum to make posits line up on their own maps;  only to
> see major errors when they view themselves on Findu or aprs.fi.
> I would guess that Australia and New Zealand may also suffer from this
> problem of a "local" datum in use rather than the world-wide WGS84.
> (The Brits established numerous local datums during the centuries of the
> British Empire in places all over the world.)
>  
>  
>  
>  
> --
>  
> Stephen H. Smith    wa8lmf (at) aol.com
> EchoLink Node:      14400    [Think bottom of the 2M band]
> Home Page:          http://wa8lmf.com  --OR--   http://wa8lmf.net
>  
> NEW!   World Digipeater Map
>   http://wa8lmf.net/APRSmaps
>  
> JavAPRS Filter Port 14580 Guide
>   http://wa8lmf.net/aprs/JAVaprsFilters.htm
>  
> "APRS 101"  Explanation of APRS Path Selection & Digipeating
>   http://wa8lmf.net/DigiPaths
>  
> Updated "Rev H" APRS            http://wa8lmf.net/aprs
> Symbols Set for UI-View,
> UIpoint and APRSplus:
>  
>  
>  
>  
>  
>  
>  
>  
>  
>  
>
> 	
>
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