[time-nuts] altitude difference between two gps

EB4APL eb4apl at cembreros.jazztel.es
Tue Dec 30 00:44:12 UTC 2008


James, 
I suppose the GPS you bought at Sure Electronics is the demo board with 
the Skylab module.
Did you made any test to know if  it has a reliable PPS output that can 
be used for timing?  I´m considering to buy one.

Your question about the height difference is almost sure due to 
different datums in each receiver, as others had pointed out.

Best regards,
Ignacio, EB4APL


James R. Gorr wrote:
> Hello everyone!
>
> I have a tbolt that I am monitoring with tboltmon.exe and some off-brand 12 channel GPS (I bought from Sure Electronics on eBay) that I am monitoring with VisualGPS.  Both are fed from the same GPS antenna through a symmetricom splitter.  There is a 30 meter difference in the altitude readings between the two.  My tbolt says my altitude (after a self-survey) is ~761 meters and the 12 channel Sure Electronics GPS says my altitude is ~791 meters after 7,500+ readings.  I took my hand held Garmin 12XL outside and it says my altitude is ~790 meters at street level.
>
> Anyone have an idea why my tbolt might be reading different from the other two devices?  I am assuming the tbolt is reading low. 
>
> Jamie
>  




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