[time-nuts] altitude difference between two gps

[James R. Gorr]

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