[time-nuts] altitude difference between two gps

[Ed, k1ggi]

On the thunderbolt, what datum do you have selected in Setup > Packet Masks
and Options? If it is 0 (WGS-84), try 2 (NAD-27).
-30m is about right for the geoid height around Las Vegas.
Ed, k1ggi

-----Original Message-----
From: James R. Gorr [mailto:n3toy at yahoo.com] 
Sent: Saturday, December 27, 2008 9:26 PM
To: time-nuts at febo.com
Subject: [time-nuts] altitude difference between two gps

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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