[time-nuts] altitude difference between two gps

[James R. Gorr]

It does appear to be a datum issue.  Although I never got the two GPS to match exactly, they are still a few meters apart.  I did find an older thread on the topic from March also.  Thanks for the replies!

Jamie

--- On Sat, 12/27/08, Ed, k1ggi <k1ggi at arrl.net> wrote:

> From: Ed, k1ggi <k1ggi at arrl.net>
> Subject: Re: [time-nuts] altitude difference between two gps
> To: "'Discussion of precise time and frequency measurement'" <time-nuts at febo.com>
> Date: Saturday, December 27, 2008, 11:12 PM
> 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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