[time-nuts] Thunderbolt Height Error

"Björn Gabrielsson" bg at lysator.liu.se
Mon May 18 12:46:42 UTC 2015


Hi Demian,

Did you make sure the altitude/height is using the same reference?

The GPS system measures relative an ellipsoid approximation of the earth.
Sometimes this is used in receiver output messages.

To translate this to "Mean Sea Level"/geoid you need to apply a location
dependant correction.

The GPS receivers will happily emit both height measures in different
messages, its important to understand which is used in the specific
messages you are comparing.

Have it better explained in the below url:

   http://www.esri.com/news/arcuser/0703/geoid1of3.html

Also not that height accuracy of GNSS is worse than its horizontal
accuracy by almost a factor of 2.

--

    Björn

> I have 2 GPSDO's. A Thunderbolt and an Arbiter 1083A. The Arbiter is old
> but
> it works fine (and has a Wenzel 5 MHz streamline oscillator in it). It has
> the 1995 firmware issue, and I could get new firmware for it ($$) but I'm
> not using it as a clock, just a frequency source.
>
>
>
> I just moved and have re-setup both. They share an antenna. I got both to
> do
> a self survey. The Arbiter was really close to what Google maps indicate
> is
> my location. The Thunderbolt was about the same except it has me
> underground. The arbiter has the height as +30M. The Thunderbolt as -6M.
> What setting do I have wrong in the Thunderbolt? Would it affect the
> operation as a frequency standard in any way?
>
>
>
>
>
> Demian Martin
>
> San Leandro, CA 94577
>
>
>
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