[time-nuts] Thunderbolt Height Error

Brian Inglis Brian.Inglis at SystematicSw.ab.ca
Tue May 19 19:32:44 EDT 2015


If it's not a reporting error as below, you could be getting signal bounce,
making it look as if your antenna is underwater, andreducing the time
accuracy - you could try bumping your elevation mask by 5 degrees,
to see ifyour position improves.

On 2015-05-19 13:45, Dave Martindale wrote:
> Which altitude do you have the Thunderbolt set up to report?
>
> If you have the datum set to WGS-84, the Thunderbolt can report either HAE
> (height above ellipsoid) or MSL (height above the geoid model) in its
> serial output.  The choice is controlled by bit 2 of byte 0 of the 0x35
> command packet.  This can be stored in EEPROM, which determines the
> power-up default.
>
> HAE is mathematically simpler to calculate but bears only an approximate
> relationship to actual sea level.  MSL requires some sort of table (inside
> the GPS receiver) to specify the geoid model, but since it's a fit to the
> actual Earth, the altitude is more likely to agree to what you think of as
> altitude.
>
> Many GPS receivers provide a choice of which altitude they report in their
> output stream, so when comparing two receivers you need to check that both
> the datum and the HAE/MSL altitude choices are configured the same.
>
> This should not have any effect on timing.  The GPS receiver knows where it
> is in Cartesian coordinates in all cases.  Your choice of map datum
> controls the conversion to latitude and longitude that the receiver
> reports, while the choice of HEA/MSL controls the conversion to reported
> altitude, but these choices should affect this output conversion only.
>
> - Dave
>
>
>>> On May 18, 2015, at 2:34 AM, Demian Martin <demianm.pds at gmail.com>
>> wrote:
>>>
>>> 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?


-- 
Take care. Thanks, Brian Inglis


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