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....@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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