[time-nuts] More Z3801/Tbolt comparisons

John Green wpxs472 at gmail.com
Thu Sep 3 19:05:02 UTC 2009

Yesterday, I thought the Tbolt was wandering around too much. So, I did a
factory reset and started a new 5K
fix self survey. At about the same time, I started a new self survey on the
Z3801 thinking that if they were
 both looking at the same satellites with the same antenna at the same time,
they might be closer together.
When I arrived back at work this morning, I looked at the final positions
they had arrived at. The latitude
difference was .000017 deg. and Longitude was .000026 deg. Great. This is
probably within the margin of error
of how they report. But, the altitude was 36.05 meters different. That, I
can't explain. I have been looking
at the time difference all morning and it seems to cycle +/- 6 ns every
couple of minutes. It also seems to move
maybe 30 nsec every hour or so.This also seems to be cyclic. I also see
sudden jumps of around 4 to 5 nsec. I
assume this is due to DAC voltage corrections. I thought some of this might
be due to the Z3801 since I was using
it as the reference to the 1992. I switched back to the internal reference
and couldn't tell any difference.
 Could some of this still be the 1992? I noticed the Tbolt was set to not
look at any satellites below 10 deg.
I changed that to 0 deg. like the Z3801 and it didn't seem to make a
difference. I am going to let a Rb start
warming up and use it as a reference later to see if some of what I am
seeing is the Z3801. Anyone have any ideas
why the altitude is so much different? I am going to look at a topo map to
see what it says. I might also change
the disciplining constants of the Tbolt to see if it makes a difference. I
can always do a factory reset later.  None of this is
meant to say that the Tbolt isn't as good as the Z3801. I just wanted to see
what they looked like compared to each other.
To folks used to seeing charts and exact numbers these casual observations
may be a bit annoying. I haven't
yet been able to use the GPIB facilities of my 1992. Hope to later. These
are only meant to be casual
 observations. Though I trust what I see and read from my instruments, these
aren't meant to be written in stone or quoted
as specifications. Just some things to think about.

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