[time-nuts] More Z3801/Tbolt comparisons

WB6BNQ wb6bnq at cox.net
Thu Sep 3 19:19:03 UTC 2009

Hi John,

With regard to the altitude, what I have found is that it is never close !  I
have seen variations all over the scale.  What I did here is determine, to the
best of my ability, from TOPO maps what my altitude is and measure the height of
the antenna off of the ground where it is mounted and manually enter that number.


John Green wrote:

> 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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