On Wed, Apr 22, 2015 at 1:47 PM, Bob Camp <kb...@n1k.org> wrote:
Hi
Backing up a bit to “getting a TBolt running”.
1) instal Lady Heather and get it connected to the TBolt
2) does it fire up and find any sats?
Yes. It had been working consistently for several days prior to my
first message.
3) are the power supplies holding regulation?
Yes.
4) nail down the antenna in the best fixed location you can find
Done.
5) run the auto-calibration feature in LH
Done. This changed the gain from -5.0Hz/V to -3.132Hz/V and changed
the initial voltage to 0.347V. I switched the time constant and
damping values back to their defaults of 100 seconds and 1.200,
respectively.
6) run a 48 hour survey with LH and write the location to ee memory
Done. The location matches the averaged location surveyed from my
Motorola Oncore UT+ (the antenna for which was about 10cm away from
that for the Tbolt, some no-name mushroom-type antenna) and a handheld
Garmin eTrex 20 (with GPS+GLONASS+WAAS) within a few meters. It also
matches with Google Maps.
In the attached screenshot you can clearly see the field of view from
the antenna's current location over the last ~20 hours.
Interestingly, the Oncore antenna (a cheap patch antenna from eBay)
seems to be causing some intermittent issues with the Tbolt: if the
antennas are too close there appears to be some sort of interference
emitted by the Oncore antenna that makes it difficult for the Tbolt to
lock onto the GPS signal and the Tbolt goes into holdover. Oddly, this
is not consistent: the Tbolt and Oncore had coexisted for a few days
with no problems but today some of the problems started up again.
The same issue occured if the Oncore antenna was too close to my
Garmin GPS 18x LVC. I have since moved the Oncore antenna further away
(it's now about 50cm) and signal reception for the Tbolt is much
better. Weird, but distance seems to resolve the issue, so not really
a problem anymore.
7) Then check the EFC voltage, it should be fairly close to 0V, and not over 2.5
If you are > 2.5, that’s probably a broken unit.
Doesn't seem to be a problem.
8) Now start watching the EFC voltage for a few days and see that it’s leveling
out and not spiking. Again spikes = something broke.
See the attached screenshot. There's a few small EFC voltage spikes
when the unit enters or leaves holdover, but otherwise it seems
reasonably smooth in my (admittedly untrained) view.
Until that’s all done, I would not dig to deep into the workings of the gizmo.
It
needs to be set up first.
Other than the intermittent issues with the Oncore antenna, everything
seems to be working reasonably well -- there's no obvious failures
that I can spot.
Cheers!
-Pete
Bob
On Apr 21, 2015, at 4:30 AM, Pete Stephenson <p...@heypete.com> wrote:
On Tue, Apr 21, 2015 at 4:25 AM, Charles Steinmetz
<csteinm...@yandex.com> wrote:
Pete wrote:
On a related note, is it possible to extract any data regarding the
training from the unit?
Not as far as the time-nuts community knows, no (other than looking at the
DAC voltage and temperature reporting during holdover and attempting to
reverse engineer the prediction algorithm by correlating those with the
long-term DAC voltage -- good luck).
Finishing my PhD is enough work already. I don't think I'll try
reverse-engineering the prediction algorithm quite yet. Perhaps later
in my Copious Free Time(tm)?
Are the training parameters saved periodically to non-volatile memory,
or are they purely stored in RAM and so will be lost if powered down?
If the latter, does the RAM have any provisions for backup power
I doubt it -- mine always act as if they are training from zero if they have
been powered down. Because of the lack of precise retrace of quartz
crystals, I don't think you'd want old (pre-power-down) data, anyway. Some
crystals will even come up drifting in the opposite direction after being
powered down, and they all take some time (days, at least) to settle down
after any disturbance (including power interruptions, however brief).
Ok. It'd be nice if there was some way to keep the crystal going
through power interruptions, even if the oven itself cooled off. I
suspect Trimble (correctly) assumed that the vast majority of these
units were to be installed in cell sites with reliable power so that
wouldn't be an issue.
Alas, the location for the antenna is suboptimal: in the best location
available to me (an outdoor balcony) I have a clear view of the
southern sky from 150-300 degrees (az) and from horizon to zenith with
only a few low-elevation obstructions. However, this is only
accessible in warm months
* * *
The surveyed position is within about 10 meters of the actual location
according to Google Maps and local building information.
That's a problem. Every meter is approximately 3.3nS, so 10m introduces a
+/- 33nS error in the raw data (as much as 33nS closer to some satellites
and 33nS farther from others). Add in the uncertainty due to noise, and you
get easily hundreds on nS of error in the computed solution.
Indeed. I'm running a 48-hour survey with Lady Heather now to see if
that can improve things a bit more.
Unfortunately, you are unlikely to do any better than this with the antenna
location you described. Time to buy a house, with no tall trees nearby.
(You may already have heard that time-nuttiness can be expensive.... ;-)
I won't be looking for a house for at least a few years, but when I do
the skyview is definitely one of the criteria, as is the friendliness
of the community to radio masts.
Cheers!
-Pete
--
Pete Stephenson
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