[time-nuts] Tuning a Trimble Thunderbolt

Bryan _ bpl521 at outlook.com
Fri Apr 24 01:14:40 UTC 2015


Bob from the screenshot what is it that shows the GPS reception as very wrong. just curious.

-=Bryan=-

> From: kb8tq at n1k.org
> Date: Wed, 22 Apr 2015 18:33:09 -0400
> To: time-nuts at febo.com
> Subject: Re: [time-nuts] Tuning a Trimble Thunderbolt
> 
> Hi
> 
> Looking at that screen shot, something is *very* wrong with your GPS reception. Your GPS
> is 10X worse than it should be. 
> 
> > On Apr 22, 2015, at 9:37 AM, Pete Stephenson <pete at heypete.com> wrote:
> > 
> > On Wed, Apr 22, 2015 at 1:47 PM, Bob Camp <kb8tq at 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.
> 
> I would bet that the amp on the “Oncore” antenna is oscillating. It may do it
> intermittently. The frequency may swing back and forth through the GPS band. It
> may be the source of your GPS problem. 
> 
> Bob
> 
> > 
> > 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 <pete at heypete.com> wrote:
> >>> 
> >>> On Tue, Apr 21, 2015 at 4:25 AM, Charles Steinmetz
> >>> <csteinmetz at 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
> >>> _______________________________________________
> >>> time-nuts mailing list -- time-nuts at febo.com
> >>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> >>> and follow the instructions there.
> >> 
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> > 
> > 
> > 
> > -- 
> > Pete Stephenson
> > <tbolt2.gif>_______________________________________________
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> > and follow the instructions there.
> 
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