Bob from the screenshot what is it that shows the GPS reception as very wrong. just curious.
-=Bryan=- > From: [email protected] > Date: Wed, 22 Apr 2015 18:33:09 -0400 > To: [email protected] > 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 <[email protected]> wrote: > > > > On Wed, Apr 22, 2015 at 1:47 PM, Bob Camp <[email protected]> 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 <[email protected]> wrote: > >>> > >>> On Tue, Apr 21, 2015 at 4:25 AM, Charles Steinmetz > >>> <[email protected]> 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 -- [email protected] > >>> To unsubscribe, go to > >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > >>> and follow the instructions there. > >> > >> _______________________________________________ > >> time-nuts mailing list -- [email protected] > >> To unsubscribe, go to > >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > >> and follow the instructions there. > > > > > > > > -- > > Pete Stephenson > > <tbolt2.gif>_______________________________________________ > > time-nuts mailing list -- [email protected] > > To unsubscribe, go to > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
