Some of the disagreement has to do with the fact that Two similar topics, each with a different answer are being mixed together here.
Magnus's point: 1) How to make the Tbolt the best that it can be? Answer: Start with a good strong signal and a quiet environment. Said's situation: 2) How to make the Tbolt work the best that it can with a less than optimized existing setup. Answer: Lower the AMU to 1, rise the elevation to 15or20, increase the TC setting to 500 sec. (It will work better than when the factory defaults are use with the #1 case above) Interesting enough, I have both cases with optimized setting running on my bench now and although the #1 is generally about 25% to 50% quieter, It is not always so. About 25% of the time the #2 case is as quiet or quieter. So the less than perfect #2 case is not really a big deal to most. There are much more important things that can be done if one likes to 'tweak & fiddle'. concerning: > that you may not get the performance of the spec-sheet. Not a problem, cause they seem careful not to include any specs concerning this except for the 1e-12 per day average. ws ******************** ----- Original Message ----- From: "Magnus Danielson" <mag...@rubidium.dyndns.org> To: "WarrenS" <warrensjmail-...@yahoo.com>; "Discussion of precise time and frequency measurement" <time-nuts@febo.com> Sent: Sunday, November 22, 2009 5:03 PM Subject: Re: [time-nuts] Thunderbolt reception problems > Warren, > > WarrenS wrote: >>> If you needed to lower your AMU limit from 4 to 2, you are feeding the >>> Thunderbolt a signal level below the intended levels. >> >> True, You MAY be feeding it a signal that is below what the cell site >> recommended High gain outdoor antenna will give it. >> But any conclusion past that sounds like pure speculation. And most of use >> are not using them in cell sites. > > True, but lowering this value should be a warning-sign that you may not > get the performance of the spec-sheet. There where some debate on wither > the signal level was an issue or not. Lowering the AMU limit only lowers > the acceptance level of signal strength for a sat in view to be accepted > for tracking. Regardless how AMU is cooked up (an issue we could ponder > over as a side-track), it remains a signal strength measure. > >> I Can not comment on the other units Magnus referred to that don't work if >> set too low, >> and I can not say what AMU is in the Tbolt >> BUT I can say with certainty that setting it to a value of 1 or 2 with >> 'Tboltmon.exe' version 1.2 works fine >> and 1 works MUCH BETTER than 4 in some setup. >> Looks like the Tbolt software is not so dumb as to use sat signals that will >> screw it up. > > It uses the AMU limit to select among the available sats. It then uses > the T-RAIM to cancel out any outliners among that subset of sats to > churn out which sats is being used for positioning/timing solution. > > The AMU limit is nothing magic, it's only that we don't have a good > reference to what the AMU value is in detail, but we do know that high > values is good and low values is bad. > > Lowering the AMU value as you did is good in the sense that you got more > sats to actively track. It is bad that the signal levels the Thunderbolt > is experience is so low that you need to take that action. Low signal > values means more timing noise and thus more timing instabilty. Having a > few sats is better than none. > > So it is an indication that the unit would like some more gain... 10 dB > or so. > >> 'Trimble GPS Monitor V1-2.pdf' instructions on page 13 shows the "signal >> level mask (AMU) set to 0.6 > > If the statement that AMU is a linear scale is correct, that would mean > that the C/N limit is set 16,5 dB lower than normally, i.e. that C/N > being 16,5 dB lower can be accepted. > > It would be fun to play around with a variable damper to see what > relationship to level the AMU value is on the Thunderbolt. > > Cheers, > Magnus > > > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.