Hi Indeed the solution is done once per second or so. In the solution they weight the significance of position versus time. If you accept a larger time error in the solution, you can come up with a smaller location error. Is that a bit of mathematical sleight of hand? - of course it is. Can you keep doing it forever? - no you can't. Eventually you need to get the time back up to date.
Put another way - if all that was going on was the same solution process in every receiver - there would be no differences in results. Software is software. The hardware in a low cost timing receiver is the same as the hardware in a low cost "location only" receiver. The difference is the firmware. You can indeed shoot timing firmware into some location receivers and turn them in to timing receivers. Bob On Dec 29, 2012, at 12:14 AM, Michael Perrett <mkperr...@gmail.com> wrote: > Bob, > That is simply not accurate - if the solution rate is 1/second, then all > parameters are solved in that time frame. There are 4 indpendent variables > and minimal processing power is required to solve all four equations. > Although I am not very familiar with commercial receivers, that is what > happens in the Rockwell, Trimble and IEC military units. If the output is > more than once per second it is *usually* an output of the Kalman Filter, > not a "true" measurement. > > Michael / K7HIL > > On Fri, Dec 28, 2012 at 6:20 PM, Bob Camp <li...@rtty.us> wrote: > >> Hi >> >> …. except… A navigation GPS doesn't care much about the time solution. >> Updating the location is a much higher priority than updating the time. The >> typical "solution" is to let the time estimate coast for a while and update >> it much less often than the location. >> >> Bob >> >> On Dec 28, 2012, at 7:18 PM, Magnus Danielson <mag...@rubidium.dyndns.org> >> wrote: >> >>> On 28/12/12 23:35, Bob Camp wrote: >>>> Hi >>>> >>>> The GPS does an estimate against the local crystal frequency. It >> generates the PPS off of it's estimate. The less often it updates the >> estimate the more odd things you see as the crystal drifts. >>> >>> A typical GPS off the shelf solves the position solution every second, >> having a 1 Hz report rate. This includes clock corrections. Some GPSes is >> capable of higher report-rates. >>> >>>> Of course, the crystal can have trouble all it's own. If the crystal >> has a rapid rate of frequency change over a narrow temperature range, the >> GPS simply can't keep up with the crystal. >>> >>> Most GPS receivers only have TCXOs, and even if tossing in an OCXO, >> excessive heat can throw the frequency and hence the GPS solution way of >> the mark. For many GPS reference stations, rubidiums is used to steer the >> internal clock, and the quality of that lock can affect how well it tracks >> it and have secondary frequency issues. >>> >>> So, it comes as no surprise that the GPS module is temperature >> sensitive. The metrology labs measure and compare the temperature stability >> of various GPS-receivers, >>> >>> There are also filters that can provide temperature effects, but the >> TCXO is where it usually hurts most. >>> >>> 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. >> >> >> _______________________________________________ >> 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. >> > _______________________________________________ > 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. _______________________________________________ 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.
