Dear Chris As far as I know, atmospheric effect can not be compensated by looking at satellites from all over the sky and averaging, since it does not have a random nature, rather it introduces bias to the solution. For example, if atmospheric effect is not removed, one can not get a relative position accuracy of sub-meter in long distances even by employing the method of RTK. All I said here is about position. Now, I would like to know about the output of time in this condition. What is the utmost reachable accuracy for a timing output from a GNSS receiver? I do not mean the precision that reflects the noise behavior. I think that the best result is obtained when the receiver supports dual frequency in order be able to deal with ionospheric delay. Am I right? In that case, is there any GNSS receiver with this ability?
Thanks a lot On Thu, May 25, 2017 at 10:01 PM, Chris Albertson <[email protected] > wrote: > The long term stability of GPS is very good. Some one here will point > out exactly how one measures it. But roughly when speaking of > accuracy you always need to specify a time interval. For example > if the 1PPS is "off" by 15ns that is not bad and yes there are much > better systems if you need to measure time intervals on the order of > one second. But if the signal is "off" by 15 ns over 100,000 seconds > that is well, 100,000 time better. > > This is a basic reference and for some specialized end use case you > might couple it with other equipment. Many of the concerns you had, > such as effects of the atmosphere get averaged out because the unit is > looking at satellites from all over the sky. (averaging over space) > And you do git better results with better antenna locations that are > away from multi-path and have a 360 degree view of the horizon. But > notice the unit has an temperature stabilized crystal oscillator that > is stable over many seconds. an is much more stable in the short term > then is a GPS receiver. Trimble uses this crystal to average over > time > > You also have to ask where is the tine data going to be used. Are you > synchronizing a computer's internal clock or trying to measure the > frequency of a microwave transmitter > > SO it falls back to the old thing about there being no "better" only > better for a specific use case. > > Some of use were lucky enough to buy Trimble Thunderbolts, a previous > version of this unit when they were on eBay for $100 each. For those > without 5 digits budget they ar pretty much the Gold Standard. I have > mine installed with a good filtered DC power supply and an outdoor > antenna on mast well above the roofs of surrounding buildings. I > get long term stability of about one part in 10E13. Yes 13 digits > over long periods. (I think?) It is really hard to know because my > measurement system is a little circular referenced > > On Thu, May 25, 2017 at 6:27 AM, Ebrahim Roghanizad > <[email protected]> wrote: > > Dear members > > > > I am a new amateur member in your group. Maybe my question has been > asked. > > Recently I found Trimble Mini-T GG, whose data sheet is attached, as a > good > > GNSS disciplined time reference. I would like to know if there exists a > > more accurate one, since it does not employ dual frequencies to > compensate > > ionospheric delay, though it handles both GPS and GLONASS. Besides, could > > anyone guide me about the presented accuracy in the datasheet? There, it > is > > stated that "When operating in Over Determined Timing Mode, the accuracy > of > > pulse per second (PPS) is within 15 nanoseconds of GNSS/UTC." Does it > mean > > that it includes both bias and the noise? In other words, is it true to > say > > that "The time-synchronization error between two of them with a long > > distance is less than 2*15 ns"? > > > > Best Regards > > > > _______________________________________________ > > 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. > > > > -- > > Chris Albertson > Redondo Beach, California > _______________________________________________ > 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.
