Magnus Danielson wrote: > You can acheive much greater speedup by a combined frequency/phase approach. > You will get a very accurate frequency error estimate, so you will very > quickly be close enought to go into phase lock. At least if your clock isn't > too noisy. So, the lock-in time should not be the major concern, but rather > the behaviour of the full setup when running. Also, another classic trick is > to vary the bandwidth, so you have a much wider bandwidth in the beginning and > then step down towards your target bandwidth as some suitable conditions have > been met prior to the step. > > My concern is that closing the loop faster by itself does nothing, if it is not stable enough. What I meant by being able to close the loop sooner was that the carrier phase data is actually better than the OCXO sooner after power up. I think you or Bruce said the Allan variance of the carrier phase signal could be as good as e-10 in 1 second, or something like that. >> It seems that in this case, the acquisition time of the receiver will be >> the most significant delay. >> > > Your OCXO needs to heat up anyway. You can usually acheive a good GPS lock in > that time. A full-fledge correction would probably require data collected over > some time anyway, so don't fool yourself here. > I was assuming the OCXO remains powered, which is fairly easy to do, but in a transportable application, you cannot guaranty continued visibility of the GPS satellites, or even continued connection of the GPS antenna, when the system has to be transported, and in a hobby application, I am not sure I can design a better set of algorithms to compensate for the OCXO variations than what the Trimble or others have come up with in their GPSDOs (in fact, I am sure I can't), so that holdover will probably not be optimized (read: suck).
Also, I am not sure what happens when you move a timing receiver, I guess the Thunderbolt for instance would have to do a new survey, here goes an hour at best... > >> I guess as a result, it will become more important to have an algorithm >> that effectively filters out outliers. Are there any such things as >> hanging bridges with carrier phase receivers? (I hate asking that >> question...) >> > > Well, the resolution of carrier phase measures is below the noise level, so > whatever errors there would be will be noised out. Also, it is not static as > the satellite orbit and speed of change will practically ensure that there is > no hanging bridge, or at least not for very long. So, effectively no. > > Good > I was kind of expecting that question, it was just a matter of time before it > came up. :) > > Cheers, > Magnus > > Well, hopefully we are done with this one :-) Didier _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts