On Mon 2016-07-25T10:37:12 +0100, Tony Finch hath writ: TVB> Right, for LSEM to work, you'd have to extend the DUT1 limit a bit TVB> beyond 0.9s. Historically, DUT1 has changed from 0.1s to 0.5s to 0.7s to TVB> 0.9s, so I doubt 1.1s or 2.0s would be the showstopper.
At least we know how to lie to the black-box software in our robotic telescope so that it could handle that without rejecting the numbers. > As I understand it the problem with |DUT1| > 0.9s is to do with radio > signal compatibility, e.g. MSF only allows |DUT1| <= 0.8s +/- 0.05s > > http://www.npl.co.uk/upload/pdf/MSF_Time_Date_Code.pdf WWVx has the same 0.7 s limit in its format. This is a result of the way that CCIR Rec. 460 came into being. The original 1969 draft that became 460 allowed leaps of multiple seconds. The 1970 February plenary assembly changed that to leaps of only one second, but Rec. 460 gave no other detail about how to implement the scheme. The 1971 February meeting of CCIR Study Group 7 produced CCIR Report 517 (Question 1/7, Resolution 53) which said maximum deviation of 0.7 s. That's what WWVx and CHU implemented because that's what the BIH had been directed to do. <sarcasm> and the BIH always accomplished what it was directed to do, especially because this directive came not just from an international scientific union but from an international regulatory agency, so no problem the BIH will just do it, right?</sarcasm> Then 1972 came along and BIH found that the reporting of input data to them and their ability to process those data could not keep the DUT1 within 0.7 s. This was pointed out at the 1973 IAU GA, and the 1974 revision of CCIR Rec. 460-1 raised the maximum departure to 0.9 s. Along with that came language that was as close to an apology to the BIH as I have ever seen in such a document. Unfortunately the WWVx and CHU formats were already set with their max of 0.7 s. Despite the recommendation in 460 that DUT1 should be provided, DCF77 has no means for that, so there is another example of an agency not bothering to implement the full text of Rec. 460. Up until 1970 the CCIR recommendations about radio broadcast time signals had been descriptions of techniques already broadly in use and tested for interoperability with existing systems. The one good thing about the ITU-R WRC-15 decision not to decide is that they did not repeat history by producing another recommendation with a prescription that had not been tested for interoperability. -- Steve Allen <[email protected]> WGS-84 (GPS) UCO/Lick Observatory--ISB 260 Natural Sciences II, Room 165 Lat +36.99855 1156 High Street Voice: +1 831 459 3046 Lng -122.06015 Santa Cruz, CA 95064 http://www.ucolick.org/~sla/ Hgt +250 m _______________________________________________ LEAPSECS mailing list [email protected] https://pairlist6.pair.net/mailman/listinfo/leapsecs
