Thanks, Joe! Good info. Andrew NO6E Sent from BlueMail
On Dec 6, 2018, 09:22, at 09:22, Joe Taylor <j...@princeton.edu> wrote: >Hi all, > >A number of comments and questions have appeared here recently >concerning the parameter DT displayed by the WSJT-X decoders. > >K6AVP: >> Only a few have posted what range of DT’s they mostly see ... > >K9YC: >> My memory is routinely seeing DTs in the range of +/_ 200msec, with >occasional outliers up to 2 sec or so. > >AI4FU: >> I would be most interested to hear if you tried pushing the limits of >how far out of sync you could push things and still manage decodes. > >NX6D: >> I see “DT” values that range from about 0.0 to about 0.5 in my >system. > >... etc. > >Positive DT means that a signal arrived late according to your >computer's clock. For example: if the computer clocks at both ends of >an EME QSO are bang on, the decoded EME signals will show DT = 2.5 s, >because the EME path delay is 2.5 s. Terrestrial propagation delays >are >a few tens of ms or less, so the DT values most of us see in HF >operating are caused by latencies in our audio systems, context >switching delays in our operating systems, and -- most importantly -- >clock errors in one or both computers. > >Because people have been asking about it, I compiled histograms of the >distribution of DT values extracted from decodes in my ALL.TXT file >from >two recent dates. The first was a few weeks ago, using WSJT-X v1.9.1. >The second was during the FT8 Roundup, last weekend, using WSJT-X >2.0-RC5. I limited the time ranges so that each data set had exactly >the same total number of decodes, 65010. > >The distribution of DT values for these two data sets are shown by red >and purple curves in the attached plot. Most decodes have DT in the >range 0.0 to 0.3 s. The bug in RC5 that eliminated decodes with >negative DT is clearly evident in the plot: the purple line cuts off to > >zero to the left of DT=0. > >I operated in the FT8 Roundup with "Save all" checked, so it was easy >to >reprocess all of those saved files with the soon-to-be-released >WSJT-X 2.0. This produced another 5290 good decodes -- essentially the > >previously missing ones that have negative DTs. > >The FT8 decoder tests for DT values from -2.5 to +2.5 s. As these >results show, most FT8 users keep their computers "on time" to within a > >few tenths of a second. > > -- 73, Joe, K1JT > > -- 73, Joe, K1JT > > >------------------------------------------------------------------------ > > > >------------------------------------------------------------------------ > >_______________________________________________ >wsjt-devel mailing list >wsjt-devel@lists.sourceforge.net >https://lists.sourceforge.net/lists/listinfo/wsjt-devel
_______________________________________________ wsjt-devel mailing list wsjt-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/wsjt-devel
