El 06/10/16 a las 16:53, Dani EA4GPZ escribió: > Hi all, > > Probably we've all heard about the recent 2m QRA64 transatlantic contact: > > http://www.arrl.org/news/transatlantic-contact-completed-on-2-meters > > What I find a bit strange is the signal reports of -36dB and -37dB SNR > that they give. Even though QRA64 is quite good, I would expect that > it's almost impossible to copy QRA64 signals at -36dB. > > I haven't seen sensitivity graphs for the QRA64 mode that has finally > made it into WSJTX, but looking at the graphs in Nico's paper: > > http://microtelecom.it/qracodes/QRACodes-Rev10.pdf > > it seems that it's almost impossible to copy anything below -31dB or > -32dB, even with lots of a priori info for the decoder. > > What do you guys think? Are the recordings of the contact available?
I answer myself: I've being doing some simulations with qra64sim. It seems that wstjx always reports less SNR than the value set in qra64sim. I've generated 100 QRA64B signals at -34dB SNR with qra64sim "CQ EA4GPZ IN80" B 1 0.0 0.0 100 -34 I only get 3 decodes with wsjtx, using a priori info (entering EA4GPZ and IN80 as DX station). The SNR's are -37dB, -37dB and -41dB. For stronger signals (say -25dB or stronger), it seems that the SNR reported by wsjtx is always 5dB less than the value set in qra64sim. So this explains getting reports of -36dB for the transatlantic contact. They probably correspond to signals around -32dB or so. 73, Dani. ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, SlashDot.org! http://sdm.link/slashdot _______________________________________________ wsjt-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/wsjt-devel
