Hi all The equatorial area of the Atlantic is prone the severe tropo ducting, the D4C beacon was heard for several hours last year in the Caribbean . I suspect if the path claimed did go it would be a higher signal level, and Joe’s conclusions are correct. This does demonstrate the need for more trans Atlantic beacons. I think we have all looked at Hepburns maps and seen the intense tropo enhancement in that area, maybe like me wishing it would be like that over Europe . IMO that path will go somewhere between the two tropics, just a case of two stations being in the right place at the right time, and deep search or priori wont be needed.
On Thu, 6 Oct 2016 13:35:45 -0400 Joe Taylor <j...@princeton.edu> wrote: > Hi Dani, > > Dani EA4GPZ wrote: > > 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. > > Evidently you have not seen the messages I posted yesterday to > "wsjtgroup". For completeness they are copied below. > > I believe V51PJ and PY1MHZ have been unaware of the way decodes using a > priori information should be used, and consequently they have been > fooled by false decodes displayed by whatever unreleased version of > WSJT-X they were using. > > -- 73, Joe, K1JT > > > -------- Forwarded Message -------- > Subject: Re: [wsjtgroup] thanks to the software team > Date: Wed, 5 Oct 2016 09:57:29 -0400 > From: Joe Taylor j...@princeton.edu [wsjtgroup] > <wsjtgroup-nore...@yahoogroups.com> > Reply-To: Joe Taylor <j...@princeton.edu> > To: n...@mtcmobile.com.na, WSJT Group <wsjtgr...@yahoogroups.com> > > Dear Pieter V51PJ, > > I do not in any way wish to throw cold water on your attempts at > trans-Atlantic communication on 2 meters, but I would like to be sure > you understand what has been accomplished. > > Evidently you are using an unreleased version of WSJT-X built from the > development branch of our open source code. The QRA64 mode there is > functional but not yet yet fully complete, and some details of its use > are not yet documented. > > Apparently both lines of decoded text shown in the screen shots I've > seen are flagged with the number "8" at the end of line. This indicator > shows how much "a priori" information (if any) has been used as part of > the decoding procedure. > > In case it would be useful, here is some (internal) documentation from > our source code describing the end-of-line return codes from the QRA64 > decoder: > > /* > Return codes: > -16 Failed sanity check > -2 Decoded, but CRC check failed > -1 No decode > 0 [? ? ?] AP0 (decoding with no a-priori information) > 1 [CQ ? ?] AP27 > 2 [CQ ? ] AP42 > 3 [CALL ? ?] AP29 > 4 [CALL ? ] AP44 > 5 [CALL CALL ?] AP57 > 6 [? CALL ?] AP29 > 7 [? CALL ] AP44 > 8 [CALL CALL G] AP72 > */ > > The information here is rather cryptic, intended for our own programming > use. But in short, the "8" flag means that the content of your > transmissions could be determined (and verified with the transmitted > message's cyclic redundancy check) only because its plausible content -- > in this case, two callsigns and a grid locator -- were known in advance > to the receiving software. (Of course, this known information is always > available for a scheduled QSO attempt.) > > For our weak-signal software development we have been using the > following somewhat "official" definition of a minimum valid QSO, which > appears in the IARU Region 1 VHF Managers Handbook: > ######################################################################### > 7.1 Minimum Requirement for a valid QSO (Vienna 2007) > > A definition for a valid QSO on VHF and on higher bands is: > > A valid contact is one where both operators during the contact have > > (1) mutually identified each other > > (2) received a report, and > > (3) received a confirmation of the successful identification and the > reception of the report. > > It is emphasized that the responsibility always lies with the operator > for the integrity of the contact. > ######################################################################### > > It seems to me that your exchanges with PY1MHZ may have satisfied item > #1 in the above list. Now, you need to persist and exchange some > previously *unknown* information, such as a signal report, followed by > an acknowledgment -- and then you will have made a truly record-breaking > QSO! > > In passing, I should also caution you and others not to take the dB > signal reports produced by our existing code too seriously. At the low > end of the S/N range for marginal signals, say below -28 dB for QRA64, > the uncertainty of S/N estimates gets very large. > > -- 73, Joe, K1JT > > -------- Forwarded Message -------- > Subject: Re: [wsjtgroup] thanks to the software team > Date: Wed, 5 Oct 2016 10:50:11 -0400 > From: Joe Taylor j...@princeton.edu [wsjtgroup] > <wsjtgroup-nore...@yahoogroups.com> > Reply-To: Joe Taylor <j...@princeton.edu> > To: WSJT Group <wsjtgr...@yahoogroups.com> > > Hi Andy and all, > > G4JNT wrote: > > I'm puzzled by the quoted -36 and -37dB S/N reports. These seem way > > too low even for QRA-64 mode. > > Perhaps this is a good time to remind everyone that estimates of > signal-to-noise ratios for very weak signals *always* have an associated > (if unexpressed) uncertainty. When S/N is quoted in dB, this can have > important consequences. > > In a stochastic (noise-like) process, experimentally measured values > will be scattered around the unknown "true" value; some will be pretty > accurate, some too high, and some too low. > > Suppose a signal's true S/N (in the detection bandwidth) is equal to > 1.0. In a series of measurements of that signal, some of the estimated > ("measured") values will be close to 1; some will be higher, maybe as > high as 2 (or even more), and some will be as low as 0 (or even less). > These are *linear* values of S/N: estimated ratios of signal power to > noise power. > > When the S/N is expressed in dB -- a logarithmic scale -- you quickly > see the problem. A perfectly plausible estimated S/N=0.1 means that in > dB, S/N_dB = -10 dB. At S/N=0 we get "minus infinity dB". > > Some people think it's a big deal when they see a JT65 decode displayed > with an estimated S/N_dB of, say, "-30 dB". This is nothing more than a > statistical fluctuation of noise and an illustration of the nature of > logarithms. > > -- 73, Joe, K1JT > > ------------------------------------------------------------------------------ > 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 > wsjt-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/wsjt-devel -- -- Best wishes /73 Richard Bown Email : rich...@g8jvm.com HTTP : http://www.g8jvm.com nil carborundum a illegitemis ################################################################################## Ham Call: G8JVM . QRV: 50-432 MHz + Microwave 23 cms 140W, 13 cms 100W & 3cms 5W Maidenhead QRA: IO82SP38, LAT. 52 39.720' N LONG. 2 28.171 W QRV VHF 6mtrs 200W, 4 mtrs 150W, 2mtrs 400W, 70cms 200W OS: Linux Mint 18 x86_64 on a Dell Inspiron N5030 laptop ################################################################################## ------------------------------------------------------------------------------ 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 wsjt-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/wsjt-devel
