Re: [wsjt-devel] QRA64 2m transatlantic contact

[Dani EA4GPZ]

El 06/10/16 a las 19:35, Joe Taylor escribió:
> 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.

Hi Joe,

Many thanks for the info. That really explains things.

Silly me, I didn't know about wsjtgroup and I thought all the "action"
happened in wsjt-devel. I'll go suscribe to wsjtgroup also.

73,

Dani.

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Re: [wsjt-devel] QRA64 2m transatlantic contact

[Richard Bown]

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  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] 
> 
> Reply-To: Joe Taylor 
> To: n...@mtcmobile.com.na, WSJT Group 
> 
> 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:
>   -16Failed sanity check
>-2Decoded, but CRC check failed
>-1No 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 
> 

Re: [wsjt-devel] QRA64 2m transatlantic contact

[Daniel Estévez]

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.


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Re: [wsjt-devel] QRA64 2m transatlantic contact

[CT1EKD]

There is a video on facebook at this link:

https://www.facebook.com/py1mhz/videos/10202179138755679/
Where it seems to be during the QSO...

Pedro - CT1EKD




Citando Dani EA4GPZ :

> 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?
>
> 73,
>
> Dani EA4GPZ.
>
> --
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[wsjt-devel] QRA64 2m transatlantic contact

[Dani EA4GPZ]

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?

73,

Dani EA4GPZ.

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