[Moon] call3.txt why?

[Wolfgang Schlaffer]

Dear Gentlemen, 

while we are discussing about Deep-Search and what is transmitted on the air or what is coming out of a data-base the next EME expedition gives us advice to feed the call3.txt data-base with the JW5E callsign. 

Excuse me, but I really dont understand why we must enter a "new callsign" 
in a data-base to work them? Whats the reason? 

The instructions are given at: 

http://www.emelogger.com/svalbard/default.asp?page=call3


vy 73 de dl5mae Wolfgang 





--- Klaus DJ5HG <v.d.heide at on-line.de> schrieb am Mo, 21.4.2008:

> Von: Klaus DJ5HG <v.d.heide at on-line.de>
> Betreff: Re: [Moon] WSJT/CW
> An: moon at moonbounce.info
> Datum: Montag, 21. April 2008, 14:57
> Dear Bernd and all,
> 
> 
> let me again comment a mail of Bernd:
> 
> 
> > Dear Hakan and all,
> > 
> > Just for clarification:
> > 
> > (1)
> > JT65 does communicate everything via the air.
> 
> JT65 indeed transmits the full information. The RS and 
> the KV-decoders can retrieve this information, DS cannot.
> 
>  
> > (2)
> > In JT65 DS the callsigns, i.e. "SM7WSJ
> DF2ZC", you are looking for are
> > detected by means of correlation (mathematically
> comparing the weak signal
> > in the noise with signal forms constructed by the help
> of the call3.txt
> > database). Of course the information you are looking
> for is already present
> > on your hard disk, though "SM7WSJ DF2ZC" is
> transmitted and received over
> > the air. The only previously unknown information you
> gather is that the weak
> > signal indeed is one of the constructions with the
> help of call3.txt, so one
> > of the some 1000 combinations. This equals ld (1000) =
> some 10 information
> > bits. The amount of information gathered roughly is as
> high as it is when
> > you receive two arbitrary alphanumerical characters,
> such "A7" for instance
> > as the ld (36*36) = 10,34 bit. If it were 8000
> possible combinations, it
> > would equal some 13 information bits, with 16000
> possible combinations it
> > would equal some 14 information bits, with 64000
> combinations some 16
> > information bits. So with increasing the call3.txt
> database the information
> > bits of a DS decode rise.
> > 
> > However, everything is still transmitted over the air!
> Only, the information
> > you gather is that the weak signal in the noise is one
> of the callsign
> > contructions with the help of call3.txt or not, so one
> of the roughly 1000
> > possibilities. This correlation is a well established
> mathematical procedure
> > used, similar to a "matched filter" which
> only delivers the output one is
> > looking for (if that signal is indeed present on the
> receiver) or nothing at
> > all. Again: The information gathered is "Yes, it
> is one of the 1000
> > callsigns." - or as DJ5HG calls it: an index.
> 
> 
> Nobody questiones that JT65 encodes two callsigns at 
> the transmitting end. But it is to the receiving end 
> what it really receives. It's the same with SSB and 
> CW. What is a measure for a communication path, the 
> information that is sent or the information that 
> actually can be read from the received signal? 
> 
> The DS problem is that it is NOT a decoder which 
> decodes the Reed-Solomon codewords. A very small 
> subset of the RS codewords are chosen (by the list) 
> to generate the corresponding signals that are to 
> be correlated with the received signal. The crucial 
> point is that the DS decoder only can make it's final 
> decision on which of the generated signals fits best, 
> not on the symbols which form the callsigns. The actual 
> index of the best fitting signal then simply is used 
> to address the associated message. So the result of 
> DS primarily is based on a decision out of restricted 
> number of choices.
> 
> I just tried to do the same with a small simulation 
> program with CW. CW was binary coded by '10' and
> '1110' 
> being the representations of dots and dashes. Then a 
> selected callsign was corrupted by 8 different binary 
> errors in each simulation. This makes the call completely 
> unreadable. In a million simulations with
> "decoding" by 
> correlation with signals generated from a subset of the 
> call3 list, 999981 receptions resulted in the correct 
> callsign. So DS by no means does concern the question 
> of WSJT vs. CW.  It only concerns the fundamental question 
> whether we are interested in COMMUNICATION via the radio 
> path or simply in detecting signals while communication 
> goes other pathes.
> 
>  
> > This is very much similar to the well aknowledged (and
> never discussed!!!)
> > sked gain on CW of some 3 dB, or to the fact that when
> you are called by a
> > weak station you nearly always copy your own callsign
> better than the
> > caller's callsign. That is what I meant with the
> memory between the ears. It
> > is always easier to copy "SM7WSJ DF2ZC" in a
> CW sked at a marginal signal
> > strength than on random an arbitrary combination such
> as "SM7WSJ AZ4GOR". We
> > all know that for decades and never put in in
> question.
> 
> The sked never needed such a discussion because there was 
> a consensus that the callsigns must have been exchanged 
> as if they were unknown. In a HSCW meteorscatter contact 
> you must receive enough fragments such that the puzzle 
> only has one solution. A single fragment received on a 
> lonely frequency is not sufficient even though it may be  
> absolutely confident that it came from your sked partner 
> who sent both calls.
>  
>  
> > BTW This means in a sked (CW and JT65 as well) your
> personal call3.txt is
> > just one callsign, "DF2ZC". Therefore you
> gain only ld (1) information,
> > which equals 0 information bits! This applies also if
> you'd copy me with
> > 599, the amount of information bits cannot be
> increased because "DF2ZC" is
> > already present on your personal hard disk in the
> head. Actually, you gain
> > not 0 but 1 bit of information: You now know that
> DF2ZC is really there for
> > the sked which is the only thing you did not know in
> advance.
> 
> Yes that's correct. What we demand for is that the
> deciding 
> stage at the receiving end does not make use of such
> information. 
> The KV-decoder really is independent of the call3 list. If
> you 
> use FSK441 in meteor scatter the decoder also is
> independent of 
> any list. But the operator could cheat. Even if he does
> not, he 
> has the advantage that he may be satisfied by a single
> reception 
> of the calls, while in random QSOs this usually is not
> confident. 
> 
> Indeed, assisting the decision process by prior knowledge
> does 
> work very much better with coding. But that should not be
> an 
> argument for really doing it systematically.
> 
> Finally, I again want to point out that this discussion is
> not on 
> digital vs. CW.  The question is:  What is demanded for a
> valid 
> contact? Is there a demand to communicate the callsigns (or
> only the 
> unknown callsign) via the radio path or is it entirely
> sufficient to 
> get the knowledge via other ways?  In other words:  
> Is the main request of ham radio the simple physical
> detection of 
> signals, or is the main request to establish bidirectional
> radio 
> contacts that communicate a specified minimal amount of
> information?
>    
>  
> > Actually the underlying information theory is even a
> little more complicated
> > as the amount of information gathered is related to
> likeliness. When a
> > rather active station such as W5UN, KB8RQ or S52LM is
> copied the information
> > content is less than for instance when SV1BTR is
> copied calling you on JT65
> > ;-) 
> > I'll leave that out to make understanding easier
> and assume all callsigns
> > are equally likely.
> > 
> > 
> > (3)
> > If you understood (2) correctly you will easily see
> that unlike some guys
> > permanently try to make us believe JT65DS does not
> communicate only two
> > letters of both callsigns via the air to have a decode
> and the rest of the
> > callsigns is added with the help of call3.txt. That is
> rubbish! Those guys
> > such as HB9..., SM2...and others do apparently not
> have the slightest clue
> > how DS works. Yet, that does not keep them from
> repeating incorrect
> > statements.
> 
> If they say "the DS decoder receives information
> EQUIVALENT to two 
> characters" then all is correct.  The information in
> JT65 is coded 
> anyway. So if they really suppressed the word
> "equivalent" there 
> is no possible misunderstanding into a wrong direction. 
> 
> The simulation mentioned above really shows that it even
> works if 
> all received CW-characters are wrong.
>   
>  
> > (4)
> > IMPORTANT! I did not and I will never say that this
> means that people using
> > CW don't receive all characters of a callsign!!!
> Whoever accuses me of doing
> > so does not at all understand what I'm saying. I
> repeat: I confirm all CW
> > friends always copy all dits and dahs in a QSO!!! This
> has no influence on
> > what I'm saying above. 
> > Sadly, there are some guys who are not serious with
> the QSO rules, but in
> > both modes. The cheat on themselves at the end. Also I
> do not say it is
> > acceptable if people exchange QSO details on
> chat/telephone etc before the
> > QSO is complete. I regard a chat as a online contact
> room to solicitate
> > short notice skeds.
> > 
> > I do not intend to go on replying replies to this post
> in public. Should you
> > (or anyone else) have any further questions I'm
> happy to discuss that with
> > you in private emails and leave this off the
> reflector.
> 
> That's a basis we can agree on. Ok, from now off the
> reflector.
> 
>  
> > vy 73 Bernd DF2ZC (JO30RN)
> 
> 
> 
> The WSJT/CW thread also concerns some other aspects which I
> 
> do not comment here. My main concern is to make clear that
> DS 
> creates a general problem. There may be arguments to
> separate 
> CW vs. digital modes. But from the basics, it is even more 
> important to separate DS from all other modes, JT65 with KV
> 
> included.  
> 
> 
> 73,
> 
> Klaus, DJ5HG
> 
> 
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