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20M JT65 possible pirate

Discussion in 'General Announcements' started by N4AY, Aug 1, 2013.

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  1. K3DCW

    K3DCW QRZ Lifetime Member #212 Volunteer Moderator Platinum Subscriber Life Member QRZ Page

    Looks to me like **POSSIBLE** bad decodes. JT65-HF, if you're using that program, was known to throw out bad/erroneous decodes from time to time, especially on very weak or corrupted/distorted/spurious signals. They almost always "looked" valid, because that's what the JT65 logic is looking for. I believe it was something to do with the deep decoder and KVASD, but can't recall for certain.


    73 de Dave
    K3DCW
     
  2. N6YG

    N6YG Ham Member QRZ Page

    Pulease...!!! JT65 is a deceptively fast mode sure it takes 4 or 5 min to complete a qso but you can bang JT65 QSO's out one right after another... all day long..

    For example Last month I made over 700 band unique JT65 qso's FROM 6 LAND and over 300 SSB QSO.. So far over 400 of the JT65 QSO's have confirmed Via EQSL.cc, while only a few dozen of the SSB contacts have confirmed.. This has put me 4 states away from 5 band WAS JT65 and only a few countries away from 4 band JT65 DXCC on 10,15,20 and 40

    While a JT65 qso might take 4 min to complete unlike SSB you don't have to deal with hoards of Lids all trying to bust some huge pileup, most of whom are blatantly ignoring the DX code of Honor.

    SO on phone unless you have a 70 foot tower and stacked mono banders with a gallon and a half at your disposal it just might require a few attempts and quite possibly a lot of time to get around that lid fest. Don't get me wrong I'm not saying it cant be done because even with my humble station I still manage to bust the occasional pile up on the first or second call, of course that's probably more the exception rather then the rule.

    But it sure takes a lot longer then busting a JT65 pile up where the playing field has been leveled and the complexity of setting up and operating the mode weeds out the vast majority of lids.

    I guess that means I'm just the opposite of you because I just don't have the patients for phone on HF anymore, to many lids trying to sound like Rush Limbaugh. ;)
     
    Last edited: Nov 6, 2013
  3. N6YG

    N6YG Ham Member QRZ Page


    JT65 is a weak signal mode and as the band opens up false decodes due to multiplexing of overlapping strong signals or harmonics from multiple stations running excessive power levels is starting to become more frequent ..

    Unfortunately we are starting to see lids filter down from phone to JT65 who don't bother reading the documentation necessary to learn how to properly setup their stations. As a result we are starting see a lot of stations running excessive audio drive as well as excessive power levels. These improperly setup QRM machines can cause false decodes among other problems such as AGC pumping and harmonics which cause QRM to other qso's, Fortunately it's really easy to determine if you're dealing with a false decode or not.

    Earlier today I decoded TR4ZVF at -21 whose apparent df was between two extremely strong and distorted signals. I already knew it was a false decode but to make sure I checked it.

    The best method I've found to check for false decodes is to run them through http://hamspots.net/history/ and http://jt65.w6cqz.org/freceptions.html . As I suspected I was the only station on the planet who decoded TR4ZVF. Obviously it was a false decode..

    On the other hand if these RB sites had shown TR4ZVF decoded by a bunch of stations that would have indicated it was a legitimate decode but not necessary a legitimate call sign. For that I run them through EQSL.cc. If they are registered as AG with EQSL.cc then they are legitimate. If they're not regestered with EQSL.cc or If they show up at QRZ.com and want 5 dollars cash for a QSL card I don't waste my time working them.
     
  4. N6YG

    N6YG Ham Member QRZ Page

    Dave I don't believe the popular program JT65-HF ever used the deep decoder. If I remember correctly only WSJT used it and mainly for moon bounce. Furthermore and correct me if I'm wrong but I do believe you have to manually turn on the deep decoder option in WSJT.
     
  5. N9DSJ

    N9DSJ Ham Member QRZ Page


    The selectable "deep decode" function was never included with either Multipsk or JT65-HF. When JT65x was first being used on HF, (prior to Multipsk support or the existence of JT65-HF), Joe Taylor strongly suggested that the "deep decode" not be used on HF; it was meant only for EME. It would not elicit corrupted decodes as the deep decode function within WSJT used a look-up of expected "real" calls. The worse would be a phantom (non-existent) decode of an actual call sign from the historical file of active calls.

    False (garbage) decodes appear in all three software packages that support JT65x protocols. They are usually not frequent, are corrupted and a function of timing, noise, intermingled tones and/or distortion.

    73,

    Bill N9DSJ
     
  6. N6YG

    N6YG Ham Member QRZ Page

    Bill thank you for your input and explanation.. I actually pulled up the documentation for the JT65 protocol to help refresh my memory a bit... As I recall there was a controversy regarding the legitimacy of qso's decoded via the deep decode algorithm..

    For those of you interested in further reading on the subject heres a start
    http://physics.princeton.edu/pulsar/K1JT/K1JT_eme2006_2.pdf

    I agree I worked about 700 JT65 contacts last month which means I probably decoded several 1000 JT65 transmissions and only saw 2 decodes that I confirmed were false. Both times the pass band was filled wall to wall with signals with quite a few of them being high power over modulated highly distorted signals. I'm sure this creates harmonics with phantom tones that intermingle with other tones creating false decodes..

    Anyhow once again thanks for clarifying the deep search decoder for us..
     
  7. N9DSJ

    N9DSJ Ham Member QRZ Page

    My pleasure.

    "controversy regarding the legitimacy of qso's decoded via the deep decode algorithm" is an understatement :)

    Mostly I was trying to convey the difference between "phantom" decodes due to the deep search algorithm and the jumbled/corrupt decodes that, on occasion, happen with JT65x modes using WSJT, Multipsk or JT65-HF. Some of this can be discerned by looking at binning information using raw decoder data when using software that supports such viewing. But, as you suggest, this is an anomaly and one gets used to discarding such abnormal decodes.

    73,

    Bill N9DSJ
     
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