1x1 WSPR callsigns only decoded by KiwiSDR

I came across an interesting phenomenon recently while running a special event WSPR beacon. Turns out that the 1x1 call sign being used (N1D) was only being spotted by the (older?) decoder built into the KiwiSDR ("1.3 Kiwi"). The decoder used the decoder used in current systems like WSJT-x 2.4, wsprdaemon, etc. Only when I changed the call sign to a compound one (N1D/4) did the spots emerge from

So this is a case where the decoder that comes with the Kiwi has a clear advantage over others, even though it falls a bit short for routine use on a busy band. I posted this same information on other WSPR-related forums; I suspect it is an obscure bug in the decoder software that will be addressed at some point. And since 1x1 call signs are rarely used, it's not surprising if this hadn't been noted previously.


  • jksjks
    edited April 2022

    "N1D" can be represented fine in the WSPR coding process. See the "callsign" section about half-way through: https://swharden.com/software/FSKview/wspr

    The actual encoding in the 6-position, bit-packed callsign field would be [space] N 1 D [space] [space] with the leading and trailing spaces getting trimmed during the unpacking process.

    One possible difference could be some filtering before the spot is uploaded. The Kiwi code handles all uploading using its own code since that function is not performed by the wsprd code the Kiwi uses from WSJT-X. I don't filter out 1x1 calls, but perhaps WSJT-X does.

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