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ISCAT Internals

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  • AC TALBOT
    What is the character to tone mapping of ISCAT A and B  modes ?The WSJT9 online documentation gives the tone frequency and baud settings, but I can t find
    Message 1 of 3 , Oct 18, 2012
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      What is the character to tone mapping of ISCAT A and B  modes ?The WSJT9 online documentation gives the tone frequency and baud settings, but I can't find  the alphabet and char/symbol mapping - that doesn't seem to be listed
       
      I'd like to do a PIC / Synthesizer implementation for some microwave tests
       
      Andy   G4JNT
       



    • booz2m
      Hi Andy et al An single ISCATmessage is encoded in this way C-style, modified for general purposes. For multiple purposes it is repeated. SYMBOLS ... int
      Message 2 of 3 , Oct 18, 2012
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        Hi Andy et al

        An "single" ISCATmessage is encoded in this way C-style, modified for general purposes. For "multiple" purposes it is repeated.

        SYMBOLS
        -------

        int ISCATMakeMessage()
        {
        char ISCATChars[]="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ .?@-";
        char Msg[MaxMessageLength+3]="@"; // add @, " " and sz
        unsigned char I,MsgLen;

        strcat(Msg,TheMessage);
        MsgLen=strlen(Msg);

        Symbol[0]=0;
        Symbol[1]=1;
        Symbol[2]=3;
        Symbol[3]=2;

        Symbol[4]=MsgLen;
        Symbol[5]=MsgLen+5;

        for (I=0;I<MsgLen;I++)
        {
        Symbol[I+6]=GetCharNo_P(ISCATChars,Msg[I]);
        Symbol[I+6+MsgLen]=MGMSymCar[0][I+6];
        }

        return(2*MsgLen+6);
        }

        ISCAT is using 11025 Hz sampling rate and ISCAT-A uses 512 samples and ~B 256.

        Details in geniscat.f90 (classic ISCAT = ISCAT-B) and WSJT home page for ISCAT-A.

        73
        Bo, OZ2M
      • booz2m
        Hi The shown implementation applies only to messages less than 18 characters, excluding the @. The is not needed so the array is only +2. It is a leftover
        Message 3 of 3 , Oct 18, 2012
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          Hi

          The shown implementation applies only to messages less than 18 characters, excluding the @.

          The " " is not needed so the array is only +2. It is a leftover from initial tests I carried out. The ISCAT carriers the message length so no " " needed to separate two decoded messages.

          73
          Bo, OZ2M
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