Afreet Software, Inc.
     Software created by Alex Shovkoplyas, VE3NEA
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RttyCompare

RTTY Software Comparison

All results are preliminary



Procedure


  1. A 200-second RTTY message (904 characters) was generated with WSCGen 1.80;
  2. AWGN channel model applied to the signal in PathSim 1.0;
  3. WAV file resampled at 11025 Hz and played back in MS Sound Recorder 5.0;
  4. Audio routed to each RTTY program via Virtual Audio Cable 2.04;
  5. Message decoded with TrueTTY 2.37, MixW 2.13b and MMTTY 1.65b
    (AFC and Squelch OFF, all other settings default);
  6. Errors counted with RttyCompare (see below);
  7. Steps 2 - 6 repeated for different SNR levels;
  8. Steps 2 - 7 repeated for other channel profiles;
  9. Charts plotted in Graph 3.2.2.




Results

















The dotted green line is for MixW in the Single Filter mode













RttyCompare




RttyCompare is a utility that compares the sent and received RTTY messages and calculates the error rate. It converts both texts to the Baudot code, removes LTRS, FIGS, CR, LF and space characters, and finds the best match between the messages using the dynamic programming algorithm. This algorithm is smart enough to find the mapping even at very high error rates when the text is completely unreadable. In fact, it is too smart and finds some similarity even between the random sequences, thus the CER values on the charts above are a bit underestimated. The calibration chart below can be used for correction.





Download RttyCompare:


   Executable

   Source code




Your comments are welcome







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