Hi All, I am trying to understand some practical and pretty basic aspects of the decoding of the various modes and have some questions because my knowledge base / brain power have not permitted me to come to a complete understanding of the issues involved, even after reviewing the source code.
So I am asking the group for help, as I know there are smarter and better educated folks in abundance here. Here are my impressions and associated questions: 1. ISCAT, JT9 Fast modes, and MSK144 repeat the message block many times during a single transmit cycle. Is there signal averaging of the data received during a SINGLE receive cycle to improve signal to noise ratio for ISCAT, JT9 Fast modes, or MSK144? I believe the answer is "no" but I would like confirmation of this. 2. I believe that received data from MULTIPLE transmit/receive cycles can be averaged by JT4 and JT65, but not by other modes. Is this correct? 3. If the answer to #1 above is that there is not averaging of the multiple message blocks WITHIN A SINGLE receive cycle, then the multiple blocks within a receive cycle give more chances for the SNR to be sufficient for decoding, but if the actual channel propagation characteristics are perfectly constant during the transmit/receive cycle, there is actually no greater probability of getting a successful decode from the entire T/R cycle than there would be for getting a successful decode if the transmit/receive cycle time were equal to the duration of a single message block. Is this correct? 4. If the answer to #1 above is that there is not averaging of the multiple message blocks WITHIN A SINGLE receive cycle, then the important time frame for determining what amount of frequency drift (in Hz/second) is important relative to the tone spacing for these modes is not a function of the tone spacing divided by the duration of the entire transmit cycle, but rather a function of the tone spacing divided by the duration of the duration of a single message block. For JT9H-Fast with a 15 second duration cycle length, the difference in tolerated frequency drift would be approximately (222.222 Hz/15 sec =) 14.8 Hz/sec vs (222.222/0.425) = 523 Hz/second, neglecting the slight difference between the actual receive cycle time and 15 seconds. Please accept my apologies for any stupidities in the above. It is my lack of understanding that is the reason for this post, and if I really understood the issues I would not need to post! (Ignorance is not Bliss.) 73, Roger Rehr W3SZ ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ wsjt-devel mailing list wsjt-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/wsjt-devel
