I used to think that Viterbi coding worked better for ham applications. For example, Pactor modes (Viterbi) work better than Clover modes (R-S). Other R-S modes include, SSTV RDFT and the Winlink 2000 initial attempt to develop a sound card mode (SCAMP) which uses the same modulation scheme as RDFT.
Actually, many of the sound card modes use Viterbi: QPSK31, PSK63F, PSK220F, MFSK16, MFSK8, and even the new DominoEX/FEC mode all use Viterbi coding. Many of the Pactor "tricks" have been applied to sound card modes, including Huffman compression which is really varicode from what I understand. The use of DPSK is common for sound card modes since PSK31 is really DPSK, is it not? In fact, the waveform is quite similar to Pactor using a raised cosine form. But it still does not explain why Pactor 2 and 3 is so much faster than the sound card modes. Even though many have determined that P2 and P3 can not work as deep into the noise as some sound card modes, other tests seem to refute this. Rick, KN6KB has indicated that the SCS product is tremendously more powerful than any desktop computer at this time since it is a dedicated unit. One other way to increase the coding is to use concatenated codes that include both R-S and Viterbi since we can do this with faster processors. The technology trends seem to replace the concatenated codes with Turbo code that is a more recent development. Is anyone planning to use this for sound card applications? I wonder what would happen if a developer speeded up some of the very weak signal approaches such as WOLF: http://www.scgroup.com/ham/wolf.html 73, Rick, KV9U Jose Amador wrote: >Well, about what´s being done the wrong way, I think >I better pass it to the codesmiths. I am not >completely clear about how the soundcard modes do it, >but the success if Pactor is wrapping all those tricks >together. > >Some of the modes use Reed Solomon codes, others use >BCH, but I am not sure if any of them uses >convolutional encoding with Viterbi decoding. > >One important point. If my memory does not betray me, >I think Pactor uses DPSK, which does better passing by >the ionosphere. Seems to be easier to take account of >the phase jumps than of the absolute phase. > >I used at times packet at 1200 baud on 28, 21 and 14 >MHz, and it worked in order of decreasing success on >the lower frequencies....but it managed to work on >14MHz quite well at times. Multipath is the deciding >factor in the link. If just one path is open, it may >work, if there is multipath, better hold back to lower >speeds. > >What surprises me (and I have never been able to test >it personally) is that in Indonesia, some hams have >used 1200 baud DPSK satellite modes succesfully on 40 >meters. Once again, DPSK does the trick. > >It would be interesting to read about what and why the >programmers have chosen their options while creating >new sound card modes. > >73 de Jose, CO2JA > > > > Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/digitalradio/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
