Hi Tony, The original reason we went to DominoEx instead of MFSK16 or PSK63 was because at VHF (we were originally using SSB), transceiver drift, in addition to multipath, is a major problem and MFSK16 is much more critical for mistuning or drift (on SSB) than DominoEx. But, when using FM, frequency drift should not be as great a problem, and it may well turn out that MFSK16 will work better overall, but we have not yet made enough comparisons to find out. FM is not usually used way under limiting, so this is rather new ground for us. On SSB, between two stations that both have TCXO's, MFSK16 works really well, but unfortunately, it is not possible to control whether or not a TCXO is being used.
Multipath is generally not a problem until the reflected signal is seen crossing the main signal on the waterfall, and then a slow "beat note" can be heard, regardless of signal strengths. At that time, the main signal is often completely cancelled by the out of phase reflected signal, and there is simply no resulting signal to decode until the reflected signal is seen to move off to the side of the main signal. Once it has, the mode with the lowest minimum S/N will work the best. Over the long path, propagation often appears to be very steady, with no atmospheric distortion, and the limiting factor is then the minimum S/N of the mode. However, at other times, there is a persistent, fast flutter, and at those times, MFSK16 might prove to be the best mode to use. We have yet to find out. As more people try using digital modes on 2 meter FM, the overall best performing mode will automatically surface, but for the longest range on digital modes (not counting CW), it is really necessary to use SSB, and in that case, we have found that MFSK16 is just too critical for tuning to be used with transceivers without a TCXO. 73, Skip KH6TY > 4c. Re: NBEMS QST article/digital weak signal FM > Posted by: "Tony" d...@optonline.net kt2q > Date: Sat Feb 21, 2009 4:44 pm ((PST)) > > Skip, > > White noise tests show DominioEX-4 to be a bit more sensitive than MFSK16, > but it doesn't seem to handle HF distortion nearly as well. > > I was surprised that it did better than MFSK16 with multipath and was > wondering if you thought the better throughput was due to MFSK16 tuning > issues rather than actual robustness? > > Tony - KHMU ------------------------------------ Announce your digital presence via our Interactive Sked Page at http://www.obriensweb.com/sked Recommended software: Winwarbler, FLDIGI, DM780, or Multipsk Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/digitalradio/ <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: http://groups.yahoo.com/group/digitalradio/join (Yahoo! ID required) <*> To change settings via email: mailto:digitalradio-dig...@yahoogroups.com mailto:digitalradio-fullfeatu...@yahoogroups.com <*> To unsubscribe from this group, send an email to: digitalradio-unsubscr...@yahoogroups.com <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
