Hi Joe Thanks for these test results. I note that your conclusion that JT65c is no better than JT4 with spreading greater than 10 to 20 Hz is based on non-DS decoding. Based on my tests with r6536 I am inclined to agree that your conclusion also applies to DS decoding although I would like to do more testing when a build of r6559 is available.
This conclusion does, however, seem to be contrary to the Text books that the use of higher Mary FSK should improve performance. Although such relative performance improvements do diminish with increased symbol error rate and perhaps at the 50% decoding margin which is important in the ham radio context (as opposed to the commercial context) increased Mary levels do not help enough to counteract the loss of performance due to partially over-lapping tones. I assume that the use of JT65d would extend the useful spreading range for JT65 compared to JT4 from the 10-20 Hz range to the 20-40 Hz range which would probably make JT65 the preferred mode up to 5.7 GHz and even 10 GHz when full spreading is below 40 Hz as is often used for small station to small station EME. Another advantage of JT65d is that as the spreading goes through a minimum that can often be as low as a few Hz at 10 GHz then JT65 can take advantage of the extra 2 dB over JT4 without having to change modes during a QSO. Thus I can see that there is value in having a JT65d Mode for small station to small station EME at 10 GHz although I accept the benefit is small. Despite having argued the case for JT65d this depends on whether JT4 has yet reached its full potential at low spreading. From my DS tests JT4f on WSJT-X is around 2 dB better than JT4f in WSJT10 when the spreading is above 20-30 Hz. However, JT4F on WSJT10 is about 2 dB better at very low spreading up to around 10 Hz. The reason why WSJT10 is better is that it is much better at gaining sync at low spreading than WSJT-X. It seems to me that if the WSJT10 method of gaining sync were applied to WSJT-X then JT4f on WSJT-X might well be as good as JT65 at low spreading such as a few Hz and thus that JT4 would be the preferred mode for all microwave bands and that JT65d would not then be required. It is also possible that the improvement in gaining sync would apply at higher spreading and as such would further improve the JT4f performance at above 20-30 Hz. At present averaging is rarely useful on JT4f DS on WSJT-X as the limit is gaining sync - thus any improvement in gaining sync should be of significant benefit to JT4f averaging. So in summary I think the next move should be to do some wider tests to compare the sync performance of JT4f on WSJT10 and WSJT-X to see if there are options to optimise this mode before you spend time on JT65d. Rex VK7MO ------------------------------------------------------------------------------ Transform Data into Opportunity. Accelerate data analysis in your applications with Intel Data Analytics Acceleration Library. Click to learn more. http://pubads.g.doubleclick.net/gampad/clk?id=278785471&iu=/4140 _______________________________________________ wsjt-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/wsjt-devel
