Interesting observations John. I can't offer any useful insight, but look forward to hearing from those that can.
Andy K3UK --- In digitalradio@yahoogroups.com, "vk2eta" <vk2...@...> wrote: > > To Tony (K2MO) in particular, but not exclusively: > > Following your simulation results on these modes in January I have done a few > tests in the field and I have to say that I don't understand the results. > > Please note that I am not trying to make a point, but to understand why the > theory does not seem to match the practical side. > > My tests simply revolve around examining the bahaviour of the Pskmail server > adapting speed to the conditions. > > We have in the latest version a table of modes that the server can use by > shifting up and down, one mode at a time. It does so by relying on the s/n > report gathered from Fldigi and the number of repeats due to damaged ARQ > frames. > > The list is arranged in an empirical order of speed vs robustness and is the > following for regions 2 and 3: > > THOR8 MFSK16 THOR22 MFSK32 PSK250R PSK500R PSK500 > > The MFSK/IFSK family of modes are normally the modes of choice for NVIS. > > This week I did some tests at 95 miles in a strait line from my server on 40 > and 80M between about 1PM to 2PM local time so obviously in NVIS conditions. > > What I noticed every time I would connect in MFSK16, the server would > progressively shift the TX mode up into the PSKR modes, up to PSK500R, but > never to PSK500. > > I also noticed that there would be no fallback from PSK250R to MFSK32 after a > shift up from MFSK32. > > So my interpretion is the following: > > If the PSKR modes had a weakness in NVIS conditions, I would see the server > moving continuously between MFSK32 and PSK250R: good reception in MFSK32, > speed up to PSK250R, poor reception, return to MFSK32, etc... > > Also since it did not go up pass PSK500R to PSK500 it indicates that in these > particular cases the PSK500R modes was starting to show signs of limitations > and the server calculated that there was not enough s/n margin to shift the > speed up. > > Selective fading is very visible especially on the PSK500R mode of course. > > So my question is: in the simulation you performed, are there parameters that > maybe would need to be looked at to explain why these modes seem to behave > well in these conditions or are there other variables to consider? > > Also trying to get a more formal comparison, how would you design some > practical tests that minimize the effects of variation in propagation in the > field? > > On this point I was thinking of sending a set text in different modes and > repeating the test several times, interleaving the modes so that in average > it would be unlikely to be just propagation. Mode1, Mode2, Mode3, Mode4 then > again Mode1, Mode2, Mode3 etc... repeated say 5 times. Then taking the > average result for comparison. > > Best regards, > > John (VK2ETA) > > > --- In digitalradio@yahoogroups.com, "vk2eta" <vk2eta@> wrote: > > > > Hi Tony, > > > > Thank you for the simulation results. I will report any field results for > > PSKR modes in NVIS conditions. > > > > Regards, > > > > John > > >
