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" <vk2...@...> wrote: > > Hi Tony, > > Thank you for the simulation results. I will report any field results for > PSKR modes in NVIS conditions. > > Regards, > > John >
