Your question is one that I have also. In our recent NVIS testing with fldigi/flarq we found BPSK250 provided better throughput than other modes we tested, and most notably MFSK32 which we thought would be our safe, robust mode.
This was with a variety of band conditions including strong signal, weak signal, selective fading, lightning QRN, grungy power line noise, and all the normal stuff we experience here in the Midwest. Path distances varied from 40 miles to 150 miles which were the distances we were interested in. There were a couple ideas we kicked around as possible reasons why BPSK250 worked so much better than we expected. One was that when the signal took a hit from something like a lightning burst, BPSK250 recovered and resynchronized very fast. The second was even more speculative in that maybe the higher phase modulation rate (250 times per second) was faster than Doppler path modulation allowing the BPSK decoder to ride through. Anyway, we expected BPSK250 to be useless on NVIS but every time we have tried it, it has worked. (and better than most modes.) Maybe there is something that the path simulators are missing. Dunno... Just throwing some ideas out. Gary - N0GW --- In digitalradio@yahoogroups.com, "vk2eta" <vk2...@...> wrote: > I also noticed that there would be no fallback from PSK250R to MFSK32 after a > shift up from MFSK32. > ...... > 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? > .... > > Best regards, > > John (VK2ETA) >
