Rein, what is the cause of the 1700hr "heaviest" multipath? Is that a ionospheric condition of some peak airport traffic issue ?
Andy K3Uk On Fri, Apr 2, 2010 at 7:35 AM, Rein Couperus <r...@couperus.com> wrote: > > > I have done several tests with DA5UWG on 80m, and the 200 km path still > shows lots of multipath. > Both antennas are low (mine is a full wave 80m loop at 10m, DA5UWG has a > dipole at 12m). > Sometimes the mode goes up to PSK500 for a few frames, but it always > switches back to PSK500R, PSK250R or > MFSK32. > > There is also a clear variation pattern involving the time of day. > Multipath is heaviest around 17:00 local time. > I have found PSK500 or PSK250 to be useable only on single hop > (Eindhoven->Stockholm) or groundwave (< 50 km) paths. > During such occasions they save a lot of time :) > > I live near an airport, and when a plane is overhead the download from > PI4TUE (20 km) switches from PSK500 to PSK500R. > Upload remains PSK500R beacause the high noise level at PI4TUE prevents > PSK500. > > The robust modes are generally better than the raw modes, that is why > PSK500 is the only PSK raw mode in the mode table of > pskmail. This mode table was established using the trial and error method > over several months and paths... > > 73, > > Rein PA0R > > > >Hi Tony, > > > >Thank you for the information. This is the issue with field tests, there > are always several variables. > > > >I will proceed with some other field tests, trying to eliminate some of > the variables. In my case I have an inverted V on 40 and 80M at only 9 > meters peak over the ground for the server. So if I use a low dipole for the > client next time (2 or 4 meters high) instead of the vertical I assume I > should be able to safely eliminate ground waves over that distance (95 > miles). > > > >Am I correct in my understanding that there is still multipath and > therefore selective fading in pure NVIS (no ground wave) conditions? > > > >Thanks again, > > > >Regards, > > > >John > > > > > >--- In digitalradio@yahoogroups.com <digitalradio%40yahoogroups.com>, > Tony wrote: > >> > >> John, > >> > >> The first thing that comes to mind is whether there were any ground wave > > >> signals mixing with sky waves during your field tests? It's been shown > >> that NVIS throughput can fail when the sky wave echoes interact with > >> ground waves. The sky waves take more time to arrive at the receiver so > >> you can imagine what the difference in timing does to copy when the two > >> signals interact. This is what the NVIS simulations were based on; two > >> channels, one with no delay (simulated ground wave) and the other with a > > >> 7 ms delay (simulated NVIS sky wave). > >> > >> January's path tests showed that PSK-R appeared to be less robust than > >> BPSK under NVIS simulation while the white noise tests clearly showed > >> PSK-R the winner in terms of sensitivity. Your field tests seem to > >> reveal the same results in terms of which modes have the edge in > >> sensitivity, but not necessarily the edge in terms of dealing with > >> multi-path timing delays. I could be wrong though and there may have > >> been strong evidence of ground wave interaction? It can be difficult to > >> tell; some paths are more obvious than others. Hellschreiber is the only > > >> mode I know of that can visually indicate this sort of thing, but that's > > >> not an option with PSKMail. > >> > >> Hope to hear from you soon John. > >> > >> Tony -K2MO > >> > >> > >> > >> > >> > >> n 4/1/2010 9:45 AM, vk2eta 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 <digitalradio%40yahoogroups.com> > >> > , "vk2eta" wrote: > >> > > > >> > > Hi Tony, > >> > > > >> > > Thank you for the simulation results. I will report any field > >> > results for PSKR modes in NVIS conditions. > >> > > > >> > > Regards, > >> > > > >> > > John > >> > > > >> > > >> > > >> > > >> > > >> > __________ Information from ESET NOD32 Antivirus, version of virus > >> > signature database 4993 (20100401) __________ > >> > > >> > The message was checked by ESET NOD32 Antivirus. > >> > > >> > http://www.eset.com > >> > > > > > > > > > >------------------------------------ > > > > >http://www.obriensweb.com/digispotter.html > >Chat, Skeds, and "spots" all in one (resize to suit)Yahoo! Groups Links > > > > > > > >
