That is interesting that they are going to name a new mode DEX that is similar to, but not the same as DominoEX. I liked using DEX as the acronym for DominoEX. But the creator gets to pick the names.
I am very pleased that Murray is helping to develop a mode for NBEMS and I am sure many of us will be quite interested when this gets to the point that we can try it out. Same for DSX. We have got to make this simple to use and I hope that there will be more interest on digital modes for public service. Nothing much happening in our area and I do promote it as much as I can. Pactor 2 is the mode to beat since it is has so many good attributes for its bandwidth. It would be great to see some comparisons between P2 and the newer sound card modes. Thanks to all of you for so much work to develop these new modes. 73, Rick, KV9U kh6ty wrote: > Hi Rick, > > FYI, our tests last night indicate that MFSK16 still copies the best > at low S/N, but only when there are no static crashes, but DEX16 or > DEX11 have much fewer errors when there are static crashes. The > problem with MFSK16, as you found, is the mistuning tolerance. For > messaging, when there is a fast series of ARQ exchanges, if one > station has uncompensated offset between RX and TX (NBEMS must work > with untrained and inexperienced operators to be successful for > emcomm), and if the offset exceeds 4 Hz, which is not so unusual, > eventually it will not be possible to decode MFSK16, and therefore the > ARQ requests or confirmations may be missed. > > This is different from using MFSK16 in a QSO, because in a QSO, it is > possible to retune with the mouse after each turnover if necessary, > but not very practical in a series of fast ARQ exchanges. > > We were also testing "DSX", which is a variant of DEX, so you would > not have been able to decode that. > > "DEX" is the name Murray, ZL1BPU, who is working with us to > develop the best mode for NBEMS, and is the desiner of MFSK16 and > DominoEX, suggested for the new mode, which is NOT compatible with the > current DominoEx modes, but uses the same IFK technology so tuning is > not critical and static crashes have minimal effect. > > When we switched to MFSK16, it was to compare very weak reception on > one station where there were no static crashes at all. Whereas DEX11 > and DEX16 outperformed MFSK16 under the high static conditions, MFSK16 > was best when signals were the weakest and there was no static. For > NBEMS, we have to compromise between weak signal performance, static > crash performance, and transfer speed, and we are still trying to > determine which mode to use as a default mode, because it is just not > practical to present an untrained operator with a huge selection of > different modes for different conditions and ask him, under the > pressures of trying to get emergency messages out, to figure out which > one to use! > > Of course, generally, the slower we go in speed, the more robust the > mode for a given bandwidth, and there is always a point where a faster > mode fails, but a slower one succeeds. In very adverse conditions, > when messages tend to be short, such as, "We are safe in a shelter at > the local school", or "The Red Cross has just arrived", any mode that > will get the message out, no matter how slowly, is the one that must > be used. Connection time tends to be much longer than the message > transfer time. > > Two days ago, a line of severe thunderstorms passed us, and spawned a > tornado which touched down about 15 air miles from here, and on 80m, I > still have a static level of S9 +10 with strong static crashes almost > every second - definitely very adverse conditions! Under these > conditions, the new DEX modes are working the best, but at the same > time, on 2 meters, there are only occassional weak static crashes, so > whenever possible, using VHF is still the best band to use for up to > 100 miles. Under these conditions, the PSK modes are quite adequate > and also give the fastest transfer speeds. Which PSK speed to use is > usually only dependent on the necessary S/N to overcome path loss. I > am hoping that most EOC's will install point-to-point VHF circuits for > their use rather than relying on 80m and 40m NVIS HF, which is prone > to static interference and propagation changes, depending upon the > time of day. > > The advantage to using a relatively narrowband mode on HF is that > there is more room for more stations to take traffic simultaneously, > which greatly shortens connection time, so the overall time from > attempted connection to completion can be much less than having to > wait in line to access a few wideband stations. Pactor-II is probably > the most efficient ARQ mode developed so far, but it is easy to tell > how often connections are not made by observing the number of times > client stations come on and never connect, probably because of the > small handful of reachable, or available, forwarding stations. I think > overall, when we have done all we can to improve our new mode, that in > a real emergency, when many stations need to pass traffic at the same > time, the throughput of NBEMS will exceed that of other HF systems on > the ham bands. > > We hope to release our latest new mode for beta testing in about two > weeks and then everyone will have a chance to try it under all sorts > of conditions. > > 73, Skip > NBEMS Development Team > >
