Hi Patrick, While you might get a lot of different opinions on what is needed for public service/emergency communications, absolute accuracy is what many of us consider to be mandatory. And because you are often going to be operating under less than ideal conditions and locations, having a robust system may make the difference between some throughput and zero throughput.
The Winlink 2000 system considers Pactor to be too slow and many of their server stations will only accept Pactor 2 and some only P3 connections. From what I have read, almost all traffic is now P3 anyway, however, during emergencies many will allow Pactor stations to connect. Of course most public service/emergency communications does not use e-mail, so having modes that allow direct connections between stations is important as well as the expected phone links. There is no current sound card HF protocol that can approach Pactor 2's faster speeds, but the new Winlink 2000 design sounds as if it will be competitive (not sure about bandwidth vs speed though). Apparently, the plan is to move toward QPSK and 16QAM and have it scale between very robust slower modes to less robust but much faster modes which we very much need. Also, memory ARQ is planned. While it would be nice to have very fast data, even moderate data speeds (100 to 500 wpm?) would be nice to have for a SC messaging system. SCAMP (with compression on plain text) could do close to 1000 wpm with about a+8 to 10 dB S/N. After all even P3 drops to a net throughput of less than 77 wpm for Speed Level 1 when operating under the most robust two tone mode. Some emergency groups may want , or even have a request from those they work with, to have the ability to not only send text messages, but also send attached files which could be anything. Here in the U.S. you can not legally send faxes and images with modes wider than 500 Hz in the RTTY/data portions of the bands, but could send text documents that are attached. This effectively means that you could send anything except digital phone through P2 or similar medium width (500 Hz) modes. SCS claims a very favorable figure of P2 and P3's ability to work deep into the noise (something around -15 dB S/N?) but I don't know how much ISI they can tolerate and no one who actually has this equipment has let us know of their experiences in testing in real world environments other than to say that they are very much superior. 73, Rick, KV9U Patrick Lindecker wrote: > Hello Rick, > > RR for all. > > > developing a similar sound card protocol for emergency use. It does not > I've never been implicated in emergency use and I don't know what are > the needs. > For example, what is the net absolute throughput required in bits/sec? > > Examples: > * Pactor 2 in the most robust scheme: Total bit rate: 200 bits/s, net > absolute: 100 bits/sec > * ARQ FAE in ALE400: Total bit rate: 150 bits/s, net absolute: 75 > bits/sec. > For 63 characters length message, the use speed (compressed) is 87 wpm. > * Pactor 2 in the worst robust scheme: Total bit rate: 800 > bits/s, net absolute: 700 bits/sec > > For files exchange, even 700 bits/sec is not sufficient, so I suppose > that it is only exchanged texts or mails? > > > If a similar medium bandwidth (500 Hz) 2 tone PSK mode was invented for > > sound cards, using the tone swapping approach of P2, it would increase > This scheme does not give a very good minimum S/N (perhaps -7 or -8 dB). > > About the minimum S/N of Pactor 2, do you know the exact figure? (I > don't speak of the SCS figure) > > 73 > Patrick >
