I am sharing this with both the HFDEC (Hams for Disaster and Emergency Communications) group as well as digitalradio as this seems very appropriate based on recent comments on HFDEC.
In essence, I have written the FCC toward the end of 2007 and had a follow up in recent weeks, but no response to a number of questions, one of which dealt with the baud rate issue. For those who do not know, John and I (and others) have done some testing with RFSM2400/8000 in order to see how well a 2400 baud mode could actually work on HF. While we US hams can not use these programs in the 300 baud restricted portion of the bands, (even though Pactor 3 is permitted and is about the same bandwidth), it is important to know that we should be able to use them in the phone/image portions where there is no baud rate limitation and maybe even more importantly, can use them in the VHF bands and higher with no restrictions. And unlike packet, the RFSM MIL-STD software modem can adapt somewhat for conditions while 1200 baud packet requires good and 9600 baud requires extremely good signals to work at all and with no fall back position. Our test drew some criticism because some felt it was unfair that we were using it in conditions that were not optimum for high speeds, but would have been usable (barely) for SSB voice (around +5 dB S/N). There still was some throughput which is not that bad compared to other modes with that level of S/N. The RFSM2400 program does not support the slower and much more robust modes of MIL-STD-188-110A down to 75 bps. In fact, it was only able to drop down to 600 bps which required the S/N noted above. The bps rates vary widely, but the baud rate remains at 2400 baud at all times with this technology. I can not help but think that if the baud rate could scale downward, the robustness might be better, particularly with severe ISI on the lower HF bands where multipath and doppler can alter the bit positions beyond the ability of the software to correct it. The RFSM2400 program is no longer being developed and the RFSM8000 program has a cost (a very modest cost for hams) but which realistically 99.999% of hams will never be willing to support and that it may mean the death knell for expanding amateur use of that software which is a shame. Will others develop these MIL-STD/STANG open modes? Probably not possible due to the development requirements, but you never know. Having said what some will think is a negative, there are those of us who are primarily interested in the faster speeds for emergency communications. A nearby group that supported local government during the 1000 year flood we had in our region last summer, was asked to provide images of the disaster scenes but did not have any practical way of doing this. It seems that programs of the RFSM type could be used to provide enough throughput for this application as well as general traffic handling with no errors from propagation/QRN, etc. Is anyone else experimenting with this software or similar software to come up with solutions for HF or VHF? 73, Rick, KV9U John Bradley wrote: > > Rick wrote: > > “The main advantage of P2 and P3 is that they have the ability to change > speeds to match conditions, something that has not been done to any > great extent on sound card modes. It is just that there does not seem > to be a great deal of interest in developing high speed HF modes by > those who have the skills to do so since as they have pointed out, their > main interest lies in keyboard and extreme weak signal modes.” > > Maybe it is time for the US hams to mount a campaign enabling the use > of modes faster than 300 baud, > > since there are several of those, RFSM8000 among them, which will vary > speed based on conditions. > > True that some developers may favour weak signal modes over high speed > HF modes, but the principal reason is the > > repressive FCC regulations which discourages development of these modes. > > John > > VE5MU > > ------------------------------------ Announce your digital presence via our Interactive Sked Page at http://www.obriensweb.com/sked Check our other Yahoo Groups.... http://groups.yahoo.com/group/dxlist/ http://groups.yahoo.com/group/contesting http://groups.yahoo.com/group/themixwgroup Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/digitalradio/ <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: http://groups.yahoo.com/group/digitalradio/join (Yahoo! ID required) <*> To change settings via email: mailto:[EMAIL PROTECTED] mailto:[EMAIL PROTECTED] <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
