I personally can not support any modes wider than a standard SSB width. I don't even support the use of wide band AM primarily because if you let one mode use such a wide mode, then it is very difficult to suggest that no other mode should use an equivalent space.
It might be acceptable to use a wide band mode during low band useage, but it is impossible to police on a volunteer basis, thus the best thing is to limit the bandwidths of our very finite resource that must be shared with so many. The fact is that there are hams who don't even get on at times because the bands are so congested. No reasonable person could argue that having wider modes would not make this even worse. We need to continue to advance our technological abilities and narrow modes do this best. We already have the modes that operate about as fast as they can for a given bandwidth and robustness. What we don't have are modes that can adaptively change with the conditions although some can have manual speed and other attribute changes. With the ability to use the internet to communicate world wide as we are doing with this reflector, and doing it with substantial amounts of data, there is no need for amateur radio to duplicate such communications. That is why the packet system has died. It had a short period of time where it was useful and when it became obsolete, it was no longer supported by the necessary critical mass of hams. As I mentioned earlier, the only possible reason for high volumes of data on HF would be for emergency communications and that is a noble goal. And as I have often said, in order to maintain an effective emergency network of any type, it must be regularly exercised, preferably on a daily basis. But there is almost no interest in any HF network of this kind and I have almost never found any other hams who want to do this. Even the ARRL NTS/D seems to not be all that successful and does not seem to be growing. Almost no other hams in our Section (state) have expressed a serious interest in emergency digital communications. Our own state ARES/RACES leadership discontinued their BBS system and later discontinued their Pactor BBS as well and moved it to the SHARES program. We have a state wide HF digital reflector and it has only had a couple of comments over the past few years and that has mostly been from me and a dwindling number of members (down to a baker's dozen), most of whom do not actually seem to be active with HF digital. So I am not really sure if there will ever be much practical HF digital emergency use in our area. Of course we have our emergency voice nets and and some CW activity and that will probably be enough for tactical communications for our area of the country where widespread disasters are rare. We have a local county level amateur radio club which has its primary focus on ARES/RACES. At the last meeting a presentation was made on basic VHF packet radio and over the next few months we will be continuing with additional information of this type. Very few of the members are familiar with any digital radio concepts and other than some minimal VHF APRS and a DX cluster, there is very little activity. In the coming year we plan to have a presentation(s) on HF digital operation, including standard keyboard modes and Winlink 2000. Setting up a portable HF emergency digital station is not all that simple to do compared to a basic voice or CW station. One of the most annoying things to me is that laptops do not run on 12 vdc. Another problem is that most of our members are Technician Class and do not plan to upgrade unless we go to a no-code license as they have zero interest in CW. So realistically, most of our digital ham radio activities will be casual contacts and contesting and not surprisingly the popular modes reflect that. Here is the question that I have been asking myself: If we could send very large amounts of data via high speed digital modes on amateur radio frequencies, especially on HF, what exactly would we be sending that we are not already sending? 73, Rick, KV9U John B. Stephensen wrote: >If radiated power is not limited, data rate is directly proportional to >bandwidth, but the maximum data rate per kHz depends on the amount of time >(multipath) spreading and amount of frequency (Doppler) spreading. NVIS has >a multipath spread of 6-12 ms and there needs to be a gap between symbols to >accomodate this. Long paths have much lower multipath. Near the equator, >there is little frequency spread (< 4 Hz), but it is larger in near-polar >paths and can be very large (up to 40 Hz) under disturbed conditions. The >maximum symbol rate is limited to much less than 1/multipath spread and this >decreases with the number of symbol states so QPSK can tolerate only half >the Doppler spread of BPSK, etc. The acheivable data rate for any given >bandwith depends on ionospheric conditions and where the two stations are >located. A good guess for maximum acheivable data rates with 1.5 kW PEP >might be 3 kbps per kHz to 1/4 kbps per kHz depending on location and >ionospheric conditions. When the doppler spread and multipath spread both >become large there is no chance for digital communication. > >As far as maximum bandwidth is concerned, most countries have no limit, but >8 kHz is in the regulations of some countries in Europe so that may be a >good upper limit. > >73, > >John >KD6OZH > >----- Original Message ----- >From: DuBose Walt Civ AETC CONS/LGCA >To: digitalradio@yahoogroups.com > >Mark you said..."The question I have been struggling with is how much is >enough/too much. I guess what I am looking for is a curve showing bandwidth >vs. throughput for parallel tone modems, or maybe more precisely where is >the point of diminishing returns? " > >Yes...perhaps you are right about seeing curve...but I'm not sure that there >is enough data (on/off the air or simulator) available to make such a curve. > >Rick...you said..."The maximum accepted bandwidth for most modes is the >width of an SSB >transmitter since you can not go wider than that and communicate with >the typical rigs of the day." > >But is this any reason to not use wider modes? > > >
